Fitness trainers are quick to tell clients to get enough protein in their diet. It’s not just bodybuilders, power athletes and fitness buffs that need more dietary protein, endurance athletes can benefit from higher protein consumption due to the stress of running or cycling long distances. During long periods of endurance exercise, protein becomes a back-up fuel source when glucose reserves run low. More recent research shows people over the age of 65 can benefit from increasing the amount of protein in their diet. According to these studies, older people may need as much as 30% more than the current recommendation of 0.8 grams of protein per kilogram of body weight daily.
Protein Absorption: It’s Not How Much You Eat It’s How Much Reaches Your Muscles and Tissues
Getting enough dietary protein is only one part of the equation. What counts is how much of that protein gets to your muscles and how much your body can use. Protein digestion and absorption involves several steps. First, it’s first broken down into smaller fragments in the stomach by an enzyme called pepsin. Pepsin needs stomach acid to be activated. As a result, people with low stomach acid (not uncommon in older people) may have difficulty digesting protein. Once proteins enter the small intestines, enzymes produced by the pancreas, called trypsin and chymotrypsin, along with other pancreatic enzymes break the protein fragments into individual amino acids. From there, the amino acids can be absorbed by the small intestine and enter the bloodstream.
As you can see, protein digestion and absorption requires several steps. A number of factors can affect one or more of these steps. As mentioned, you need adequate amounts of stomach acid to break down dietary protein. Older people produce less stomach acid. That’s one reason their protein requirements may be higher. Also, antacids neutralize stomach acid and interfere with protein digestion. Other factors like how much trypsin and chymotrypsin you produce, what you eat a protein meal with, when you eat a protein food and even the temperature of the food may affect protein absorption.
Protein Absorption: Is There a Limit to How Much Protein Your Body Can Absorb at One Time?
Is there a limit to how much protein your body can digest and absorb at one time? Some research suggests your muscles are only able to use 20 to 30 grams of protein at a time to synthesize muscle. Based on this, it would be best to divide your protein intake into several small meals and snacks rather than getting it all at a single meal. Other studies refute this idea.
Whether there is a limitation to how much protein you can absorb at one time or not, it makes sense to get protein several times a day rather than at one meal. For example, research shows eating a protein/carbohydrate snack after a workout when your muscles are “primed” to use it helps with muscle synthesis. It also helps with muscle recovery. Carbohydrates combined with protein maximize the insulin response so you can get amino acids into cells where they can be used for growth. More protein isn’t better. Beyond a certain intake, protein will be used for energy or the extra calories will be stored as fat.
Protein Absorption: Do You Need a Protein Supplement?
It’s not difficult to meet your protein requirements without protein supplements and there are advantages to doing so. With natural food sources of protein, you also get the benefits of the macronutrients and micronutrients in the food, unlike a protein supplement that has synthetic vitamins and minerals added. Plus, protein supplements got bad publicity after Consumer Labs found almost one in three didn’t have what was stated on the label. Some had less protein than listed while others had more carbs. Even worse, one was contaminated with lead.
Consumer Reports also tested a variety of protein drink mixes and found some contained heavy metals including lead, mercury, and cadmium. Although all of these heavy metals negatively impact health, cadmium is the most concerning. It’s readily stored in your body and not easily eliminated. Cadmium is known to cause kidney damage and is likely a carcinogen.
Protein Absorption: Get Protein from Natural Sources Whenever Possible
Natural protein sources are the way to go. Eggs have the highest “biological value” of any natural protein source. Biological value is a measure of how well your body can digest, absorb and use protein in a food. It’s determined by comparing the amount of protein consumed to the amount excreted as waste.
Protein digestibility scores can also be calculated for different protein sources. As you might expect, proteins with higher digestibility scores are more easily absorbed. Eggs rank high in terms of biological value and protein digestibility. Cottage cheese, milk, egg whites, fish, beef, chicken and tofu are also high on both scales. Nuts, legumes and whole grains contain protein but rank lower in terms of digestibility and biological value. Nuts, legumes and whole grains also don’t contain the full spectrum of essential amino acids your body needs but can’t make.
The Bottom Line
Protein absorption varies depending on a variety of factors, including the amount of stomach acid you produce. Some proteins are more easily digested and absorbed than others. These proteins have higher protein digestibility scores and biological values. You can’t go wrong with eggs! They top the list.
It’s still not clear what the maximum amount of protein you can absorb at one time is. Regardless, it makes sense to consume smaller amounts of protein at every meal and after a workout. Don’t forget to get some protein and carbs on board first thing in the morning since your body has been in fasting mode for seven or eight hours.
Getting enough protein is important for preserving and building lean body mass but it also helps with appetite control due to its satiety effects. Enjoy a variety of sources of protein, including some plant-based ones throughout the day.
Consumer Labs. “31% of Protein Powders and Drinks Fail Tests by ConsumerLab.com”
Consumer Reports. “Protein Drinks”
Purdue University News. “Elderly women may benefit from higher amounts of protein”
J Allergy Clin Immunol. Jun 2008; 121(6): 1301-1310.
Journal of the International Society of Sports Nutrition 2007, 4:8 doi:10.1186/1550-2783-4-8.
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