A Scientific Guide To Protein Intake With Training: What to Eat, How Much and When by Langer Henning & D'Hulst Gommaar

Author:Langer, Henning & D'Hulst, Gommaar [Langer, Henning]
Language: eng
Format: epub
Published: 2020-11-04T00:00:00+00:00

3.5. What about other macronutrients? Do carbohydrates and fat augment muscle protein synthesis?

By Henning Langer

We extensively discussed the amount and quality of your protein sources, but obviously we do not eat ‘only’ protein. Especially after a workout most people co-ingest some form of carbohydrates with their protein supplement and many natural protein sources inherently come with fat. Does this help or potentially hamper protein synthesis?

When you ingest carbohydrates, insulin concentrations in the blood rise because the pancreas starts to secrete insulin to keep blood glucose in narrow ranges. The amount of glucose in the blood is one of the most tightly regulated processes in the human body.

Let us rewind to the biological processes that regulate protein synthesis. It is well known that insulin alone and in sufficient dosages can robustly increase mTOR signaling and muscle protein synthesis in vitro (meaning in cell culture experiments) (Yoon, 2017 ). This happens independently of muscular contractions or amino acids. Intriguingly, the opposite in not true: findings in skeletal muscle cells indicate that amino acids can only stimulate mTOR and protein synthesis when there is insulin available (D'Hulst, 2020 ).

However, a review of clinical trials in humans found that when insulin is exogenously administered in physiological ranges in the absence of amino acids, MPS does not increase (Trommelen, 2015) . The reason appears to be that insulin itself causes hypoaminoacidemia (meaning a decrease of amino acid levels in the blood stream), which is a natural function of insulin shuttling nutrients into cells. This basically “cancels out” any directly stimulatory effects of insulin on MPS. If insulin is administered together with amino acids, MPS increases. However, that is an effect that can be attributed to the amino acids themselves, as we have discussed in chapter 1.5.

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