So many dogmatic claims are flying around about low-carb diets being the weight loss and cardiovascular health panacea. Almost every diet book in the last few years focuses on some variant of the low-carb diet. Carbs = bad! Everyone is jumping on the bandwagon, from journalists, entrepreneurs, celebrities, and other self-proclaimed obesity “experts”. They present all kinds of hypotheses about the influence of carbohydrates on insulin function and cardiovascular disease risk factors. I find this puzzling from a clinical and research standpoint—-I watch people go through the weight loss process every single day. Some fail, some succeed, and the difference between the two never is as simple as whether they have committed to a low-carb or low-fat diet. In fact, I have seen very few people truly successful at losing weight using a low-carb approach, mostly due to difficulties with adherence. Balanced diets appear to be the “secret” of successful losers, but don’t take my word for it, the National Weight Control Registry is filled with thousands of successful long-term losers and only 10% purported to have done so via a low-carb approach, all others were low-fat, balanced diets (Phelan et al 2006). Low-carb dieters were no more or less likely to keep the weight off. All of that is observational data though, it doesn’t suggest cause-and-effect.
Let’s visit the randomized trial data. Randomized trials are the ideal research design to demonstrate cause-and-effect because people are randomized to conditions which in most cases controls all differences between the groups besides the intervention itself. Dr. Michael Dansinger at Tufts University did a study in 2005 when he compared the Atkins (very low-carb), Weight Watchers (low-fat/balanced), Ornish (really low-fat), and Zone (low-carb) diets and examined weight loss and cardiovascular risk factors (blood pressure, cholesterol, insulin, and C-reactive protein) after 1-year (Dansinger et al 2005). There were no differences between diets. The only thing that predicted weight loss and improvements in cardiovascular disease risk was adherence to the diet, regardless of condition.
Yesterday, a group at Harvard published a similar trial (de Sousa et al 2012). They compared 4 different diets varying in nutrient composition on weight loss, fat mass, lean mass, abdominal fat, and liver fat (the latter two of which are very dangerous areas to have excess fat in terms of risk for diabetes and heart disease). The 4 diets were as follows: low-fat/average protein, low-fat/high protein, high-fat/average protein, high-fat/high-protein. All diets were equivalent in terms of the calories (750 cal deficit from energy requirements per day—which is typical for weight loss). Findings revealed no differences between groups on any outcome and that the only predictor of weight loss was.. wait for it… calorie intake. People who ate less, lost more weight! Another finding of the study is that in spite of tight controls and intensive counseling, people asked to eat the high-protein diet (25% protein) on average did not reach the targeted level of protein intake (people averaged 22% protein as compared to 18% protein in the other conditions), thus the difference in protein intake between the groups was not as large as they had planned. Does this mean the trial failed? No, it means that even under the best circumstances, it is difficult for people to stick to a high-protein diet.
While these are only two studies, De sousa provides a nice review of this literature in their paper. To summarize it, there are as many studies that have found an advantage of low-carb diets (on abdominal fat loss only) as there are ones that have not found an advantage, but those that have found the advantage failed to account for important factors when measuring abdominal fat. At the end of the day, there is no scientific case to make for a low-carb/high protein or any specific diet being any better than just eating less food. Period.
Why then are all the best-selling diet books peddling low-carb/high-protein diets? I submitted my book proposal called none-other-than FUdiet to a high-powered publisher in New York City. He said what exactly is your “diet.” I said, “I don’t have a “diet,” I help people lose weight. I have published over 70 studies and book chapters on the topic. I treat patients for obesity in a hospital. Weight loss is my job. It’s all I do. In my experience, weight loss is about behavior, not specially-formulated diets. I want to write about the behavioral path to successful weight loss.” He said you need a “diet” or you need to be a “celebrity” to sell a diet book. Well I have neither, but this exchange revealed a lot about the diet book publishing world. They want to market a diet, and so diet books are what the consumers get. I think you can guess what I think of that: FU diet.
Bottom line: To lose weight, eat less.
How do you eat less? Now THAT’S what I can help you with.
Phelan, S., Wyatt, HR, Hill, JO, and Wing, RR (2006). Are the eating and exercise habits of successful habits changing? Obesity, 14(4), 710-716.
Dansinger, ML and colleagues (2005). Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. Journal of the American Medical Association, 293(1), 43-53.
de Sousa, RJ, Bray, GA, and colleagues (2012). Effect of 4 weight loss diets differing in fat, protein, and carbohydrate on fat mass, lean mass, visceral adipose tissue, hepatic fat: Results from the POUNDS trial. American Journal of Clinical Nutrition, epub ahead of print.
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