Most people know all about the benefits of a high-protein diet to improve body composition and build muscle, but what are the health risks of eating too much protein? Despite the longstanding paradigm of high-protein diets in fitness and bodybuilding subcultures, some evidence suggests that excess protein intake may lead to deleterious long-term health problems and undesirable side effects .
However, for every study that incriminates high-protein diets for conditions like kidney disease, there are equally as many that find no untoward effects of a high-protein intake (at least not in otherwise healthy individuals). In fact, several studies cite a higher protein intake as being prudent for weight loss and promoting athletic performance .
Nonetheless, there is a fine line between eating enough protein and overeating protein. As with just about every substance you put in your body, too much of a "good thing" can cause health problems. The question then is, "How much protein is too much?"
When weighing the empirical data, it's quite clear that the amount of protein each person should eat is relative to their body weight, activity level, preexisting health conditions, age, and a range of other variables. Intuitively, a lean, active 180-lb young adult who wants to build muscle will require more protein than a 120-lb 70-year old who lives a sedentary lifestyle.
To further complicate things, the United States' recommended daily allowance (RDA) for protein is just 0.36 grams of protein per pound of body weight (or 0.8 grams of protein per kilogram of body weight) . For an adult weighing 160 lbs (72.7 kg), that comes out to just 57.6 grams of protein per day — a negligible amount in the mind of most gym-goers.
Frankly, most adults could meet the RDA for protein with two protein shakes a day and literally nothing else.
Despite the ongoing debate over whether the U.S. should revisit the protein RDA, some researchers and public health officials are hesitant to set the standard higher for fear that people will eat too much protein. Yet, a recent systematic review contends that there is no consistent evidence that protein intakes above the U.S. RDA are associated with declines in kidney function of healthy adults .
Additional evidence suggests that the more appropriate amount of dietary protein intake is at least 0.54 – 0.73 grams of protein per pound of body weight (or 1.2 – 1.6 grams per kilogram of body weight) for optimal health outcomes .
The RDA does not reflect how much protein active individuals should eat for optimal muscle growth and athletic performance. Instead, the RDA for protein is the minimum amount of protein a healthy, sedentary adult should eat to maintain normal tissue turnover and biological function.
Moreover, aging adults typically require more protein to help combat sarcopenia (age-related muscle loss) and decreases in muscle protein synthesis . Researchers often recommend upwards of a 20% increase in protein intake above the RDA for the elderly.
When you throw athletes, gym-goers, and bodybuilders in the mix, the "optimal" protein intake may be quite a bit higher than the RDA. For example, there is compelling evidence that active individuals who regularly lift weights may benefit from daily protein intake as high as 1.5 grams per pound of body weight (or 3.3 grams per kilogram of body weight) [7, 8].
While that might seem like an astronomical amount of protein to someone who follows the RDA guidelines, it's really the "norm" in fitness subculture.
Don't misconstrue the above as saying that you need that much protein daily. The vast majority of athletes and active individuals really only need between 0.7 grams of protein per pound of body weight for optimal performance, health, and muscle growth. If you want to eat a little more, that's fine.
Assuming you're an otherwise healthy individual, there is currently no strong evidence to suggest eating 1.0 – 1.5 grams of protein per pound of body weight is harmful. In some cases, it might even be beneficial for those trying to lose weight while preserving as much lean body mass as possible.
But again, protein intake is relative to your goals and specific needs. Consulting with a registered dietitian is generally wise before making big changes to your diet, especially if you have preexisting health conditions. In particular, those with kidney dysfunction or kidney disease are more susceptible to fluctuations in dietary protein intake and should always follow a healthcare professional's guidance.
People must understand that a high-protein diet can be healthy and sustainable for certain individuals. Even in the studies mentioned earlier that showed the merits of higher protein intake, subjects were still consuming what most gym-goers would consider to be "modest" amounts of protein.
High-protein diets are not synonymous with eating too much protein. There is undoubtedly a point where excess protein becomes problematic.
If you look back at bodybuilding periodicals and magazines from the late 20th and early 21st centuries, they typically recommended absurd amounts of protein (e.g. 2+ grams per pound of body weight).
If you're eating superfluous amounts of protein daily, the long-term health risks and side effects may start to outpace the theoretical benefits. Overeating protein, particularly from red meat, can stress the kidneys over time by chronically elevating the glomerular filtration rate (GFR) . In turn, this can increase the risk of kidney disease .
When a healthy individual consumes protein, the GFR increases in response to the rise in nitrogenous metabolites and corollary blood pH changes. The kidney's capacity to elevate GFR after consuming a protein-rich meal is known as the renal functional reserve; when the kidneys lose this capacity, chronic kidney disease is imminent.
However, an increase in GFR is not necessarily "bad" after eating protein; it's actually a normal biological process since the kidneys are responsible for filtering metabolic waste and byproducts. It seems that the source of protein and how frequently protein is consumed are the more important factors.
For example, a few studies implicate frequent protein feeding as a probable cause of declining renal function in otherwise healthy adults [11, 12]. The notion that you need to eat protein every two to three hours or the body becomes "catabolic" is nonsensical and may actually be counterproductive for a handful of reasons.
Furthermore, red meat and fatty poultry meat have been shown to increase GFR significantly more than equal amounts of protein from egg whites, white meat from fish and poultry, milk protein (i.e. whey and casein), and especially plant-based sources like pea protein and rice protein [13, 14]. These findings lend credence to the health benefits of eating more plant-based foods, even if you're not on a strict vegan diet. If anything, those following high-protein diets should try and incorporate a generous amount of vegan protein sources to take some of the load off the kidneys.
In addition, frequently consuming acidic protein sources like red meat and organ meat can contribute to gout and uric acid kidney stones . While eggs and milk protein come from animals, they yield a rise in GFR comparable to that of plant proteins and facilitate uric acid excretion. As such, protein powder that contains whey or casein is not bad for the kidneys.
Bodybuilding dogma tends to pervade society until researchers have time to "catch up" with the ebbs and flows of current trends. Thankfully, the literature referenced throughout this article provides plenty of proof beyond a reasonable doubt that eating 2+ grams of protein per pound of body weight is not necessary, nor is it optimal.
Many people who jump on the bodybuilding bandwagon consume a greater amount of animal meats like beef and pork. The amino acids in these proteins are more acidic than those in low-fat sources like milk, Greek yogurt, lean white meat, eggs, pea protein, and rice protein.
Since one of the primary roles of the kidneys is to regulate blood pH, it's best to get a variety of protein sources in your diet and limit intake of red meat, organ meat, fatty fish, and dark meat from poultry. This doesn’t mean you need to go on a full-blown vegan diet, but rather that you should be cautious about eating things like steak and pork daily. It just so happens that many alkaline foods, like dark, leafy vegetables and beans, are plant-based, and these foods appear to protect the kidneys. So, if you needed another reason to eat more vegetables and add a vegan protein powder to your supplement stash, add this to the list.