Quick Summary tl;dr
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There is no clear consensus on what defines a “high-protein” diet. Often, “high-protein” diet in studies is what most people would consider a normal protein diet.
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There are multiple ways to measure protein intake, including the percentage of calories from protein or grams of protein per pound body mass.
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Being lean, active, and caloric restriction can increase your absolute protein needs.
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High-protein diets, within reason, do not harm healthy kidneys, bone health, or shorten lifespan.
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Protein quality matters. This can be assessed by PDCASS and DIASS scores. In general, animal proteins are of higher quality than plant proteins.
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There is no good reason for most people to be targeting extremely high protein intakes.
“High-protein” diets are all the rage right now. And with all the enthusiasm there is an equal amount of confusion. How much protein should I eat? Can too much protein be harmful? What are the best sources? In this article, we will try to clarify the confusion.
High Protein is Poorly Defined
The “high-protein diet” is poorly defined. For example, the U.S. Food and Drug Administration has set the Daily Value for protein at 50 grams per day on a 2,000 kilocalorie diet. That’s only 10% of calories from protein. If we were to use these recommendations, the average American adult man or woman consuming 16.3% and 15.8% of calories from protein, respectively, would already be eating a high-protein diet ( CDC data).
The Dietary Reference Intake for protein is similarly low at 0.36 g/lb of body weight. For a 160 person, that is 57.6 grams of protein. In other words, a single 6 ounce cooked chicken breast is supposedly sufficient to supply a fully grown adult male with all his protein needs (USDA Food Central).
These values are generated based on the amount of protein required to protect against overt nutrient deficiencies. They are not meant to suggest a recommended protein intake for optimal health in any individual. Nevertheless, these values — especially 0.36 g/lb of body weight — are important to acknowledge in any discussion of high-protein diets because they serve as the reference point in many studies for how “high-protein” is defined in the scientific literature.
As a result, some studies use values similar to 0.36 g/lb as a control. And, consequently values such as 0.5 g/lb body weight ( Soenen et al, 2012) become “high-protein.” However, on the other end of the spectrum, some studies will use the term high-protein diet to refer to diets containing 1.4 g/lb body weight. ( Helms et al, 2014)
The enormous variation in how we define “high-protein” has led to tremendous confusion in the field. In six words: high-protein diets are poorly defined.
By Daily Reference Intake standards, a single chicken breast can meet the protein needs of a fully grown man. Is that reasonable?
Percentage of Calories vs. Grams per Pound
Now, while our goal is not to define what “high-protein” means, it will be useful to distinguish between the two most common ways to measure protein intake. These are:
- (i) % Calories from protein
- (ii) Protein consumed per pound of body weight.
Each of these metrics has their benefits. % Calories from protein provides an energy intake control, as in research settings. For example, if a study compares a 15% protein diet to a 30% protein diet, then 15% of dietary calories needs to be adjusted for by lowering fat and/or carb calories.
Protein per pound of body weight is perhaps a better measure in free-living individuals. 1 g/lb protein will almost certainly meet most people’s needs, and yet could contribute 15% or 30% of a person’s total intake depending on their energy needs.
The central point here is that, again, defining “high-protein” is tricky. Not only do we lack a consensus threshold to determine if a diet is “high-protein,” but we are often using entirely different measuring sticks altogether.
Benefits of High Protein Diets
Satiety per Calorie: High Protein Diets Will Keep You Full For Longer
With those caveats in place, let's turn to the purported benefits of high-protein diets, beginning with satiety. It is argued that eating a high-protein diet will make you feel full, helping to naturally limit energy intake. In other words, protein-rich foods have the highest “satiety per calorie.”
In general, we tend to agree with this point. Here’s a thought experiment: imagine eating a 6-jumbo egg-white omelet (protein), or sipping one tablespoons of olive oil (fat), or eating one banana (carbs). Each of these options contains approximately the same calories but one is obviously more filling than the others.
That said, the “satiety per calorie” concept misses an important point: eliminating sugar, refined carbohydrates, and processed foods from the diet are more potent tools for controlling overeating. In fact, I’d wager that if you simply added a donut to your egg-white omelet breakfast, you’d be hungrier in three to five hours, not less. (Side bar: That's rhetorical. Don't try this at home kids!)
Simply put, when it comes to controlling hunger and cravings, it’s less about what you do eat than what you don’t.
Otherwise stated, and to pose an ironic analogy, when it comes to controlling overeating, consuming a clean diet free of sugar is the sundae, and eating high-protein is the cherry on top.
Higher Thermic Effect of Food
It is also argued that protein has a higher thermic effect of food (TEF) than fat or carbohydrates. At some level, this is true. For example, one meta-analysis ( Eisenstein et al, 2002) calculated that TEF as % of total energy burned could be calculated using the following equation:
TEF (%Energy intake) = 0.132P + 0.051F + 0.054C, where P, F, and C are grams of dietary protein, fat and carbohydrates.
The Thermic effect of food can be calculated as: TEF (%Energy intake) = 0.132P + 0.051F + 0.054C, where P, F, and C are grams of dietary protein, fat and carbohydrates.
Clearly, the coefficient of 0.132 on protein is the largest number, suggesting that TEF is greatest if you eat more protein. That said, the absolute increase in TEF is pretty small when you do the math. On a 2,000 Calorie diet, doubling protein intake from 15% to 30% only increases TEF by about 23 Calories per day.
The magnitude of this effect is relatively small. By comparison, the Framingham Food Study and follow-up analyses show trading carbohydrate calories in for fat calories, while controlling protein at 20% of caloric intake, increased total energy expenditure by 200 - 300 Calories per day. (NN Blog on CIM)
Thus, one could argue the metabolic benefits of substituting carbs for fats, in terms of energy expenditure, are an order of magnitude greater than those of increasing percent calories from protein under some circumstances.
And, as an added nuance, newer research suggests that the presence of insulin resistance decreases TEF by uncoupling insulin from the upregulation of thermogenesis in muscles. ( Habtemichael et al, 2021) Those are a lot of big words, but this implication is that your metabolic health also determines your TEF, and perhaps does so to a greater extent.
So how do you achieve metabolic health? That’s a big question. But it’s worth mentioning a randomized crossover trial demonstrated that decreasing carbohydrate intake reversed metabolic syndrome far more effectively than decreasing fat intake, even when both total calories and protein were controlled. (NN Blogs on Mets) This study didn’t test whether TEF increased on a low-carb diet after reversal of metabolic syndrome, but it is an interesting hypothesis!
Again, when it comes to energy expenditure (and possibly TEF too), metabolic health may be the proverbial ice-cream sundae, and high-protein is the cherry on top.
Protecting Muscle During Caloric Restriction
One circumstance under which increasing protein intake is certainly beneficial is when a person is undergoing forced caloric restriction. This could be an obese participant in a research study, or a body builder prepping for a contest, or any circumstance in between.
When your body is deprived of energy, muscle tissue can get broken down to make glucose. This is especially true when you are not fat-adapted because the body will be more dependent on glucose and will not benefit from the muscle-protecting effects of ketones.
In fact, if you are a lean and highly trained athlete in and in a meaningful caloric deficit (e.g. preparing for a body-building competition), some research suggests consuming as high as 1.4 g/lb of lean body mass could be beneficial ( Helms et al, 2014). At 12% total body fat that would equate to ~1.6 g/lb, which is “high-protein” equal to 440% of the dietary reference intake. That said, newer literature and current recommendations for weight loss in athletes suggest intake of 1 g/lb during weight loss is plenty. ( Hector at al, 2018)
The extreme example of ~1.4 g/lb lean mass is helpful in that it sets an upper bound for where the purported benefits of high-protein may end. That said, data from a recent meta-analysis suggest that eater higher protein can increase lean mass up to the highest level tested (~1.6 g/lb) and supposedly without limit. ( Tagawa et al, 2020)
But there’s always an added nuance. For example, this analysis also found that increasing protein intake beyond a certain point was associated with a decrease in lean mass when individual were not resistance training and when body weight was controlled.
The bottom line is that protein needs are not only dependent on gender, age, and size, but also protein quality and other environmental factors, like whether you’re exercising.
Functionally speaking, and as relates specifically to weight management and body composition (not health per se), these are important factors to keep in mind:
- The more active you are, the more protein you will need. Being more active will increase your protein needs in g/lb body weight but decrease your % Calories from protein as your increased overall energy needs will likely outweigh your increased protein needs.
- The higher your body fat, the less protein you will need in terms of g/lb from protein. Protein is required by lean muscle tissue. So, if less of your total body mass is lean mass, you will need less protein per pound of body weight.
- If you are restricting caloric intake, your protein needs will go up to protect against loss of lean mass. The leaner you are, the stronger this effect might be as you have less local fat tissue to fuel muscle.
Keep these questions in mind when you’re determining how much protein you need.
- Are you active?
- Are you lean?
- Are you restricting calories?
Myths About High-Protein Diets
High-Protein Diets Harm The Kidneys
The notion that a high-protein diet could put strain on and harm the kidneys has always been theoretical and never really materialized in clinical trials including persons with baseline normal kidney function.
Furthermore, a systematic review and meta-analysis of 28 trials including 1,358 participants comparing a high-protein diets (defined as ≥ 0.7 g/lb body weight or ≥ 20% energy intake or ≥ 100 g protein/day) to lower protein diets in adults without kidney disease found that “high-protein intakes do not adversely influence kidney function.” ( Devries et al, 2018)
That said, it is important to caution that, in patients with pre-existing kidney disease, high-protein intake can be contraindicated.
Furthermore, because intakes at the extreme end of high-protein diets have not been rigorously tested in large-scale trials, one can’t rule out the possibility that there is a threshold above which high-protein diets could theoretically be harmful to the kidneys of even healthy people.
Absence of evidence is not evidence of absence. But neither does the literature doesn’t support the claim that high-protein diets harm the kidneys.
High-Protein Diets Harm Bones
This myth can be busted quite quickly. The National Osteoporosis Foundation itself conducted a systematic review of 16 randomized controlled trials and 20 perspective studies and found, “Current evidence shows no adverse effects of higher protein intakes.”
Protein, in fact, is essential for bone health, and low-protein diets confer a higher risk of developing low bone mass (especially in the spine) than do high-protein diets. ( Shams-White et al, 2017)
High-Protein Diets Shorten Lifespan
The notion that high-protein diets shorten lifespan usually comes down to discussion about the protein complex, mTOR. On the one hand, mTOR activity signals growth. Stimulation of mTOR by protein is necessary to build healthy lean muscle mass. On the other hand, some people fear mTOR activity because inhibiting mTOR activity in animal models, such as yeast, fruit flies, nematodes, and mice, leads to lifespan extension. ( Saxton et al, 2017)
That said, it is a huge leap of logic to suggest that eating high-protein shortens lifespan in humans. There is no evidence in humans that high-protein diets shorten lifespan or that low-protein diets improve longevity.
To try to label mTOR as either good or bad misses critical nuances about this important protein complex that are beyond the scope of this blog. But, if you want to read more about “mTOR mysteries,” specifically as relates to brain health and cognitive longevity, you can see this review.
Finally, high levels of lean muscle tissue are an excellent predictor of longevity in humans, so eating a low-protein diet might even be detrimental to living a long and healthy life.
Protein Quality Matters
“How much?” is one question. “What source?” is another.
Not all protein sources are created equal. In general, animal proteins are more available to the body and contain a better composition of amino acid building blocks for constructing lean tissue.
The PDCAS Score
One measure of protein quality is the PDCASS score, which stands for protein digestibility corrected amino acid score. Using the PDCASS method, proteins are given a score ranging from 0.0 to 1.0, with 1.0 being an ideal protein. Most animal proteins score a 1 or near a 1. For example, milk, eggs, beef, fish, pork, and chicken all score 1.0. By contrast, chickpeas score a 0.74, peanuts or wheat bran score a 0.5, and almonds score a 0.4.
The DIASS Score
A newer method for assessing protein quality is the DIASS score system, which stands for Digestible Indispensable Amino Acid score. DIASS score is considered a better metric than PDCASS, for reasons you can read about here, but isn’t as popular because fewer foods have been given a DIASS score. Still, we see a similar pattern where animal proteins are superior. Foods given DIASS scores of 1.0 or higher are “excellent” proteins, those given scores of 0.75 - 0.99 are “good” proteins, and those that receive scores of <0.75 get “no protein quality” claim.
Using DIASS, whey, beef, lamb, pork, chicken, fish, and eggs are “excellent,” whereas spinach, beans, tree nuts, and many vegetables get “no protein quality” claim.
Using DIASS scoring, beef, lamb, pork, chicken, fish, and eggs are “excellent,” whereas spinach, beans, tree nuts, and many vegetables get “no protein quality” claim.
Plant Proteins - Are They Good?
That said, among the plant proteins, soy protein concentrate scores a 1.0 on PDCASS and 0.9 on DIASS, which makes it a “good” protein source as far as plant-based proteins go.
Pea protein similarly scores a 0.89 and 0.82 on these metrics, so is also a “good” protein. Soy protein is also considered a “complete protein” because it contains all nine essential amino acids — protein building blocks that the body can’t produce from other amino acids. Pea protein falls just shy of being a complete protein because it’s low in methionine.
Admittedly, even protein digestibility and bioavailability scores still don’t reveal a complete picture. Different protein sources have different compositions of amino acids, just like different Lego sets include different Lego pieces. In our opinions, it makes more sense to eat animal protein to build an animal than to eat plant protein to build an animal.
That said, it is possible to eat a healthy vegetarian diet. And, if you do choose to make this your lifestyle, perhaps consider reading more on PDCASS, DIASS and protein quality metrics so that you can make informed choices about the best protein sources available to you.
Should I Be Following a High Protein Diet?
The notion that trading protein for carbs or fats is better for health is overly simplistic. First, we don’t have a good definition for “high-protein.” If we are using 0.36 g/lb as our reference, then a high-protein diet of 0.7-1.0 g/lb probably is better for health. But it does not follow that more protein is always healthier. In my opinion, there is no good reason for most people to be targeting extremely high protein intakes.
Building on that point, the discussion of extremely high-protein diets usually focuses on optimizing body composition at the extreme limits of lean.
Most people are not competitive body builders. And most people (I hope) are more interested in being healthy than shredded to 4% body fat, which is not necessarily healthy. Trust me. I’ve been there. Unfortunately, this nuance gets lost in discussions about high-protein diets, which the focus primarily on body composition.
In closing, I personally am for high-protein diets, within reason. The only purpose of this blog was to prompt you to ask that very question: what does “within reason” mean to you?
Is a high-protein diet actually better? Scientific reason, not click bait.
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