If you've ever gotten into a debate about protein with someone, one of you probably brought up one of these myths. Hope it wasn't you.
Get enough protein and you'll build and preserve muscle, feel more satiated, and benefit from the increased thermogenic effect from food: all things which contribute to an improved body composition.
Protein is crucial for athletes and lifters. It's involved in a large number of functions that are important for physique and performance. But some people, even some doctors and nutritionists, still don't give it the credit it deserves. Many will even spread outdated misinformation about the macronutrient. Here are the claims they make and the reasons we can put those claims to rest.
Myth: A high protein diet is bad for bone health.
How This Myth Got Started: The original data was published in 1982. Robert Heaney and colleagues showed that in middle-aged women (who were studied in a metabolic ward and ingested diets that matched their everyday intakes of protein and phosphorus) calcium losses were positively correlated with protein intake, and calcium balance was negatively correlated. This study contributed to the common belief that protein is harmful to bone.
Why It Should End: Heaney later took it upon himself to revisit his original data in light of all of the evidence from studies showing that protein intake is actually beneficial for bone. After almost two decades, in an editorial in the American Journal of Clinical Nutrition, he critiqued his own study, stating that the women in the initial study were in a metabolic ward receiving abnormally low amounts of calcium. He speculated that under such conditions protein may have some negative effects. In addition, he criticized the twisting of the scientific evidence by special interest groups. (Guess which ones.)
Heaney stated, "Analysis of the diets of hunter-gatherer societies, and nitrogen isotope ratios of fossil bone collagen, indicate that human physiology evolved in the context of diets with high amounts of animal protein. Although caution has been urged in the interpretation of such analyses, it remains true that there is certainly no evidence that primitive humans had low intakes of either total protein or animal protein. That, coupled with the generally very robust skeletons of our hominid forbears, makes it difficult to sustain a case, either evidential or deductive, for overall skeletal harm related either to protein intake or to animal protein. Indeed, the balance of the evidence seems to indicate the opposite."
Further Evidence: In a review published in the Journal of American College of Nutrition, researchers discussed the major role of protein in the development and maintenance of bone structures. In addition to calcium in the presence of an adequate vitamin D supply, protein is an important nutrient for bone health and the prevention of osteoporosis.
The primary purpose of the review was to investigate the claim that animal proteins cause an increased incidence of bone fractures. Contrary to that claim, experimental and clinical data often indicate that LOW protein intake negatively affects bone health. "Thus, selective deficiency in dietary proteins causes marked deterioration in bone mass, micro architecture and strength, the hallmark of osteoporosis."
In older adults, low protein intakes are often observed in patients who suffer from hip fractures. In these patients, protein supplementation reduces post-fracture bone loss, increases muscle strength, reduces medical complications, and reduces time spent in the hospital. Dietary proteins also enhance IGF-1, which has positive benefits on skeletal development and bone formation.
"Consequently, dietary proteins are as essential as calcium and vitamin D for bone health and osteoporosis prevention." A high protein diet that lacks sufficient amounts of calcium and Vitamin D may be bad for bones. However, a high protein diet that contains sufficient amounts of calcium and Vitamin D can have positive effects on bone health. The claim that consuming high protein diets leads to negative impacts on bone health has been taken out of context.
Myth: A high-protein diet will damage the kidneys.
How This Myth Got Started: A study was conducted to determine whether protein intake influences kidney function change in women over an 11-year period. The participants included women with abnormal and normal kidney function. The results indicated that high protein intake was NOT associated with renal (kidney) dysfunction in women with normal renal function. However, high protein intake (specifically high intake of nondairy animal protein) may have a negative impact on renal function in women with mild renal problems.
Why It Should End: In a review published in Nutrition & Metabolism, researchers looked at the effects of protein intake on kidney function with a particular emphasis on kidney disease. The researchers found: "Although excessive protein intake remains a health concern in individuals with preexisting renal disease, the literature lacks significant research demonstrating a link between protein intake and the initiation or progression of renal disease in healthy individuals."
In addition, it was mentioned that there isn't sufficient evidence to justify public health directives aimed at restricting dietary protein intake in healthy adults for the purpose of preserving kidney function. Protein restriction is common treatment for people with kidney problems, but the same type restriction isn't warranted for people who have normal functioning kidneys.
Further Evidence: This claim is sometimes asserted with such authority that you'd think there must be a lot of evidence supporting it. But it's not unusual for bodybuilders to consume upwards of 300 grams of protein per day. Other athletes and casual lifters routinely consume what would be considered high levels of protein by the people making these claims.
With this type of intake it's reasonable to suggest -- assuming protein is detrimental to the kidneys -- that there should be a lot of people with kidney damage needing dialysis. Where are they? How come we're not hearing about all the lifters with kidney damage? (Hint: It's just not happening.)
Protein 101: The Facts
Enough with the myths, let's get to the protein facts:
- The word protein comes from the Greek word "proteios" which means "of first rank of importance." It's vital for life processes.
- Proteins are made up of carbon, hydrogen, oxygen, nitrogen, and sulfur (cysteine and methionine are amino acids containing sulfur). The nitrogen portion of protein is what distinguishes it from both carbohydrates and fats.
- Humans can't take in nitrogen from the air like plants; they need a dietary source. The body's only avenue for getting nitrogen is through the consumption of dietary proteins.
- While fats can be converted from carbs and carbs from proteins, bodily proteins are acquired only from food.
Protein's Primary Functions
- Maintain and grow tissues (like muscle)
- Act as chief structural molecule of all living things
- Produce enzymes and hormones
- Act as an energy source
- Participate in immune system function, wound healing, fracture healing, and antibody production
The term "complete protein" is often used to describe a protein that contains all of the indispensable amino acids. Incomplete proteins are often described as proteins that lack one or more indispensable amino acids.
Every dietary protein contains all of the amino acids in varying amounts, with a few exceptions like gelatin. So, the concept of complete and incomplete protein is incorrect. Because all proteins are complete, it's more accurate to refer to the limiting amino acid of a given protein, which is the indispensable amino acid occurring in the lowest quantity relative to what's required.
Amino Acids 101
Approximately 300 amino acids have been found in nature. Only 20 are common components of mammalian proteins (the 20 amino acids coded for by DNA). In the human body, there are millions of proteins and each one contains 100-300 amino acids. So even though there are an enormous number of proteins in the human body they are constructed mainly from 20 amino acids.
Dispensable amino acids can be made in the body from metabolic intermediates and other aminos. Indispensable amino acids can't be made at all or in sufficient quantities by the body to support normal protein synthesis, so you have to get them from your diet.
Dispensable and Indispensable Amino Acids
- Bonjour, J. (2005). Dietary protein: an essential nutrient for bone health. Journal of American College of Nutrition, 24(6), 526S-536S.
- Heaney, R. (2001). Protein intake and bone health: the influence of belief systems and the conduct of nutritional science. American Journal of Clinical Nutrition, 73(1), 5-6.
- Heaney, R. & Recker, R. (1982). Effects of nitrogen, phosphorus, and caffeine on calcium balance in women. Journal of Laboratory and Clinical Medicine, 99,46-55.
- Knight, E., Stampfer, M., Hankinson, S., Spiegelman, D., & Curhan, G. (2003). The Impact of Protein Intake on Renal Function Decline in Women with Normal Renal Function or Mild Renal Insufficiency. Annals of Internal Medicine, 138, 460-467.
- Martin, W., Armstrong, L., & Rodriguez, N. (2005). Dietary Protein intake and Renal Function. Nutrition & Metabolism, 2-25.
- McDonald, L. (2001). Protein, Part 1: Definitions and Technical Background. Meso Rx.