Myth: Protein is Bad for You?
Basically: NO. Protein, even in large amounts, isn’t harmful to your bones or kidneys (unless you suffer from a pre-existing condition).
Protein is bad for you? Carbs and fats often take the blame for various health issues, but the third macronutrient isn’t always spared by the media. Protein has often been accused of harming bones and kidneys.
Let’s tackle those two claims one at a time.
Bone loss
More protein in the diet has been linked to more calcium in the urine. Two reasons have been suggested to explain this phenomenon:
- Your body draws from its calcium stores (in bones) to buffer the acid load caused by dietary protein. This has led researchers to suggest that higher protein intake could cause greater bone loss.
- Most studies that looked at protein intake and calcium excretion list dairy products as a protein source, so higher urinary calcium could simply be the result of higher calcium intake (i.e. , more calcium in, more calcium out).
Therefore, looking only at calcium excretion wasn’t enough. Subsequent studies showed that dietary protein promotes dietary-calcium absorption and that:
“high protein intake promotes bone growth and retards bone loss (whereas) low-protein diet is associated with a higher risk of hip fractures.”
What happens is that when you ingest more protein, you absorb more of the calcium in your food, so less calcium ends up in your feces. Later, your body gets rid of the calcium it doesn’t need, so more calcium ends up in your urine, but not as much as would have otherwise ended in your feces. Therefore, an increase in protein intake leads to an overall decrease in calcium excretion, which points to an increase in calcium retention.
All in all, current evidence suggests that protein actually has a neutral or even protective effect on bones.
Kidney damage
Other studies determined that high protein diets increased glomerular filtration rate (GFR), a marker for waste filtration in the kidneys. It was argued that increased GFR was a sign that undue stress was put on the kidneys, but later research has shown that kidney damage does not occur as a result of diets high in protein.
In conclusion, randomized trials thus far have not shown high-protein diets to harm the bones or kidneys of otherwise healthy adults.
References:
- Barzel US, Massey LK. Excess dietary protein can adversely affect bone. J Nutr. (1998)
- Schwingshackl L, Hoffmann G. Comparison of high vs. normal/low protein diets on renal function in subjects without chronic kidney disease: a systematic review and meta-analysis. PLoS One. (2014)
- Hunt JR, Johnson LK, Fariba Roughead ZK. Dietary protein and calcium interact to influence calcium retention: a controlled feeding study. Am J Clin Nutr. (2009)
- Shams-White MM, et al. Dietary protein and bone health: a systematic review and meta-analysis from the National Osteoporosis Foundation. Am J Clin Nutr. (2017)
- a b Calvez J, et al. Protein intake, calcium balance, and health consequences. Eur J Clin Nutr. (2012)