In a recent New York Times article, Abigail Zuger takes a crack at the diet wars, and does a reasonable job. There are many points left to be made, however.
The question is, essentially, how to maintain a healthful and desired weight. In broad brushstrokes, the variable are — how many calories people consume, what kind of calories are consumed (the proportion of macronutrients — fat, protein, and carbohydrates) and how much people exercise. These are the (allegedly) controllable variables. The variable we cannot control is our genetics, which largely determines our inherent metabolism and hormonal function.
Different people have different interpretations of the evidence. There are also countless popular diets that don't even attempt to square with the evidence, but I will largely ignore them for this post.
Zuger spends much of the article discussing the writing of Gary Taubes – a science journalist and author of Good Calories, Bad Calories, and now an updated and streamlined version titled, Why We Get Fat: And What to Do About It. I have not yet read the book, but I have read many of Taubes' articles and lectures. Zuger summarizes his main points:
We’ve got the whole thing backward, he argues. The overweight are not lazy hogs who eat too much and exercise too little. The thin are not virtuous and disciplined. Rather, all of us are fulfilling a fixed biological mandate, just as growing children are. Our bodies have a nonnegotiable agenda, and our behavior evolves to make that agenda happen, he writes: “Eating in moderation and being physically active (literally, having the energy to exercise) are not evidence of moral rectitude. Rather, they’re the metabolic benefits of a body that’s programmed to remain lean.”
This all sounds nihilistic – our weight is genetically determined, so why bother trying to control your eating and exercise regularly? But Taubes goes on to endorse the low-carb diet. He argues that insulin is the one hormone we can affect, by eating a low-carb diet. Carbohydrates are the villain – the cause of the obesity epidemic.
Taubes knows that his opinions go against the consensus of expert opinion, and he too casually tosses the consensus aside, in my opinion. I do not maintain that the experts are always right, but it's rare that they are systematically wrong in a field with a lot of evidence. At the very least, I would be very concerned if my read of the evidence was not shared by the experts – I would assume that I was missing something, and not the experts.
Here is what I think Taubes is missing: Interpreting the research is complex – and you have to balance basic science with clinical research. I think Taubes is overemphasizing the basic science (and putting it in the wrong context) and is dismissing the clinical research.
For example, Zuger makes her best point when she writes:
How to account for the fact that in virtually all head-to-head comparisons of various diet plans, the average long-term results have invariably been quite similar — mediocre all around? The party line holds that backsliding is universal. Mr. Taubes makes much of the addictive effect of carbohydrates: once you taste them you never forget them.
Zuger is correct – if low carb dieting were the answer, then the clinical research would show it. What the research shows is that any advantage to low carb diets are minimal (if they exist), and short lived. They are not the answer to weight control. Zuger then lets Taubes off the hook too easily with his reply that carbs are addictive. This is a massive bit of special pleading, a casual dismissal of a large body of clinical evidence that cuts the heart out of Taubes' interpretation of the research.
In addition Taubes and other low-carb enthusiasts get the context of basic science research wrong. First, I agree that genetics largely determine our inherent tendency to maintain a certain weight. Most people who are obese are so because of their genetically determines hormonal function and appetite control. But genetics are not destiny. While our genetics strongly influence our behavior, they do not control it. We have the ability to hierarchicaly supersede our default behavior. It's not easy, as the research also indicates, but it is possible.
So far we have not found a safe and effective way to alter our hormones. Low carb diets do not accomplish this (as an aside, they are useful for avoiding and treating diabetes, but don't seem to help in weight control). There are appetite suppressants, but these are of limited utility. Maybe one day we'll have an obesity pill, but we don't now.
So – bottom line, we can't change our inherent metabolism or appetite. It is also true that if we decrease our caloric intake we will tend to exercise less, and if we exercise we will get more hungry and tend to eat more. Our bodies manage to balance our caloric intake and output fairly well over long periods of time. But if one exercises regularly and limits their caloric intake at the same time that would avoid this automatic compensation.
Another factor that has recently received research attention is that lack of sleep results in hormonal changes that also correlates with obesity, either through increased appetite or decreased physical activity. Getting a good-night's=sleep is one way to alter our hormonal status in a favorable way.
As evidence that genetics are not destiny is the fact that obesity has been steadily increasing over the last thirty years, and not just in the US but in many industrialized countries. There is a great deal of argument over what, exactly, is causing the increase. It does seem to correlate with an increase in overall caloric consumption. Others, however, point to computers and increased time spent on sedentary activities.
Also (and here is where I think Taubes gets the context wrong) focusing on the hormonal and metabolic differences among people may help explain why person A is overweight and person B is not, but it does not help person A maintain a healthier weight. For that we need to focus on those variable that can be changed. Because the body is a horrifically complex system, even though we can explore and understand many aspects of the system, in order to understand the net effect of making specific changes to one's behavior, these have to be studied clinically.
The clinical research shows various things. First – there is no significant difference among the various diets based upon macronutrient ratios. Adjusting macronutrients does not seem to have a significant net effect on weight control. Finding a way to control overall caloric intake does work. To be clear, nothing works for most people, since most people fail most attempts at long term weight control. But the variables that do seem to help are utilizing convenient methods for estimating caloric intake. Even just writing down what one eats every day helps. Also, healthy eating should, as much as possible, be the default behavior. Having low calorie healthful snacks around the house, rather than tempting calorie dense snacks, is helpful. Eating at restaurants that publish the caloric content of their meals also makes sense, but I'm not aware of any data on this yet. Meal replacements are helpful, probably because they help estimate caloric intake and help avoid accidentally overeating.
There is recent evidence for a strategy of eating only when their is initial hunger, which correlates with low blood sugar. The idea here is that overall caloric intake will be decreased if one reinforces the pattern of eating only when there is a sensation of hunger.
These types of strategies work for some people, but if we want to have a societal impact on weight then there probably has to be regulations that make default behavior more healthful. We don't need to take choice away from people – but just make the lower calorie or more healthful choice easier.
Also, there is no question that there are many health benefits to regular exercise. Exercise alone is probably not enough to maintain weight. But if one engages in regular scheduled exercise, that would override any inherent tendency to reduce calorie expenditure, either from reducing caloric intake, or just with age or a sedentary job or lifestyle. It doesn't matter how much your genetics tell you to exercise, if you stick to a schedule of regular exercise.
I don't think there is any simple, easy, or universal solution to the problem of weight control. Reversing the obesity trends will likely take societal changes as well as a focus on the many small things that all help. Perhaps they can add up to a significant effect. I also think that a large part of moving in the right direction is to get away from the distraction of focusing on gimmicks. Ultimately, the low-carb diet is just another weight-loss gimmick. There may be some interesting basic science behind it – but bottom line, it doesn't work.