Thursday, November 1, 2007
Food Addiction: Snacking on Serotonin
The neurology of carbohydrate craving.
Eighteen years ago, Richard and Judith Wurtman, a husband and wife research team at the Massachusetts Institute of Technology (MIT) reported in Scientific American:
"We wondered whether the consumption of excessive amounts of snack carbohydrates leading to severe obesity might not represent a kind of substance abuse, in which the decision to consume carbohydrates for their calming and anti-depressant effects is carried to an extreme--at substantial cost to the abuser’s health and appearance."
In the case of certain carbohydrate cravers, the Wurtmans discovered, dietary tryptophan was being converted into serotonin, like always—but this concentrated serotonin surge acted like a powerful mood-booster. It acted like medicine.
The Wurtmans had hit on something important. People who tended to binge late in the day on carbohydrate foods, particularly simple sugars, got a drug-like “buzz” that was highly reinforcing. In the experiments, these people quite specifically, if unconsciously, selected the kinds of foods richest in serotonin-building compounds.
The serotonin-boosting effects of carbohydrates may explain why addicts in recovery, as well as carbohydrate cravers and PMS sufferers, show a tendency to binge on sugar foods. Abstaining addicts apparently turned to the overconsumption of carbohydrates as a means of attempting to redress the neurotransmitter imbalances at the heart of their disorder. Perhaps some addicts discover early in life that carbohydrate-rich foods are their drug of choice.
None of this should be taken to mean that large doses of supplemental tryptophan constitutes some sort of easy remedy for serotonin-mediated disorders. It isn’t that simple. However, many drug treatment experts are convinced that dietary alterations, vitamin therapy, and nutritional supplements--as well as strenuous exercise, which also has a marked effect on neurotransmission—play vital roles in addiction treatment programs.
Dopamine is involved with eating behaviors, too. A Princeton University animal study compared dopamine levels while rats were experiencing stimulant drugs, and while they were eating preferred foods. The researchers found that “amphetamine and cocaine increase dopamine in a behavior reinforcement system which is normally activated by eating. Conversely, the release of dopamine by eating could be a factor in addiction to food.”
The idea of a link between addiction and appetite control is not new, and the controversy over the addictive properties of sugar foods is an old one. Heroin addicts, alcoholics, and cigarette smokers, when deprived of their drug of choice, will sometimes binge on sugar foods in a pattern highly suggestive of cross-addiction or substitute addiction. Old-time alcoholics tell stories of pouring bottles of pancake syrup down the gullets of colleagues in dire need of sobering up. (Fructose does indeed speed the elimination of alcohol.) The practice of referring to drug cravings as “drug hunger” may be closer to the mark than we realize. Intense physical hunger may be as close as any non-addict ever comes to experiencing the mind/body sensations of drug craving.
Many addicts with alcoholic relatives report that they have experienced substitute addictions and multiple addictions repeatedly—and sometimes, these substitutions and additions center on food.
As usual, some of the best hard evidence comes from rats. In a study by Dr. Neil Grunberg at the Uniformed Services University of the Health Sciences in Bethesda, Maryland, rats were regularly injected with nicotine over long periods. When the injections were suddenly withdrawn, the rats chose sweetened food over regular food--a complete reversal of the food preference they had previously shown.
Not all overeaters are abstaining drug addicts, of course. Obesity, like drug addiction, comes in a variety of forms, and is influenced both genetically and environmentally. But the spotlight is now on a subset of obese people in which obesity does not seem to be a behavior learned from obese parents, any more than alcoholism is inevitably a learned behavior picked up from alcoholic parents.