Energy supplementation and productivity of Guatemalan sugar-cane cutters: a longitudinal approach

A long-term energy supplementation program was carried out to determine its effect on the productivity of agricultural workers in Guatemala. The program provided, free of charge, a low-energy (24 Kcal) and a high-energy (350 Kcal) bottled, orange-flavored soft drink to two groups of long-term resident sugar-cane cutters who worked on the same plantation, located in the Pacific Coast. Previous to, and periodically thereafter during implementation of the program, data relative to energy intake and anthropometry were collected. Through data obtained from payroll lists, a longitudinal series of average productivity (tons of sugar cane cut and loaded per day) covering 48 weeks of pre-supplementation, 90 weeks of supplementation and 21 weeks post-supplementation, was constructed. Control of the supplement consumption was daily observed. Random assignment of workers to the high-energy supplement (HES) and the low-energy (LES) groups, was not possible. Prior to supplementation both groups presented the same characteristics in terms of age, energy intake level, weight, height, tricipital adiposity and daily productivity. Little variation was found throughout the time the supplement was consumed by the HES Group. Energy intake of workers increased significantly in absolute terms in relation to the LES Group, except towards the end of the 28 months' supplementation period. Energy balance was maintained by workers throughout the study period. A time series of the difference in mean productivity of the two supplement groups (Yt) was modeled using the ARIMA techniques. No auto-regressive term was present in the Yt series. The ARIMA (0,0,1) model was fitted and expanded with different intervention components. None of the estimated parameters of the intervention components were statistically significant. It was therefore concluded that no abrupt, or gradual and sustained energy supplementation effect on productivity was present.