Your protein digestion and absorption are based on three main factors: the structure of the food you eat, how you prepare that food, and your individual capacity to process it.
Each type of food has a unique chemical and physical structure, making it more or less efficient for protein digestion. The first main dichotomy is between proteins in animals and plants. Meat and dairy will have a higher absorption rate of above 90% than plant proteins with an absorption rate between 70-90%. While plants have many micronutrient benefits, plants are often missing an essential amino acid and contain anti-nutritional factors, such as protease inhibitors, tannins, phytic acid, and saponins that decrease protein digestibility.
Here is a ranking of protein quality based on estimated biological value, which is a measurement of how efficiently the body utilizes consumed protein (1)(2). When the scale was originally designed, whole eggs received the highest score of 100 with a 94% efficiency rating. Now certain food products like whey protein have been shown to have higher efficiency rating, which is why biological values now exceed 100.
Protein Type Biological Values
- Whey Protein Isolate: 159
- Whey Protein Concentrate: 104
- Eggs Whole: 100
- Beef: 92
- Tuna: 92
- Eggs Whites: 88
- Pork: 85
- Chicken: 79
- Turkey: 79
- Casein Protein Powder: 77
- Soy Protein Powder: 74
- Fish: 70
- Lean Beef: 69
- Cow's Milk: 60
- Brown Rice: 57
- White Rice: 56
- Peanuts: 55
- Peas & Legumes: 55
- Whole Wheat: 49
- Soybeans: 47
- Whole-grain Wheat: 44
- Peanuts: 43
- Corn: 36
- Beans: 34
Optimal Vegan Pairing Biological Values
- 85% Rice & 15% Yeast: 118
- 55% Soy & 45% Rice: 111
- 55% Potatoes & 45% Soy: 103
- 52% Beans & 48% Corn: 101
The second major factor in protein digestion and absorption is the way you prepare and cook your food. Common techniques can include low and high heat treatments, pressure cooking, fermentation, enzyme hydrolysis, marinating, soaking, germination, alkaline treatment, or certain meat processing techniques.
Heat treating food is the essence of cooking. Using lower heat for shorter durations will help denature protein, deactivate anti-nutritional factors, and increase overall protein absorption (3). For example, heating egg whites increases protein digestibility in humans from 51.3% to 90.9% (4). However, using higher heat for longer durations can actually decrease protein absorption because it causes maillard reactions, crosslink formation, and protein aggregation.
The maillard reaction is the fusing of proteins with sugars through frying, searing, or broiling food to change its taste, texture, and smell. Although this reaction may create tastier food by caramelizing and crisping the exterior, it lowers the bioavailability of amino acids (5). Crosslink formation and protein aggregation occur when food is treated with high temperatures, usually in highly processed foods. The amino acids break down and combine to form insoluble or indigestible compounds (6). For example when freeze-dried chicken was reheated, it significantly reduced the rate of protein digestion (7).
Pressure cooking can both increase and decrease protein digestibility depending on the temperatures, cook time, and the food source. A pressure cooker can reduce cooking time by raising the boiling temperature, which can break down insoluble fiber, predigest proteins, and eliminate anti-nutritional factors. However, as cook times increase, protein aggregation can occur. For example, pressure cooking legumes for three minutes resulted in less loss in vitamin C than boiling for 15 minutes. However, longer pressure cooking times resulted in lower vitamin C and other nutrients (8).
Fermentation is the use of bacteria or fungi to alter food. Yogurt and kefir use lactic acid bacteria to partially digest milk proteins and create extracellular proteases to help increase digestibility (9). Fermented soybeans such as miso and soy sauce use fungi Aspergillus oryzae to increase protein digestion through secreting proteases enzymes and trypsin inhibitors (10).
Proteins can be hydrolyzed partially or extensively by adding enzymatic, acidic, or alkaline compounds (11). Products such as baby formula, elder supplement drinks, and of course protein powder use hydrolysis to increase protein availability and digestion. This is why hydrolyzed whey or soy protein are the fastest digesting and highest absorption protein supplements on the market (12). If you are looking for a great guide on picking the perfect protein powder, check out this article.
Alkaline treatment is often used in food processing to improve protein solubility by extracting protein from soybean, cereal grains, corn, and peanuts. For example, the lime treatment of corn for preparing tortillas, known as nixtamalization, boosted the protein content and the bioavailability of the aminoacid lysine (13). If you have a tough cut of meat, marinate it for 24 hours with some baking soda to tenderize it (14).
Soaking can improve protein digestibility by lowering anti-nutritional factors, such as phytic acid, saponins, and polyphenols. For example, soaking uncooked beans increased protein digestion by reducing 30% phytic acid after 18 hours (15).
Allowing the soaked seed to sprout can further improve protein digestibility. For example, a legume soaked for 12 hours and then allowed to germinate for 48 hours was 7.7% greater than only soaking. This is probably because it reduces anti-nutritional factors, such as phytic acid, tannins, and saponins (16).
Regular meat processing techniques such as salting, mincing, and aging can influence protein digestion (17). However, the most significant factor affecting protein digestibility was temperature and duration, with higher heat and longer cook times negatively affecting digestion (18).
Lastly, your body will process protein differently than anyone else. Your protein absorption is measured by how quickly and efficiently you can break down plant and animal sources into amino acids and then use them for energy, muscle growth, and other bodily functions.
Here are three supplements that can help boost your digestion: digestive enzymes, probiotics, and leucine (19).
Digestive enzymes are complex proteins that help break down food into smaller molecules so they can be absorbed. Your small intestine is the major site of protein digestion. There are numerous prescription and non-prescription supplements containing proteases, lipases and glycosidases that can aid in your protein digestion and absorption (20).
Probiotics can also help increase digestive enzymes such as protease and peptidase, to aid in protein digestion (21). Probiotics can facilitate positive change in the gut microbiota and improve the absorption of amino acids, especially in regards to plant protein (22).
The branched chain amino acid leucine is responsible for stimulating muscle protein synthesis by signaling that amino acids are available to be converted into new muscle (23)(24). Leucine supplementation also has the added benefit of significantly improving endurance performance and upper body power (25).
Tips for improving protein digestion:
Pick foods with the highest biological values
Cook with lower heat when possible
Eat fermented, soaked, dehulled, and hydrolyzed food
Increase your personal digestion by taking digestive enzymes, probiotics, and leucine
Now, go forth and chase those gains.