Bioavailability means the degree to which your body digests, absorbs and uses food. Dietary protein is not only needed to build bigger muscles, it’s also necessary for vibrant-looking skin and lustrous hair. Some protein-rich foods are easier to break down than others, which increases their bioavailability. Furthermore, some protein sources are complete and contain all the essential amino acids, whereas others are incomplete, which can prevent your body from building or repairing the structures it needs to.
Eggs are considered by nutritionists as the most bioavailable source of protein, which is why the biological value scale is based on egg protein. A food’s “biological value” is a measure of how efficiently a protein is metabolized, absorbed and used by your body. The biological value scale ranks eggs the top protein source and assigns them a value of 100; all other foods containing protein are ranked comparatively. In addition to containing all the essential amino acids, egg protein is quickly digested -- usually within two hours -- and is completely absorbed by your body. A regular-sized egg contains approximately 6.2 grams of protein, which is about 15 percent of your recommended daily amount. On the other hand, eggs are arguably the most allergy-causing of all proteins; they are also high in cholesterol and sulfur, which can lead to the production of intestinal gas, bloating and flatulence.
Whey is a naturally occurring protein found in milk and cheese. Whey protein has an extremely high biological value of about 95 because it’s so quickly digested and absorbed. It's particularly high in branched chain amino acids such as leucine, isoleucine and valine, which are metabolized in your muscle tissue as opposed to your liver. In general, the higher the percentage of branched chain amino acids in a protein, the higher its bioavailability. On the downside, whey protein is also highly allergenic and contains some cholesterol. Whey is commonly consumed as a supplement powder, which is made from the by-products of cheese manufacturing.
Spirulina is a type of blue-green algae that’s very dense in protein and an excellent source of some vitamins and minerals. Spirulina is composed of about 70 percent complete protein in its natural state, which is higher than any other unprocessed food. The biological value of spirulina is about 92, in part because it doesn’t have cellulose in its cell walls, which allows your body to easily break it down. The main issues with spirulina are that it is relatively expensive, not very tasty and can accumulate toxins from polluted water.
In addition to whey, milk also contains casein protein. Both types are easily digested and absorbed, which is why milk has a biological value of up to 90. Furthermore, an 8-ounce glass of regular milk contains almost 9 grams of complete protein. The main issue with cow’s milk is that tens of millions of Americans are lactose intolerant or allergic to it. Milk is one of the leading causes of food allergies, manifesting as diarrhea, fatigue, hives, congestion and breathing problems. Milk is also a significant source of saturated fat, and hormone residues have been found in some batches.
Of all the different types of edible flesh, poultry such as chicken and turkey are the most bioavailable sources of protein. Poultry has a biological value of between 80 and 82, which is a little higher than pork and significantly higher than fish and beef. Chicken is an excellent source of complete protein, with about 54 grams in a 6-ounce serving, but it’s not as easily digested as other sources. Furthermore, chicken contains saturated fat and is sometimes contaminated with antibiotics. Buying organic free-range chicken ensures the best quality.
- Contemporary Nutrition: Functional Approach; Gordon M. Wardlaw et al.
- The Nutribase Complete Book of Food Counts; Art Ulene
- Encyclopedia of Human Nutrition; Benjamin Caballero et al.
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.