Can some foods really make you sleepy?

Eating roast turkey is often blamed for the sleepy feeling that follows. The reason cited is that it contains the substance L-tryptophan. But other foods have more, for example, egg white, cod or pork chops, or sea lion kidney.

To understand why some meals make you drowsier, you need to know how the body and brain absorb nutrients.

• L-tryptophan is an essential amino acid, meaning your body can't produce it. You obtain it from your diet. Your body uses L-tryptophan as a building block to make serotonin, which is associated with happiness. Pharmaceutical preparations of tryptophan can indeed treat insomnia.
• But tryptophan as a pharmaceutical preparation is not the same as tryptophan from the diet. The protein in a meal also contains large neutral amino acids (LNAAs), and these compete with tryptophan to cross the blood-brain barrier.
• For tryptophan to produce serotonin, it needs to be eaten on an empty stomach and without other competing amino acids.
• Studies showed eating butternut squash seeds (high in tryptophan) with sugar dextrose improved sleep. This is because sweet carbohydrates cause the secretion of insulin which encourages other amino acids to be absorbed in tissues, leaving the typtophan to cross the blood-brain barrier.