Protein Intake: What, When, and How Much Affects Longevity

The consumption of protein is a must from the simple fact that humans cannot make certain amino acids required for building and maintaining muscle protein mass as well as all the other critical functions of proteins, both structural and functional, in humans cells. These required amino acids are referred to as the essential amino acids. Numerous studies have demonstrated that protein consumption is directly correlated to the maintenance of muscle mass in aging adults. In addition, numerous studies have clearly demonstrated a correlation between the consumption of protein and reduced desire for food intake. Protein consumption, especially when the composition of the protein is enriched in the branched-chain amino acids, leucine, isoleucine, and valine (e.g. whey protein) results in significant increases in satiety (the sensation of being full). Protein-induced satiety results from changes in the release of hormones in the brain (specifically from the hypothalamus) that control feeding behavior. The major contributor to the sensation of fullness with protein consumption is the amino acid leucine. For more details on proteins and feeding behavior go the the Gut-Brain Interrelationships page of my website:

Protein-rich diets have been recommended by clinicians and dietitians for many years as part of an overall lifestyle designed to reduce and control weight. With respect to protein consumption, animal proteins are not as healthy as plant proteins. Associated with the use of high protein diets has been the use of calorie-restriction diets as a means for healthy longevity. Calorie restriction has been shown to extend lifespan of numerous simple organisms but has not proven effective at life extension in primates, including man.

A new research study published in the prestigious journal, Cell Metabolism, demonstrates that how much protein one eats and when, in the course of ones life, is a major determinant of healthy longevity:

Low Protein Intake Is Associated with a Major Reduction in IGF-1, Cancer, and Overall Mortality in the 65 and Younger but Not Older Population

In this study the effects of protein consumption were correlated to cancer risk and longevity in both laboratory animals and in adult humans (data from 6,381 adult men and women aged 50 and older). The study found that consumption of a high protein diet in the period spanning the ages of 50-65 resulted in significant increase in the incidence of cancer and earlier mortality than in individuals of equivalent age who did not consume a high protein diet. However, and of dietary significance was the finding that the disease association was attenuated, and even abolished, when individuals consumed a high protein diet where the source of the protein was plant-derived. Conversely, when examining individuals older than 65 it was found that consumption of a high protein diet resulted in a significant reduction in cancer and mortality. An added complication to the determination of exactly what might be the optimum protein content is that high protein diets led to a 5-fold increase in diabetes mortality across all age groups. Thus, ensuring an adequate caloric and nutrient balance to prevent the onset of diabetes is of critical importance when considering diet control of disease and longevity.

The biochemical and molecular basis of the the effects of dietary protein composition are related to the levels of growth hormone, the growth hormone receptor, and the resultant effects on the levels of insulin-like growth factor 1 (IGF-1). In both mice and humans, deficiency in growth hormone receptor activity is associated with significant reductions in age-related diseases. For example, humans harboring deficiencies in growth hormone receptor, and thus reduced IGF-1 levels, had no diabetes nor did they have morbidity due to cancer. Protein restriction can, in part, explain the benefits of calorie restriction since protein restriction results in reduced levels of IGF-1. With respect to IGF-1 levels and the results of this study the increase in disease and mortality was highest in the high protein consuming group of individuals aged 50-65 who also had high level of circulating IGF-1.

In comparisons of the source of protein, when the protein was of animal origin there was a significant increase in cancer and other diseases which is in agreement with several other recent studies that correlated consumption of red meat and death from cancer and other diseases. In this study it was found that the levels of IGF-1 were highest in individuals who consumed a high protein diet where the source of the protein was animal-based.

The change in the risk-benefit ratio of high protein consumption with age is most likely related to the change in muscle mass that occurs naturally during the aging process. Longitudinal studies demonstrate that ones weight tends to increase throughout life until around age 50-60 when it tends to become stable. After this period there is a gradual loss of weight of around 0.5% a year after the age of 65. Therefore, the observed health benefits of high protein consumption after 65 are most likely due to the prevention of muscle mass that normally occurs as we age.

The TAKE HOME from this study is a bit complicated due to the changing needs of protein intake as we age. During middle age (e.g. ages 50-65) it is best to consume a low protein diet for the prevention of overall mortality especially from cancer and type 2 diabetes. Then, when reaching the mid-60's one should increase protein intake (suggested to be on the order of 1.0-1.3 grams of protein per kilogram of body weight) and one at these ages should definitely avoid a low protein diet. Of additional significance to how much and when to eat protein is the type of protein to eat. This study, as well as numerous others, demonstrated that a diet where the protein (as well as other nutrients) are primarily plant-derived is most beneficial for maximizing health benefits at all ages.

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