Weight gain and metabolic rate
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Basal and Resting Metabolic Rate as Predictors of Weight Gain
Research on the relationship between metabolic rate and weight gain shows mixed results. Some studies suggest that a low basal or resting metabolic rate (BMR/RMR) can predict future weight gain, while others find no significant association. For example, a large study in a typical Western population found that adults with low BMRs did not gain more weight than those with high BMRs, suggesting that differences in food intake or physical activity may offset the effects of metabolic rate on weight gain . However, other studies in specific populations, such as adult Caucasian Italians and Native Americans, found that a lower RMR, especially when adjusted for fat-free mass, was associated with greater long-term weight gain 359. Similarly, in children, a lower RMR at age 10 predicted greater weight gain during adolescence .
Energy Expenditure, Substrate Oxidation, and Weight Change
Lower total energy expenditure (EE) and reduced fat oxidation rates have also been linked to increased weight and fat mass over time. Studies show that individuals with lower-than-expected 24-hour EE tend to gain more weight and fat mass, even after accounting for body composition and demographic factors . Additionally, low rates of fat oxidation and low sympathetic nervous system activity are considered metabolic predictors of weight gain, particularly in populations prone to obesity .
Respiratory Exchange Ratio and Weight Gain
The fasting respiratory exchange ratio (RER), which reflects the balance between fat and carbohydrate oxidation, has been identified as a weak but significant predictor of weight gain, especially in non-obese men. A higher fasting RER is associated with a greater risk of substantial weight gain, indicating a preference for carbohydrate over fat oxidation may predispose individuals to gain weight .
Individual Variability and Metabolic Phenotypes
There is significant variability among individuals in how metabolism influences weight gain. Some people, described as "metabolically thrifty," are more prone to weight gain due to their tendency to conserve energy during periods of undernutrition or dietary restriction. These differences in metabolic response to diet and environmental factors highlight the importance of considering individual metabolic profiles when assessing weight gain risk .
Special Populations: Narcolepsy and Anorexia Nervosa
In patients with narcolepsy, weight gain is common, but most evidence does not support a consistent difference in BMR compared to controls, except possibly at disease onset. Other factors, such as changes in eating behavior, physical activity, and hormonal regulation, may play a larger role in weight gain in this group . In contrast, patients with anorexia nervosa experience a disproportionate increase in RMR during refeeding, which may make weight gain more difficult for them compared to healthy individuals .
Body Composition, Fat Mass, and Metabolic Rate
Strong correlations exist between body fat percentage and the BMR-to-weight ratio, suggesting that body composition is closely linked to metabolic rate. Indices that account for fat mass may provide better insight into the relationship between metabolic rate and weight gain than those based solely on body weight .
Conclusion
Overall, while a lower metabolic rate can be associated with greater weight gain in some populations, this relationship is not universal. Other factors, such as energy intake, physical activity, substrate oxidation, and individual metabolic phenotypes, play important roles in determining weight gain risk. Understanding these complex interactions is key to developing personalized strategies for weight management and obesity prevention.
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