The study compares over 75,000 rural people and follows them up over ten years. The study has the interesting finding that the lower the BMI, the higher the mortality. This underscores once again that the problems of rural India are different from those of urban India. A similar study based on our city-based population could throw up interesting results.

From the abstract:

Background Although the detrimental effect of overweight and obesity has been extensively reported in Western populations, little is known on the association between body weight, weight change and mortality in Asian populations whose weight distribution and mortality differ considerably from the West.

Methods A cohort of 75 868 subjects aged 35 years and above, participants of the Trivandrum Oral Cancer Study—a cluster-randomized controlled trial originally implemented to evaluate the efficacy of visual inspection on oral cancer, in Kerala State, South India—were followed up from 1995 to 2004. Weight and height were measured both at baseline and in 3.5-year follow-up surveys. Early years of follow-up were excluded from the analyses. Relative risks of overall death and cause-specific death were estimated according to the body mass index (BMI) category of the WHO Asian population definitions, and to weight changes between two surveys.

Results Low BMI was a predictor of mortality, while high BMI was not. Mortality risks in men adjusted for age, smoking habits and other potential confounders, as compared with a BMI 18.5–22.9 kg/m², were 1.26 (95% CI 1.03–1.55) for BMI < 16 kg/m²; 1.16 (1.03–1.32) for BMI = 16–18.4 kg/m²; 0.95 (0.81–1.12) for BMI = 23–24.9 kg/m²; 0.85 (0.69–1.05) for BMI = 25–27.4 kg/m²; and 0.89 (0.65–1.21) for BMI  27.5 kg/m². Similar findings were observed in women. BMI was not associated with deaths from cancer, cardiovascular and cerebrovascular diseases, and diabetes. A low BMI (<16 kg/m²) was associated with increased deaths from chronic respiratory diseases. Smoking and socio-economical status did modify the association. A moderate weight gain of 4–10% between the two surveys was associated with decreased risk of death, while moderate and severe weight loss were predictive factors of death. Similar results were observed in both men and women.

Conclusions Among this Indian rural population, mild to severe leanness (BMI < 16 kg/m²) and weight loss were important determinants of mortality, especially from chronic respiratory diseases, while overweight and above (BMI > 23 kg/m²) did not show any detrimental effect.

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