Do change in healthy individuals during the day the body component composition indicators?

Electrical impedancemetry analysis of the human body component composition has proven itself to be a widespread and quite effective biophysical method of research. One of the conditions for ensuring comparability of the results obtained by different authors is a complete account of the influence of external factors, including the time of day for conducting the study. The objective of this study is the daily dynamics of the indicators of the component composition of the body of practically healthy individuals. The study involved 42 cadets of the Kirov Military Medical Academy, studying in the first year. The indicators of body component composition were assessed using the Tanita 780 MC fat mass analyzer, which allows calculating the content of fat, muscle, and bone mass in the body, body mass index, metabolic age, basal metabolic rate, index of sarcopenia, physical development rating, and others, in total, 41 indicators were assessed. The component composition of the body was assessed immediately at 6:10 after getting up, at 6:40 after morning physical exercises, including a morning jog of 2 km, at 8:45 after breakfast before the start of classes, at 15:00 after classes before lunch, at 16:20 after lunch before self-study and at 21:30 after dinner before lights out. The conducted factor analysis of the obtained data showed that daily changes in the indicators of the component composition of the body are made up of two rhythms: «physical», including indicators of the muscle component, water, basal metabolism and having morning and evening peaks. The second rhythm is «metabolic», associated with the proportion of the fat component of the body, characterized by minimal daytime values reaching a plateau in the evening and night time. The most labile are the changes in the fat component of the body. Asymmetry or specific features of the daily dynamics of the indicators of the component composition of the body of the upper and lower extremities were not revealed. It is shown that the most optimal time for studying the component composition of the body is morning (immediately after waking up) or evening (before going to bed.