Understanding blood sugar and insulin can be tricky. While someone might not be a full-blown diabetic, experiencing sleepiness or drowsiness after meals can be a sign of imbalance.
The Thanksgiving meal is the most well-known classic example where Americans eat too much deliciously rich food, and afterwards lay around in a half-coma wondering why they took that last bite.
Unfortunately, many experience this phenomenon even after a typical everyday lunch or dinner that does not involve cooking a turkey all day or multiple side dishes. This state is known as postprandial somnolence.
There are several reasons people crash after meals.
First, there are two parts to the nervous system. One can either be in a parasympathetic (“rest and digest”) or sympathetic (“fight or flight”) state.
During meal time, the parasympathetic system is supposed to dominate over the sympathetic system, resulting in the ability to properly digest and assimilate the food being eaten. People may find their “get up and go” or “fight or flight” down-regulated after meals, especially heavier meals that involve a lot of carbohydrates.
Second, when food — specifically carbohydrates — are consumed, they are broken down into sugars known as glucose that rapidly enters the blood stream. In response, the pancreas produces the hormone insulin to push glucose into cells in order to be used as energy or stored for a later time.
When a great deal of insulin is produced, it is commonly called an “insulin spike,” rapidly decreasing glucose in the bloodstream and resulting in fatigue, sleepiness and brain fog. Many people then find themselves craving an afternoon snack of a sugary treat like chocolate or coffee.
Third, carbohydrate-rich meals result in higher insulin surges that decrease several amino acids in the blood, except for tryptophan. It is decreased, but not nearly as much comparatively.
Tryptophan is the precursor to the brain hormone serotonin which is known to help with mood, appetite control and sleep.
1) Harvard T.H. Chan School of Public Health. (2016). Carbohydrates and Blood Sugar. http://www.hsph.harvard.edu/nutritionsource/carbohydrates/carbohydrates-and-blood-sugar
2) Wurtman R, Wurtman J, Regan M, McDermott J, Tsay R, and Breu J. (2003). Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios.