Tryptophan supplements tend to diminish the desire for carbohydrates
. And since most overweight people seem to favor sweet, processed carbohydrate foods, it may be helpful in weight loss. Phenylalanine suppresses the appetite by increasing the production of the neurotransmitter norepinephrine. Amphetamines, or diet pills, work in much the same way, but, unlike amphetamines, phenylalanine does not cause a depressive crash when it is stopped.