Are High Protein Diets Safe?

Ever since the day I first touched a weight I’ve heard them, the myths surrounding weightlifting and bodybuilding.  I’m sure you’ve heard some of them at one time or another as well.  Everything from “weightlifting stunts your growth” to “lifting weights shrinks your penis” to “you know creatine is a steroid, right?”  While many myths are easy to write off as being ridiculous, the myths surrounding protein intake are more widespread.  Many people have the impression that high protein diets are unhealthy. Kidney damage, liver damage, heart disease, osteoporosis and others have all been blamed to some degree high protein intakes.  What is even more shocking is that many in the medical and scientific community have accepted this as fact without hardly any evidence.  So what does the actual research say?  Is protein going to kill us?

Kidneys

The kidneys are involved in nitrogen excretion, and thus it has been theorized by some that a high nitrogen intake (protein) may cause stress to the kidneys.  Additionally, low protein diets have typically been recommended to people who suffer from renal disorders.  To conclude that a high protein intake damages the kidney is very tenuous however.  A study examining bodybuilders with protein intakes of 2.8g/kg vs. well trained athletes with moderate protein intakes revealed no significant differences in kidney function between the groups. [1] Additionally, a review of the scientific literature on protein intake and renal function concluded that “there is no reason to restrict protein in healthy individuals.”  Furthermore, the review concluded that not only does a low protein intake NOT prevent the decline in renal function with age, it may actually be the major cause of the decline! [2]  This conclusion is supported by the fact that low proteins diets have NOT been shown to be beneficial for blunting the progression of chronic renal failure. [3]

Liver

There is absolutely no evidence to support the notion that a high protein intake is detrimental to the liver.  Protein is needed to repair liver tissue and for the conversion of fats to lipoproteins so that they may be removed from the liver. [4]  Amino acids are also the main fuel source for the liver.  Additionally, in alcoholic liver disease a high protein diet has been shown to improve liver function and reduce mortality and BCAAs are also being investigated as a treatment for liver disease. [5][6]  It could even be postulated that in the case of liver damage/disease a high protein diet may be required in order to repair liver tissue damage and to aid in recovery.

Bone

Another major knock on high protein diets is that they cause increased calcium excretion.  Thus a hypothesis stands that over a long period of time, a high protein diet may contribute to the onset of osteoporosis.  However, the real world data is somewhat equivocal as early studies that demonstrated calcium loss due to increased protein intake. [7]  However, there is some recent evidence suggesting that an increase in dietary protein may not cause an increase in calcium excretion at all and an increase in dietary protein may potentially improve bone mass in the elderly. [8]  Moreover, several epidemiological studies actually found a positive association between protein intake and bone mineral density. [9][10]  Furthermore, low protein diets may actually have a detrimental effect on bone.  Although low protein intakes cause less calcium to be excreted, they also cause a reduction in calcium absorption through the intestine. [11]  The net effect is a DECREASE in calcium balance due to a reduction in protein intake.  Thus, while increasing protein may increase calcium excretion, there is no evidence that the increased calcium lost in urine is from bone, and the overall net calcium balance is either unaffected or actually improved by a high protein diet.

Heart Disease

Not only does the scientific literature not support the statement that a high protein diet may have a negative impact on the heart, it actually supports a high protein diet for the prevention of heart disease.  Research suggests that replacing dietary carbohydrates with protein may decrease the risk of heart disease.[12]  This is supported by the fact that replacing dietary carbohydrates with protein improves blood lipid profiles by decreasing triglyceride levels and increasing HDL (good) Cholesterol levels.[13]  Furthermore, metabolism of carbohydrates and/or fats increases the production of free radical levels to a much greater degree than the metabolism of protein.[14]  High levels of free radicals are thought to accelerate the formation of atherosclerosis, the major cause of heart disease.[15]

Diabetes and Weight Loss

A high protein diet may also be beneficial for combating obesity and diabetes.  Recent research indicates that a diet consisting of 30:40:30 (protein:carbs:fats) was superior to the food guide period diet of 15:55:30 in maintaining glucose homeostasis, increasing insulin sensitivity, and improving glucose control in normal people and those suffering from type II diabetes. [13][16][17]  This same high protein diet has also been shown to be superior to the food guide pyramid diet for weight loss.  Furthermore, subjects consuming the high protein diet maintained more lean muscle tissue and lost a greater proportion of fat than those subjects consuming the high carb diet. [17]  Several investigators have also reported increased satiety with the high-protein diet compared to a control high carb diet. [18][19]  In summary, a high protein, lowered carbohydrate diet is superior to a high carb (i.e. food guide pyramid) diet in promoting fat loss, muscle maintenance, and appetite suppression.

You can have your high protein cake and eat it too!

Much of this evidence I have presented not only contradicts statements that high protein diets are unsafe, but supports high protein diets in the prevention/treatment of heart disease, diabetes, and obesity.  Those are three of the world’s biggest killers, and a high protein diet may be the key to reducing the incidence of all of them!  Perhaps the American Heart Association and the rest of the high protein naysayers would be best served to get the facts first, rather than making statements with little to no scientific support.  So next time someone tells you that a high protein diet is bad for you, slide this article on over to them, then sit back and enjoy your next high protein meal.

References

1. Poortmans JR, Dellalieux O. Do regular high-protein diets have potential health risks on kidney function in athletes? Int J Sports Nutr 2000;10:28-38.
2. Walser M. Effects of protein intake on renal function and on the development of renal disease. In: The Role of Protein and Amino Acids in Sustaining and Enhancing Performance. Committee on Military Nutrition Research, Institute of Medicine. Washington, DC: National Academies Press, 1999, pp. 137-154.
3. Klahr S, Levey AS, Beck GJ et al. The effects of dietary protein restriction and blood-pressure control on the progression of chronic renal failure. N Engl J Med 1994;330:877-884.
4. Navder KP, Lieber CS. Nutrition and alcoholism. In: Bronner, F. ed. Nutritional Aspects and Clinical Management of ChronicDisorders and Diseases. Boca Raton, FL: CRC Press, 2003, pp. 307-320.
5. Mendellhall C, Moritz T, Roselle GA et al. A study of oral nutrition support with oxadrolone in malnourished patients with alcoholic hepatitis: results of a Department of Veterans Affairs Cooperative Study. Hepatology 1993;17:564-576.
6. Suzuki K, Kato A, Iwai M.  Branched-chain amino acid treatment in patients with liver cirrhosis.  Hepatol Res.  2004 Dec;30S:25-29.
7. Ginty F. Dietary protein and bone health. Proc Nutr Soc 2003;62:867-76.
8. Dawson-Hughes B, Harris SS, Rasmussen H et al. Effect of dietary protein supplements on calcium excretion in healthy older men and women. J Clin Endocrinol Metab 2004;89:1169-73.
9. Geinoz G, Rapin CH, Rizzoli R et al. Relationship between bone mineral density and dietary intakes in the elderly. Osteoporos Int 1993;3:242-8.
10. Cooper C, Atkinson EJ, Hensrud DD et al. Dietary protein intake and bone mass in women. Calcif Tissue Int 1996;58:320-325.
11. Kerstetter JE, Svastislee C, Caseria D et al. A threshold for low-protein-diet-induced elevations in parathyroid hormone. Am J Clin Nutr 2000;72:168-173.
12. Hu FB, Stampfer MJ, Manson JA et al. Dietary protein and risk of ischemic heart disease in women. Am J Clin Nutr 1999;70:221-227.
13. Layman DK, Boileau RA, Erickson DJ, Painter JE, Shiue H, Sather C, Christou DD.  A reduced ratio of dietary carbohydrate to protein improves body composition and blood lipid profiles during weight loss in adult women.  J Nutr. 2003 Feb;133(2):411-7.
14. Mohanty P, Ghanim H, Hamouda W et al. Both lipid and protein intake stimulates increased generation of reactive oxygen species by polymorphonuclear leukocytes and mononuclear cells. Am J Clin Nutr 2002;75:767-772.
15. Paolisso G, Esposito R, D’Alessio MA, Barbieri M.  Primary and secondary prevention of atherosclerosis: is there a role for antioxidants?  Diabetes Metab. 1999 Sep;25(4):298-306.
16. Layman DK, Baum JI.  Dietary protein impact on glycemic control during weight loss.  J Nutr. 2004 Apr;134(4):968S-73S.
17. Layman DK.  Protein Quantity and Quality at Levels above the RDA Improves Adult Weight Loss.  J Am Coll Nutr. 2004 Dec;23(6 Suppl):631S-6S.
18. Hill AJ, Blundell JE. Composition of the action of macronutrients on the expression of appetite in lean and obese human subjects. Ann N Y Acad Sci. 1990;580:529–31
19. Stubbs RJ, van Wyk MC, Johnstone AM, Barbron CG. Breakfasts high in protein, fat or carbohydrate:  effect on within-day appetite and energy balance.  Eur J Clin Nutr 1996;50:409–17