"Here is where serotonin comes in.  The gene also controls serotonin production in the gut. Humans who have genetic osteoporosis or fragile, weak bones had much more serotonin in their gut than people with normal bones. And patients with abnormally dense bones had 50% less serotonin than those with healthy bones.

"However the researchers had to see whether it was simply a coincidence that serotonin levels seemed to be connected to bone formation. They tested the link between the gene, serotonin and bone formation by tinkering with the serotonin levels of mice. Mice who were born with one form of the mutation make too much serotonin in their gut and develop breakable bones. The serotonin is made from tryptophan, which the mice get from the protein they eat. So the researchers gave the mice a diet very low in tryptophan and the serotonin levels dropped to normal. As a result, the mice had healthy bones."

Now my neighbor looked worried. "Do you mean to say that if I keep taking the serotonin supplement, I might have problems with my bones?" " No one knows," I answered. "After all, until very recently, there was no such thing as a serotonin supplement. And maybe the amount of serotonin in the supplement is less than what your gut is making anyway. But since you are interested in serotonin in your brain, why don't you get your brain to make it the way nature intended? Eat carbohydrates. That way, your brain, not your intestinal tract, will be making more serotonin, which is what you want. When you eat carbs, your brain is able to capture some of the tryptophan in your bloodstream and make the serotonin it needs. And whatever is happening in your gut won't be affected at all.

"And fortunately, there is a normal and natural way of getting serotonin to increase in your brain without risking the health of your bones. Eat carbohydrate. As long as you eat something starchy or sweet on an empty stomach, there will be plenty of serotonin in your brain."

"But won't my gut make more serotonin if I eat carbohydrates?"

 "No, it only works for the brain."

As we finally parted from each other, I heard her muttering, " I think I'll go the bakery and get some fresh bread,"