1. The structure and existence of different ways
From the perspective of protein molecules, proteins are a peptide chain (primary structure) connected by amino acids. The peptide chain forms a helix or fold (secondary structure), and further winds to form a group (tertiary structure). Various groups are combined in a certain pattern (quaternary structure). The secondary structure of plant proteins is dominated by β-sheets, while animal proteins are dominated by α-helices. From the state of protein in food, vegetable protein is often combined with carbohydrates (non-starch polysaccharides and dietary fiber), while animal protein mainly coexists with fat.
These factors will lead to differences in the nutritional value of plant protein and animal protein. For example, the intake of animal protein is often accompanied by a large amount of saturated fat; edible soybeans include both soy protein and functional ingredients such as dietary fiber, isoflavones, and soy phospholipids.
The human body's demand for protein, first of all, needs to have a sufficient amount (adults need 1 gram per kilogram of body weight per day), and secondly, it is necessary to ensure the "quality" of protein. Protein that can fully meet the needs of human nutrition and health is high-quality protein.
We need dietary protein to provide 20 amino acids; some of these amino acids, if not enough, can be "borrowed" (the body uses other nutrients to directly or indirectly synthesize non-essential amino acids), and some must be obtained from food itself (at least 8 essential amino acids are not borrowed).
2. Different digestibility
Digestibility refers to the degree to which proteins are decomposed by digestive enzymes and the degree to which digested amino acids and peptides are absorbed. The more food is absorbed by the body, the higher the nutritional value. In general, egg protein is often used as a reference protein, and its digestibility is 100%. A well-established measure of protein quality is the Protein Digestibility Corrected Amino Acid Score (PDCAAS), which is a perfect score of 1. The four players currently tied for first place are: whey protein, casein, egg protein, and soy protein isolate.
A PDCAAS of 1 means that the protein contains all 9 essential amino acids needed by the human body, and each of them reaches the required amount (there should be a wooden barrel and 9 boards in my mind immediately, and any short one will not be filled with water). In other words, if you are capricious and want to eat only one protein and be healthy, then only a protein with PDCAAS 1 is possible.
Plant proteins often coexist with antinutritional factors that affect protein digestion, such as phytic acid, protease inhibitors, phytohemagglutinin and tannic acid. Coupled with structural differences, plant proteins tend to be less digestible than animal proteins. Therefore, food processing is particularly important for improving the digestive utilization of plant proteins. Just cooking food can increase the digestibility of protein by 18%. The protein digestibility of soybean meal is only 80%, while soybean protein isolate can reach 98%.
3. Health effects are different
Compared with animal protein, plant protein has more health benefits, including reducing the risk of cardiovascular disease, type 2 diabetes and certain tumors. For example, milk protein has the effect of controlling weight and reducing triglycerides, while soy protein isolate has a more obvious hypolipidemic effect (triglycerides, total cholesterol and low-density lipoprotein cholesterol can all be reduced); soy protein It also has the effects of lowering blood pressure, improving insulin sensitivity, and reducing the level of inflammatory response in the body.
Regulatory authorities in 13 countries and regions, including the US FDA, have certified that eating 25 grams of soy protein a day can reduce the risk of heart disease.
4. Different environmental impacts and sustainability
Compared with animal protein, plant protein has obvious advantages in environmental protection and sustainability. For example, the production of 1kg of soy protein isolate emits 2.4kg of carbon dioxide into the environment, while the production of the same amount of beef protein is 178kg! Other animal proteins, such as chicken and pork, also emit far more greenhouse gases than soybeans. The production of 1kg of soy protein isolate takes up 8 square meters of arable land for one year, while beef protein is 1311 square meters.