Changes in energy metabolism in response to 48 h of overfeeding and fasting in Caucasians and Pima Indians

OBJECTIVE: Differences in the metabolic response to overfeeding and starvation may confer susceptibility or resistance to obesity in humans. To further examine this hypothesis, we assessed the changes in 24 h energy metabolism in response to short-term overfeeding and fasting in Caucasians (C) and Pima Indians (I), a population with a very high propensity for obesity. METHODS: We measured the changes in 24 h energy expenditure (24 -EE) and 24 h respiratory quotient (24-RQ) in response to 48 h of mixed diet overfeeding (100% above energy requirements) and fasting in a whole body respiratory chamber in 14 male subjects (7 C/7l, age 30±6y, mean±s.d.). Results were compared to a 24 h measurement under eucaloric conditions. RESULTS: Mean 24-EE increased in response to overfeeding and decreased in response to fasting (all changes P < 0.01), with no differences between C (+9.1% and -9.1%) and l (+8.6% and -9.6%). Similarly, mean 24-RQ increased/decreased in response to overfeeding/fasting, respectively (all changes P < 0.01), again with no differences between C (+ 0.06 and -0.05) and l (+0.05 and -0.05). The changes in 24-EE in response to overfeeding and fasting were positively correlated (r=0.70, P < 0.01), whereas those in 24-RQ were not (r= 0.40, NS). CONCLUSIONS: Pima Indians do not appear to have an impaired metabolic response to short-term overfeeding and fasting that could explain their propensity for obesity. Individuals with a large increase in energy expenditure in response to overfeeding appear to have a small decrease in energy expenditure in response to starvation (spendthrift phenotype) and vice versa (thrifty phenotype).