Warning signs for Protein Over-consumption
Two recent epidemiological studies warn of potential dangers associated with relatively higher dietary protein consumption: In Swedish women higher protein relative to carbohydrate intake was associated with an increase in incidence of cardiovascular diseases (1) and another observational study on the effect of macronutrient composition of diets found protein content to be the only significant predictor of increased obesity (2). These associations may have some plausibility in view of recent findings on amino-acid regulation of autophagy. Note that autophagy is key process in detoxifying cells as described in the section on Cell Refuse Disposal. An abundance of amino-acids quickly suppresses autophagy (3) as does an abundance of glucose via insulin (4) both by separate pathways impacting mTOR, the master controller of autophagy.
In very broad terms, aging and many of the diseases related to aging are caused by deterioration in various aspects of cell function that lead to cell death and inflammation. Increasing degrees of mitochondrial dysfunction leading to widespread disruption of mitochondrial integrity within the cell is one of the final events in cell death. One must appreciate the highly dynamic state of protein recycling in order to understand how critical autophagy relates to cell function; for instance mitochondria are the pivotal components of cells that generate energy and they are subject to wear and tear necessitating complete recycling over a 20 to 30 day time frame. Dysfunctional components of mitochondria split off by fission from larger networks and are engulfed in “autophagosomes” broken down and their amino-acids and other building blocks recycled for mitochondrial resynthesis. Autophagy is therefore critical to quality control of mitochondrial function which if left to deteriorate results in cell death. In the wider context of the whole organism excessive rates of cell death can overload the scavenging (immune) system and lead to inflammation in various organs and tissues that are the hallmarks of age related diseases such as atherosclerosis, neurodegeneration, arthritis and so on.
The bottom line as far as dietary advice on protein consumption is that a level of 0.8 gm/kg body weight may be ideal (5). This amounts to just 56 gms (2 oz) of protein a day, much more than we might be accustomed to in our typical Western Diet. The challenge is how to comfortably restrict protein whereas protein supplementation at least for mature adults is likely to do much more harm than good.
1. Lagiou, Sandin, Weiderpass, et al. Low carbohydrate-high protein diet and incidence of cardiovascular diseases in Swedish women: prospective cohort study. . s.l. : BMJ 2012;344:e4026.
2. Vergnaud A-C, Norat T, Mouw T, Romaguera D, May AM, et al. Macronutrient Composition of the Diet and Prospective Weight Change in Participants of the EPIC-PANACEA Study. s.l. : PLoS ONE (2013) 8(3): e57300. doi:10.1371/journal.pone.0057300.
3. Efeyan, Zoncu, Sabatini. Amino acids and mTORC1: from lysosomes to disease. s.l. : Trends Mol Med. 2012 September ; 18(9): 524–533. doi:10.1016/j.molmed.2012.05.007.
4. Emilie Vander Haar, Seong-il Lee, Sricharan Bandhakavi, Timothy J. Griffin, Do-Hyung Kim. Insulin signalling to mTOR mediated by the Akt/PKB substrate PRAS40. . s.l. : Nature Cell Biology 9, 316 – 323 (2007) | doi:10.1038/ncb1547.
5. Edda Cava, Luigi Fontana. Will calorie restriction work in humans? . s.l. : AGING, July 2013, Vol. 5 No.7. http://www.impactaging.com.