E Ravussin

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±13.9 h/week, P<0.001).CONCLUSION: These data support a significant role for physical activity in the prevention of obesity in genetically susceptible populations.

Energy balance and weight regulation: genetics versus environment.

The prevalence of obesity is reaching epidemic proportions in many industrialized countries. There is growing evidence that, even if the trigger of this epidemic is found in changes in the environment, genes are interacting with the environment to cause weight gain. Studies of twins reared apart indicate that approximately two-thirds of the variability in BMI is attributed to genetic factors. From prospective studies in Pima Indians we can ascribe 12% of the variability in BMI to metabolic rate, 5% to fat oxidation, and another probable 10% to the level of spontaneous physical activity. These data indicate that at least 40% of the variability in BMI is related to genetic factors involved in the regulation of food intake and/or volitional activity. This indicates that the most likely successful therapy for obesity may target pathways of the regulation of food intake. Similarly, an environment favouring engagement in physical activity should be promoted.

Studies of the etiology of obesity in Pima Indians.

Studies have been conducted on various metabolic characteristics of lean and obese Pima Indians, including studies of fat-cell morphology, glucose transport, and lipolysis; lipoprotein lipase activities; sodium-potassium ATPase in red cells, adipocytes, and fibroblasts; lipids and lipoprotein metabolism; fatty acid metabolism; and sterol balance. Insulin concentrations, insulin binding, insulin action on glucose disposal, fatty acid metabolism, and islet function were compared in lean and obese individuals, and the relationship between insulin resistance and muscle morphology was explored. To explore potential abnormalities in energy balance, calorie intake and gastric emptying were compared in lean and obese Pimas and measurements of energy expenditure were performed. The data suggest that there are multiple metabolic differences that accompany obesity in Native Americans. A lower metabolic rate was a determinant of future weight gain, and abnormalities in use of free fatty acids and cell insulin action were suggested, which emphasize the need for further studies in these areas.