Age-Related Differences in Carbohydrate and Fat Oxidation Over 24 Hours and During Daily Activities in Humans

A study examined how advanced age influences the oxidation of energy substrates, specifically carbohydrates and fats, in humans for a full day and during daily activities. Researchers compared the substrate oxidation between 17 young adults (mean age 29 ± 5 years) and 16 older adults (mean age 72 ± 5 years) who were overall healthy and physically active.

To determine substrate oxidation, oxygen consumption (VdotO2) and carbon dioxide production were measured in a 32,500 L room calorimeter, with the results normalized to body mass and total energy expenditure. Additionally, VdotO2peak was assessed during an incremental treadmill test to exhaustion.

VdotO2peak was found to be lower in older adults compared to their younger counterparts. Across 24-hour periods, older adults oxidized fewer carbohydrates than the young. This difference was also observed during sleep and daily living activities (ADLs). However, older adults exhibited greater fat oxidation over 24 hours and ADLs. Contrary to expectations, fat oxidation was higher in older adults during a 30-minute treadmill walk at a higher intensity than the younger adults.

These findings suggest that older adults metabolize energy differently than younger adults, primarily relying on fats during daily tasks. The increased fat contribution to daily energy needs in older adults could potentially contribute to the development of metabolic diseases in this population.