Web edition: March 5, 2001
Some people undertake seemingly impossible tasks without frustration, while others become anxious or depressed. A Dutch study now finds that the latter individuals might cope with pressure better if they tailored their diet to fuel the brain with more tryptophan.
The brain uses this essential amino acid, a building block of many proteins, to fashion serotonin,
a mood-enhancing neurotransmitter.
Neuropsychologist C. Rob Markus of the TNO Nutrition and Food Research Institute in Zeist, the Netherlands, and his colleagues identified a milk-derived protein--alpha-lactalbumin--that
is unusually rich in tryptophan. Moreover, this protein is low in amino acids that compete with tryptophan for absorption by the brain. For their tests, the researchers enriched a chocolate drink with either this protein or with casein, the primary protein in milk. Casein possesses a
low ratio of tryptophan to those competing amino acids.
On each of two days, 58 men and women drank one or the other of these drinks both with breakfast and as a late-morning snack. Half the volunteers had a history of deteriorating mood
when subjected to acute stress.
Around lunchtime, against a backdrop of loud industrial noise, each volunteer spent 20 minutes at a computer screen calculating math sums. The better the volunteer's problem-solving skills, the more challenging--to even insoluble--were the problems given.
"Not everyone got stressed" by the tests, as measured by mood and biochemical changes, notes Markus. Most people who showed notable effects were in the stress-vulnerable group.
For them, this test-noise combo triggered a marked deterioration in mood, an increased pulse rate, a rise in stress hormones, and a drop in brain serotonin--but only on the day that the volunteers drank the casein-laced chocolate. Markus suspects that chronic stress may deplete serotonin, which the tryptophan-rich drink replenishes. His team's findings appear in the June 2000 American Journal of Clinical Nutrition.
Richard J. Wurtman of the Massachusetts Institute of Technology and others have shown that spiking brain tryptophan by eating sugar- or starch-rich foods improves some people's moods. However, adding protein to the foods made tryptophan ratios fall, leaving the volunteers again vulnerable to anxiety.
Wurtman says, "This important [Dutch] paper shows we shouldn't generalize about the role of proteins based on one or two individual proteins"--like the casein that he and others studied.
Indeed, the Dutch study "opens the possibility that people can learn to self-regulate moods through diet," observes Bonnie Spring of the University of Illinois at Chicago. Her data show that the magnitude of tryptophan changes seen in this study "unquestionably can be produced by changes in the ordinary diet." However, she can't yet offer a nutritionally balanced menu to counter stress.
C. Rob Markus
TNO Nutrition and Food Research Institute
Division of Target Organ Toxicology
P.O. Box 360
3700 AJ Zeist
Department of Psychology
University of Illinois, Chicago
1007 West Harrison Street
Chicago, IL 60607
Richard J. Wurtman
Massachusetts Institute of Technology
Clinical Research Center
E25-604, 45 Carleton Street
Cambridge, MA 02139
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______. 1995. Got them low-fat, polyunsaturated blues. Science News 148(Sept. 2):153.