Why does meat have more protein than vegetables?

It's well known that vegetarians and vegans need to work a little harder to get their protein. Even popular meat replacements often aren't as protein-dense as their animal-based counterparts; for example, tofu has about 8 grams of protein per 100 grams, whereas chicken breast has 31 grams.

But why, on a biological level, does meat generally contain so much more protein than plants do?

According to Christi Calhoun, scientific communication resource officer at the American Meat Science Association, the main reason is that plants and animals have different cellular needs, which result in different cellular compositions.

"Animals store more protein in their tissues because their bodies are designed to support active functions such as muscle movement, energy metabolism, and cellular repair," Calhoun told Live Science in an email. Key molecules in Animals' bodies like enzymes and hormones are actually just specialized proteins, and other proteins like actin and myosin make up muscle fibers and enable active movement.

"Plants, on the other hand, rely more on carbohydrates and other molecules for structure and energy storage," Calhoun continued, "so their tissues naturally contain less protein."

While carbohydrates are an important energy source in both plants and animals, they can't complete the same diverse cellular functions that proteins can due to their simpler molecular structure.

But total protein levels don't tell the full story; it's also important to consider the kind of protein. To do that, it's necessary to understand protein on a molecular level.