Updated: Dec 18, 2021
Not all protein is same. It can very significantly in terms of its bioavailability, growth stimulation, application in sports performance, protein-energy ratio, and presence of other nutrients (or antinutrients). This paper delivers on all these points of discussion. It compares various whole-food proteins as well as supplements while also discussing nuances related to high-protein diets and their impact on health.
In human physiology, protein serves as the major structural component of muscle and other tissues in the body. In addition, they are used to produce hormones, enzymes and haemoglobin. Proteins can also be used as energy; however, they are not the primary choice as an energy source.
Depending on the source, proteins differ in their amino acid composition, bioavailability and hence their ability to stimulate growth, support performance and recovery. Animal-source protein in meat, fish, dairy, and eggs are known to be more bioavailable because they don’t contain antinutrients that are present in plant foods.
“Antinutritional factors such as trypsin inhibitors, lectins, and tannins present in certain protein sources such as soybean meal, peas and fava beans have been reported to increase losses of endogenous proteins at the terminal ileum (Salgado et al., 2002)”
Comparisons of efficacy of various proteins including whole animal and plant foods as well as supplements like whey and casein are made using several methods discussed in this paper. As discussed above animal-source proteins and soy score higher in those comparisons.
“Although the PDCAAS is currently the most accepted and widely used method, limitations still exist relating to overestimation in the elderly (likely related to references values based on young individuals), influence of ileal digestibility, and antinutritional factors (Sarwar, 1997).
Amino acids that move past the terminal ileum may be an important route for bacterial consumption of amino acids, and any amino acids that reach the colon would not likely be utilized for protein synthesis, even though they do not appear in the feces (Schaarfsma, 2000). Thus, to get truly valid measure of fecal digestibility the location at which protein synthesis is determined is important in making a more accurate determination. Thus, ileal digestibility would provide a more accurate measure of digestibility. PDCAAS, however, does not factor ileal digestibility into its equation. This is considered to be one of the shortcomings of the PDCAAS (Schaafsma 2000)”
Animal Protein and Plant Protein
“Vegetable proteins, when combined to provide for all of the essential amino acids, provide an excellent source for protein considering that they will likely result in a reduction in the intake of saturated fat and cholesterol. Popular sources include legumes, nuts and soy.” But as we saw earlier these foods contain a number of antinutrients that not only hinder absorption of proteins and minerals, but lectins are also known to contribute to a leaky gut by opening tight junctions in gut epithelium. Additionally, these foods provide much lesser protein per calorie (protein:energy ratio) than meat and eggs. Inclusion of animal protein thus becomes valuable. “Proteins from animal sources (i.e. eggs, milk, meat, fish and poultry) provide the highest quality rating of food sources. This is primarily due to the ‘completeness’ of proteins from these sources. Although protein from these sources are also associated with high intakes of saturated fats and cholesterol, there have been a number of studies that have demonstrated positive benefits of animal proteins in various population groups”
“Low intake of protein from dairy and meat sources during late pregnancy was associated with low birth weights”
“elderly subjects have also benefited from consuming animal sources of protein. Diets consisting of meat resulted in greater gains in lean body mass compared to subjects on a lactoovovegetarian diet (Campbell et al., 1999). High animal protein diets have also been shown to cause a significantly greater net protein synthesis than a high vegetable protein diet”
“Protein is important for the liver not only in promoting tissue repair, but to provide lipotropic agents such as methionine and choline for the conversion of fats to lipoprotein for removal form the liver (Navder and Leiber, 2003a). The importance of high protein diets has also been acknowledged for individuals with liver disease and who are alcoholics. High protein diets may offset the elevated protein catabolism seen with liver disease (Navder and Leiber, 2003b), while a high protein diet has been shown to improve hepatic function in individuals suffering from alcoholic liver disease (Mendellhall et al., 1993).”
Animal Protein and Disease Risk
This paper discusses these issues and dispels and debunks several outdated and flawed notions pertaining to meat. I will quote some of these here:
“ the concern for elevated risk for cardiovascular disease from high protein diets appears to be without merit.” If you review all the available evidence, it doesn’t suggest meat increase risk of CVD.
“ In healthy individuals there does not appear to be any adverse effects (on kidneys) of a high protein diet.” High protein intake may place a toll on those already having compromised kidney function. Protein restriction appears to benefit such population, but this does not apply to healthy population. Restricting protein may also come with its own side effects of weight gain and difficulty maintaining muscle mass.
“Hannon and colleagues (2000) demonstrated that animal protein intake in an older population, several times greater than the RDA requirement, results in a bone density accruement and significant decrease in fracture risk. Dawson-Hughes et al (2002), not only showed that animal protein will not increase urinary calcium excretion, but was also associated with higher levels of IGF-I and lower concentrations of the bone resorption marker N-telopeptide.”
“the intake of calcium may have an essential function in maintaining bone. A higher calcium intake results in more absorbed calcium and may offset the losses induced by dietary protein and reduce the adverse effect of the endogenous acidosis on bone resorption (Dawson-Hughes, 2003).”
In my opinion, adequate protein intake is a necessity for growth, hormones and proper functioning of immune system. There are several myths related to animal-source foods and their “adverse impact on health” which, as we saw earlier are either without merit or have been shown to be untrue as per latest studies. One may choose to consume plants as tolerated but it should never be a replacement to meat, fish and eggs.