Well I'd intended to get up this morning and write a run of the mill rant about the stupid article accompanying an interview the other day on NPR Morning Edition with my buddy John Durant. Here's the link to the thing, along with 7 minutes of audio that's substantially better than the article. There's now 441 comments. When last I scanned through them, around 360 of them or something, it was about the most idiotic comment thread I've ever seen.
OK, so no rant this time.
I got wind of this study this morning via a link to Glenn Reynlds from a friend of mine, then chasing down rabbit holes. This appears to be the full text: Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance. I haven't scrupulously picked through it but figured why not let everyone who want to go through it just like I will.
Here's a couple of media reports for those wanting just a summary.
- USA Today: Low-carb diet burns the most calories in small study
- The New York Times: Which Diet Works?
And from the Abstract of the actual study:
Objective To examine the effects of 3 diets differing widely in macronutrient composition and glycemic load on energy expenditure following weight loss.
Design, Setting, and Participants A controlled 3-way crossover design involving 21 overweight and obese young adults conducted at Children's Hospital Boston and Brigham and Women's Hospital, Boston, Massachusetts, between June 16, 2006, and June 21, 2010, with recruitment by newspaper advertisements and postings.
Intervention After achieving 10% to 15% weight loss while consuming a run-in diet, participants consumed an isocaloric low-fat diet (60% of energy from carbohydrate, 20% from fat, 20% from protein; high glycemic load), low–glycemic index diet (40% from carbohydrate, 40% from fat, and 20% from protein; moderate glycemic load), and very low-carbohydrate diet (10% from carbohydrate, 60% from fat, and 30% from protein; low glycemic load) in random order, each for 4 weeks.
Main Outcome Measures Primary outcome was resting energy expenditure (REE), with secondary outcomes of total energy expenditure (TEE), hormone levels, and metabolic syndrome components.
Conclusion Among overweight and obese young adults compared with pre–weight-loss energy expenditure, isocaloric feeding following 10% to 15% weight loss resulted in decreases in REE and TEE that were greatest with the low-fat diet, intermediate with the low–glycemic index diet, and least with the very low-carbohydrate diet.
Alright, here's some of my initial, off the cuff thoughts having just skimmed through. I believe I saw somewhere that the participants were eating food prepared for them by the research team; if so, that does add a bit of credibility. Also, if REE and TEE (resting and total energy expenditure) was less with the LF diet compared to the LC diet it seems more plausible to me that the LF, high-carb diet would generally be prone to more cheating, hence more caloric intake, hence an even more curious result if that were the case.
Here's a blurb from the comments I found interesting:
The results of our study challenge the notion that a calorie is a calorie from a metabolic perspective. During isocaloric feeding following weight loss, REE was 67 kcal/d higher with the very low-carbohydrate diet compared with the low-fat diet. TEE differed by approximately 300 kcal/d between these 2 diets, an effect corresponding with the amount of energy typically expended in 1 hour of moderate-intensity physical activity.
The physiological basis for the differences in REE and TEE remains subject to speculation. Triiodothyronine was lowest with the very low-carbohydrate diet, consistent with previously reported effects of carbohydrate restriction23 ; thus, changes in thyroid hormone concentration cannot account for the higher energy expenditure on this diet. The thermic effect of food (the increase in energy expenditure arising from digestive and metabolic processes) dissipates in the late postprandial period and would not affect REE measured in the fasting state. Because the thermic effect of food tends to be greater for carbohydrate than fat,24 - 25 it would also not explain the lower TEE on the low-fat diet. Although protein has a high thermic effect of food,16 the content of this macronutrient was the same for the low-fat and low–glycemic index diets and contributed only 10% more to total energy intake with the very low-carbohydrate diet compared with the other 2 diets. Furthermore, physical activity as assessed by accelerometry did not change throughout the study. Alternative explanations for the observed differences in REE and TEE may involve intrinsic effects of dietary composition on the availability of metabolic fuels13 - 14 or metabolic efficiency, changes in hormones (other than thyroid) or autonomic tone affecting catabolic or anabolic pathways, and (for TEE) skeletal muscle efficiency as regulated by leptin.26 - 29 Regarding the last possibility, the ratio of energy expenditure to leptin concentration has been proposed as a measure of leptin sensitivity,30 and this ratio varied as expected in our study among the 3 diets (very low carbohydrate>low glycemic index>low fat).
Maybe I'm missing something here, but if the participants were eating isocaloric diets (just the different macro ratios), they were in weight maintenance (no participants gaining or losing), yet the LC participants had total energy expenditure 300 kcal per day greater than the LF participants, and..."Furthermore, physical activity as assessed by accelerometry did not change throughout the study"...then what's the point?
What am I missing?
OK, perhaps I'll put up an addendum or another post once I've gone through this more, but don't let that stop any of your science, metabolism or science geeks in comments.
Update: Synthesis: Guyenet, Colpo, Calories Count, Food Quality Matters, Macronutrient Ratios are Qualitative (my extensive follow-up post on the matter)