Factors contributing to intra-individual variation of serum constituents. 2. Effects of exercise and diet on variation of serum constituents in healthy subjects.

A previous report of within-day variation of serum constituents was based on values in healthy subjects who did not undergo strenuous exercise and who were in a fasting state. In this study we consider the effects of exercise and of a noon meal on the same serum constituents. The statistical significance (ttest) was computed on the basis of the ratios of values (after/before) on the day of exercise vs. the ratios on the nonexercise day, or, for the effect of meal, the ratios of values (after/before the noon meal) on the eating day vs. the ratios of values taken at the same hour on the fasting day. Significant effects seen after exercise (P <.05) included: potassium, phosphate, creatinine, total protein, albumin, uric acid, and alanine aminotransferase. After the noon meal, significant (P <.05) changes were seen for: sodium, phosphate, uric acid, iron, total lipids, alkaline phosphatase (phenyl phosphate substrate), and lactate dehydrogenase. The effects of eating on serum constituents are separated into (a) physiological factors and (b) methodological considerations.