Is Excessive Protein Intake Harmful?

To function properly, our bodies require a constant turnover of proteins including structural, transporter and enzymatic proteins.  Protein turnover is defined as the ongoing process of all proteins being broken down and resynthesized (1).  The National Academy of Sciences estimates that about 250 grams of protein turns over daily in the average adult.  This means that although proteins are being broken down constantly, our bodies require dietary intake of protein, especially the essential amino acids to ensure it can keep up with the synthesis of new proteins.

The dietary reference intake for protein is 0.8 grams of protein per kilogram of body weight each day.  This averages to about 56 grams per day in men and 46 grams per day in the average woman (2).  A study in the American Journal of Clinical Nutrition assessed the current protein intake in Americans by using the NHANES data from 2003-2004.  They calculated the average protein intake was 56 ± 14 g/d in young children, increased to a high of ≈91 ± 22 g/d in adults aged 19–30 y, and decreased to ≈66 ± 17 g/d in the elderly.  Although when combining genders this study shows that the protein consumption in America is well over the recommended amount, a significant percentage of adolescent females and older women showed to have inadequate protein intake (3).

So the biggest question is, “Is this excess protein intake safe?”  A review article broke down high protein diets in relation to cancer, cardiovascular risks, blood glucose, bone health, weight loss, satiety, thermogenesis, and renal disease.  There was increased evidence showing protein intake as high as double or triple the recommended amount (which we found from the study above is the average American consumption) to have harmful effects on calcium homeostasis affecting bone mass.  This harm was associated more with animal sources of protein rather than plant based.  This review also found harmful effects on the cardiovascular system and carcinogensis, as well as the kidneys (4).

Although that review found negative effects, there is a lot of research showing positive effects of increased protein consumption.  A separate review article found improved blood glucose levels and blood lipid levels.  One study had two groups consuming equal calories, however one group was consuming high protein while the other group was on a high carbohydrate diet.  The high protein group lost not only more weight but also, more fat compared to lean body mass than the high carbohydrate group (5).

It seems lately protein is being marketed everywhere and I do not think this is a bad thing.  We see products like Greek Yogurt and protein bars on the shelves.  I would promote these products over a similar product that had less protein and more simple sugars.  We all know the effects of simple sugars, spiked blood glucose followed by a crash.  Protein does the exact opposite.  It will keep clients fuller longer, without the over activity of insulin.  So although some may argue products like Greek Yogurt and protein bars are continuing to encourage Americans to consume more protein than many other cultures, when thinking of the alternative food options they are turning to, the extra protein is not showing to be as harmful as the excessive sugar consumption also present in the American diet.

  1. Thompson J., Manroe M., Vaughan L. The Science of Nutrition. Proteins: Crucial Components of All Body Tissues.  3rd ed. Boston, MA: Pearson; 2014: 217-255.
  2. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Institute of Medicine. Published 2002. http://iom.nationalacademies.org/reports/2002/dietary-reference-intakes-for-energy-carbohydrate-fiber-fat-fatty-acids-cholesterol-protein-and-amino-acids.aspx.  Accessed November 22, 2015.
  3. Fulgoni V. Current protein intake in America: analysis of the National Health and Nutrition Examination Survey, 2003-2004. The American Journal of Clinical Nutrition. 2008.  http://ajcn.nutrition.org/content/87/5/1554S.full.  Accessed November 22, 2015.
  4. Eisenstein J, Roberts S, Dallal G, Saltzman E. High-protein Weight-loss Diets: Are They Safe and Do They Work? A Review of the Experimental and Epidemiologic Data. Nutrition Reviews [serial online]. July 2002;60(7):189-200. Available from: Academic Search Complete, Ipswich, MA. Accessed November 24, 2015.

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