I explain this in detail in several of my books, including Food & Mood, Eat Your Way to Happiness, and Eat Your Way to Sexy. In a nutshell, it is no coincidence that people turn to carbohydrate-rich foods, such as pasta or cookies, when they feel stressed, tired, or blue. Carbohydrates have a profound effect on numerous body chemicals that regulate how we feel and act.
From pasta to pie, carbohydrates stimulate the release of the hormone insulin from the pancreas which, in turn, lowers blood levels of protein fragments, called amino acids. All except, that is, for one – tryptophan. Normally, tryptophan must compete with other amino acids for entry into the brain, but with reduced competition, tryptophan has a clear shot into the brain where it is converted into serotonin, a “neurotransmitter” that sends messages between nerve cells. A rise in serotonin is associated with improved sleep, reduced appetite, and a better mood. In contrast, current low-carb/high-protein diets, by supplying more of the competing amino acids, reduce tryptophan and serotonin levels in the brain. Consequently, carbohydrate-sensitive people who eat a high-protein diet may experience fatigue or mood swings and “crave” a carbohydrate-rich snack in an effort to raise brain serotonin levels and feel better. Several conditions associated with depression and fatigue also are linked to low serotonin levels and increased cravings for carbohydrate-rich foods, suggesting that people unknowingly self-regulate their moods with food. For example, people who battle Winter Blues or Premenstrual Syndrome (PMS) also crave carbohydrates during their cyclic bouts of depression, lethargy, and inability to concentrate.
Timing is key here. Besides boosting mood, serotonin also calms us down and helps us sleep. Chowing down on a carb-packed meal of pasta marinara with garlic bread and a tossed salad could dull your concentration and leave you feeling groggy, which is fine after dinner, but could interfere with that board meeting mid-afternoon. Also, it only takes 30 grams of carbs to get the serotonin boost, which is the equivalent of a couple of cups of air-popped popcorn. Anything more than that, and you are just pigging out. Photo credit: Blue Square Thing via Compfight