US dietitians told the Daily Mail that high protein diets can cause weight gain and increase the risk of health problems.
A review of more than 350 studies published last week found lower protein diets were linked to a healthier weight, a lower risk of cardiovascular disease and sometimes a longer life.
High protein products now fill grocery store shelves, including protein-enriched yogurts, pretzels, cereals, breads and ice cream.
"Some people have the misconception that if you consume too much protein, it just kind of disappears," US dietitian Lindsey Schoenfeld said. "But studies show that consuming a high-protein diet may cause weight gain, diabetes and many other health problems."
Protein is one of three essential macronutrients alongside carbohydrates and fats. It builds and repairs tissue, maintains muscles, supports the immune system and keeps organs, skin, hair and nails healthy. It helps older adults preserve strength and mobility to remain independent later in life.
For years, the US Government recommended about 0.36 grams of protein per pound of bodyweight daily. This was revised up to 0.54 grams to 0.72 grams per pound in guidelines released this January.
Health and Human Services Secretary Robert F Kennedy Jr. backed the change. He said protein had been "wrongly discouraged" for too long. Kennedy is famous for his meat-heavy diet and enjoyed a steak for his 72nd birthday this January. Influencers including the Liver King and Joe Rogan have also promoted the benefits of high protein diets.
The new guidelines mean an average 170-pound American woman should consume 92 grams to 122 grams of protein a day. An average 200-pound man needs about 108 grams to 144 grams.
A three-ounce serving of cooked chicken breast contains 26 grams to 30 grams of protein. A large egg provides about six grams. A cup of Greek yogurt offers 20 grams to 25 grams. Half a cup of firm tofu has about 22 grams, and a cup of cooked lentils provides around 18 grams.
Most foods contain some protein. A cooked cup of oats provides about five grams, and a cooked cup of broccoli has around four grams. Two slices of wholemeal bread contain about eight grams, while two tablespoons of peanut butter have seven grams. A medium baked potato offers about four grams.
A woman aiming for the lower recommendation could reach 85 grams of protein with a cup of Greek yogurt for breakfast, a chicken breast at lunch, a cup of lentils with dinner and two eggs as snacks. She would easily make up the remaining amount from grains, vegetables and dairy consumed throughout the day.
A 200-pound man aiming for the upper limit could hit around 140 grams by eating two chicken breasts, a cup of Greek yogurt, a cup of lentils, two eggs and half a cup of tofu.
Consuming too little protein causes brittle hair and nails. A deficiency can lead to muscle loss, weakness, frailty, falls and bone fractures.
However, the average American already consumes about 0.6 grams of protein per pound of body weight each day. This is enough to comfortably meet current recommendations.
Meanwhile, about 95 percent of adults fail to consume the recommended amount of fiber. Fiber is linked to a lower risk of heart disease, type 2 diabetes, bowel cancer and obesity.
Limits to muscle growth
Evidence suggests there is a ceiling to the benefits of protein. A 2018 meta-analysis led by McMaster University researchers found that consuming more than 1.6 grams of protein per kilogram of body weight a day does not produce further gains in muscle mass or strength.
The review, published in the British Journal of Sports Medicine, found this ceiling applied even to people who lift weights regularly. Extra protein from shakes or food provided no additional benefit.
While some short trials lasting a few weeks or months have shown high protein diets can help with weight loss, these participants typically cut calories and exercise regularly on a structured program. Longer studies suggest the advantage is modest. One review found high protein diets offered only a small benefit for maintaining weight loss after one year or more.
Excess calories and weight gain
A 2013 study of nearly 400,000 people found that those getting at least 20 percent of their calories from protein were 24 percent more likely to become overweight or obese over the next five years.
Dietitians said people often increase their protein intake by relying on fatty cuts of meat, processed foods and extra calories.
"Many people interpret a high-protein diet as a green light to eat as much fatty red meat, processed meats such as bacon, and protein-fortified snacks as they like," Schoenfeld said. "In reality, they're simply consuming excess calories."
A 12-ounce sirloin steak contains about 700 calories and 38 grams of fat. A ribeye of the same size contains 900 calories and 65 grams of fat. A 12-ounce portion of chicken breast contains 580 calories and 12 grams to 14 grams of fat. The same amount of cod contains 300 calories and nine grams of fat.
Brands now advertise protein content on breakfast cereals, popcorn, chocolates and Pop-Tarts to cash in on the craze. Dietitians noted many of these are ultra-processed products high in calories, added sugars or saturated fat.
"People see 'high protein' on the label and assume they can eat more of it," Schoenfeld said. "But calories still count."
Kidney and cancer risks
High protein diets carry long-term health risks. About one in ten people carry genetic variants that reduce the ability of their kidneys to cope with very high protein intakes. This can potentially increase their risk of kidney disease.
Diets high in red and processed meat are often rich in saturated fat, which is linked to an increased risk of heart disease. Very high protein intakes may also be associated with cancer and a shorter lifespan.
A 2014 study led by researchers at the University of Southern California followed more than 6,000 adults over the age of 50. The study found that people consuming diets where protein accounted for about 20 percent of calories had a higher risk of cancer, diabetes and death.
Animal studies have also suggested protein-heavy diets may accelerate aging, though it remains unclear if the same effect occurs in humans. Jack Lalanne, considered the spiritual founder of today's fitness movement, ate a high protein diet before it was trendy and died aged 96 years old in 2011.
Focusing on fiber
Experts warn that focusing heavily on protein can cause people to neglect other nutrients. Eating large amounts of meat and protein-fortified foods may lead to consuming fewer fiber-rich foods like whole grains, beans, fruit and vegetables. Fiber lowers the risk of heart disease, type 2 diabetes and colorectal cancer.
Dr Don Layman is a leading researcher at the University of Illinois who helped develop the latest dietary recommendations. He said the previous government guideline reflected the minimum needed to prevent deficiency, while the newer advice is a target for optimal health.
Dietitians advise that most people do not need to obsess over hitting a specific daily number. They recommend eating a variety of high-quality protein sources such as poultry, fish, eggs, dairy, beans, lentils, tofu, nuts and seeds.
Simple changes like adding nuts and seeds to yogurt or eating beans with a meal can boost protein intake without fortified snacks or shakes.
"I do hope the craze moves to fiber next," Schoenfeld said. "With 95 percent of Americans not getting enough, that's where we really need to focus."
