Protein For Energy
While the most important role protein seems to play in the body is maintenance, it is by no means its only role. Certain amino acids can also be converted into glucose, the sugar fuel for our body and more particularly for our brain. When we exercise or fast, our body runs low on a substance called glycogen, which is a starch-like molecule our liver stores to provide short-term glucose and buffer the effects of hunger and lowering blood sugar. Whereas our muscles and certain other organs can run off fat if they need to, our brain can only use glucose, so it’s important for a glucose buffering system to be built into our body. This is where gluconeogenesis comes in.
When glycogen has been exhausted and glucose runs low, the body turns up gluconeogenesis, which takes certain amino acids and turns them into glucose. At the same time, the muscles begin to utilize fat more readily for energy, helping to conserve the glucose being created from protein for the brain. Some scientific reviews assign gluconeogenesis as being the primary role for dietary amino acids (proteins), not maintenance of muscle. At the very least, protein seems to serve a vital purpose as a glucose reserve for the brain and other organs.
When the body begins gluconeogenesis, one source for extra amino acids is skeletal muscle. Contrary to many fears, drawing amino acids from muscle does not cause muscular atrophy in the short-term, though prolonged periods of intense exercise (such as working out for weeks in a row without rest) and starvation do eventually lead to atrophied muscles. Amino acids taken during gluconeogenesis are replenished once protein is consumed once more, leading to no net loss of muscle.
Increasing dietary protein will increase the rate of gluconeogenesis and ensure there is no net loss, though it is not fully understood as to whether this is because the dietary protein instantly replenishes the muscles post-workout or because the amino acids are converted to glucose first, reducing the need to take protein from the muscles. Either way, eating a higher protein diet (28% protein) increases the rate of gluconeogenesis by about 40%, creating a very effective buffer for low blood sugar and increasing total energy available, which is especially useful for endurance activities.