While I was looking into the effects of various diets, I happened upon this study:
Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance
A summary of its findings can be found here in Science Daily:
Dieting? Study Challenges Notion That a Calorie Is Just a Calorie
Why is it so hard to lose weight after the first loss, when one plateaus? Basically, after an initial 10% weight loss, they fed subjects 3 eucaloric diets, meaning diets with all the same calorie content. The diets were low carb high fat, low fat high-glycemic carb, and low-glycemic medium carb. They found that their subjects Resting Energy Expenditure (REE) and Total Energy Expenditure (TEE) decreased the most on the low fat, high-glycemic high carb diet, TEE/day by 300 calories! Unfortunately the study does not say whether these subjects gained weight during their low fat diet intervention, but I suspect they did. On the low carb diet, TEE decreased the least.
Though it seems from the weight loss implications of this study that a very low carb diet would be best, the authors do not recommend it due to other factors noticed during the study:
This above, however is just the lead-in to the subject of this post: Leptin. The researchers theorize that the decrease in TEE is due to low leptin levels. Other researchers have found that they can restore "healthy" leptin levels through leptin injections, which reverses the decrease in TEE:Although the very low-carbohydrate diet produced the greatest improvements in most metabolic syndrome components examined herein, we identified 2 potentially deleterious effects of this diet. Twenty-four hour urinary cortisol excretion, a hormonal measure of stress, was highest with the very low-carbohydrate diet. Consistent with this finding, Stimson et al31 reported increased whole-body regeneration of cortisol by 11β-HSD1 and reduced inactivation of cortisol by 5α- and 5β-reductases over 4 weeks on a very low- vs moderate-carbohydrate diet. Higher cortisol levels may promote adiposity, insulin resistance, and cardiovascular disease, as observed in epidemiological studies.32- 34 In a 6-year prospective, population-based study of older adults in Italy,35 individuals in the highest vs lowest tertile of 24-hour cortisol excretion, with or without preexisting cardiovascular disease, had a 5-fold increased risk of cardiovascular mortality. C-reactive protein also tended to be higher with the very low-carbohydrate diet in our study, consistent with the findings of Rankin and Turpyn.36 Other studies also have found reductions in measures of chronic inflammation, including CRP with a low–glycemic index diet.37- 39
Low-dose leptin reverses skeletal muscle, autonomic, and neuroendocrine adaptations to maintenance of reduced weight.
Effects of weight loss and leptin on skeletal muscle in human subjects.
There are even websites which tell us that eating certain foods and supplementing with leptin will get us back on track with weight loss, by increasing our TEE and REE:
Maybe that's true.
But what if we've already lost weight and now want to improve our endurance performance? What if we want to be able to go further and faster on the same food? What if we want to bike or run like the Kenyan marathoners? Well then, we should adopt a diet which is proven to improve our muscular efficiency and thus dietary efficiency by decreasing our leptin levels: the low fat, high carb diet studied in my first link, which has similar macros to the Kenyan marathoner diet.
Very good article on this complex subject here:
Decreasing total body fat mass in endurance athletes.