Changing perspectives on aging and energy requirements: aging and digestive function in humans, dogs and cats

When considering the question of energy balance, it is important to take into account energy provision and the ability of aging animals to digest macronutrients and thus obtain their maintenance energy requirement. A large number of studies have been conducted in humans in an effort to establish whether aging of the gastrointestinal tract has a significant effect on availability of dietary energy. The results of these studies have been conflicting, with indications that some aspects of gut functionality do decline with age, but little evidence overall to suggest that aging humans are at risk of energy deficit due to compromised digestive efficiency. A number of digestibility studies carried out with dogs confirm that there is no evidence of an age-related decline in digestive efficiency. This knowledge makes the determination of energy provision to senior dogs relatively straightforward to calculate. Many senior cats appear to exhibit quite a marked reduction in their ability to digest macronutrients, particularly fat, efficiently. Because this reduces the overall capacity to obtain energy from the diet, it is recommended that old cats should not routinely be offered reduced energy diets. For senior cats, the feeding regimen in later life should be to offer highly digestible diets that provide as much energy as adult maintenance rations.