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

dOBJECTIVE: Differences in the metabolic response to overfeeding and starva tion may confer susceptibility or resistance to obesity in humans. To furth er examine this hypothesis, we assessed the changes in 24 h energy metaboli sm in response to shortterm overfeeding and fasting in Caucasians (C) and P ima 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 overfeedin g (100% above energy requirements) and fasting in a whole body respiratory chamber in 14 male subjects (7 C/71, 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 r esponse to fasting (all changes P < 0.01), with no differences between C ( 9.1% and -9.1%) and 1 (+8.6% and -9.6%). Similarly mean 24-RQ increased/de creased in response to overfeeding/fasting, respectively (all changes P < 0 .01), again with no differences between C (+ 0.06 and -0.05) and I (+ 0.05 and -0.05). The changes in 24-EE in response to overfeeding and fasting wer e positively correlated (r= 0.70, P < 0.01), whereas those in 24-RQ were no t (r= 0.40, NS). CONCLUSIONS: Pima Indians do not appear to have an impaired metabolic respo nse to short-term overfeeding and fasting that could explain their propensi ty for obesity. Individuals with a large increase in energy expenditure in response to overfeeding appear to have a small decrease in energy expenditu re in response to starvation (spendthrift phenotype) and vice versa (thrift y phenotype).