Opening Comments

In the wake of a recent study published in JAMA [1], wherein participants on a low-carbohydrate, higher-protein diet had greater improvements in metabolic syndrome parameters (insulin sensitivity, HDL and triglycerides), I was asked the question, “why would anyone want to consume higher protein given the inherent risks for kidney damage;” and, secondly, “why anyone would want to consume protein over the current RDA (0.8g/kg bodyweight) at all?”

To begin, the RDA is an established minimum for protein intake and does not – in any way, shape or form – correspond to an optimal intake [2]. In all honesty, it may even be sub-optimal in many cases, which I will argue in a little bit. Nevertheless, it is becoming more and more evident that there is still a lingering irrational fear of higher protein diets, if not a complete misunderstanding of the potential benefits from consuming them. Furthermore, as a point of understanding, a high-protein diet does not automatically mean a low-carbohydrate diet, although, as I will allude to throughout, there may be some benefits from altering the ratio of the two macronutrients within either weight loss and/or weight maintenance diets (i.e. replacing carbs with protein). Still, the two are not synonymous as one can easily consume a high-protein AND a moderate- and/or high-carbohydrate diet.

Lastly, I would like to point out the definition of a “high-protein” diet. Most of the literature supports the notion of a high-protein diet being any diet with protein intake contributing ~25-30% of total kcals for a given day (this usually does not go above 40% although 98% protein diets have been studied before). My definition, however, will include any figure over the current RDA of 0.8g/kg bodyweight, as it better addresses the initial questions posed to me earlier. That being said, my goal today is two-fold; 1) to show you that consuming a higher protein diet is not harmful to several health parameters; those being kidney functioning, bone health and cardiovascular disease, and 2) to show you why the current RDA for protein may be insufficient for various conditions in both typical, sedentary populations and healthy, athletic ones; like the elderly who are at greater risk for sarcopenia and strength/power athletes looking to preserve lean body mass.

Are higher protein diets dangerous?

Kidney functioning

Over the years there has been a prevailing notion that higher protein diets can be detrimental to kidney functioning. This seems to stem from the fact that patients with renal disease fare much better on diets with restricted protein intakes [3]. Although lowering and/or restricting protein intake does seem to slow the progression of renal disease due to decreased filtration rates [3], it is grossly inaccurate to state that higher protein intake actually causes kidney damage, especially for healthy persons. In fact, numerous reviews and individual studies on high protein diets have come to the same conclusion that diets higher than the RDA in protein are not detrimental to kidney functioning in otherwise healthy persons [4-7]. Furthermore, there is virtually no evidence (because it doesn’t really exist) to suggest that active individuals (i.e. athletes) are at any risk for kidney damage even though they traditionally consume well over the RDA for protein [8]. For instance, when evaluating dietary nitrogen losses through urine, Poortsmans and Dellalieux [9] compared a habitual, very high-protein diet of bodybuilders to a moderate protein diet (yet still way over the RDA) of other athletes and saw no adverse effects on renal functioning in participants consuming either of the diets, even when intakes reached 2.8g/kg (3.5 times higher than the RDA!). Furthermore, in another acute study looking at 37 male bodybuilders and 20 healthy young males of the same age [10], it was shown that although renal filtration and urinary acid excretion increased as part of a higher protein diet, the capacity for the renal load was far from maxed out. To quote the authors:

“The concomitant increase of renal net acid excretion and maximum renal acid excretion capacity during high periods of high protein intake appears to be a highly effective adaptive response of the kidney to a specific and still physiological pattern of food intake leaving a large renal surplus capacity for an additional renal acid load.”  

Unfortunately, not much else has been done in terms of research on kidney functioning in athletes during periods of high protein intake (probably because there is no need for such studies because protein doesn’t damage the kidneys!) Nevertheless, it is without question that there is a huge lack of convincing evidence that higher protein intakes are harmful to an otherwise healthy person, especially a physically active one.

Bone health

Again, over the years, high protein diets – and even just protein in general – have gotten a bad rap due to their (supposed) deleterious effects on bone health. This usually revolves around the notion that protein promotes and acidic environment in the body, and, in order to correct this pH discrepancy, bone calcium is released in order to neutralize the acidity. This notion is a gross misinterpretation of the facts and some serious homework needs to be done by anyone who thinks that protein is harmful to bones. Let me explain.

Indeed, as urinary net acid excretion (NAE) goes up (due, say, to increased protein), so too does urinary calcium excretion (uCa); no argument there. However, this is not a direct measure of bone calcium balance. Simply put, measuring only urinary calcium is to assume that it’s coming from bone; this just isn’t the case. What people choose to forget – or just flat out don’t know – is that there may be other factors at work that may be contributing to the increase in uCa. In fact, a recent systematic review and meta-analysis shows that there is no evidence to suggest that diets that increase NAE lower overall calcium balance (i.e. deplete bones of calcium) [11]. This is because increased protein in the diet leads to greater intestinal absorption of calcium, which in turns contributes to the increase in uCa [12-15]. For example, in 2005, Kerstetter et al. [14] looked at the impact of a low-, moderate-, and high-protein diet on calcium absorption, urinary calcium excretion, and overall bone turnover using stable isotopes of calcium in healthy subjects. Although uCa was shown to increase as the protein content of the diet got higher, it was shown to be directly caused by the increased intestinal absorption of calcium and not from an increase in bone resorption. Therefore, acutely speaking, a diet high in protein (2.1g/kg) was not shown to affect bone resorption or have any negative affect on overall bone health. Furthermore, diets considered low in protein (0.7g/kg) could have profound effects on bone health due to low protein intake inducing subsequent hyperparathyroidism which leads to reduced calcium absorption in the intestine [16-18]. Low serum calcium (via malabsorption) leads to PTH (a major hormonal regulator of bone) being secreted and causing calcium to be leeched from the bones in order to maintain serum calcium levels. What’s more is that these effects were seen in only a matter of 4 days! Therefore, it might actually be better to consume slightly more protein when it comes to bone health.

Cardiovascular disease

Originally it was thought that diets containing higher amounts of protein may have a negative impact on cardiovascular health [19, 20]. This, more or less, was largely due to protein being so closely associated with saturated fats and cholesterol (think high-fat red meats, milk, dairy, etc.) as well as data showing lower risk of cardiovascular disease (CVD) in vegetarian populations [21]. However, subsequent epidemiological data seems to contradict this premise [22, 23], dismissing at least some of the initial claims about protein increasing risk for cardiovascular outcomes. One must remember that, intakes showing increased red meat being correlated to increased risk of cardiovascular outcomes do not mean that higher protein leads to the same risk. In fact, substituting red meat for other forms of leaner meats has been shown to reduce risk for cardiovascular disease [24]. It is also worth noting that observational data looking at meat intake usually shows that the higher intakes of meat are usually accompanied by lower intakes of fruits and vegetables and higher intakes of fats (i.e. poorer quality diets altogether).

More recently, however, a well-written systematic review [25] of randomized controlled trials using low-carbohydrate, high-protein diets (LCHP) showed that LCHP diets were more effective than traditional diets at 6 months and just as effective, if not more, at reducing weight and cardiovascular disease risk for up to one year. Whether the effects can be attributed to the increased protein or the decrease in carbohydrate is irrelevant. The fact remains that the higher protein content of the diet had no detrimental effect on cardiovascular outcomes as was once thought and even edged out a traditional weight loss diet in terms of CVD management.

Evidence in support of consuming higher-protein diets

Now that we’ve established that it is completely safe to consume higher protein diets – given that the rest of your diet isn’t crap (there’s always the fine print) – let’s try and build a case for why someone would benefit from consuming more protein on a daily basis. In the case of bone health, I mentioned the fact that consuming higher protein – that is, protein intake above the RDA – may work in your favor when it comes to calcium absorption and protecting against hyperparathyroidism. There are, however, some other situations that could, and in all likelihood do, warrant higher protein intakes. Let’s see what they are!

Sarcopenia in the elderly

Over the years much research has gone into preventing sarcopenia (age-related muscle wasting) in the elderly. It is well known that those who are older are at an increased risk for muscle wasting, and this may be due to some refractory effects to muscle protein synthesis that occur as one naturally ages [26]. It has been shown that the elderly do not respond similarly to a given dosage of protein under ~20g when compared to those who are younger [27]. Therefore, the elderly may need considerably more protein (~30g or more/meal spread out over 3 or more meals) in order to stave off muscle loss, regardless of grams per kilogram bodyweight [28]. This may require intakes well above the current RDA for a given person.

Higher protein intakes for athletes

I find it humorous that those who vilify higher protein needs for athletes usually base their argument around the fact that those “needs” were justified using an imperfect method (i.e. nitrogen balance; NBAL). I hate to break it to you, but the RDA you so fervently defend was forged using the same imperfect method. Therefore, the case can be made for athletes to consume higher protein diets. Whether or not they already do is beside the point.

Numerous reviews have covered the subject, all with similar conclusions about protein intakes for both endurance and resistance athletes [29-32], with intakes ranging between 1.2-1.7g/kg for strength/power athletes and 1.2-1.4g/kg for endurance athletes. Furthermore, some unpublished work by Eric Helms [33] thoroughly examines the literature to-date on higher protein needs for athletes who are in caloric deficit and already lean. He makes a convincing case for the increased needs of protein for those types of athletes who still need to perform at a high level but are considerably lean to begin with.

Higher protein for weight loss

Considerable data has also shown us that diets higher in protein compared to ones higher in carbohydrate are as equal if not superior in terms of fat loss and lean mass preservation [25, 34]. In fact, in a recent well-designed 12-month randomized clinical trial (4 months weight loss, 8 months weight maintenance) [35], it was shown that a diet comprised of 1.6g/kg (twice the RDA) protein outperformed a traditional diet using 0.8g/kg protein in terms of percentage of fat mass lost (about the same for both groups) and lean mass preserved (about 10-14% more for the high protein group). Furthermore, in conjunction with a resistance exercise program, the fat-loss and muscle-preservation effects of a higher protein diet are even greater when compared to an isocaloric, traditional, higher carbohydrate diet [36-39]. Simply put, if you want to lose weight, reduce your calories and call it a day, independent of diet strategy. However, if you want to lose more fat and preserve more lean body mass, you may fare better on a diet higher in protein, especially if you’re involved in some sort of resistance training protocol.

Glucose homeostasis

In some instances, weight loss diets comprised of higher protein and lower carbohydrate have been shown to improve glucose homeostasis in overweight and obese people more so than traditional weight loss diets [40, 41].  Furthermore, it has even been shown that higher protein diets improve glucose homeostasis in type 2 diabetics without weight loss [42, 43]. This is important because it illuminates the power of altering the dietary composition of one’s diet. Simply by replacing some carbohydrates with protein can make all the difference.

Protein and satiety

Lastly, from a dieting standpoint and regardless of health parameters, protein and higher protein intakes have been shown time and again to be more satiating than diets comprised of less protein (i.e. higher carbohydrate) [44-46]. Obviously, if you’re a 200lb bodybuilder or football player with high caloric needs, satiety may not be an issue until you get to extreme levels of leanness. Nevertheless, for the average American, higher protein would most likely be beneficial in terms of dietary adherence and satisfaction. Therefore, I see no reason why anyone would want to diet otherwise. And, just to clarify, this does not mean reducing carbohydrate intake to astronomically low levels (<10% of intake). This may, and has been shown, to cause subjects to fall off their diet plan. Rather, simply replace some carbohydrate with an equal amount of protein in order to benefit from increased satiety without depriving yourself of too much carbohydrate.

Conclusions and Comments

In conclusion, it seems evident that higher protein diets are neither harmful nor useless when it comes to health parameters such as kidney, bone, cardiovascular disease, type 2 diabetes, obesity, lean mass preservation and satiety. Obviously, if you have some preexisting medical condition, such as kidney disease, a higher protein intake would not be of benefit. However, this is of triviality because you’re probably already in the hospital (or under some form of medical watch) with strict dietary monitoring anyway.

The overall message is that high protein diets should no longer be feared based on misinterpreted data and outdated theories. There is no convincing evidence to suggest that high protein diets cause kidney damage, bone resorption or cardiovascular disease in otherwise healthy individuals. Furthermore, there is accumulating evidence for the consumption of more protein, above the RDA, for multiple populations in order to improve health status. So enjoy your protein, especially if it means better glucose homeostasis, lean mass preservation and bone health. Or, at the very least, because it tastes great!

References

1. Ebbeling CB, Swain JF, Feldman HA, Wong WW, Hachey DL, Garcia-Lago E, Ludwig DS. Effects of dietary composition on energy expenditure during weight-loss maintenance. JAMA 2012;307(24):2627-2634.

2. Tomé D, Boss C. Dietary protein and nitrogen utilization. J Nutr. 2000;130:1868S-1873S.

3. Brenner BM, Lawler EV, Mackenzie HS. The hyperfiltration theory: a paradigm shift in nephrology. Kidney Int. 1996;49:1774-7.

4. Einstein J, Roberts SB, Dallal G, Saltzman E. High-protein weight-loss diets: are they safe and do they work? A review of the experimental and epidemiologic data. Nutr Rev. 2002;60(7):189-200.

5. Martin WF, Armstrong LE, Rodriguez NR. Dietary protein intake and renal function. Nutr Metab. 2005;2:25.

6. Brinkworth GD, Buckley JD, Noakes M, Clifton PM. Renal functioning following long-term weight loss in individuals with abdominal obesity on a very-low-carbohydrate diet vs. high-carbohydrate diet. J Am Diet Assoc. 2010;110:633-638.

7. Skov AR, Toubro S, Bulow J, Krabbe K, Parving HH, Astrup A. Changes in renal functioning during weight loss induced by high vs. low-protein low-fat diets in overweight subjects. Int J Obes Relat Metab Disord. 1999;23(11):1170-1177.

8. Lowery LM, Devia L. Dietary protein safety and resistance exercise: what do we really know? J Int Soc Sports Nutr. 2009;6:3.

9. Poortsmans JR, Dellalieux O. Do regular high protein diets have potential health risks on kidney function in athletes? Int J Sport Nur Exerc Metab. 2000;10:28-38.

10. Manz F, Remer T, Decher-Spliethoff E, Höhler M, Kersting M, Lausen B. Effects of high protein intake on renal acid excretion in bodybuilders. Z Ernahrungswiss 1995;34(1):10-15.

11. Fenton TR, Tough SC, Lyon AW, Eliasziw M, Hanley DA. Causal assessment of dietary acid load and bone disease: a systematic review and meta-analysis applying Hill’s epidemiologic criteria for causality. Nutr J. 2011;10:41.

12. Cao JJ, Johnson LK, Hunt JR. A diet high in meat protein and potential renal acid load increases fractional calcium absorption and urinary calcium excretion without affecting markers of bone resorption or formation in postmenopausal women. J Nutr. 2011;141(3):391-7.

13. Kerstetter JE, O’Brien KO, Insogna KL. Dietary protein, calcium metabolism, and skeletal homeostasis revisited. Am J Clin Nutr. 2003;78(3 Suppl):584S-592S.

14. Kerstetter JE, O’Brien KO, Caseria DM, Wall DE, Insogna KL. The impact of dietary protein on calcium absorption and kinetic measures of bone turnover. J Clin Endocrinol Metab. 2005;90(1):26-31.

15. Cao JJ, Nielsen FH. Acid diet (high-meat protein) effects on calcium metabolism and bone health. Curr Opin Clin Nutr Metab Care 2010;13(6):698-702.

16. Kerstetter JE, Caseria DM, Mitnick ME, Ellison AF, Gay LF, Liskov TA, Carpenter TO, Insogna KL. Increased circulating concentrations of parathyroid hormone in healthy, young women consuming a protein-restricted diet. Am J Clin Nutr. 1997;66:1188-96.

17. Kerstetter JE, O’Brien KO, Insogna KL. Dietary protein affects intestinal calcium absorption. Am J Clin Nutr. 1998;68:859-65.

18. Kerstetter JE, Svastisalee TM, Caseria DM, Mitnick ME, Insogna KL. A threshold for low-protein-diet-induced elevations in parathyroid hormone. Am J Clin Nutr. 2000;72:168-73.

19. Keys A. Seven countries. Cambridge, MA: Harvard University Press, 1980.

20. Wilson PW, Kannel WB, Silbershatz H, D’Agostino RB. Clustering of metabolic factors and coronary heart disease. Arch Intern Med. 1999;159:1104-9.

21. Phillips RL, Lemon FR, Beeson WL, Kuzma JW. Coronary heart disease mortality among Seventh-Day Adventists with differing dietary habits: a preliminary report. Am J Clin Nutr. 1978;31(10 Suppl):S191-S198.

22. Hu FB, Stampfer MJ, Manson JE, Rimm E, Colditz GA, Speizer FE, Hennekens CH, Willet WC. Dietary protein and risk of ischemic heart disease in women. Am J Clin Nutr. 1999;70(2):221-7.

23. Appel L, Sacks F, Carry V, et al. for the OmniHeart Collaborative Research Group. Effects of protein, monounsaturated fat, and carbohydrate intake on blood pressure and serum lipids. JAMA 2005;294:2455-64.

24. Bernstein AM, Sun Q, Hu FB, Stampfer MJ, Manson JE, Willet WC. Major dietary protein sources and risk of coronary heart disease in women. Circulation 2010;122(9):876-83.

25. Hession M, Rolland C, Kulkarni U, Wise A, Broom J. Systematic review of randomized controlled trials of low-carbohydrate vs. low-fat/low-calorie diets in the management of obesity and its comorbidities. Obes Rev. 2009;10:36-50.

26. Breen L, Phillips SM. Skeletal muscle protein metabolism in the elderly: interventions to counteract the ‘anabolic resistance’ of ageing. Nutr Metab. 2011;8:68.

27. Cuthbertson D, Smith K, Babraj J, et al. Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle. FASEB J. 2005;19:422-424.

28. Paddon-Jones D, Rasmussen BB. Dietary protein recommendations and the prevention of sarcopenia. Curr Opin Clin Nutr Metab Care 2009;12(1):86-90.

29. Tipton KD, Wolfe RR. Protein and amino acids for athletes. J Sport Sci. 2004;22:65-79.

30. Phillips SM, Hartman JW, Wilkinson SB. Dietary protein to support anabolism with resistance exercise in young men. J Am Coll Nutr. 2005;24(2):134S-139S.

31. Lemon PW, Proctor DN. Protein intake and athletic performance. Sports Med. 1991;12:313-25.

32. Phillips SM, van Lonn LJ. Dietary protein for athletes: from requirements to optimum adaptation. J Sport Sci. 2011;29(S1):S29-S38.

33. Helms E. The effect of protein intake on fat free mass in lean weight lifters during energy restriction: a case for higher protein intakes. Unpublished, 2012.

34. Layman DK, Bioleau RA, Erickson DJ, et al. A reduced ratio of dietary carbohydrate to protein improves body composition and blood lipid profiles during weight loss in adult women. J Nutr. 2003;133:411-417.

35. Evans EM, Mojtahedi MC, Thorpe MP, et al. Effects of protein intake and gender on body composition changes: a randomized clinical weight loss trial. Nutr Metab. 2012;9:55.

36. Wycherley TP, Noakes M, Clifton PM, et al. A high-protein diet with resistance exercise training improves weight loss and body composition in overweight and obese patients with type 2 diabetes. Diabetes Care 2010;33:969-976.

37. Meckling KA, Sherfey R. A randomized trial of a hypocaloric high-protein diet, with and without exercise, on weight loss, fitness, and markers of the metabolic syndrome in overweight and obese women. Apply Physiol Nutr Metab. 2007;32:743-752.

38. Josse AR, Atkinson SA, Tarnopolsky MA, Phillips SM. Increased consumption of dairy foods and protein during diet- and exercise-induced weight loss promotes fat mass loss and lean mass gain in overweight and premenopausal women. J Nutr. 2011;141(9):1626-34.

39. Kerksick C, Thomas A, Campbell B, et al. Effects of a popular exercise and weight loss program on weight loss, body composition, energy expenditure and health in obese women. Nutr Metab. 2009;6:23.

40. Layman DK, Shiue H, Sather C, Erickson DJ, Baum J. Increased dietary protein modifies glucose and insulin homeostasis in adult women during weight loss. J Nutr. 2003;133:405-10.

41. Farnsworth E, Luscombe ND, Noakes M, Wittert G, Argyiou E, Clifton PM. Effect of a high-protein, energy-restricted diet on body composition, glycemic control, and lipid concentrations in overweight and obese hyperinsulinemic men and women. Am J Clin Nutr. 2003;78(1):31-9.

42. Nuttall FQ, Gannon MC. Metabolic response of people with type 2 diabetes to a high protein diet. Nutr Metab. 2004;1(1):6.

43. Gannon MC, Nuttall FQ. Control of blood glucose in type 2 diabetes without weight loss by modification of diet composition. Nutr Metab. 2006;3:16.

44. Keller U. Dietary protein in obesity and in diabetes. Int J Vitam Nutr Res. 2011;81(2-3):125-133.

45. Veldhorst M, Smeets A, Soenen S, et al. Protein-induced satiety: effects and mechanisms of different proteins. Physiol Behav. 2008;94:300-307.

46. Paddon-Jones D, Westman E, Mattes RD, Wolfe RR, Astrup A, Westerterp-Plantenga M. Protein, weight management, and satiety. Am J Clin Nutr. 2008;87(suppl)1558S-61S.