The effect of a nutritional source of tryptophan on dieting-induced
changes in brain 5-HT function.
Psychol Med. 2003.
Dieting in healthy women results in a decrease in the availability of tryptophan, the amino-acid precursor of serotonin, for brain serotonin synthesis. This is associated with increases in the prolactin response to serotonin drug challenge suggesting a 'supersensitivity' of serotonin neuroendocrine responses. The aim of the study was to assess whether increased tryptophan intake during dieting would prevent the changes in tryptophan availability and serotonin neuroendocrine function. Fifty female subjects underwent a 1000 kcal daily diet for 3 weeks. In the final week of the diet subjects were randomly allocated to receive either nutritionally-sourced tryptophan ( g daily) or placebo in a double-blind, parallel group, design. Tryptophan supplementation failed to modify the dieting-induced reduction in fasting tryptophan availability to the brain. However, in contrast to placebo-treated subjects, subjects receiving additional tryptophan did not show enhanced prolactin responses to intravenous tryptophan challenge. The decrease in tryptophan availability produced by dieting may be due to increased tryptophan metabolism rather than decreased tryptophan intake. While tryptophan treatment did not increase fasting tryptophan availability it may have modified the effect of dieting on brain serotonin function. Further studies will test the effect of tryptophan has consequences for the effectiveness of dieting as means of weight control.
"I'm 53 years old and my passion is surfing the oceans worldwide – big waves. Since taking Andro400, I'm now down to my ideal weight – from 185 to 175 now which is probably a net 15 pound loss, taking into account that the increased muscle I have now is heavier than the fat it replaced. My energy level is up. I feel strong and more physically fit in general. Also, from surfing I have been injured many times – for example I've broken my neck and pelvis among other things. Taking Andro400, I have much less pain overall – and I've been able to take less pain medication and anti-inflammatory drugs .”
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The second theory is similar and is known as "evolutionary neuroandrogenic (ENA) theory of male aggression".   Testosterone and other androgens have evolved to masculinize a brain in order to be competitive even to the point of risking harm to the person and others. By doing so, individuals with masculinized brains as a result of pre-natal and adult life testosterone and androgens enhance their resource acquiring abilities in order to survive, attract and copulate with mates as much as possible.  The masculinization of the brain is not just mediated by testosterone levels at the adult stage, but also testosterone exposure in the womb as a fetus. Higher pre-natal testosterone indicated by a low digit ratio as well as adult testosterone levels increased risk of fouls or aggression among male players in a soccer game.  Studies have also found higher pre-natal testosterone or lower digit ratio to be correlated with higher aggression in males.