What happens to body protein when we exercise?
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During prolonged aerobic (cardiovascular) exercise, muscle protein is broken down and amino acids, mostly alanine and glutamine are released into the blood. Alanine is one of the principle amino acids used to make glucose in the liver and the new glucose can help maintain blood glucose levels and fuel muscle during long aerobic exercise bouts. This process is driven by primarily by cortisol as well as epinephrine, both of which are elevated in circulation during exercise. Cortisol promotes muscle protein breakdown during the exercise while epinephrine promotes the conversion of amino acids to glucose in the liver. Since cortisol is a stress related hormone, the degree to which this happen depends on how hard you are exercising and for how long. Thus for shorter, less intense exercise sessions (e.g. walking, casual bicycling) this isn’t a consideration; however for recreational and competitive endurance athletes and heavy weight trainers it is (see Exercise/Fitness). |
What happens to the nitrogen when amino acids are used for energy purposes?
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The composition of elements in amino acids differs from carbohydrate and fat, as they contain nitrogen (N). This creates an additional consideration for the body if it wishes to use amino acids for energy or to make fat (in an overfed state) or glucose (in a fasting or exercise state). Thus an important step in using amino acids for any of these purposes is to remove the nitrogen-containing portion of the molecule. The removed nitrogen portion of amino acids will become ammonia (NH4+), which is potentially toxic to the brain. Thus it must be removed from the body before it builds up in the blood. |
The most prevalent way to rid the body of the nitrogen removed from amino acids is as urea. Urea is made by the liver and released into the blood, circulates to the kidneys and is subsequently lost from the body in urine. Each molecule of urea allows us to efficiently remove two nitrogen atoms from our body.
How important is protein during weight loss?
Protein can be advantageous to weight loss for a couple of reasons. First, current research suggests that when a meal derives more of its calories from protein, versus saturated fat and simpler carbohydrates the meals can promote greater satiety (fullness) and possibly reduce hunger a couple hours later. Furthermore, amino acids require special (energy requiring) processing if they are to be used for energy. That means that more calories are burned to use protein for energy during weight loss than many carbohydrates and saturated fat which can promote greater weight loss over time. Furthermore, eating more protein during weight loss may help a person maintain more muscle mass during the weight loss process, which in turn can be more beneficial to his or her metabolism (the number of calories burned).
Can amino acids affect our mood and sleep?
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Because certain neurotransmitters in the brain are made from amino acids, amino acids from the diet or supplements are often touted to be able to influence mood, memory, and emotions. For instance, tryptophan and tyrosine are used by brain cells to make serotonin and the catecholamines, namely norepinephrine and dopamine, respectively. Also, choline, which can be made from the amino acid serine, is a building block for the neurotransmitter acetylcholine. Serotonin is a neurotransmitter mostly associated with a calming and sleepy feeling. In order for serotonin to be produced, tryptophan must exit the blood and enter our brain cells. The movement of tryptophan out of the blood requires a special transport system. However, tryptophan must compete with several other amino acids, namely valine, leucine, tyrosine, and phenylalanine, to do so. |
One of the most commonly associated foods with calmness and sleepiness is milk, particularly warm milk. Some of this notion is derived from watching what happens to babies after they drink warm milk (either from the breast or milked-based formula). While some of calming effect is related to the suckling action itself, some the remaining effect might be related to either protein fragments created during the digestion of milk. So, the old believe warm milk can produce tiredness which lacks scientific confirmation might have some merit and future research should add greater clarity to this issue.
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