By Diana Rodgers, RD, and Robb Wolf

You have probably heard that women need 46 grams of protein per day and men need 56 grams a day. But are these numbers correct? Where did they come from? And is there “too much” protein?

According to the US Dietary Guidelines, the recommended daily allowance (RDA) is 0.8 grams of protein per kilogram of body weight. It’s important to note, however, that this is a minimum requirement, not the optimal amount in order to thrive.¹ Also, just to be clear, this is grams of protein, not the total weight of the food in grams. For example, 100 grams (about 3.5oz in weight) of broccoli has 2.4 grams of protein. By contrast, 100 grams of roasted beef has 27.2 grams of protein.

Translating the RDA of 0.8 grams protein per kilogram of body weight to the public is difficult, so the USDA put together the US Dietary Guidelines to give actual quantities. They based the numbers on a “reference” man of 70 kilograms (154lbs) and a “reference” woman at 57 kilograms (125lbs), and calculated the numbers based on those references. So, if you go to the internet and look up, “How much protein should I eat?” the numbers you’ll often find are 56 grams a day for men and 46 grams per day for women. This is also what most health professionals will tell you.

The first problem is, how many men do you know who are 154 pounds and women who are 125 pounds? The CDC says the average American man is 88.6 kilograms (195.5lbs) and the average woman is 75.6 kilograms (166.2lbs).² That’s a big difference from the above “reference” man and woman. According to the 0.8 grams of protein per kilogram of body weight calculation, the average American man needs 71 grams of protein per day and the average American woman needs 60 grams.

The next problem? Remember, this is the minimum you need to avoid disease, not the “optimal” amount of protein.

The current RDA for protein is explained in the Dietary Reference Intakes by the Institute of Medicine, which based their original protein recommendations on nitrogen balance studies. Nitrogen balance is the difference between nitrogen intake and excreted nitrogen. It’s difficult to measure and varies greatly between individuals. It’s very easy to underestimate adequate protein levels based on these studies. In fact, here is a direct quote from the report:

In adults, it is generally presumed that the protein requirement is achieved when an individual is in zero nitrogen balance. To some extent, this assumption poses problems that may lead to underestimates of the true protein requirement.³

It also doesn’t account for the satiating quality of protein or the nutrient density of the best protein sources. Humans don’t really need “protein”; we need amino acids, and foods such as eggs, fish, and poultry have a good balance of amino acids plus micronutrients. 

Long before the current guidelines were introduced, much higher protein recommendations were proposed. In a nutrition text from 1912, nitrogen balance studies were questioned as inaccurate measures of protein requirements, and a recommendation of at least one hundred grams of digestible protein (so, not just grams of total protein, but bioavailable protein) be consumed. Anything under one hundred grams a day was found to lead to ill effects.⁴

What would the “optimal” or even “adequate” amount of protein look like? There’s another set of numbers we can look at called the acceptable macronutrient distribution range (AMDR). The AMDR is defined as “a range of intakes for a particular energy source that is associated with reduced risk of chronic diseases while providing adequate intakes of essential nutrients.” The recommended range for protein according to the AMDR is 10 to 35 percent of caloric intake.⁵ 

How does this translate to our diet? The USDA estimated calorie needs per day recommends a diet of about 2,000 calories per day for average, moderately active women and about 2,600 calories per day for moderately active men. Using 10–35 percent of calories from protein, the reference woman at 125 pounds would need 50 to 175 grams of protein per day, and the reference man needs 65 to 228 grams of protein per day. This is a huge range! This makes the commonly accepted 45 grams per day for women and 54 grams per day for men below the AMDR range.

Most Americans are getting about 16 percent of their calories from protein, and a recent study showed that American adults over fifty were getting much fewer, with 46 percent not even hitting the RDA of 0.8 grams per kilogram of body weight. From the paper, “Those not meeting the protein recommendation were more likely to have intakes of other nutrients below recommended levels. Those below the protein recommendation had significantly more functional limitations across all age groups, while grip strength was significantly lower in those over 70 years old.”⁶ 

At a conservative 20 percent of calories from protein, the average woman on a 2,000 calorie per day diet would need one hundred grams per day. This number is more than double the commonly assumed protein requirement of forty-five grams per day. In fact, when we’re telling women to only eat forty-five grams of protein, we’re recommending less than 10 percent of total calories, lower than the ADMR. 

A lot of people (especially women) push back and feel like this is “too much.” However, once people actually get this level of protein in their diet, they generally feel a lot better and eat fewer calories because they feel fuller.

Won’t Too Much Protein Hurt My Body?

You may have heard that too much protein causes too much acid in the body, or that it is useless to eat more than the minimum RDA. The Dietary Reference Intakes by the Institute of Medicine actually sets no upper level for protein on the basis of chronic disease risk because high protein intake has not been found to have a detrimental effect.

You may have heard that animal sources of protein are too “acidic.” While it’s true that urine strips can show a higher urine acid level depending on what food is consumed, the fact is that urinary pH has little to tell us about health, other than in extreme metabolic conditions, and the human body tightly controls blood pH at 7.4. Our food intake has no effect on this and eating a more “acidic” diet from meat will not affect bone health.⁷

What about the concerns that protein causes kidney disease and cancer? In healthy people, no danger has been found in protein intake above three grams per kilogram.⁸ It’s true that those with kidney disease should limit their protein intake, but there’s no proof that increasing your protein intake actually causes kidney disease.⁹ 

What Are the Dangers of Too Little Protein?

Your body needs protein, and if you don’t get enough through diet, your body will start breaking down your muscles and other tissues in order to get it. This leads to muscle wasting and weakness. Immune function decreases because protein is required for antibodies. You also need protein to make enzymes and to carry oxygen to tissues, so low protein can cause lethargy. Low protein is also associated with hair loss, brittle nails, and cold hands and feet. Low protein can cause weight gain.¹⁰ B12 deficiency, which is common in vegetarians and vegans, has been shown as an independent risk factor for coronary artery disease and serious neurological disorders in infants of vegan mothers.¹¹

So How Much Protein Should You Eat?

In summary, it’s incredibly confusing to determine how much protein to eat and the recommendations don’t really seem to be based on much science, due to the inaccuracy of nitrogen balance studies and the broad ranges from the AMDR.

As a very reasonable starting point, it seems that 100 grams of protein on a 2,000-calorie diet is a great place to begin if you’re consuming less. Most Americans report eating between 1,800 and 2,500 calories per day (and self-reported data is usually on the low end), so this means at 20 percent of calories, intake for many Americans should be between 90 and 125 grams of protein per day. We see great success with people upping their protein to 30 percent of total calories.

Higher levels of protein are effective for weight loss. According to the protein-leverage hypothesis, people will continue to eat food in order to satisfy their protein needs. If the food you’re eating is ultra-processed, low in protein but high in calories and carbohydrates, the brain will tell you to continue eating that food until you reach your protein minimum. 

Because protein is highly satiating, when we increase our protein intake, our overall caloric intake generally reduces. Protein is the most satiating of the macronutrients, and intake of 15–30 percent of total calories can be quite helpful in regulating appetite by increasing leptin sensitivity and inducing weight loss and increasing blood sugar control.¹² In one meta-analysis of randomized control trials (the gold standard of nutrition research), high protein diets of 25–32 percent of calories compared to the control groups of 15–20 percent (which is still higher than the RDA), showed beneficial effects on weight loss, HbA1C levels, and blood pressure in patients with type 2 diabetes.¹³

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Diana Rodgers, RD, is a “real food” nutritionist and sustainability advocate. She’s an author, runs a clinical nutrition practice, and is the host of the Sustainable Dish podcast. Diana writes and speaks internationally about the intersection of optimal human nutrition and environmental sustainability. Diana is an advisory board member of Animal Welfare Approved, Savory Institute, and Whole30. 

Robb Wolf, a former research biochemist is the two-time New York Times/Wall Street Journal bestselling author of The Paleo Solution and Wired to Eat. Robb has transformed the lives of hundreds of thousands of people around the world via his top ranked iTunes podcast, books, and seminars. Robb has functioned as a review editor for the Journal of Nutrition and Metabolism (Biomed Central) and as a consultant for the Naval Special Warfare Resiliency program. He serves on the board of Directors/Advisors for: Specialty Health Inc, The Chickasaw Nation’s “Unconquered Life” initiative and a number of innovative startups with a focus on health and sustainability.

Well Being Journal adapted the excerpt from Sacred Cow: Why Well-Raised Meat is Good for You and Good for the Planet by Diana Rodgers, RD and Robb Wolf, and printed with permission of BenBella Books.

References available: https://benbellabooks.com/shop/sacred-cow/