Dietary Link to Depression

NEW YORK (Reuters) -- People who feel tired, sluggish, and down may well blame it on what they ate -- or rather, what they didn't eat. For the first time, researchers have found direct evidence of a link between depression and diet.

The new findings lay some of the blame for the blues on low blood levels of the amino acid tryptophan -- a component of food proteins.

Tryptophan is a precursor of the neurotransmitter serotonin, the chemical messenger in the brain which has been shown to be involved in depression. The production of serotonin in the brain depends on the availability of tryptophan concentrations in blood plasma.

According to a report in this week's issue of the British medical journal The Lancet, Oxford University researchers studied 15 women who had suffered recurrent episodes of major depression but had recovered and were no longer on drug treatment.

Over two days separated by at least one week, all the women were asked to drink either a nutritionally balanced amino acid mixture with 1.92 grams of tryptophan in it or a mixture without the amino acid. Participants were unaware of which mixture they were given at each session.

Then, during seven hours alone in the laboratory, resting, with material to read, the women scored themselves on a scale of mood each hour.

Before and after the rest periods, blood samples were drawn to measure tryptophan concentrations.

"The tryptophan-free mixture produced a 75% reduction in plasma tryptophan concentrations," the researchers report. "After drinking the tryptophan-free mixture, 10 of the 15 women experienced temporary, but clinically significant, depressive symptoms."

Some of the women claimed they experienced a "full relapse" of depressive symptoms.

Two hours after drinking the tryptophan-free mixture, one women "experienced a sudden onset of sadness, despair, and uncontrollable crying," the researchers note.

"She feared that a current important relationship would end. She recognized that she was depressed, but still considered that her fears were appropriate. The evening of the test day she started to feel better and the next day was fully recovered."

No such changes in mood were found after drinking the mixture containing tryptophan.

The Oxford team says the findings support previous research evidence implicating serotonin deficiency as a cause of depression. They note that the new findings may also have implications for people on diets or who have eating disorders such as the binge-purge syndrome known as bulimia.

"Even modest changes in serotonin activity of the type produced by dieting could have adverse effects in those vulnerable to clinical depression," they state.

"Equally, it is possible that dietary and other environmental manipulations that enhance brain serotonin function might exert protective effects in those at risk of depressive disorders," conclude the researchers. SOURCE: The Lancet (1997;349:915-919)