The best sources of protein
Behaviorally, most of us are omnivores, but biologically, humans are herbivores. (Interesting fact: Only herbivores can get atherosclerosis!) Our digestive system is optimally designed to metabolize plant foods, not animal foods. We can digest animal products, just like our carnivorous dogs and cats can digest the grains in the foods we give them, but doing so results in poor health and disease.
And if you want to get technical about it, we have the anatomical qualities of frugivores (plant-eaters that eat fruit, vegetables, and nuts): we can’t metabolize cellulose, our digestive system is about 9 times our body length (compared to 20 times body length in herbivores), and we have hands that can pick fruit and seeds and dig for roots. While fruit is low in protein, it contains plenty of free amino acids, which our bodies use to produce the proteins we need.
Would a plant-based diet that provides excess protein result in the same diseases as a diet with excess animal protein? Based on the research we have so far, the answer is no. The increased cancer risk and overall mortality resulting from high animal protein diets is not present in high plant protein diets. One reason that excessive plant protein is not harmful is that protein in plant foods is accompanied by base precursors (substances that are converted into bases in the body). Animal products contain acid precursors, which convert into acid in the body.
Animal protein comes along with lots of other bad stuff (listed in the previous section) that leads to disease and shortens our lives. Plant protein comes along with vitamins, enzymes, antioxidants, prebiotics, and fiber, all of which improve our health and lengthen our lives. Ninety-seven percent of Americans don’t get the RDA of fiber by a long shot—they get less than half of the RDA—and fiber protects us against diabetes, various cancers, metabolic syndrome, cardiovascular disease, obesity, high cholesterol, and high blood pressure. As Dr. Davis says, everyone asks vegans “Where do you get your protein?” but really, vegans should be asking everyone else “Where do you get your fiber?”
If you’re worried about getting enough protein on a plant-based diet, don’t. A study of over 71,000 people found that vegetarians and vegans get an average of 70% more protein than they need every day. As Dr. Davis assures us repeatedly throughout his book, if you’re eating enough calories of anything, even pizza and potato chips, you’re getting enough protein.
There are five places in the world where people live significantly longer, healthier lives than the rest of us: Okinawa, Japan; Sardinia, Italy; Nicoya, Costa Rica; Icaria, Greece; and the community of Seventh-day Adventists in Loma Linda, California. Dan Buettner describes these cultures in his book The Blue Zones, and Dr. Davis refers to them often. People living in Blue Zones cultures have remarkably low rates of obesity, heart disease, diabetes, and cancer, and they also eat diets low in animal protein and high in plant-based carbohydrates. Most of the calories in traditional Blue Zones diets come from grains, starchy tubers, legumes, vegetables, and fruit; animal products are eaten about once a week as a treat or garnish. For example, the diet of people living in Okinawa (where there are more centenarians per capita than anywhere else in the world) has about 7% protein (compared to the 15% that most Americans eat), and their diet is heavily based on a purple sweet potato they call “imo.”