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 with increased mortality rate. Contrarily, among obese people, weight loss reduces other risk factors for disease and death. We hypothesised that this paradox could exist because weight is used as an implicit adiposity index. No 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 and fat loss.


METHODS
Analysis of 'time to death' in two prospective population-based cohort studies, the Tecumseh Community Health Study (1890 subjects; 321 deaths within 16y of follow-up) and the Framingham Heart Study (2731 subjects; 507 deaths within 8y of follow-up), in which weight and fat (via skinfolds) loss were assessable.


RESULTS
In both studies, regardless of the statistical approach, weight loss was associated with an increased, and fat loss with a decreased, mortality rate (P < 0.05). Each standard deviation (s.d.) of weight loss (4.6 kg in 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 fat 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 Tecumseh and Framingham, respectively. Generalisability of these results to severely (that is, body mass index BMI) > or = 34) obese individuals is unclear.


CONCLUSIONS
Among individuals that are not severely obese, weight loss is associated with increased mortality rate and fat loss with decreased mortality rate.
Obesity Research Center, St Luke's/Roosevelt Hospital, Columbia University College of Physicians and Surgeons, New York, NY 10025, USA. dba8@columbia.edu
D B
DB
Allison
R
R
Zannolli
M S
MS
Faith
M
M
Heo
A
A
Pietrobelli
T B
TB
VanItallie
F X
FX
Pi-Sunyer
S B
SB
Heymsfield
D000273:Adipose Tissue / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D002318:Cardiovascular Diseases / Q000401:mortality; D002423:Cause of Death; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008404:Massachusetts / Q000453:epidemiology; D008824:Michigan / Q000453:epidemiology; D008875:Middle Aged; D009765:Obesity / Q000401:mortality*; D011446:Prospective Studies; D017678:Sex Distribution; D015431:Weight Loss