This is my first post in a series of planned commentaries based on my reading of Jonathan Bailor's highly recommended book, "The Smarter Science of Slim."
This first commentary is my perspective on the history of the issues and how I perceive they have been resolved scientifically so far.
The Low Carb Revolution
Years ago, Dr. Atkins shocked popular culture and infuriated proponents of low fat diets with the claim that people could lose weight and reduce their risk of heart disease by minimizing the mainstay of the typical diet, carbohydrates, replacing them with proteins and fats.
This was a controversial claim not only because low fat diets were popular at the time but also because in emphasizing a low carbohydrate diet, Atkins was claiming that we could be healthy with minimal amounts of important dietary elements like fiber and the nutrition we get from vegetables. He was opposed by the people who promoted an ever higher proportion of vegetables in our diet and who encouraged us to minimize saturated fats, which were long widely thought to increase the risk of heart disease and obesity. At the same time, a lot of people argued that obesity can and should be sensibly addressed with the reasonable commonsense approach of eating a little less and moving a little more: get active and cut back a little on calories each day.
Two Battles Emerge
This turned into two polarized contests of opinion in popular culture.
First, there was a conflict between the folks who think quality of food is important in weight control and those who think that emphasis is misplaced, that we should just measure calories in and calories out. The implication of the food quality view: eating more of some things and less of others should affect our weight over time without making constant efforts to otherwise monitor and control our intake by counting calories. The implication of the calorie balance model: just eat a few calories less and move around a little bit more to burn a few more calories and you will lose weight consistently.
Second, among those who consider the quality of food to be important, there was the battle of the low-carb lobby vs. the vegetable lobby. Should you eliminate carbohydrates because of their effect on metabolism, or should you eliminate saturated fats because "fats make us fat" and raise blood cholesterol?
As is often the case in polarized positions it seems from our perspective today that both sides (in both contests) got some things right and both sides got some things wrong.
Calorie Balance vs. Metabolism: The Result
The standard and consensus view of obesity among researchers is that passive overeating is the best overall description of the cause. It is widely accepted, though not universally, that the amount of caloric energy we take in plays a causal role in obesity. Further the standard and consensus view is that this results from a combination of global economic factors and local environmental factors (the "obesogenic environment").
It is also a standard and consensus view among obesity researchers and physiologists that body weight is regulated by metabolic factors (via chemical messengers) that are not not related to the number of calories we take in and the number of calories estimated for the activity we perform.
What the calorie balance model captures: our biology doesn't violate the laws of conservation of mass and energy. Eating less and catabolizing body mass for energy does cause us to lose body mass. Eating more and demanding less energy utilization does cause us to gain body mass.
What the metabolism model captures: The calorie balance model clearly predicts that our body weight should consistently fluctuate according to the overall energy balance between what we take in and our activity. This is demonstrably not the case both from common experience and controlled studies. The prediction of the calorie balance model only apply for a short time and then our body changes internally to absorb food differently and to use it differently for energy. Our appetite and subjective energy levels are also changed. This is collectively expressed as the body regulating its mass in various ways around a relatively stable point.
The common experience of a "weight loss plateau" coincides with the concept of a "weight set point" around which our body maintains itself in a narrow range over time.
When we simply eat less, we lose weight for a little while and then the loss slows down and eventually stops and tends to reverse itself into return to baseline weight and sometimes even gain above that original level.
Further, the signficance of metabolism implies that quantity of energy taken in and demanded is only part of the causal model. Metabolism is affected differently by the specific foods we eat over time and the specific kinds of activities we engage in, not just or even primarily the total amount of energy involved. The metabolism model better captures the importance of food quality than does the calorie balance model.
Low Carb vs. Veggies: The Result
Given the consensus view that metabolism is an important factor in weight control and that the kinds of food we eat are an important factor in metabolism, we arrive at the second battle, over what it means to eat higher quality food more conducive to health and fighting obesity.
What the low carb lobby got right and the vegetable lobby got wrong: saturated fat isn't itself an important cause of heart disease and obesity. You can consume reasonable amounts of fat, including saturated fat from animal sources, and still have a very healthy diet.
What the low carb lobby got wrong and the vegetable lobby got right: The low carb lobby deals with the problems of insulin response in a gross and overly restrictive way by choosing proteins and fats over carbohydrates in general rather than balancing them and eliminating high glycemic carbohydrates. This makes levels of fiber too low and eliminates important sources of nutrients and often crowds out vegetable nutrition sources using animal ones. This is probably healthier than the typical high glycemic diet, but not nearly optimal. Minimizing carbohydrates is a bad strategy because we get many nutrients from carbohydrates, especially vegetables.
What both the low carb lobby and the vegetable lobby both got right from the start: Sugars and starches as a mainstay of our diet are killing many people. Insulin resistance is a precursor to type 2 diabetes and is associated with and exacerbated by a high glycemic diet as well as by obesity. Starches are high glycemic.
The low carb lobby recognizes the role of high glycemic foods in obesity and chronic illness but they generallize it too far to all carbohydrates as an overly restrictive and overly simplified strategy.
The vegetable lobby is too concerned with the role of animal fat in nutrition and focuses on that rather than the more important distinction of higher glycemic vs. lower glycemic carbohydrates and a more balanced diet.
Saturated fat doesn't itself cause heart disease or obesity. Combined with a high glycemic diet, saturated fat exacerbates the problems caused by constant massive triggering of the insulin response because of a combination of factors:
(1) fats plus sugars tend to increase appetite dramatically,
(2) fats have a high energy density compared to their nutrition,
(3) saturated fats in particular have no protective effect for heart disease compared to omega-3 from polyunsaturated fats.
People tend to lower their risk of heart disease when they switch from saturated to unsaturated fats. This is one of the strongest arguments for eliminating saturated fat from our diet. However it turns out that this benefit is probably not because saturated fats cause heart disease. It is more likely because unsaturated fats have a protective effect compared to saturated fats.
Lowering glycemic load allows us to use nutrients more effectively, to metabolize all fats more effectively, and tends to reduce the risk of heart disease and obesity far more than reducing saturated fats.
So what works?
What dietary strategy best lowers our risk of chronic illnesses and obesity? Do they all fail equally? Do different people respond differently to different regimens?
It turns out that individuality is a real factor, both biochemical and psychological, and learning to make the principles work in your own life and for your own biology is critical. Still, there are also some general principles that we can rely on as a very good start.
The low carb strategy often works for as long as people can manage to maintain it and is healthier than the typical diet but it is not optimal for health and most people find it hard to sustain and eventually have health problems or fail to sustain it. It is not balanced nutritionally, it is too severe in limiting valuable and healthy vegetable sources of nutrition.
A vegetarian strategy often works at least for a while and is also healthier than the typical diet but it is also difficult for most people to maintain and as a general strategy it is too severe in limiting valuable and healthy animal sources of protein and what for many people are satisfying sources of texture and flavor in animal fats.
Taking what they both get right and eliminating what each gets wrong, we end up with:
1. Avoid high glycemic carbohydrates as far as possible or only under very specific conditions.
As a mainstay of our diet are a primary cause of both obesity and chronic illnesses via their effect on our response to insulin and our ability to absorb and metabolize nutrients. In other words, these commonly accepted processed products of agriculture cause a "clogging" of our metabolism over time that defeats our evolved ability to regulate our own metabolism. High glycemic carbohydrates are not essential for health and we tend to become dependent on them in various ways so minimizing them is an important first step to better health. There are specific strategies you can use to minimize their negative effects if you want to use them for athletic reasons or because you can't bear to eliminate them from your life entirely, but you have to be wary of how often you do this and the timing of it.
2. Balance the remaining nutrients between proteins, low-glycemic carbohydrates, and fats.
Compared to high glycemic foods, these categories all contain many healthy and valuable sources of nutrition.
Why a balance? In addition to just having a variety of nutrients of different kinds as well as a variety of tastes and textures to make eating more satisfying, there are also some specific nutritional reasons.
A diet of too much fat and too little protein and carbohydrate fails because fat contains relatively little nutrition compared to its energy density and tends to crowd out our intake of fiber important to digestive health as well as various nutrients. A diet of too much fat also fails because we have to eat a lot of it to make us feel satisfied in lieu of protein, fiber and water because of its low nutritional density.
A diet of too much protein fails because it avoids fiber and avoids important sources of vitamins and minerals and because it requires us to limit our protein sources very severely. It is also unhealthy to take in extreme amounts of protein. You can live on a high protein diet for a while if it isn't too high, but it isn't optimal. Temporary protein-sparing fasts are effective and popular among some athletes.
A diet of too much low-glycemic carbohydrates (taken to an extreme this would basically be a vegetarian diet that not only minimizes starches and sugars, but also seeds, nuts, and soy) is not really something anyone seriously recommends or practices as far as I know, but if they did it would fail because it would not have adequate protein sources to sustain health and would be relatively unsatisfying. Even strict vegans eat vegetable protein and fat sources, they just avoid animal sources. A diet with a huge amount of low-glycemic carbohydrates is perfectly healthy and sustainable so long as it also includes a reasonable amount of plant fat and protein sources.
The lesson here is just to mostly eat natural foods while avoiding high glycemic carbohydrates rather than striving for extremes of individual components. Avoid high glycemic foods and otherwise eat to satisfy your hunger. The specifics of satisfying our hunger are important however, balance is important in order to get a good combination of fiber, protein, water, nutrition, taste, texture, and other factors to satisfy us.
3. Take advantage of the "Paleo" principle but don't be limited entirely by it
I think the principle behind "Paleo" diets is basically correct, that our metabolism seems to be tuned by evolution to process natural animal and plant sources of nutriton that we could hunt or gather, and has not adapted yet to our dietary preponderance of processed agricultural products. This is another way of saying that high glycemic carbohydrates (the main category of highly processed and cultivated foods in our diet: the wheat, corn, potato, and rice products) are a very bad thing to emphasize all of the time.
In general the principles behind paleo eating agree with those proposed here, however they also focus on a rationale that can be misleading, which is why I consider it a fad even though it gets things mostly right. Trying to guess what our ancestors might have eaten and in what amounts is not nearly as useful a way to figure out what is healthy as just applying general principles and nutritional research results. By all means it makes sense to look to Paleo recipes and products as candidates for making it easier to maintain good nutrition. Also it is convenient and useful to imagine whether something could be hunted or gathered to know whether it is a nutritional source likely to be compatible with our metabolism.
Just don't limit yourself to the principle that we can only eat what our ancestors ate or elaborate arguments about the Pleistocene lifestyle. You have more options which you can intelligently apply to use modern foods and still be healthy.
4. Don't expect restricting calories to help you in the long run if you are eating poorly.
If you stop eating competely, you eventually die because your body eats its own tissue to try to meet its energy requirements. So when we talk about calorie restriction we aren't talking about not eating. We are talking about changing the timing of when we eat and eating less in a given period relative to what we would normally eat. We might eat less in a given period than we otherwise would, or we might eat nothing for a specific period of time. There are many strategies for calorie restriction. Some of them have a place in athletic performance and some of them can also have a place in a health regimen, but we have to be careful about how we go about it and how much we rely on it.
Sometimes the most reasonable approach is not the best. Portion control and light or moderate exercise seem perfectly reasonable and have been long recommended as a treatment or prevention for obesity. But for the vast majority of people they don't work for this purpose. Our metabolism and appetite conspire to maintain a stable weight against our efforts to make small reasonable changes in how much we eat and how much we move. We have to more directly influence our appetite and metabolism to deal with obesity. Simply eating less of the same things we are eating does not neccessarily help because it does not address the metabolic causes of our problems.
Fasting, as opposed to portion control, is a more potentially valuable and effective health strategy. This is because it can help you learn how to better control cravings, and can help you get your body fat lower than you could reasonably get with frequent eating and for longer periods. Some evidence suggests that fasting itself might trigger healthy changes in the body, although these are hard to distinguish from just the benefits of controlling body fat and eating more healthy overall. Fasting is much more difficult to do effectively, much less sustainable, and much less effective and healthy when combined with a high glycemic diet.
Your best bet is probably to eliminate high glycemic carbohydrates and get the hang of eating well first, then try fasting as an additional strategy if you want to, to make it even more effective and sustainable.
5. Don't just load up on "low fat" foods. But do emphasize lean protein sources over fatty ones.
By the best evidence available now, it seems that reducing fat by itself plays virtually no role in controlling obesity or chronic illness. Nutritionally, fat should be considered "neutral" or "filler" compared to good nutritional sources like non-starchy vegetables and good protein sources like seafood, lean meats, and egg whites. The problem with a "low fat" strategy is that if you go out of your way to avoid fats, you will also tend to replace the missing energy with starches and sugars.
If you could eliminate fats without replacing them with high glycemic foods, this strategy would probably work a lot better. Lean protein sources are an important part of modern nutrition, not because fat is bad, but because protein is so valuable. Fatty protein sources are really fats, not proteins, so they should be considered filler in your diet, rather than assuming they are good sources of protein. You have to eat an unreasonable amount of fatty protein sources to get enough protein to be valuable for satiety and nutrition.
6. If you find yourself eating something high-glycemic, at least mitigate its effects with fiber and protein and avoid fat under those conditions.
The effect of food on our insulin levels is the primarily culprit in obesity and many chronic diseases. However this glycemic effect is not just a result of what individual foods we eat, it is result of their combined effect on the amount of glucose circulating in our blood. There is no way to simply counter-act the glycemic effect short of avoiding high glycemic foods entirely but you can reduce it by lowering the combined glycemic effect by increasing the amount of fiber and protein you eat along with high glycemic foods. If you are going to indulge in high glycemic food, you can reduce the damage it causes by avoid simultaneous eating of fats (which boost appetite strikingly when combined with starches and sugars) and eat lean protein and good fiber sources with the high glycemic foods instead.
Note: This article was inspired by Jonathan Bailor's highly recommended book, "The Smarter Science of Slim."
Todd I. Stark