Why some foods make you feel good..

Do you ever find yourself sitting on the sofa with a bar of chocolate when you're feeling stressed, bored, or just lonely?

Or find that you get cravings for certain foods — such as cookies, bread or pastries — even when you're not hungry?

Many people turn to food for reasons other than physical hunger. They put this down to a lack of discipline, get very "down" on themselves... and then eat even more so they feel better again.

This is a little like getting a flat tire, jumping out of the vehicle, and shooting out the remaining three tires!

What they don't realize is that these cravings could be due to a drop in the levels of serotonin in the brain. In fact, some studies show a direct link between obesity (due to overeating) and decreased brain serotonin levels.

So, what is serotonin?

Serotonin is a type of neurotransmitter known as a monoamine. Neurotransmitters are chemicals that send messages from one nerve cell to another. In short, a neurotransmitter helps different parts of your brain "talk" to each other. Without adequate levels of serotonin, you'd probably suffer from depression, sleep disorders, and various addictions.

Some overweight people with low levels of serotonin feel almost compelled to eat more. Once they get their carbohydrate "fix", serotonin levels rise and they feel better again, albeit temporarily.

It might also interest you to know that nicotine increases serotonin levels. Nicotine withdrawal has the opposite effect. This is one reason why people who quit smoking find that they rapidly gain weight. They're trying to get their serotonin "fix" from food instead of cigarettes.

The food you eat has the potential to raise or lower your serotonin levels. That's why the ingredients of a meal have such a powerful impact on the way you feel after you eat it. To understand why, you need to know a little more about an amino acid called tryptophan (pronounced trip-toe-fan).

The protein in the food you eat is made up of "strands" of amino acids. Your body can't make serotonin without the help of tryptophan. If you were to eat just tryptophan by itself, then it would enter the blood, flow into the brain, and raise serotonin levels.

Tryptophan requires the use of a transport molecule to cross the blood-brain barrier. Several other amino acids "compete" for this transport molecule. And whole foods contain other amino acids besides tryptophan. The presence of these competing amino acids (tyrosine, phenylalanine, valine, leucine and isoleucine) can inhibit the transport of tryptophan into your brain.

That's why eating a food high in tryptophan, such as cottage cheese, is not the best way to raise serotonin levels.

Tryptophan is present in foods in relatively small amounts in comparison to these other amino acids. According to some estimates, as little as one percent of the tryptophan in your diet actually crosses the blood-brain barrier.

Richard and Judith Wurtman, researchers from the Massachusetts Institute of Technology, have shown that meals high in carbohydrate can actually help tryptophan to enter your brain [3].

When you eat a food high in carbohydrate, your body releases insulin. Insulin helps to clear the competing amino acids from your blood. However, insulin has no effect on tryptophan. Consequently, once insulin has cleared the competing amino acids from your blood, tryptophan is free to enter your brain.

The link between serotonin and sleep is one reason why some people feel tired after eating a high-carbohydrate meal. It also helps to explain why foods high in carbohydrate are often described as "comfort" food.

Dr. Albert Stunkard, a professor of psychiatry at the University of Pennsylvania, thinks that people with an almost uncontrollable urge to raid the fridge late at night are doing it to help themselves sleep by boosting serotonin levels. If you've ever wondered why dieting affects your mood, low serotonin levels could be the explanation [4, 6, 7].

The drop in tryptophan appears to be greater in women, rather than men.

For instance, researchers from the University of Oxford found that just three weeks on a low calorie diet significantly reduced both tryptophan levels and the ratio of tryptophan to competing amino acids in a group of 15 men and women [1]. Despite a similar drop in weight, the decline in tryptophan was greater in women than men.

In other words, women appear to be more vulnerable than men to a diet-induced reduction in serotonin levels. This could be because estrogen levels are higher in women than men, which can increase the number of serotonin receptors in the brain.

There are also genetic variations in the serotonergic system (specifically, the 5-HT2A receptor gene) shown to affect both food and alcohol intake in overweight people [2]. This means that some people will respond in very different ways to the same diet.

One solution to the problem of low serotonin levels is to include some kind of high-carbohydrate cheat meal (as opposed to an entire cheat day) in your diet once or twice a week. Complete instructions on how to do this are available in Lyle McDonald's A Guide to Flexible Dieting: How Being Less Strict With Your Diet Can Make it Work Better.

Based on research into rigid versus flexible dieters, as well as both the physiological and psychological reasons that dieters so often fail, A Guide to Flexible Dieting offers a solution to the problems that face dieters in the real world.

In A Guide to Flexible Dieting, you'll learn how deliberately breaking your diet (in a controlled fashion) can make it work better in the long run. Free meals, structured refeeds and even a full diet break (where you take a full two weeks off of dieting) are all discussed and explained in detail.

References
1. Anderson, I.M., Parry-Billings, M., Newsholme, E.A., Fairburn, C.G., & Cowen, P.J. (1990). Dieting reduces plasma tryptophan and alters brain 5-HT function in women. Psychological Medicine, 20, 785-791
2. Aubert, R., Betoulle, D., Herbeth, B., Siest, G., & Fumeron, F. (2000). 5-HT2A receptor gene polymorphism is associated with food and alcohol intake in obese people. International Journal of Obesity and Related Metabolic Disorders, 24, 920-924
3. Wurtman, R.J., & Wurtman, J.J. (1995). Brain serotonin, carbohydrate-craving, obesity and depression. Obesity Research, 3, 477S-480S
4. Goodwin, G.M., Cowen, P.J., Fairburn, C.G., Parry-Billings, M., Calder, P.C., & Newsholme, E.A. (1990). Plasma concentrations of tryptophan and dieting. British Medical Journal, 300, 1499-1500
5. Greiwe, J.S., Holloszy, J.O., & Semenkovich, C.F. (2000). Exercise induces lipoprotein lipase and GLUT-4 protein in muscle independent of adrenergic-receptor signaling. Journal of Applied Physiology, 89, 176-181
6. Schweiger, U., Laessle, R., Kittl, S., Dickhaut, B., Schweiger, M., & Pirke, K.M. (1986). Macronutrient intake, plasma large neutral amino acids and mood during weight-reducing diets. Journal of Neural Transmission, 67, 77-86
7. Wolfe, B.E., Metzger, E.D., & Stollar, C. (1997). The effects of dieting on plasma tryptophan concentration and food intake in healthy women. Physiology and Behaviour, 61, 537-541