You may have heard rumblings over the last couple of weeks about a new weight-loss study published in the New England Journal of Medicine. The study got major play in national news outlets because of its apparently revolutionary findings: namely, that all diets are created equal. According to the study, it doesn't matter if you go South Beach, Atkins, Weight Watchers, or Your Grandma's Diet—so long as you reduce your caloric intake, any old diet will work.
At least, this is how the story was widely reported, and the nutritionist community is in turmoil. But, is the reporting on the study true? And what are the implications of this research? To get the lowdown, we spoke to our Weight Loss Challenge nutritionist, Manuel Villacorta. Not surprisingly, he offered us a more nuanced picture of this new research.
The two-year study, conducted by researchers at several universities, including Harvard's School of Public Health, took on a central confusion of the diet industry: that, as the authors write, "The possible advantage for weight loss of a diet that emphasizes protein, fat, or carbohydrates has not been established, and there are few studies that extend beyond one year." So, the researchers randomly assigned 811 overweight (BMI 25 to 40) adults to one of four diets, each differently balancing the ratios of fat, protein and carbohydrates. Diet #1 was 20 percent fat, 15 percent protein, and 65 percent carbohydrates; diet #2 was in percentages of 20/25/55; diet #3 was 40/15/45; and diet #4 was 40/25/35. After six months, participants in all of the diets had lost an average of six kilograms, an average weight loss of seven percent. After 12 months weight was creeping back; and after two years, average weight loss was at four kilograms. Researchers also reported that all diets had similar levels of satiety, hunger, and satisfaction with the diets. So, the researchers concluded, "Reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize." In other words, cut calories and, however you do it, and you will lose weight.
Enter Manuel Villacorta MS, RD, CSSD, one of the leading nutritionists in the San Francisco Bay Area, creator of the RealJock Healthy Weight-Loss Programs, and founder of the interactive weight-management web site Nutrition for You, to trouble that picture. The media, he contends, has largely distorted the outcome of the study, with headlines such as Study of diets shows what truly counts: calories. In fact, he says, the study wasn't really about counting calories at all; it was about different macronutrient distributions. And that means that the subjects in the study did not eat just any old thing. All were given a "heart healthy" diet: "All diets," Villacorta says, "were required to eat 20 grams of fiber per day, they used whole grains for the carbohydrates and saturated fats were at eight percent or less." In other words, this was hardly the Cheeto's diet. Furthermore, the participants did not merely reduce calories. "All participants were doing record keeping," Villacorta says, "and participants either had group or individual counseling sessions. The study demonstrated that those that participated in group or individual counseling sessions lost more weight." So infrastructure surrounding a diet makes a big difference.
Villacorta also points out that a pound is not always a pound, and that the NEJM study did not record the kind of weight subjects lost. "The study only reported weight loss, and did not look at muscle retention and fat loss," Villacorta warns. "The quality of the weight lost does matter in the long run. Participants only exercised 90 minutes per week and we do not know the type (cardio or weight training), so they ignored the effect of macronutrient distribution and how it relates and contributes to muscle mass retention while losing weight." In other words, we know what these people weighed at the beginning and end of the study, but not what that weight was made up of. There is a big difference between a pound of fat and a pound of lean muscle.
Finally, it would be easy to take the conclusions of this study too far. "If you were to just count calories," Villacorta says, "you could have a slice of pizza and four chocolate chip cookies and meet your calories for the day. With this scenario you would be lacking vital nutrients, however, including protein, which will decrease your metabolism in the long run." If you want to lose weight, he counsels, a balanced diet that lets your stomach feel full and provides the full nutrient spectrum is still the way to go.