Читать книгу Pathy's Principles and Practice of Geriatric Medicine - Группа авторов - Страница 341

Population‐based nutritional surveys have shown a gradual decline in energy intake in old age. Shifts in the proportion of energy coming from various macronutrients with ageing is unclear. Between populations, the macronutrient composition appears to vary considerably. Across studies, intakes range from 12 to 18% protein, 20 to 42% fat, and 38 to 65% carbohydrate.¹⁹

Prentice²⁰ considered the extent to which the development of recommendations for dietary energy needs to account for the sources of energy (i.e. macronutrient profiles). He discussed the issue with a view to avoiding undernutrition in addition to obesity. He concluded that ‘at the metabolic level, only diets with the most extreme macronutrient composition would have any consequences by exceeding the natural ability to modify fuel selection. However, diets of different macronutrient composition and energy density can have profound implications for innate appetite regulation and hence energy consumption’. The Omni‐Heart study,²¹ a randomized three‐period cross‐over feeding trial, studied self‐reported appetite and selected fasting hormone levels by comparing the effects of three diets, each with a different macronutrient profile. It was concluded that a diet rich in protein from lean meat and abundant in vegetables reduces self‐reported appetite when compared with diets high in carbohydrate and unsaturated fats. Satiety was not explained by hormonal changes, leaving putative mechanisms unclear.

The role of proteins in the diet is currently being extensively studied and discussed, not only because of the satiating effect. Alterations in the ability of cells to regulate homeostasis underlie the pathogenesis of severe human diseases. Even in the absence of disease, deterioration of protein homeostasis likely contributes to different aspects of ‘normal ageing’. This makes it difficult to formulate evidence‐based requirements for proteins in the diet of (frail) elderly people. There is a general consensus to moderately increase protein intake above 0.8 g /kg⁻¹ body weight in the elderly (up to 1.5 g /kg⁻¹), which may help to reduce progressive muscle loss and stimulate muscle protein anabolism. Current gaps in our understanding of altered protein homeostasis in ageing urgently require further studies.²²