Daily energy expenditure in Mexican and USA Pima Indians: low physical activity as a possible cause of obesity

BACKGROUND: Obesity is caused by an imbalance between energy intake and energy expenditure. However, it is unknown whether increased physical activity protects susceptible populations against the development of obesity and type 2 diabetes. OBJECTIVE: To investigate the potential protective role of environment and physical activity against obesity by measuring total energy expenditure in Mexican and USA Pima Indians. METHODS: We compared the physical activity level of 40 (17 female and 23 male; 37 +/- 11 y, 66 +/- 13 kg) Mexican Pima Indians from a remote, mountainous area of Northwest Mexico, with 40 age-and-sex matched (17 female and 23 male; 37 +/- 12 y, 93 +/- 22 kg) Pima Indians from the Gila River Indian Community in Arizona, USA. We measured total energy expenditure (TEE) by doubly labeled water and calculated physical activity by different methods: physical activity level (PAL) as the ratio of TEE on resting metabolic rate (RMR), TEE adjusted for RMR by linear regression, activity energy expenditure adjusted for body weight (AEE), and activity questionnaire. RESULTS: Physical activity was higher in Mexican Pima Indians when compared with USA Pima Indians as assessed by PAL (1.97 +/- 0.34 vs 1.57 +/- 0.16, P < 0.0001), TEE adjusted for RMR (3289 +/- 454 vs 2671 +/- 454 kcal/day, P < 0.0001) and AEE adjusted for body weight (1243 +/- 415 vs 711 +/- 415 kcal/day, P < 0.0001). Questionnaires revealed more time spent on occupational activities among Mexican Pima compared with USA Pima (23.9 +/- 13.3 vs 12.6 +/- 13.9h/week, P < 0.001). CONCLUSION: These data support a significant role for physical activity in the prevention of obesity in genetically susceptible populations.