The increase in obesity in developed societies drives interest in the interplay of energy intake, metabolic energy expenditure, and body energy stores. A better understanding of energy management in physically active and undernourished humans should help guide strategies to manage obesity safely and effectively. This review focuses on field studies of men and women engaged in prolonged strenuous activities, ranging from ranger training to extreme expeditions.
Although scientifically unconventional and limited, field studies of exercise and food deprivation have yielded interesting findings: 4–5% body fat is the normal lower limit to fat reserves in physically active underfed young adult men, and in response to exercise and underfeeding, women used more fat mass and less fat-free mass to meet metabolic fuel requirements.
Field studies have shown that fat energy reserves in young adult men can be estimated as percentage body fat minus 5%, and initial body fat mass has a significant positive influence on fat oxidation rates per kilogram of fat-free mass during rapid weight loss associated with underfeeding and exercise. Data logging pedometers, activity monitors, global positioning systems, and wireless body and personal-area networks promise to make it easier to study and care for free-living humans.
US Army Research Institute of Environmental Medicine, Natick, Massachusetts, USA
Correspondence to Reed W. Hoyt, PhD, Biophysics and Biomedical Modeling Division, US Army Research Institute of Environmental Medicine, Kansas Street, Natick, MA 01760-5007, USA Tel: +1 508 233 4802; fax: +1 508 233 5298; e-mail: firstname.lastname@example.org
Disclaimer: The opinions and assertions contained in this paper are the personal views of the authors and do not necessarily represent the official views or policy of the US Department of the Army.