Yesterday, I was annoyed to read a Denver Post article on a new diet study. Here’s the opening of the article:
Two decades after the debate began on which diet is best for weight loss, a conclusion is starting to come into focus. And the winner is not low-carb, not low-fat, not high-protein, but any diet.
That is, any diet that is low in calories and saturated fats and high in whole grains, fruits and vegetables — and that an individual can stick with — is a reasonable choice for people who need to lose weight. That’s the conclusion of a study published Wednesday in the New England Journal of Medicine, representing the longest, largest and most rigorous test of several popular diet strategies.
Simply based on my own experience — let alone what I’ve read in Good Calories, Bad Calories and elsewhere — I was skeptical of those conclusions. But mostly, I was irritated that the article didn’t provide even the basic data required to support the opinions of its many quoted experts. It didn’t discuss the methods used, the diets tested, or the results. (Seriously!) It was all assertion without any supporting facts.
So I dug up some actual facts about the study at Scientific American:
The study subjects were divided into four groups, each assigned to a special diet. One group ate a “low-fat, average-protein” diet (20 percent fat, 15 percent protein, 65 percent carbs); a second consumed a “low-fat, high-protein” diet (20 percent fat, 25 percent protein, 55 percent carbs); a third followed a “high-fat, average-protein” diet (40 percent fat, 15 percent protein, 45 percent carbs); and the remaining group ate a “high-fat, high-protein” diet (40 percent fat, 25 percent protein, 35 percent carbs). All four regimens were heart-healthy (low in saturated fat and cholesterol) and included 20 grams (0.7 ounce) of daily dietary fiber. For each study participant, the researchers calculated personalized daily consumption levels ranging from 1,200 to 2,400 calories per day.
Duh! The requirement of low saturated fat is really dumb, and the requirement of low dietary cholesterol is even dumber. But more importantly, not one of those diets is genuinely low-carb, and the high-fat diet isn’t that either. As Richard Nikoley of Free the Animal observes in his debunking:
The lowest carbohydrate intake of all the diets was a whopping (yea, I can do the media hype, too) 35%. Presuming an average 2,500 kcal intake per day, that’s about 220 grams of carbs — not “low carb” by any means. So, this is merely a comparison between various moderate to high carb approaches — approaches that leave insulin high and fat mobilization low.
The highest fat intake is only 40%. A true high fat diet is 60%+ of energy from fat. You can’t go above about 35% from protein, and that’s pushing it (25% is more realistic). Simple: protein remains about the same, and the tradeoff is between carbs and fat. This study was heavily weighted in favor of carbs, particularly when one considers that carbs hammer insulin and fat has little to no effect. High insulin = no fat mobilization.
So, given those defects, what did the study actually find? Here’s what the Scientific American article reports:
“No matter which way you look at it, there were no [statistically significant] differences between any of the groups,” Loria says. At six months, the average total weight loss for all of the groups was approximately 14 pounds (6.5 kilograms); by the end of two years that number had dipped to about nine pounds (four kilograms). “A lot of times in these weight loss studies, people tend to regain,” notes Loria, adding that she will now study strategies that help people keep lost pounds off.
In other words, the recommendation of weight loss via “any diet that is low in calories and saturated fats and high in whole grains, fruits and vegetables” cited in the Denver Post article is wholly unjustified. The study didn’t test diets varying along any of those dimensions — e.g. more or less refined grains versus no grains, low in saturated fats versus high in saturated fats, more or less fruits and veggies, etc. So any conclusions about the value of those foods in weight loss are completely unwarranted. More particularly, as Richard observed, the study “proved that all diets with excess carbohydrate are crap and deliver virtually no results for most people.”