Vegetables and even plant-based meat alternatives rarely contain as much protein as real meat. But why is that? (Image credit: wildpixel via Getty Images)
It is known that vegetarians and vegans need to work a little harder to get the protein they need. Even widely used meat substitutes are often not as rich in protein as their animal counterparts; tofu, for example, contains about 8 grams of protein per 100 grams, while chicken breast has 31 grams.
But what is behind the fact that biologically meat often contains significantly more protein than plant products?
As Kristi Calhoun, science communications specialist for the American Meat Science Association, explains, the main reason is that plants and animals have different cellular needs, which leads to differences in their cellular composition.
“Animals accumulate more protein in their tissues because their bodies are designed to support active functions like muscle movement, energy metabolism, and cell repair,” Calhoun told Live Science in an email. Key molecules in animal bodies like enzymes and hormones are actually specialized proteins, and other proteins like actin and myosin form muscle fibers and enable active movement.
“Plants, on the other hand, rely more on carbohydrates and other molecules for structure and energy storage,” Calhoun added, “so their tissues are inherently lower in protein.”
Although carbohydrates are an important source of energy for both plants and animals, they cannot perform the same variety of cellular functions as proteins because of their simpler molecular structure.
However, overall protein levels do not tell the whole story; it is also important to consider the type of protein. To do this, it is necessary to look at the protein at the molecular level.
“You can think of proteins as ‘necklaces of beads,’ where each bead is made up of different amino acids,” explained Kinga Balogh, a registered dietitian at JM Nutrition in Canada, in an email to Live Science. She noted that human bodies “assemble different ‘necklaces’ of different amino acid ‘beads’” to create different proteins for specific functions.
There are 20 different amino acids, and each plays a unique role in cellular processes such as tissue repair, nutrient transport, and brain function. Nine of these are called essential amino acids because the body cannot produce them on its own. People must get essential amino acids from food.
Proteins found in animal products contain all nine essential amino acids, so they are classified as “complete” proteins. In contrast, plant proteins often lack one or more of the nine essential amino acids, making them “incomplete” protein sources.
Moreover, the body processes animal and plant proteins differently.
“Animal proteins, like those found in meat, have higher bioavailability,” Calhoun noted. That means the human body can more easily break down and absorb these proteins. Because plant proteins may contain more indigestible substances, like fiber, the body has to work harder to process them.
In 1993, the U.S. Food and Drug Administration and the World Health Organization developed a scale that quantifies different protein sources based on their amino acid composition and overall bioavailability. This scale, known as the Protein Digestibility Amino Acid Score (PDCAAS), gives a score from 0 to 1, with 1 indicating high protein quality and 0 indicating low quality.
According to the PDCAAS scores compiled and presented at the International Society of Sports Nutrition Symposium, beef and eggs have scores between 0.9 and 1, black beans get 0.75, and peanuts are rated at 0.52. However, soy — the basis of foods like tofu and tempeh — scores the highest
Sourse: www.livescience.com
