A person feels sleepy after eating carbohydrates because carbs make tryptophan and serotonin more accessible to the brain, according to WebMD. Simple carbohydrates can also make a person feel sleepy, explains Brian Willett on the Jillian Michaels website.
Tryptophan comes from proteins found in certain foods. When it reaches the brain, it is converted to serotonin, which is a neurotransmitter. Serotonin is then converted to melatonin. Melatonin is a hormone released by the pineal gland at night, which regulates sleep and increases drowsiness, notes the National Sleep Foundation. Foods that contain tryptophan include protein-rich and starchy foods, such as rice, potatoes, poultry, turkey, game meat, eggs, seaweed, soy protein, milk and spinach.
Simple carbohydrates can increase sleepiness because the carbs are absorbed by the body quickly, which causes sugar levels to rise and drop rapidly. The quick absorption may make a person feel energized for a little while but the energy does not last a long time and is generally followed by fatigue, according to Willett. Types of simple carbohydrates include many processed or refined foods, such as candy, soda, sugary cereals, pastries with high sugar and juices with sugar. Eating protein with simple carbohydrates prevents the quick absorption that causes the energy crash.