When people think tryptophan, they think Thanksgiving turkey, and warm milk. But researchers at MIT dispelled those myths about a decade ago.

Tryptophan is one amino acid among many found in proteins, and they all compete with one another for transport across the blood-brain barrier into the brain. And, since tryptophan is present in most animal proteins in relatively small quantities, it gets muscled out of the way.

If you eat plant foods, though, the carbohydrates cause a release of insulin, which causes your muscles to take up the non-tryptophan amino acids as fuel. And so, your tryptophan can be first in line for brain access.

Animal foods can even make things worse: “When tryptophan is ingested as part of a protein meal, serum tryptophan levels rise, but brain tryptophan levels decline…due to the mechanism of transport used by tryptophan to cross the blood–brain barrier.”

The tryptophan levels in those given a high-protein turkey, egg, cheese breakfast dropped, whereas in the waffle-OJ group, their tryptophan levels went up.

This may actually explain the carbohydrate cravings one sees in PMS—your brain may be trying to get you to boost tryptophan levels to feel better. “Consumption of a carbohydrate-rich, protein-poor evening test meal during the premenstrual period improved depression, tension, anger, confusion, sadness, fatigue, alertness, and calmness scores [significantly] among patients with premenstrual syndrome.”

“Because synthesis of brain serotonin, which is known to be involved in mood and appetite, increases after carbohydrate intake, premenstrual syndrome subjects may overconsume carbohydrates in an attempt to improve their dysphoric mood state.”

Ideally, though, it would be more than just carbs—we’ll cover the ideal mixture in tomorrow’s video-of-the-day.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Kerry Skinner.

If you haven’t yet, you can subscribe to my videos for free by clicking here.