Day-to-day weight changes in young men.

1. Body weight changes from day-to-day have been recorded in 140 young soldiers. A total of 2087 weight changes were examined, and 32% of these represented changes of 0.5 kg or more; on 6.2% of all occasions the change was 1.0 kg or more. 2. There were significant correlations between change in body weight and food intake, and also with energy expenditure. Of the large weight changes (0.5 kg or more) 11% were associated with days of exceptionally high or exceptionally low levels of activity; 7% were associated with days when food intake was unusually large or small. 3. On occasions when fluid intake and urine volume were measured, there was a significant correlation between fluid balance (fluid intake less urine volume) and weight change. 4. The weight of faeces varied from 75 to 210 g. It is concluded that irregularity of defaecation can be only a minor cause of weight irregularity.