Study under review: Metabolic adaptation characterizes short-term resistance to weight loss induced by a low-calorie diet in overweight/obese individuals
Individual responses to the same dietary intervention vary significantly. This variance poses a problem during weight loss because some people don’t lose the expected amount of weight for a given calorie deficit. The underlying reason(s) for the different response is not completely understood. The body does, however, experience adaptive reductions in energy expenditure meant to minimize the loss of precious energy stores. In the context of a calorie deficit, compensatory mechanisms can act to both reduce energy expenditure and increase energy intake. One of the mechanisms allowing reductions in energy expenditure appears to be a reduction in resting metabolic rate (RMR), which is the amount of energy expended for maintaining bodily functions.
It has been observed in multiple studies that RMR decreases by a larger amount than expected from the loss of body mass. Scientists refer to this phenomenon as “metabolic adaptation.” Differences in the magnitude of adaptation to reduced energy intakes might affect the weight loss response to a given calorie deficit. Even though researchers have known about this phenomenon for many years, its exact physiological mechanisms are not well characterized. Identifying metabolic markers that differentiate people who are sensitive and resistant to weight loss would help to design better interventions for specific individuals. On the other hand, it is theoretically possible that defects at any level of fat oxidation might also contribute to a reduction in the amount of fat loss during a caloric deficit.
The authors of the study under review hypothesized that participants who don’t lose the expected amount of weight after a low-calorie diet have impaired fat oxidation and increased metabolic adaptation after a low-calorie diet.
In real life and scientific studies, weight loss success on otherwise identical diets is highly heterogeneous, with some people not losing the expected amount of weight. There are compensatory physiological mechanisms meant to slow down the loss of energy stores. One of them is a reduction in metabolic rate that is greater than predicted by changes in body mass, called metabolic adaptation. Therefore, it is possible that individual differences in weight loss might be related to different degrees of metabolic adaptation. It has also been speculated that alterations in fat oxidation pathways may also contribute to the comparatively low reduction in body fat.
Other Articles in Issue #81 (July 2021)
Will cardio hurt your strength gains? It depends on your training level!
This recent meta-analysis suggests that concurrent endurance and resistance training only hurts strength gains for more experienced athletes.
Fit and full: Exercise does not reliably affect appetite or calorie intake
According to this meta-analysis, exercise may boost caloric intake a tad, but not enough to matter.
Nulls: March-April 2021
A quick run-through of recently published studies that didn't find evidence of an effect.
Safety Spotlight: Omega-3 fatty acid supplementation can increase the risk of atrial fibrillation
Here's a quick rundown of a recent meta-analysis which explored whether EPA and DHA supplementation can increase the risk of atrial fibrillation. Currently, the answer appears to be "yes."
Deeper Dive: What is the best weight loss strategy for treating knee osteoarthritis?
Bariatric surgery helped the most, probably because it helped shed the most pounds.
Deeper Dive: How effective are behavioral methods for preventing weight gain?
Interventions that set specific, measurable goals worked better for preventing weight gain than those that allowed more leeway, but weight gain is hard to curb entirely.
Zest with zinc: Fighting fatigue with zinc supplementation for older adults
This trial examined whether zinc supplementation could put the pep back in older adults' step. While the results look promising, the fact that it wasn't blinded or placebo-controlled means more follow-up is needed.