Roni Caryn Rabin in The New York Times:
Protein has achieved a venerated status in the dietary world for everything from building muscle to preventing weight gain. But can you get too much of a good thing? Protein powders that come in chocolate, strawberry, and cookies and cream flavors are doled out by the scoopful and mixed into smoothies, making it possible to effortlessly consume protein in amounts that far exceed dietary recommendations. A canned protein drink can contain almost as much protein as an eight-ounce steak, and snack bars or a small bag of protein chips can pack more of the macronutrient than a three-egg omelet. But while some nutritionists have encouraged the protein craze, a number of experts are urging caution. They point out that protein powders and supplements, which come from animal products like whey and casein (byproducts of cheese manufacturing) or from plants like soy, rice, pea or hemp, are a relatively new invention. The vast majority of Americans already get more than the recommended daily amounts of protein from food, they say, and there are no rigorous long-term studies to tell us how much protein is too much. “It’s an experiment,” said Dr. John E. Swartzberg, chairman of the editorial board of the University of California, Berkeley, Wellness Letter. “No one can tell you the long-term effects, and that’s what worries me as a physician. No one can tell you what the results are going to be in people’s bodies 10 or 15 years later.” People need sufficient protein in the diet because it supplies indispensable amino acids that our bodies cannot synthesize on their own. Together they provide the essential building blocks used to make and maintain muscle, bone, skin and other tissues and an array of vital hormones and enzymes.
But the average adult can achieve the recommended intake — 46 grams of protein a day for women, and 56 grams for men — by eating moderate amounts of protein-rich foods like meat, fish, dairy products, beans or nuts every day. There are about 44 grams of protein in a cup of chopped chicken, 20 grams in a cup of tofu or serving of Greek yogurt, and 18 grams in a cup of lentils or three eggs. American men already consume much greater amounts, averaging nearly 100 grams of protein a day, according to a 2015 analysis of the 2007-2010 National Health and Nutrition Examination Survey. The revised Dietary Guidelines for Americans, released in January, cautioned that some people, especially teenage boys and adult men, should “reduce overall intake of protein foods” and eat more vegetables.