I just got done working out, sort of; I did manage to break a sweat. Then I made myself a high-protein shake and was sure to include a banana for carbs. Why do I do this again? Aren’t carbs a bad thing?
Well, it turns out that I need those carbs to stimulate insulin secretion to promote tissue cell uptake and use of the amino acids (1p206)(1). For this reason, it doesn’t make too much sense to take protein with some other kind of sweetener. The insulin affects movement of amino cid transporters to the membrane and their activity while also antagonizing activation of some enzymes that oxidize amino acids—very important if you’re trying to put on muscle (1p206-207)! You don’t want glucagon to dominate, leaving you with protein degradation (1p207). At least I don’t. Insulin stimulates protein synthesis and inhibits its degradation (1p207).
My shake’s protein content happens to be made up of contain whey and casein. That’s a good thing for me because whey is considered a “fast” protein that’s quickly digested, absorbed and oxidized to get that protein synthesis I want (1p207); the casein, a “slow” protein, prolongs amino acid concentration in the plasma at a low degree to keep protein synthesis up and protein degradation by around 30 percent (1p207). It’s unclear if older people are better off with the faster proteins and if younger people are better off with the slower proteins (1p207), but I’m 30 so I take both just in case. Plus, that casein keeps me feeling full longer (personal experience).
What’s also great about my protein shake is its amino acid profile. Leucine is important for promoting protein synthesis in my liver, muscles and skin because it accelerates phases of mRNA translation (1p207); plus, it’s involved in a signaling cascade to stimulate the mRNA translation (1p207). Leucine is great for me. And the whey apparently causes a rapid absorption of that leucine along with other branched-chain amino acids isoleucine and valine (2). The other amino acids will promote protein synthesis too along with cell volume through intracellular signaling, like leucine does (1p207).
Pretty much because I’ve just eaten (and just worked out), protein synthesis is dominating in my body (1p208) and the high-protein is speeding recovery of my muscles, specifically the whey more than the casein (3;4). About 20 percent of the amino acids going into the liver end up used for protein synthesis (most of what stays in the liver) and nitrogen-containing compounds (like creatine, glutathione, carnitine, carnosine, and choline) (1p198). The other amino acids end up in the plasma (1p198). Some of the amount will be used for purine and pyrimidine bases, which mainly make up DNA and RNA.
Because 40 percent of body protein is in muscle, a lot of activity occurs there (1p223). The muscle catabolizes aspartate, asparagines, glutamate and the branched-chain amino acids to a greater extent (1p223). My muscles are especially liking the content of branched-chain amino acids from the whey (2) that are circulating (1p218). Enzymes in my muscles as well as heart, kidneys, diaphragm, adipose and other organs like the liver transaminate them to be further oxidized into energy or for reamination (1p224).
Glutamine, for example, is generated in the muscle through several pathways (1p226). One such pathway includes transamination of branched-chain amino acids combined with alpha-ketoglutarate to form branched-chain alpha-keto acid and glutamate, then an enzyme combines glutamate with ammonia to form glutamine (1p226). Glutamine synthesis is relatively higher in skeletal muscle, lungs, brain and adipose tissues (1p226).
Creatine, which contains nitrogen from amino acids arginine and glycine with methyl groups donated from methionine, is also functioning in the skeletal muscle for energy (1p226). If not used it doesn’t stay there forever, but leaves the muscle as creatinine to the kidney and is excreted in urine (1p226). I can use the excretion, in fact, as a great indicator of my existing muscle and rate of degradation (1p226).
Along with creatinine, the urine will have nitrogen from urea, amino acids, ammonia and uric acid (1p238). Feces may have amino acids and ammonia too (1p238). A calculation that shows my nitrogen balance—how much protein I consume versus how much nitrogen comes out—can help me measure whether or not my protein intake is adequate and if the quality of my protein is good (1p237). After a high-protein meal the balance may be more likely to be on the side of delivering a positive result.
1. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.
2. Farnfield MM, Trenerry C, Carey KA, Cameron-Smith D. Plasma amino acid response after ingestion of different whey protein fractions. Int J Food Sci Nutr 2008;1-11.
3. Buckley JD, Thomson RL, Coates AM, Howe PR, Denichilo MO, Rowney MK. Supplementation with a whey protein hydrolysate enhances recovery of muscle force-generating capacity following eccentric exercise. J Sci Med Sport 2008.
4. Cribb PJ, Williams AD, Carey MF, Hayes A. The effect of whey isolate and resistance training on strength, body composition, and plasma glutamine. Int J Sport Nutr Exerc Metab 2006;16:494-509.