Saturday, July 11, 2015

Obesity - What is the real problem?


 

To me it seems critical that we get a realistic and accurate sense of the overall problem, since much of the difficulty is confusion regarding how to think of it in the face of seemingly conflicting information.  I am going to offer my understanding of the scientific consensus as a framework.   

 

For all the confusion we often have over various aspects of nutrition and fitness, I think there are a handful of principles that are particularly reliable based on the evidence we have so far.  

 

The reason so many people around the world have been getting so much fatter so quickly is that they are taking in more energy than their bodies need in order to be nourished and satisfied.  And they do this for reasons that they are mostly unaware of having to do with reward, preference, palatability, expectancy, reliance on cues, and satiety.  Let's call this the mindless surplus intake theory of obesity. 

 

As intuitive as it might seem at first, the mindless surplus intake theory of obesity doesn't have to be true.  There could be other reasons for our growing fatness.  Our bodies or environment might have changed to make many of us store fat more efficiently from the same amount of energy intake (the broken metabolism theory of obesity).  A number of authors in recent years have promoted variations of the broken metabolism theory.  The broken metabolism theory sounds scientific and some variations of it have been promoted with long lists of research citations or even with the limited blessing of some researchers, especially when it is combined with reasonable actionable advice as well.  In general though it seems to me that the "broken metabolism" theory itself has been pretty thoroughly falsified as a primary driver of obesity.  And that fact matters in some  important ways.

 

Our bodies or environment might also have changed to make many of us more impulsive about eating  and we have failed to compensate by exercising our willpower adequately (the gluttony theory of obesity).  Similarly, our bodies or environment might have changed to cause us to be less motivated to move and we have failed to compensate by exercising our willpower adequately (the laziness theory of obesity).  The gluttony and laziness theories are compelling to us individually because we have a strong intuitive sense of the importance of personal responsibility, and self-control is indeed a powerful factor in success across many endeavors.  However the laziness and gluttony theories exaggerate the role of deliberate self-control in the myriad decisions we make every day about eating and activity.  People successful at controlling their weight use their self-control not to make every decision deliberately but to create better habits for themselves and shape their environment to help them.  It is not a failure of willpower that drives obesity.  That fact also matters in some very important ways. 

 

Our bodies or environment might also have changed to cause us to need less food while still eating  enough to create a surplus (the inactivity theory of obesity).   Activity levels contribute significantly to both health and obesity, and especially to the maintenance of healthy weight, but we know the driver of obesity is mostly intake and that just moving more without also cutting back energy intake doesn't reverse weight gain in the obese in general.  This is almost certainly a major factor in both health and obesity, but it is clear from the existing evidence that it is not the primary driver of obesity.  The trend in fatness corresponds far more closely to changes in intake than changes in activity.  Also the experimental evidence shows activity being far more useful for maintaining weight loss than for simply "burning off calories" in most people, largely because we often tend to eat more to compensate for exercising.

 

In addition, more than one of these might be a factor.  But from my reading of the evidence patterns, the primary driver of obesity is now clear.   We have been taking in increasingly more energy than we need, mostly because we have been eating more than we would need to fuel our activities and nourish our minds and bodies.    And we have been doing this for reasons that do not involve the specific discretionary macronutrients we eat most of (e.g. carbs vs. fats), do not involve us simply failing at deliberate self-control, and do not involve us having inadequate knowledge of which diets are best for weight loss. 

 

What are these mysterious reasons for creeping intake if it is not eating too much fat or too much sugar or too much starch in particular as many authors have claimed?

 

  1. Our intake is regulated primarily by mechanisms of reward, preference, palatability, expectancy, reliance on cues, and satiety.  We learn what to eat and how much based largely on stimulus cues, what we expect from food, how palatable foods are to us, and how they make us feel.
  2. Our reward and satiety mechanisms are optimized for regulating our weight under natural stimulus conditions by relying primarily on volume and weight of food and secondarily on energy content.  We mostly tend to eat about the same volume of equally palatable and rewarding foods every day.  
  3. Our metabolism is optimized for efficiency of energy storage rather than for maintaining a stable weight.
  4. We are bad at estimating how much energy we need in order to be nourished and feel satisfied.
  5. We are bad at estimating how much energy we are taking in in order to compensate for well-engineered distortions of reward and palatability.
  6. We have come to rely increasingly on cues in our environment to determine how much energy we need and how much we are taking in
  7. We have come to increasingly exploit our reliance on cues in our environment in order to market food and health and fitness products, and this distorts the cues we rely upon so heavily
  8. We have come to increasingly rely on strategies which overemphasize small or irrelevant metabolic effects, rely on outdated theories, rely on willpower, ignore the long term, and in general are unsustainable and make us feel like failures when we can't sustain them.  

 

If my understanding of the scientific consensus is correct, the mindless surplus intake theory of obesity reflects it well and can be understood in more detail in terms of the satisfaction theory of intake regulation.   This says that we eat mostly what satisfies us because of the way the reward and satiety mechanisms work in our nervous system rather than because of metabolic or nutritional effects.   What gets "broken" in obesity in general is that we stop being satisfied with a nourishing amount of food and we keep eating even though we are taking in more than we need.  The reasons for this have little directly to do with willpower or carbs or fats and everything to do with the mechanisms of  reward, preference, palatability, and satiety.

Why is the problem of obesity so damned tricky?


  1. Why is the problem of obesity so damned tricky?

 

A lot of us are fat. Fatness increased dramatically in the 20th century, especially since the 1980's in the US.  We don't like being fat in general.  When it becomes extreme, body fat usually doesn't look good to us and can lead to health problems, diminished longevity, and restricted quality of life.  Some distributions of body fat are worse than others for health or for appearance, but at some point it eventually looks bad to us and detracts from our lives.  

 

  1. Just Theories are Well Communicated and Popular but Wrong

 

If we find fat so problematic, why haven't we simply found good solutions for it and begun to apply them?  Most people can lose some body fat temporarily by some combination of depriving themselves of some particular kinds of preferred foods, trying to force themselves to eat less,  and trying to force themselves to be more active.  Most people end up going back to their original body fat levels, or greater, after a few weeks, months, or years of that effort.    There is no lack of simplistic just theories about why this is happening:

 

Fat people are just lazy and not exercising enough self-control over their eating and exercise

Fat people are just gluttons who eat too much

Fat people are just eating too much carbohydrate

Fat people are just eating too much starch

Fat people are just eating too much sugar

Fat people are just eating too much fat

Fat people are just maintaining their weight at a genetic set point

 

Although each of those ideas is wrong in its own particular way, and they are each perhaps partly right in some sense,  it is the just part that is most wrong of all.  The just theory is a special kind of problem in itself that is part of the reason fatness is so difficult to address.

 

Here's my central claim: scientific consensus is not just a matter of certain opinions winning out over others, the problem of obesity is understood in broad form as a scientific consensus even though many the details are complex and some of our knowledge of the factors is undoubtedly incomplete.  There is a rough scientific consensus about various aspects of obesity across fields of physiology, nutrition, psychology, neuroscience, and medicine.  It is not just the confusing mess that appears in popular media.

 

I also claim: this consensus understanding is not what is published in most diet, fitness, and weight control books.  In fact, a sizable number of popular books on diet and weight control conflict dramatically with the scientific consensus, but are marketed as if they were new and revolutionary new findings.    This has contributed heavily to the confusion and so added to the problem. 
 
 


B. The Scientific Consensus is Poorly Communicated
 
In the stories that journalists tell to try to communicate their own interpretations of the obesity and health research, they have often engaged the science compellingly but not faithfully.  We now know some very useful things that are not well communicated, or are even ignored or denied by popular authors with their own agendas, or get lost in the media confusion:
 
  1. The theory that people can control their weight by exercising self-control at each eating or activity decision is simply wrong.  
 
No one has that much self-control against an environment that constantly tempts them.  The psychological study of self-control reveals that variation in impulsiveness is indeed a factor in all sorts of problems, including obesity, and that people can often learn skills to compensate for impulsiveness, but these do not rely on individual acts of self-control.  Self-control is always finite, and we successfully compensate for impulsiveness by not just exercising self-control in each decision, but also even more importantly by altering our environment and altering our habits so that we reduce the need to exercise our always finite capacity for self-control.
 
  1. All of the theories of specific  macronutrients causing  us to become fat are simply wrong.
 
The theories of metabolic advantages of particular diets (low carb, low fat, vegan, paleo, etc.) have all been falsified scientifically so far.  Obesity is in general at the population level not caused by everyone's metabolism being "broken" by certain foods nor is it "fixed" by eating certain foods. 
 
We know for a fact for example that low carb diets do not cause people to lose weight by any special "fat burning mode" as is often claimed in popular diet books.   We know that simply eating a lot of fat or a lot of sugar while keeping energy intake constant does not cause us to gain more body fat.  We know for a fact that the theory of obesity being caused by insulin levels rising due to eating  too much starch or sugar is simply wrong.  People become fat when they take in too much energy regardless of the source and they lose body fat when they take in less energy regardless of the sources they eat less of. 
 
That doesn't mean people respond equally to every kind of diet.  It's just that the reasons are not metabolic.  The reasons have to do with reward, satiety, and sometimes individual differences.  But the metabolic differences between different macronutrient strategies is based on thinking that has already been tested and falsified.  
 
Also  this wouldn't have to be true necessarily.  It isn't a logical necessity that foods have no powerful differential effect on absorption and conversion to fat and fat storage.  It's not just a matter of thermodynamics or conversation of mass and energy.  It is possible that our biology might have allowed us to take in some kids of nutrient, extract energy or chemicals from it, and excrete most of it without gaining body fat.  But it turns out to be false.  The reason is not conservation of mass and energy, the reason that our biology is particularly efficient in using nutrients and in storing the surplus energy. 
 
We might truly have discovered some  differential metabolic effects that prevent us from processing certain foods into fat (and that is exactly what many popular authors have claimed) but … it turns out that it doesn't seem to be true in general, and certainly not as a reliable  way to lose body fat permanently.  The small differential effects of nutrients on metabolism are sometimes used to good effect in short term efforts at bodybuilding and fitness, but they are not a reliable approach to obesity in general.
 
  1. Consequently, No macronutrient restriction strategy is a best practice diet for everyone. 
 
Framing the problem of fatness as if we  need to choose between popular branded diets is more often part of the problem than part of the solution.  Branded diets are generally based on a particular just theory.  
 
Debates over low carb, low fat, low sugar, low starch, low glycemic, high fiber, vegan, paleo, and so on are mostly based on asking the wrong question: "what specific food is making me fat?" 
 
Cutting out problematic "trigger" foods can be helpful for particular people, but not for metabolic reasons.  Also cutting out entire classes of food can help at least temporarily lose weight.  This is also not for metabolic reasons.  This is because we tend to reduce intake more than we compensate, at least for a while, when we cut out entire classes of food. 
 
Some of those strategies work better than others in the short run.  But it turns out with those macronutrient restriction strategies that it really doesn't matter which class we chose to cut out in the long run. 
 
People who successfully reduce intake by restricting carbohydrates and people who successfully reduce intake by eating vegan or by eating "paleo" are all losing weight because they are taking in less energy, not because of metabolic advantages. 
 
So long as we can sustain the calorie deficit with that strategy, we lose body fat.  That's wonderful for the people who end up with a strategy they can sustain, and we can find some success stories for many different strategies.  Strategies that restrict entire classes of nutrients end up being unsustainable for most people  in the long run though and the claims often made about any of these having unique metabolic advantages for weight control have been soundly falsified.  
 
  1. People do not regulate their weight to a particular inherited set point.
 
This is the opposite problem from the panacea solutions.  This one reinforces our tendency to give up.  Fatness and leanness often run in families, but not because our genes have a built in weight that we are fated to maintain.  It is because of all of the various factors that go into activity, reward, impulse control, individual metabolism, and habit formation, how those interact with specific environments, and because we often inherit things in addition to our genes.  Animals in their native ecological niche tend to regulate their weight very tightly and people who try to lose weight often end up back at the same weight.  But these are as much a result of stable aspects of their environments as stability in their weight regulation.  When we re-engineer out environments we end up altering weight regulation.  The efficiency of our biology and the stability of our dispositions are powerful factors in making obesity a difficult problem but they do not  make it impossible to solve. 
 
I'm going to try to do more than just add my own personal just theory to the already confusing and conflicting list.  What I'm going to try to do is navigate the available evidence to show what is going on and make sense of why the problem is so difficult and what people are doing when they do manage to succeed.

 

  1. The Backlash Culture Against Obesity Does More Harm Than Good

 

So the "obesity epidemic," as it has often been called, has led to a culture of backlash against fatness.  By that I mean a commonly shared negative attitude toward fatness and toward fat people.  We have mobilized mightily against the problem in all sorts of ways.  Some of those have unfortunately probably made the problem worse. 

 

The backlash against fatness might have been a good thing if it had led to a problem solving culture that recognized the biological, psychological, cultural, and economic dimensions problem realistically, helped us understand it, and began providing realistic solutions.  Obesity researchers have sometimes attempted to offer realistic solutions, especially focusing on preventing obesity in children where we can potentially have the most effect.   

 

But realistic problem solving is definitely not most of what has happened so far.   What we have instead is:

 

  1. The problem remains: most people who try to lose body fat end up going from diet to diet or from one exercise program to another , succeed for a while, and then give up.  Eventually many give up on the problem entirely as hopeless.  In effect, we often give up on ourselves.  This is especially true when we buy in to the popular misconception that obesity reflects a simple failure of willpower.  Fat people are often stigmatized as lazy and they feel like failures, which generally makes the problem worse rather than better.

 

  1. The food industry exploits the situation by creating and marketing niche "diet" and "health" products that supposedly address the problem but which rely on outdated theories, popular misconceptions, and strategically selective interpretations of research.  The market for high density rewarding "diet" foods for example was created to exploit medical advice to eat less food by eating less fat.  The advice was oversimplified and the new market for diet foods probably added to the problem significantly by exploiting it.  Their goal is selling more food product rather than improving health, which most often turn out to be conflicting priorities.     They become part of the problem by flooding us with false solutions and misleading information. 

 

  1. The fitness industry exploits the situation by creating complex dietary and exercise programs that are oriented to short term bodybuilding or fitness goals and then marketing those as solutions to obesity. 

 

  1. Popular authors tout their range of idiosyncratic interpretations and solutions, each trying to make sense of the confusion but they mostly end up increasing it.  Popular diet just theories by journalists and doctors very often end up inadvertently creating even more confusion.  

 

So the backlash culture in these various dimensions,  far from helping to lessen the problem, has exacerbated and perpetuated it in several specific ways:

 

  • It increases the difficulty of the problem for individuals psychologically, by fostering confusion and then discouragement and self-loathing.  By emphasizing willpower in unrealistic ways, and relying on solutions that require extraordinary short term efforts, we make people less able to succeed rather than more able to succeed in the long run.

 

  • It adds to choice confusion when we try to make decisions and are led astray by the marketing of product rather than decisions in our own best interests.  Unless things like "diet foods" and "bootcamps" and "extreme weight loss" are themselves actually viable solutions to obesity (which they are not in general) they become new sources of both confusion and discouragement.

 

  • It reinforces the epistemological problem of cynicism.  Thinking we are all scientific experts  who are well situated to simply choose between the popular diets and popular theories that seem most plausible to us prevents us from learning from the actual research and prevents us from moving toward more realistic solutions.  We become easy prey for every scheme that comes along. 

D. Science Cynicism and Overly Broad Mistrust of Expertise

 

Journalists writing about the problem of obesity have responded to this ongoing confusion by either claiming we don't know what causes obesity or by trying to promote a particular new finding.  The problem is very complex in some ways, but it is very misleading to say that we don't know enough about it to move toward better solutions.  The journalists who say we don't know the answer are a minor concern though, they are at least sincerely trying to be good communicators of the science and clear up the confusion.  The ones who are really dangerous are the grandiose prophets of false information. 

 

What we usually have is a theory that catches the interest of the journalist and then they confirm it by gathering information and telling stories that reinforce their own theory.  This is a compelling and powerful way to communicate, but it offers no assurance that they are getting the science right.  And while we sometimes find out about truly revolutionary ideas this way, as it turns out, these "sciencey" storytellers are most often getting as much of the science wrong as they are getting right.   

 

These "sciencey" journalists often end up asking bad questions and then we end up talking about the wrong things.  I think this is a big part of the problem and the reason I have written this book.  I hope to describe what we know about the problem of fatness without falling into the common trap of arrogance and confirmatory bias, but of course I can only argue my own perspective.  I could be wrong about the scientific consensus, but I will do my best to communicate it as faithfully as I can. 

 

The unconstrained confirmatory bias by journalists wouldn't be so bad by itself in some cases, since they do sometimes bring information to light that was not previously well known.  At least some people would benefit from some of this information.    But these folks often then read some scientific literature to try to bolster their articles and books and I feel they often do a hatchet job on it.  They can't reconcile their idiosyncratic theories with the existing evidence so they start claiming that the evidence that conflicts with their own theory was due to "corrupt researchers."  This ad hominem strategy has been a highly successful one for some authors, but it is an unfair way to argue and much worse, it plays into general cultural cynicism of science.  That part is extremely bad for the rest us.  It means we perceive the science as arbitrary or a matter of choosing sides based on what sounds plausible or what seems to work for some people.  It feeds the popular trend for imagining that everyone is naturally capable of evaluating scientific evidence by virtue of "common sense." 

 

What often happens, I believe, is that we end up mistrusting expertise, which is in itself a very serious problem.   That fact that we find so many false or misleading claims of expertise makes the problem of finding, trusting, and interpreting legitimate expertise even more of a challenge.    Nutrition and health sometimes involve on complex technical knowledge and interpreting rich patterns of seemingly conflicting evidence.  This kind of interpretative skill and knowledge is not something we possess as part of our "common sense."  It is something that requires not only understanding "critical thinking" in general, but also requires domain-specific knowledge in the specific fields in question. 

 

The backlash culture and especially cynicism of real expertise has fed bias and arrogance by various popular journalists who then set the tone for popular conversations in unproductive ways.  Although they may have a lot of charts and graphs and selectively cite and interpret a lot of research, rarely do journalists engage the research deeply and competently and systematically and put it into context.  Rarely do they make a distinction between different kinds of evidence and different quality of evidence in order to do a skilled job or drawing general conclusions from the existing science. 

 

The biggest problem with many of these popular authors is their grandiosity.  They think they've discovered a pattern that everyone else has missed or they have some limited success with some people and they proclaim to the world that they have the solution.  Grandiosity exploits uncertainty and cynicism to produce cults of misinformation that are self-perpetuating and extremely difficult to address with reasoning and evidence.  
 
 

Summary of Why the Big Fat Problem is So Tricky

 

Summary of broad factors making the Big Fat Problem so nasty:

 

Problem Factor
Class of Factor
Associated Bad Thinking
We tend to think in terms of simple actionable heuristics we can act upon when we make decisions.  What food is causing me to get fat, so I can stop eating it and lose weight?  What foods should I eat to lose weight instead?  Our need for actionable heuristics makes us especially vulnerable to just theories, and just theories of complex outcomes are typically wrong.  
Oversimplification
"Obesity is just a matter of eating more of … or eating less of  …"
The science is often distorted into oversimplified advice.  The scientific consensus relies on expertise to understand and is hard to communicate in terms of actionable steps so it gets lost in the confusion of just theories.   We end up systematically asking the wrong questions and arguing without regard to the existing patterns of evidence.
Oversimplification
 "One study constantly contradicts the previous one, so it's all really useless information, we should just pick the authors we agree with and follow their advice"
Our collective cultural assault on fatness has led to a backlash culture that makes things worse and leads to additional problems.
Unintended Consequences
"Being fat is really bad, stop being so lazy!  Just do this… "
Journalistic arrogance and widespread science cynicism exploit the problem of ubiquitous expertise
Knowledge Cynicism
"We're all scientific experts, including me!  Forget the scientific consensus, this sounds like a good way, follow me!"
"Sciencey" storytelling journalism
Poor science communication
"Telling stories about research and researchers is a great way to learn the science!  The details of weighing evidence are boring and irrelevant and people aren't able to handle it."
Industry interests driven by economic and business concerns that often end up conflicting with public health or individual interests of consumers
Economically Driven Consumer Culture
 "People citing research in their ads and branding their products for health are generally offering valuable new choices for us."

Saturday, June 13, 2015

Can Blender Food Help Us Lose Body Fat?

I use the blender for weight control as do a lot of people, but I've been very careful about tracking my results and I've found that I've had  varying success using the blender as a weight control tool.    I think I've discovered some of the reasons for the variance.   I'm not interested in motivational stories or anecdotes or testimonials  or selling recipes or blenders here, I'm interested in the specifics of what makes the blender a useful tool for weight control and what makes it less useful in some cases.   

The main ingredients in a smoothie intended for weight control are fruits and vegetables.  Protein powders often figure in recipes but I want to consider them separately because in most cases they are not used for weight control specifically.  There are exceptions to that such as protein-sparing fasts, but it is the fruits and vegetables that most advocates of blender foods are talking about for the most part. 

In general we think of fruits and vegetables as healthy.  Not much to argue with there, but I want to first examine the basis of this idea so we have a clear understanding of what we are talking about because in this case the details matter and not just the general principle that fruits and vegetables are mostly very healthy food.   

In general we tend to accept the assumption that fruits and vegetables are healthy compared to most of what most people eat.  The most convenient and least expensive foods and ones we value most tend to be the least healthy in general.  Compared to those, fruits and vegetables are clearly more conducive to good health.  

There are two important points of contention though:

  1. "Smoothies" often contain ingredients for flavor that are not just blended fruits and vegetables and maybe some protein powder.  They can contain a lot of added sugar, and significant added fats because  those often make the drink a lot more appealing.  However that is a concern mainly if you buy commercial drinks or  if you are careless about the recipes you use.

  1. There is also evidence that drinking food can sometimes have completely different effects on satiety than eating it.  This is a much more important concern to me and one that I want to examine in more detail.  The tricky part is that the effects of drinking calories can be good or bad depending on other things. 

For the moment let's assume we are intelligently blending fruits and vegetables, and that the resulting drink is healthier in most ways than commercial soft drinks.   That assumption is probably not too much of a stretch.  The question I'd like to address is specifically whether we can generalize that adding daily smoothies to our diet can improve our ability to regulate our weight, whether it can be a detriment, or whether it tends to be a neutral or indeterminate factor.       

First, let's get a scientific handle on fatness.  The problem of obesity at a population level has a lot of complicated aspects and the biology of metabolism is also very complex, but advocates of various products and services have often used that complexity to distract us from what are fairly simple overall facts of the matter.  So let's start by taking a very simple high level cut at the problem of human fatness from a biological perspective.

Kelly Brownell, an expert in nutrition and weight disorders, describes the overall situation as clearly as any problem description can be stated:

"The simple story is that biology seeks out an energy-dense diet, the environment provides it, and we have runaway obesity." [1] (p. 35)

This is sometimes known as the "mismatch" framework because it reflects our observation that our environment has become less well matched over time with our biology in some ways.  We have made great strides in exploiting the widespread animal evolutionary selection for efficiency in the form of preferring an energy dense diet when it is available.  We seek out sugar, fat, variety, and the flavors we associate with fats and carbohydrates especially.  Our cultural environment exploits this in selling food.    That's the simple truth of why so many of us are fat.  Our stable biology preferring energy dense foods  provides a vulnerability that our environment has come to exploit. 

Obesity, or runaway excess fat tissue, is relatively uncommon outside of humans, the companion animals of humans, and the animals domesticated by humans.  In general when animals have equally palatable or equally unpalatable choices of different macronutrients, they tend to balance them pretty well rather than becoming malnourished or overnourished.    Under conditions of their natural environment, animal preferences in food tend to serve them well most of the time, just as we would expect.  Weight is regulated in a very stable way under those conditions.     Animals evolved to eat in a way that helps them survive in their natural habitat, by taking advantage of the food sources available to them.  

The bad news is that something relatively uncommon in nature is now very common in human environments:  abundance in the form of an amount and variety of energy dense foods that was very rare in earlier times.  The seemingly good intake regulation animals do in natural environments, where scarcity is the rule, is easily overridden by simply making greater amounts and greater variety of foods available of the sort we tend to prefer. 

We are not wired to regulate our weight, we are wired to thrive in natural environments by strongly preferring energy dense foods in order to take advantage of them when we find them, and there is apparently no natural mechanism that effectively compensates for that preference by eating less of them under those conditions. 

In experiments with rats, the preference is so strong that they eat themselves into protein deprivation when either more fats or more carbohydrates or both are provided than proteins.  [2]  Rats may seem pretty far removed from us in some ways, but the pattern is suspiciously familiar in human environments as well.  Greater availability of higher energy density foods leads to eating more of those and neglecting other sources of nutrition, to the detriment of our health.

So we don't need to look at a lot of complicated issues in nutrition to see why fruits and vegetables are offered as favored foods for weight control.  However I think we do need to be suspicious of whether simply adding more of  those to our diet will have the desired effect of competing successfully with the higher energy density foods that make us fat.  Will drinking more green smoothies lead to eating less loaded fries and mega burgers and drinking less gargantuan soft drinks?  That's the promise of the blender as a weight control tool, at least in the ads for smoothies and blenders and smoothie recipes. 

We have clear-cut evidence that fruits and vegetables are in general less energy dense and yet are still satisfying sources of nutrition compared to most of the food that comprises the average American diet.  The strategy of reducing energy density in general has been supported by research and argued by leading experts in weight regulation such as Barbara Rolls :

"A growing body of laboratory-based, clinical, and epidemiological data suggests that low-energy-dense diets are associated with better diet quality, lower energy intakes, and body weight. Dietary energy density can be lowered by adding water-rich fruits, vegetables, cooked grains, and soups to the diet, and by reducing the diet’s fat content." [3] p. S98 

So the argument for replacing at least some portion of our energy dense foods filled with added sugars and fats with satisfying but far less energy dense foods like fruits and vegetables appears to be very defensible, so long as we are also somehow still getting the nutrients we need that might not be easily found in fruits and vegetables.  The advocates of smoothies rarely suggest that they should entirely replace other foods with smoothies, so that doesn't seem like a big concern to me so long as people are not relying entirely on smoothies for their nutrition.

Replacing some of our energy dense convenience foods with less energy dense fruits and vegetables certainly seems reasonable.  So we might well agree in principle that adding fruits and vegetables to our diet can help regulate our weight.  But does it actually work that way if we simply add fruits and vegetables to diet otherwise filled with convenience foods?   Do we actually start eating less of other things if we somehow get ourselves to eat more fruits and vegetables?  Or do we end up just adding more "healthy" calories on top of what we already eat?

The question is not just the trivial one of whether forcing ourselves to eat tons of veggies temporarily prevents us from eating a cheeseburger, or whether that would be a good strategy.  The question is whether adding fruits and vegetables in some enjoyable way actually  helps us eat less of other things in the long run in a way that causes us to take in less total energy.   That would be a legitimate aid to weight control. 

Or are green smoothies a minor convenience that still relies on brute force self-control to replace the more attractive foods we crave? 

And if eating more fruits and veggies does help, does it still help if the fruits and vegetables are eaten as a liquid?  There is a real possibility that it might make a difference.    These are the real questions I want to explore.

Phrased this way, many of the vast complexities of nutrition and metabolism are mostly irrelevant.  What I want to know is whether smoothies can actually help with weight control, which means the ultimate deciding factor is whether adding them to our diet causes us to take in less energy overall, without taking other measures.  That's a strongly stated but relatively common version of the claim made for why smoothies are supposed to be useful for weight control.

Fruits and vegetables are low in energy density mostly because of their high water content and their low fat content.  Their fiber content contributes as well, but to a lesser and more variable extent.  The low energy density due to high water content and low fat content also seems to be the primary reason why fruits and vegetables are relatively high in satiety (we  tend to compensate for eating them by eating less later) as well as satiation (we tend to find smaller amounts satisfying  and stop eating sooner).   [4] p. 6

If fruits and vegetables are generally useful in regulating our weight, the best argument I can find is that they replace higher density nutrition with lower energy density nutrition without motivating us to eat more to compensate.  If we ended up more hungry a few hours later as a result of taking in less energy dense foods now, we would still be relying on our willpower to lose weight and the fruits and vegetables would not actually be helping us lose weight in the strongly stated sense. 

So do fruits and vegetables have this effect of helping us take in less energy while not compensating later? 

And do they still have this effect if prepared in a blender first?

In the latter 20th century, the rate of obesity rose dramatically and unexpectedly along with the amount of money we spent marketing and buying convenient foods that are very high in added sugars, added fats, enhanced flavors, portion sizes, and energy.   It is very unlikely that this was a coincidence.  We started eating more because  foods that exploited our preferences became more readily available and appealed particularly to our decision making by appealing to our taste preferences and our preference for economic value.  Nor did we compensate for the increased intake by moving more.  If anything technology changes have led us to move less and exert less physical effort in our daily lives.  As a result the environment came to overwhelm our ability to regulate our own weight. 

Popular theories that preferentially blame fats or carbohydrates for obesity are mostly missing the point.  We became fat when we started eating more of everything, and we did that because of increased availability of high energy foods that suit our natural preferences, not simply because fats or carbohydrates are fattening.      

The crux of the problem of fatness is increased intake, not whether we eat "healthy" foods.  That's why the question of whether fruits and vegetables help us eat less is crucially important.  We eat more now across all of the major food groups, not just the "unhealthy" foods, so we can't lay the blame for obesity entirely on those.  The increased intake that led to increased obesity included fruits and vegetables, not just French Fries  and soft drinks.   Adding fruits and vegetables to our diet in general as a population has not by itself magically pushed out junk food or reduced our overall calorie intake, and there is little population evidence to suggest that it should.   The evidence that simply adding fruits and vegetables to our diet would compensate for overeating is not terribly compelling at a population level.    But what about experimental evidence? 

Considering how commonly it is recommended, there is surprisingly little direct evidence regarding the effect on weight control of adding fruits and vegetables to our diet.  Most research where higher energy density foods were replaced with fruits and vegetables was relatively short term and also included explicit instructions and assistance in avoiding compensating for the added calories.  So we don't really know whether (or how much) adding fruits and vegetables really helps us eat less or helps us eat less in a later meal.  We strongly suspect it is at least a factor though because low energy density foods do tend to result in both higher satiety and higher satiation.   The fiber content of those foods may also play a secondary role. 

For the most part when we are not relying on external cues for how much to eat and we make use of internal sensation, it is the  weight and volume of what we eat that makes the difference in how much we eat rather than the amount of energy it contains or the glycemic loading, so long as it has the right sensory properties that we experience it as substantial food. [5]   Surprisingly, since so much diet advice mentions glycemic index, it does not appear that carbohydrate content or glycemic index are reliable predictors of satiation or satiety compared to energy density and fiber content.   For example, boiled potatoes, which are relatively high in glycemic index, are also particularly satiating.  

The available evidence from intervention studies seems to support the idea that adding fruits and vegetables to meals can assist in weight control by adding water and fiber and reducing energy density, increasing satiation and satiety, and helping us to eat less overall while still getting good nutrition.  Supporting this idea, restricting high energy density foods while allowing unlimited amounts of fruits and vegetables has sometimes been a successful weight control strategy.  [3] 

This doesn't necessarily tell us that that adding fruits and vegetables to our diet causes us to eat less of other things, but it does tell us that we tend not to overeat fruits and vegetables, which suggests that many people find them either relatively satiating or relatively unpalatable.   So it leaves the door open to the possibility that they can be useful for weight control for those who do find them palatable as well as satiating. 

So let's assume for now that fruits and vegetables do help us with weight control by helping us eat less of other things.  That being the case does this still apply when the fruits and vegetables are prepared in a blender?

The answer to this might seem obvious depending on how you think about satiation and satiety.  The counter-intuitive reality though is that some foods increase in satiety when in liquid form and some foods decrease in satiety in liquid form.  The case is most clearly established for high sugar drinks, which have been unambiguously established to have very low satiation and satiety and are believed by obesity researchers to be an important  contributor to obesity.  The case is more equivocal for liquid meals that also contain more satiating ingredients such as fiber and protein.   In those cases, the variation in outcomes may be because the behavioral context plays a crucial role in their effect on intake. 

First, on the plus side, the water content of foods is one of the main things that increases how well they satisfy our appetite.  This happens by increasing their volume and their weight.  When you make a soup out of ingredients, you are getting both a greater weight and greater volume of food than when you eat the ingredients without the liquid, and in general that tends to increase the satiation of the same food without increasing the energy intake.  More interestingly, and more surprisingly, it can also increase the satiety of the same energy-equivalent of food, causing us eat less later.  [6]  For foods that are already satiating, adding water while still making them palatable and perceived as food, tends to increase satiation and satiety. 

The same effect is not seen simply by drinking water with a meal or before a meal as when the water is part of the food.  Hunger and thirst are regulated separately in the body, the satiating effect of fluids are because we  experience the food as heavier and higher volume (and as food!), not simply because there is more water in our stomach. 

Blending fruits and vegetables into a drink obviously increases the water content, and they are already satiating, so we have reason to suspect it might increase the satiety and satiation.  Assuming we experience it more as food rather than more as water.  So the case for losing weight with green smoothies seems plausible scientifically. 

On the minus side, we don't seem to regulate our own intake as well with a liquid diet as we do with a solid food diet. 

Under controlled conditions, where we are not inundated with abundance, variety, and other cues that tell us eat more, we tend to regulate our intake from one meal to the next during the day  to eat relatively the same amount from day to day, and we also seem to regulate out intake to some extent from day to day.    This is especially true of the volume of food we eat, but under some conditions it is also true of calories

Given the same weight and volume of solid food, we also tend to eat more or less from meal to meal to take in about the same amount of energy every day.    In experiments, secretly adding more calories to the same amount of food each day results in people eating less in subsequent meals.  This phenomenon of energy-specific satiety is sometimes known as dietary compensation.  [7],[8]    The argument against liquid diets is based on the finding that dietary compensation seems to be much weaker with liquid meals than with solid meals.  [9]  However this is mostly based on findings regarding fruit juices vs. fruit and sugary drinks vs. sugary solid foods, and almost entirely based on liquid vs. solid carbohydrate intake.  Liquid diets have also been used successfully for weight control under some conditions.  [10]

This means that different forms of a food (at least a carbohydrate) can alter its satiety and satiation, and the liquid form of carbohydrates in general seem to bypass our tendency to compensate by eating less.  With fruit for example, the case is quite clear, the liquid form is considerably less satisfying to our hunger when used as a "preload" just before eating.[11]    As usual, the energy density plays a big role, and fiber plays a smaller role, but simply drinking calories rather than eating them seems to have an independent effect on satiation as well.  This may be due to structural factors involved in eating and digestion or it may be due to expectations we have regarding how satisfying the food will be and the context in which we are eating. 

We probably don't expect fruit juice to satisfy our hunger as well as fruit, and that may in part be why it doesn't.  Do we expect smoothies to satisfy our hunger?  That might tell us whether they can serve us in weight control by helping us eat less in total. 

One strategy for eating less is sequencing.  Starting a meal with a low energy density food (as an appetizer or "pre-load") seems to reliably help us reach satiation with less total energy intake, but starting with solid low energy density food seems significantly more effective than starting with liquid low energy density food, regardless of fiber content.   This is in direct contrast to the popular advice to drink water prior to eating in order to fill up.  That seems relatively ineffective even if we replace the water a high fiber carbohydrate drink. 

Using a blender to conveniently add fruits and vegetables to our diet seems a reasonable strategy for weight control, by providing satisfying nutrition at lower energy intake, but the way we use it probably matters a lot.  It appears that blender meals are best used as weight control aids when: 

  1. We enjoy them and find them palatable and satisfying  and expect them to be satisfying while still keeping them at low energy density. 
  2. We do not make them energy-dense with sugars and fats, even "healthy" ones.
  3. We use them to replace rather than just add more intake to higher energy density sources
  4. They contain satiating ingredients such as high fiber carbohydrates and lean protein
  5. We don't rely on them as our only strategy for getting good nutrition while taking in less energy

 References

[1](2004) Brownell, Kelly and Katherine Battle Horgen, "Food Fight: The Inside Story of the Food Industry, America's Obesity Crisis, & What We Can Do About It." McGraw-Hill

[2]  Michael G. Tordoff  (2002) "Obesity by choice: the powerful influence of nutrient availability on nutrient intake" 

American Journal of Physiology - Regulatory, Integrative and Comparative Physiology Published 1 May 2002 Vol. 282 no. 5, R1536-R1539 DOI: 10.1152/ajpregu.00739.2001  URL:  From http://ajpregu.physiology.org/content/282/5/R1536

[3] (2005) BARBARA J. ROLLS, PhD; ADAM DREWNOWSKI, PhD; JENNY H. LEDIKWE, PhD "Changing the Energy Density of the Diet as a Strategy for Weight Management"  Supplement to the Journal of the AMERICAN DIETETIC ASSOCIATION, May 2005 S98-S103

 [4]  (2004) Barbara J. Rolls, Ph.D., Julia A. Ello-Martin, M.S., and Beth Carlton Tohill, Ph.D., M.S.P.H.  "What Can Intervention Studies Tell Us about the Relationship between Fruit and Vegetable Consumption and
Weight Management?"  Nutrition Reviews , Vol. 62, No. 1 January 2004: 1–17 URL: http://www.researchgate.net/profile/Barbara_Rolls/publication/8674390_What_can_intervention_studies_tell_us_about_the_relationship_between_fruit_and_vegetable_consumption_and_weight_management/links/5405d2cb0cf2c48563b1ba87.pdf

[5]  (2005) Tohill, Beth Carlton, "Dietary intake of fruit and vegetables and management of body weight," World Health Organization , ISBN 92 4 159284 2 URL: http://www.who.int/dietphysicalactivity/publications/en/f&v_weight_management.pdf

[6]   (1998) Barbara J Rolls, Victoria H Castellanos, Jason C Halford, Arun Kilara, Dinakar Panyam, Christine L Pelkman, Gerard P Smith, and Michelle L Thorwart    Am J Clin Nutr 1998;67:1170–77.
"Volume of food consumed affects satiety in men"  URL:  http://ajcn.nutrition.org/content/67/6/1170.full.pdf

[7]"Short Term Dietary Compensation in Free-Living Adults"
F. McKiernan, J.H. Hollis, and R.D. Mattes
Physiol Behav. 2008 March 18; 93(4-5): 975–983.

[8] "Dietary compensation in response to covert imposition of negative energy
balance by removal of fat or carbohydrate"
Gail R. Goldberg*, Peter R. Murgatroyd, Aideen P. M. McKenna, Patricia M. Heavey
and Andrew M. Prentice
British Journal of Nutrition (1998), 80, 141–147
http://www.researchgate.net/profile/Peter_Murgatroyd/publication/13457513_Dietary_compensation_in_response_to_covert_imposition_of_negative_energy_balance_by_removal_of_fat_or_carbohydrate/links/0deec52cbd1ac48ea3000000.pdf

[9] (2000) "Liquid versus solid carbohydrate: effects on food intake and body weight"
International Journal of Obesity (2000) 24, 794±800
DP DiMeglio and RD Mattes
http://cibr.refrescantes.es/ka/apps/cibr/docs/06_2000_Solido_y_liquido_efecto_peso.pdf

[10] (2007) "Liquid calories, sugar, and body weight"
Adam Drewnowski and France Bellisle
Am J Clin Nutr March 2007 vol. 85 no. 3 651-661
URL: http://ajcn.nutrition.org/content/85/3/651.long

[11]  (2009) Julie E. Flood-Obbagy and Barbara J. Rolls "The effect of fruit in different forms on energy intake and satiety at a meal"   Appetite. 2009 April ; 52(2): 416–422. doi:10.1016/j.appet.2008.12.001.