SEASONAL-VARIATIONS IN ENERGY-BALANCE AMONG AGRICULTURALISTS IN CENTRAL MALI - COMPROMISE OR ADAPTATION

Objective: This paper considers whether seasonal variations in the ene rgy balance of adult agriculturalists in Central Mall exceed acceptabl e risk, or whether they represent a short-term adaptive response witho ut functional consequence. Design: Prospective/longitudinal study desi gn. Setting: Agricultural village in rural Mall. Subjects: From a tota l population of 166 adults aged greater than or equal to 16 years, two cohorts of 63 men and 73 non-pregnant women with complete records wer e retained for analysis. Interventions: Over a 12-month period, monthl y anthropometry and biweekly retrospective assessments of morbidity we re made on every adult in the sample. Direct measures of household foo d consumption were collected twice in harvest, dry and rainy seasons r espectively. Continuous 15-h observations of time-use and work intensi ty were conducted on a sub-sample of active adults and used to calcula te mean seasonal energy expenditure. Results: Energy balance as measur ed by body mass index (BMI; kg/m(2)) declines significantly in the rai ny season (P < 0.01), corresponding to a seasonal weight loss of 2-3 k g. A similar seasonal trend in % body fat (P < 0.0001) suggests that m ost of this loss represents adipose tissue. A rainy season increase in arm muscle area (AMA) implies that there is no seasonal compromise in lean tissue. Among men and women with BMI > 18.5, seasonal fat loss i s significantly greater than their leaner counterparts. Considering th e likely determinants of variations in energy balance, an increase in the duration and incidence of adult morbidity is observed; however, no significant intercorrelations exist between it and seasonal nutrition al indices. Comparing trends in energy expenditure and intake, a distu rbance in energy homeostasis is apparent as energy expenditure increas es in the rainy season relative to constant household food consumption across seasons. While seasonal variations in energy expenditure are n ot as dramatic in the female sample, they appear to have less opportun ity to recover from so-called 'heavy' levels of expenditure experience d in successive dry and rainy seasons. Periods of 'light' activity in both harvest and dry seasons provide the male sample with a reasonable length of time in which to reconstitute energy stores after the physi cal demands of the rainy season. Conclusions: In the year of study, th e modest loss of body fat recorded in the rainy season (< 5% body mass ) represents a successful physiological response to energy imbalance, and is unlikely to compromise adult productive and reproductive functi on.