Whether to build muscle or boost your immune system, getting enough protein is crucial. But often people up their protein intake without realizing that the body can only absorb so much. You may be able to up protein absorption by choosing the right sources, spacing your intake and taking probiotics.
Eating less protein at one time, prioritizing animal proteins and supplementing with probiotics may improve protein absorption.
Protein Digestion and Absorption
If you want to improve your body's ability to absorb protein, you first need to understand how protein is digested and absorbed. Get ready to take a little trip back in time to high school biology class.
Protein digestion starts when you take your first bite. Chewing begins to break the protein into smaller pieces. Saliva assists the passage of the chewed food through the esophagus and into the stomach. Gastric juices in the stomach contain hydrochloric acid and pepsin, an enzyme that breaks down protein into even smaller pieces.
This, in combination with strong stomach contractions, creates a uniform mixture called chyme. Chyme enters the small intestine, where the majority of protein digestion takes place. Digestive juices secreted by the pancreas contain more enzymes, including chymotrypsin and trypsin. Ultimately, these are the enzymes that break down protein into its smallest parts — individual amino acid, or small chains of amino acids called peptides.
All protein is absorbed as amino acids and peptides in the small intestine and released into the intestinal bloodstream, which carries them to the liver. The liver is responsible for regulating amino acid levels in the blood and using them to either synthesize new proteins or send them throughout the body to be used by other cells.
Factors Affecting Protein Absorption
Protein digestion and absorption aren't always textbook. Many factors affect how your body digests and uses amino acids, including stomach acid levels and enzyme production. As people age, their bodies may be less efficient at processing protein. Additionally, the other foods consumed with the protein and the quality of the protein itself make a difference. Gut health also plays an important role, according to an article in Probiotics and Antimicrobial Proteins in December 2018.
For those involved in resistance training, a limited amount of protein can be absorbed and used at one time for building lean muscle mass. Above that, undigested protein may move to the colon where it ferments and releases potentially toxic substances including ammonia, according to Michael Greger MD, FACLM.
Eating two 3.5-ounce chicken breasts providing over 60 grams of protein for dinner may seem like a good way to pack in as much as you can in one sitting, but it's probably not going to be any more effective than having just one chicken breast.
Improving Protein Absorption
Gut health plays a major role in your body's ability to absorb the nutrients in food. The intestine is colonized by bacteria that aid digestion, immune function, disease prevention and serve many other important purposes. These helpful bacteria can be compromised through unhealthy diet, stress and infections, which can affect nutrient absorption and digestion.
According to the Probiotics and Antimicrobial Proteins review, a specific probiotic called Bacillus coagulans, a hardy lactic acid-producing, spore-forming bacterial species, can withstand the stomach's acidic environment and reach the intestine. Once there, it germinates, becomes active and has been shown to improve protein and carbohydrate digestion.
The protein sources you choose also matter. Some protein foods are better digested than others, which can increase the amount of protein your body can actually absorb and use. According to an article published in Food and Nutrition Bulletin in June 2013, animal proteins such as milk, eggs and meat have the highest digestibility rate.
Concentrated or purified plant protein in which the cell walls have been removed, such as wheat gluten and soy protein isolate, also have increased digestibility. Less purified plant products, such as cereals, peas and soybean flour have lower digestibility.
Due to the body's ability to use a limited amount of protein at one time, eating smaller amounts more frequently may improve absorption. How much you should consume at one time is based on age and recent resistance exercise volume and intensity.
According to the International Society of Sports Nutrition, a good goal for healthy exercising individuals is about .25 grams per kilogram of body weight or an absolute dose of 20 to 40 grams. You can divide your total daily protein needs by this number to find the ideal number of protein servings, which the ISSN recommends distributing evenly throughout the day.
If your goal is muscle-building, when you consume protein in relation to your workouts may make a difference in how well your body is able to uptake and use it. There are many theories as to the optimal window of time in which to consume protein around a workout. The ISSN says this is likely more of a personal preference, since the anabolic effect of exercise lasts at least 24 hours. However, the effects decline as post-exercise time increases.
If you aim for the ISSN's recommendation of evenly spaced, limited protein doses throughout the day, you will be able to get an optimal amount at an optimal time to get results.
Getting Enough Protein
To optimize absorption and utilization, be sure you're meeting your daily protein needs. This may be more difficult than it seems, since there are varying opinions on how much protein people should be eating. The recommendation for the general population from the Food and Nutrition Board of the National Academies of Medicine is 46 grams per day for women and 56 grams daily for men. This is based on about .8 grams of protein per kilogram of body weight.
But many experts say that is not enough. At the Protein Summit 2.0 held in Washington, D.C. in 2013, over 60 nutrition scientists, health experts and nutrition educators convened to discuss protein's role in human health and the optimal intake to maximize health benefits.
According to a summary of findings published in the American Journal of Clinical Nutrition in April 2015, intakes of 1 to 1.6 grams per kilogram of body weight each day may aid weight management, metabolic activity, muscle growth and healthy aging.
- Medical Libre Texts: "5.4: Protein Digestion, Absorption and Metabolism"
- Bioinfo.org: "Peptides"
- Kaiser Health News: "Why Older Adults Should Eat More Protein (and Not Overdo Protein Shakes)"
- Probiotics and Antimicrobial Proteins: "Probiotic Bacillus coagulans GBI-30, 6086 Improves Protein Absorption and Utilization"
- NutritionFacts.org: "What Animal Protein Does in Your Colon"
- USDA: " Basic Report: 05064, Chicken, Broilers or Fryers, Breast, Meat Only, Cooked, Roasted"
- Food and Nutrition Bulletin: "Digestibility Issues of Vegetable Versus Animal Proteins: Protein and Amino Acid Requirements—Functional Aspects"
- International Society of Sports Nutrition: "International Society of Sports Nutrition Position Stand: Protein and Exercise"
- National Academies of Medicine: Summary Tables, Dietary Reference Intakes
- American Journal of Clinical Nutrition: "Introduction to Protein Summit 2.0: Continued Exploration of the Impact of High-Quality Protein on Optimal Health"