By Marie Spano, M.S., R.D., Contributing Editor
Some foods just make you feel better. But, is it just our perception that smooth, silky chocolate can calm us down after a bad day and caffeine makes us more alert, or can food-based compounds cause actual physiological changes to our state of mind?
A caffeinated world
Caffeine is perhaps the most widely used legal psychoactive agent (substance that affects brain functioning) in the world. Chemically speaking, caffeine is a xanthine alkaloid compound that is completely absorbed by our body within approximately 45 minutes after ingestion (European Journal of Clinical Pharmacology, 1981; 21:45-52). Caffeine binds to adenosine receptor sites in our central nervous system, leading to a decrease in adenosine activity. This decrease in adenosine activity results in an increase in dopamine, a neurotransmitter that stimulates the central nervous system (Pharmacology Reviews, 1999; 51:83-133).
If you think caffeine can help you get through that last hour of work, you aren’t imagining anything. Studies show that caffeine in doses of approximately 4 mg per kilogram of body weight can increase mental alertness and improve semantic memory, logical reasoning, free recall and recognition memory tasks (Appetite, 1994; 22(1):39-55). In addition, multiple small doses of caffeine given over a period of time seem to be equally as effective as a single large dose in improving alertness and performance on reactive and cognitive tasks (Psychopharmacology, 2002; 164:188-192).
Though the time it takes to eliminate caffeine completely from one’s body depends on a variety of factors, in general, half of caffeine consumed at any given time is eliminated in three to four hours (“Physician’s Drug Handbook,” 11th edition, 2005), which means that nighttime caffeine consumption could interfere with sound sleep.
Synthetic and natural sources of caffeine can be found in a variety of foods and beverages. Caffeine does more than just stimulate our central nervous system, it also lends a bitter flavor to foods and beverages, and may enhance sweet and salty tastes, as well (Journal of Sensory Studies, 2007; 15:449-457).
Theanine and tea
Tea is the most widely consumed beverage worldwide, trumped only by water—and with good reason. It is calorie-free, widely available and can both increase alertness and help us maintain focus (Nutrition Reviews, 2008; 66:82-90).
Tea’s unique relaxation and enhanced-concentration properties stem from its naturally occurring combination of caffeine and the amino acid l-theanine. Both caffeine and l-theanine stimulate areas of the brain that increase our alertness, and l-theanine increases alpha-brain-wave activity, which induces relaxation (Alternative Medicine Reviews, 2005; 10:136-138). Approximately 200 mg of l-theanine can reduce psychological and physiological stress (Biology and Psychology, 2007; 74(1):39-45), and l-theanine produces a dose-dependent relaxed, yet alert, state about 40 minutes after it is consumed (Alternative Medicine Reviews, 2005; 10:136-138).
Craving carbohydrates
Foods high in carbohydrates provide immediate energy and the preferred fuel source for our brain, glucose. Cut carbohydrates out of your diet, and your cognitive functioning, focus and memory may suffer (Psychopharmacology (Berl), 1999; 145:378-385; Appetite, 2009; 52:96-103).
