Weight loss increases and fat loss decreases all-cause mortality rate: results from two independent cohort studies

OBJECTIVE: In epidemiological studies, weight loss is usually associated wi th increased mortality rate. Contrarily, among obese people, weight loss re duces other risk factors for disease and death. We hypothesised that this p aradox could exist because weight is used as an implicit adiposity index. N o study has considered the independent effects of weight loss and fat loss on mortality rate. We studied mortality rate as a function of weight loss a nd fat loss. DESIGN: Analysis of 'time to death' in two prospective population-based coh ort studies, the Tecumseh Community Health Study (1890 subjects; 321 deaths within 16 y of follow-up) and the Framingham Heart Study (2731 subjects; 5 07 deaths within 8 y of follow-up), in which weight and fat (via skinfolds) loss were assessable. RESULTS: In both studies, regardless of the statistical approach, weight lo ss was associated with an increased, and fat loss with a decreased, mortali ty rate (P < 0.05). Each standard deviation (s.d.) of weight loss (4.6 kg i n Tecumseh, 6.7 kg in Framingham) was estimated to increase the hazard rate by 29% (95% confidence interval CI), (14%, 47%, respectively) and 39% (95% CI, 25%, 54% respectively), in the two samples. Contrarily, each s.d. of f at loss (10.0 mm in Tecumseh, 4.8 mm in Framingham) was estimated to reduce the hazard rate 15% (95% CI, 4%, 25%) and 17% (95% CI, 8%, 25%) in Tecumse h and Framingham, respectively. Generalisability of these results to severe ly (that is, body mass index BMI) greater than or equal to 34) obese indivi duals is unclear. CONCLUSIONS: Among individuals that are not severely obese, weight loss is associated with increased mortality rate and fat loss with decreased mortal ity rate.