Protein is one of the three macronutrients that humans get from their diets. It plays an important role in muscle maintenance, feeling full, and offers a slew of health benefits.
The Dietary Guidelines for Americans suggest that Americans eat between 5 and 7 protein ounce “equivalents” every day, depending on their calorie needs. Although these guidelines do suggest eating a variety of protein sources from both meat and plant-based sources, they quantify “ounce equivalents” of each variety to be essentially the same.
In other words, both 1 ounce of meat and 0.5 ounces of mixed nuts contain the same amount of protein, and, in the eyes of the guidelines, are equivalent when it comes to protein. And on MyPlate, a website created by the United States Department of Agriculture (USDA) to help people build their meals in a healthy way, the “protein” category is not broken down by animal-based or plant-based.
But researchers recently aimed to determine whether all proteins are truly created equal.
“Animal-based proteins have a greater density of protein than plant-based proteins, and more importantly, a greater abundance of essential amino acids per gram of food source,” study author Robert Wolfe, PhD, professor at the University of Arkansas for Medical Sciences, tells Verywell.
He adds that “essential amino acids are the ‘active’ components of dietary protein with regard to maintaining the lean body mass.”
The results of this study were published in the March issue of the Journal of Nutrition. The study was funded by the National Pork Board, Egg Nutrition Center, and Beef Checkoff.
Are All Forms of Protein Equal?
To determine how the body breaks down and utilizes various protein sources and to see if protein “ounce equivalents” are truly equal, investigators grouped people into seven groups. All groups contained the same amount of “ounce equivalents.” Some options were animal-based and others were plant-based.
The animal-based options included:
2 ounces (56 grams) of cooked beef sirloin2 ounces (56 grams) of cooked pork loin2 cooked eggs
The plant-based options included:
½ cup (140 grams) of red kidney beans2 tablespoons (30 grams) of peanut butter4 ounces (112 grams) of tofu1 ounce (28 grams) of mixed nuts
Participants followed a weight-maintenance diet created for their personal caloric and protein needs for three days prior to the study day and then fasted overnight. Researchers measured their body composition—including lean body mass—at the beginning of the study. After the fast, they ate their designated protein.
Researchers then assessed participants’ net whole-body protein balance—the difference between muscle buildup and breakdown—and compared it to their initial measurements.
Although “ounce equivalents” of protein were eaten among all participants, those who ate animal-based proteins showed a greater gain in net protein balance versus those who ate plant-based proteins. Digging further, researchers found that the improvement in whole-body net protein balance seen among the animal-protein eaters was due to an increase in protein synthesis. Protein synthesis occurs regularly in the human body as muscle tissue breaks down and rebuilds.
“This study shows that ounce-for-ounce, animal protein provides a more biologically active protein source, and more total protein than plant-based sources,” Sarah Anzlovar, MS, RDN, LD, a Boston-based registered dietitian and owner of Sarah Gold Nutrition, tells Verywell.
Researchers found that the “ounce equivalents” of protein food sources are not metabolically equivalent in young healthy individuals. So, eating an ounce of animal-based protein can result in greater protein build-up in the body—which is a good thing.
Wolfe explains that “the difference in density of essential amino acids means that a greater amount of calories must be consumed when eating plant-based protein food sources as opposed to animal-based protein food sources to achieve the same anabolic [building] effect.”
Incorporating Protein in Your Diet
Protein is an essential macronutrient for supporting your body’s ability to function. And while animal proteins may pack more punch in the amino acid density department, that is not the only factor that should be considered when selecting your food.
“What’s important to remember though is that protein is not the only valuable nutrient to consider when choosing a food,” Anzlovar explains. “Plant-based proteins such as beans, lentils, and soy products also provide fiber, vitamins, minerals, and antioxidants that support overall health. Nuts and seeds, which do contain some protein, also provide healthy fats."
Anzlovar adds that “eating a variety of foods will ensure you get the amino acids you need in your diet.”
