The human body is capable of digesting large quantities of protein, but not all of it is used to synthesize muscle. Once protein is digested, the body can utilize the breakdown products called amino acids to build and repair many types of cells within the body including skin, blood cells, connective tissue, organs, create enzymes, DNA, RNA neurotransmitters, and of course, synthesize muscle.
Following a meal, protein digestion starts in the stomach aided by an enzyme pepsin in the presence of hydrochloric acid and continues in the small intestines. The stomach ideally is very acidic with a pH of 1.5, and this is necessary to enhance the proteolytic enzymes.
Pepsin is the only protease (protein enzyme) that can break down collagen, a fibrous protein that is important in connective tissue repair. Pancreatic and intestinal enzymes such as trypsin and chymotrypsin work to break down protein into more manageable constituents for your body to use.
The end products include peptide fragments and free amino acids that are absorbed almost exclusively in the small intestine. There are various factors which affect the time required to fully breakdown proteins for use in the body. The concentration of enzymes is one such limiting factor and can be enhanced by taking protease supplements.
This is especially important for older people whose level of enzymes fall. Another factor limiting the timely digestion of protein is the acidity of the stomach. Taking antacids or other substances that interfere with digestion (certain drugs) because they reduce the level of stomach acidity slows protein digestion.
Another way of ensuring adequate protein breakdown is to take pre-digested protein sources. This may be important for older people as research has shown that the hydrochloric acid level in older people also dips.
Taking predigested proteins results in more rapid and complete appearance of amino acids in the blood stream and greater incorporation into new protein synthesis.
Fast digesting proteins include meat and whey from milk, whereas the casein from milk is a slow digesting protein. Athletes, as well as older people can benefit from taking proteases or pre-digested proteins because athletes tend to overwhelm their systems with high levels of protein, which their digestive systems cannot assimilate.
Taking digestive enzymes which may be in fact, in many protein shake formulas, helps reduce the risk of inflammation in the gut as well as speed protein digestion.
Although skeletal muscle is a large depository for amino acids, in a recent study tracing the path of protein throughout the body, investigators found that only about 2.2 grams or eleven percent of the amino acids provided to young men in a 20-gram serving of protein were used for muscle protein synthesis.
Muscle protein synthesis activated by a protein meal reverts to baseline levels after two or three hours. Therefore, eating additional protein within this time frame does not further increase synthesis rates. To maximize muscle protein synthesis, protein meals should be separated by three to five hours.
The type of protein you consume also matters. Lower-quality proteins, such as soy protein, are low in one or more essential amino acids, and fail to stimulate muscle protein synthesis to the same degree as higher quality sources like whey.
The constituent amino acids are also less likely to be incorporated in muscle tissue. Assuming the consumption of high-quality proteins, a protein intake of beyond 0.3 grams per kg of body weight per meal is not going to provide muscle tissue with significantly more amino acids. For a 200-pound male, this is around 27 grams.
While the additional protein may be used for other purposes, this level is the upper limit of what can be taken up by the muscle over several hours after eating.
For most people, the recommended amount will fall between 20 and 30 grams of high-quality protein per meal. However, protein requirements have been reported to be greater for older individuals who may become less sensitive to the muscle synthesis effects of protein.
Numerous studies have demonstrated that ingestion of 35 to 40 grams of protein stimulates greater rates of muscle protein synthesis than lower doses of protein for this group.
A study published in the American Journal of Clinical Nutrition, in November 2017, noted that for older people to metabolize protein well from meat sources, it should be well cooked rather than less well-done.
Dr. Jane Riley, Ed.D., certified personal fitness trainer, nutritional adviser, behavior change specialist, orthopedic exercise specialist. She can be reached at email@example.com, 212-8119 cell/text, www.janerileyfitness.com