Every cell and drop of our blood contains many thousands of different types of proteins, and each of these proteins is built from the protein we eat. It is found in every imaginable type of food. Animal products (including red meat, pork, chicken, fish and eggs) are usually considered the most protein-rich. But worldwide, it is the protein found in plants that supplies at least 60 percent of the total protein consumed by humans.
So if you think protein equals meat and dairy, think again. Whole grain cereals, nuts, beans and legumes, and an amazing array of fermented plant foods such as tofu and tempeh, are all rich sources of protein.
And while the importance of proteins for human health has long been known, what is still debated is how much and what types of proteins are best for human health.
How do animal and plant proteins differ?
We humans need all 20 of the amino acids that make up proteins, but these differ between animal and plant foods. Animal foods generally contain “complete” proteins, while plant foods are often made of “incomplete” proteins. A complete protein contains all of the nine “essential” amino acids – the ones that cannot be made inside the body, so must be consumed.
Although all the amino acids are necessary, the remaining 11 can be either sourced from food or manufactured inside the body. While plant foods may still have all the essential amino acids, the levels tend to vary. Also, plant proteins are generally harder to digest and are absorbed more slowly.
These differences affect our metabolism. Plant proteins are lower in a group of amino acids known as “branched chain amino acids” (BCAA). This group includes leucine, the superstar amino acid found in high concentrations in bodybuilding protein powders.
However, the relative benefits of animal and plant proteins are not straightforward. While it might be great for building muscle, for example, high levels of circulating leucine are also present in people at risk from diabetes.
And while plant proteins may not supercharge muscle building after exercise, they may help with longer term health. Huge population data from the USA, analysing death rates over 26 years, has shown high consumption of protein from animal sources (meat, eggs or dairy) slightly increases mortality. It was processed and unprocessed red meats (including pork products), not fish and poultry, that were most dangerous.
At the same time, higher consumption of protein from plant sources (including breads, cereals, pasta, beans, nuts and legumes) improved longevity. The health effects of protein-rich plant foods may come down to specific benefits from the combinations of amino acids within each food type, although it is likely the full nutritional mix of plant foods is also important. Plant foods also have healthy mono- and poly-unsaturated fatty acids, omega-3 fatty acids, antioxidants, vitamins, minerals, phytochemicals and dietary fiber – a healthy cocktail of ingredients.