mentioned earlier, exercise boosts plasma tryptophan
(remember, this is serotonin’s precursor) and decreases
levels of the branched-chain amino acids, which, though
important, compete with tryptophan for entry into the brain.
This substantial boost in tryptophan’s availability to the
brain persists even after the workout is finished.^24 In another
powerful and illuminating head-to-head study, no SSRI was
as effective as exercise, three times per week, in combating
depression. That’s game, set, and match!
There is another means of boosting serotonin in the brain
that you may already be familiar with, and that is with
carbohydrates and sugar. This temporary mood boost is
behind one of the more addictive qualities of carbohydrates.
And then when carbohydrate levels curtail in between
meals, serotonin drops, sending us reaching for something
starchy or sugary—demonstrating why carbohydrate
consumption is not a sound strategy for increasing
serotonin.
In pivotal psychological studies, feeding sugar to
subjects has been shown to temporarily improve willpower
and executive function, but it’s hard to tease out whether the
sugar actually boosts function or simply treats withdrawal
from the lack of it. It would help to see these studies
replicated on fat-adapted subjects. Regardless, though,
short-circuiting the reward systems of the brain with external
stimuli, whether with sugar, drugs, sex, or chronic bouts of
extended and high-intensity cardio, rarely leads anywhere
positive in the long term. But sugar in particular keeps you
on an insulin roller coaster throughout the day, can cause
you to gain weight, and can lead to metabolic dysfunction,