Feeding the machine: caloric intake and output during strenuous backcountry expeditions

Humans increase their energy intake within 24 hours of acute exercise. However, they generally maintain their typical dietary intake rather than increase it when taking part in a regular daily exercise routine. However, the majority of studies looking at caloric intake and output only assess limited recreational activity. Currently, there are no studies looking at this relationship among a group of humans taking part in rigorous physical activity over an extended period. Here total energy expenditure (TEE) and caloric intake were measured among healthy adults (N=59) participating in National Outdoor Leadership School (NOLS) semester long courses. During these courses, subjects took part in rigorous physical activities; where laborious days were followed by rest days. TEE ranged from 2593-4517 kcal day-1. It was found that subjects increased caloric intake on rigorous activity days (p=0.035, r2=0.008), but did not increase their caloric intake on the following rest days (p=0.25, r2=0.003). However, there is a high degree in variability in both instances. Overall, subjects were in a negative energy balance, experiencing weight loss and body composition changes, including loss of muscle mass, suggesting that even with increased caloric intake, they were not meeting their nutritional needs. NOLS courses, like any high-energy activity, are physically and mentally demanding. It is likely that subjects were too exhausted to prepare a proper meal after a difficult day. This highlights the need for greater ease of proper nutrition during extended periods of high-energy expenditure whether it is rigorous physical expedition or pregnancy and lactation