Role of insulin in age-related changes in macronutrient metabolism

Abstract

Age is associated with an increase in body fat mass and a decrease of protein mass. As body substrate turnover is under insulin control, defects in insulin secretion andaor action may in part account for these changes. As regards secretion, current evidence suggest that no clear defect in insulin secretion is found in the aged. The wide spectrum of glucose tolerance of the elderly may be associated with different patterns of insulin secretion. Insulin sensitivity to glucose metabolism is more or less normal in the aged, despite subtle delays in the onset of its action. Normalization of the data by either body weight or lean body mass is important in de®ning the insulin sensitivity of the elderly. Increased rates of free fatty acid (FFA)¯ux and oxidation rates have been found in healthy elderly subjects, both when post-absorptive and during hyperinsulinemia. These differences however disappeared following normalization by fat mass, suggesting that FFA kinetics re¯ect the established changes in fat mass. Thus, the mechanism(s) leading to an increase in the fat mass in elderly cannot simply be derived from studies of fat kinetics. The operation of the Randle cycle (ie, inverse relationships between fat and glucose oxidation) in the elderly has also been suggested. Finally, the insulin effects on whole-body amino acid and protein metabolism do not seem to be impaired in the aged. However, in the human muscle a decreased synthesis of contractile as well as mitochondrial proteins was found, in association with decreased speci®c gene expression. The degree of physical activity probably interacts with these changes, possibly playing a causative role. The possible interaction between insulin and exercise in the maintenance of muscle mass in the elderly needs to be studied further. Descriptors: aging; insulin; macronutrient metabolism

Familial resemblance for glucose and insulin metabolism indices derived from an intravenous glucose tolerance test in Blacks and Whites of the HERITAGE Family Study

“…It should be noted that the present estimates of heritability based on familial correlations are the maximal estimates, and also may include effects due to familial environmental factors especially when there are significant spouse correlation in addition to significant parent–offspring and sibling correlations. Physical activity and diet are two possible major environmental factors contributing to the individual differences in these indices for glucose and insulin metabolism [41,42].…”

Assessment of influence of pro-health nutrition education and resulting changes of nutrition behavior of women aged 65-85 on their body content

“…In the course of conducted classes, participants led a normal life that was unchanged, especially as regards physical activity, so the cause of this phenomenon cannot be sought in the influence of physical effort on the size of muscle mass. It seems that one of the causes of the phenomenon could be connected with diet correction and a decrease in the fat influence on amino acids and proteins metabolism [ 27 ]. It was shown that even with the decreased muscle mass this influence is not lower in the liver [ 28 ].…”

Assessing effects of diet alteration on selected parameters of chronically mentally ill residents of a 24-hour Nursing Home. Part 2. Effects of nutritional changes on anthropometric parameters and composition of the body.

“…Było to związane z równoczesną utratą tkanki tłuszczowej zlokalizowanej w talii i na biodrach. Można przypuszczać, że był to wpływ stosowanych leków, które nie pozwalały, pomimo wprowadzonych zmian w sposobie żywienia, na pełną normalizację stężeń insuliny i kortyzolu, hormonów odpowiedzialnych za gromadzenie i lokalizację tkanki tłuszczowej [33]. W badaniu z udziałem kobiet w okresie menopauzalnym wykazano, że prawidłowa korekta diety sprzyja utracie wisceralnej tkanki tłuszczowej, której utrata jest większa (często nawet około 2,5 razy) od traconej podskórnej tkanki tłuszczowej [7].…”

“…Dlatego ważniejsze jest utrzymanie bezwzględnej zawartości beztłuszczowej masy ciała, a w niektórych wypadkach nawet jej wzrost. Jedną z przyczyn tego zjawiska mogła być poprawa wrażliwości receptorów insulinowych i tym samym poprawa metabolizmu aminokwasów i białek, który nawet przy zmniejszonej masie mięśniowej u osób z niedożywieniem nie zmienia się w wątrobie [33,38]. Jest to o tyle istotne, że jednym z częściej opisywanych efektów towarzyszących źle prowadzonej korekcie diety jest stymulacja procesów odkładania substratów energetycznych [39], a utrata masy ciała związana jest przede wszystkim z utratą beztłuszczowej masy ciała [40].…”