As the holiday season approaches, we anticipate gatherings with friends and family where memories are often shared during the preparation and consumption of comfort foods. Indeed, foods and eating may powerfully awaken memory and its associated mood.
Basic neurophysiology teaches us that olfactory neurons are not myelinated, effectively potentiating perception and processing of these kinds of stimuli. It may be that the unique imbrication of olfactory data with emotion is somehow entirely discrete on some dimensions from visual or auditory processes.
Equally intriguing are observations that women and men demonstrate differences in sensitivity to these stimuli, and that obesity, anorexia, and bulimia nervosa affect these neurological responses. These gender differences in response to and identification of comfort foods may provide emerging opportunities in the functional foods market.
The relationship between food and mood in normal subjects appears to depend on many variables. The time of day, the type and macronutrient composition of food, the amount of food consumed, the age and dietary history of the subject, and beliefs and expectations about the impact of a particular food all may influence cognition. Changes in the macronutrient composition, particularly fat-to-carbohydrate ratio, of breakfast have differential effects on mood and cognitive function. Raising brain serotonin levels by administering tryptophan or supplementing a carbohydrate-rich/protein-poor diet with tryptophan produces changes in mood. Dexfenfluramine, an agent known to promote serotoninergic neuronal activity, also may elevate mood state.
A reduced level of brain serotonin is associated with depression and cognitive dysfunctions and may also underlie some memory deficits frequently associated with premenstrual syndrome. Administration of bovine α-lactalbumin, a protein with a high tryptophan content, during the premenstrual phase may, in part, improve memory performance and some aspects of long-term memory. A tryptophan-rich diet not only raises brain serotonin levels but may also reduce cortisol concentration, an indicator of physical and emotional stress, while improving one’s mood. Since α-lactalbumin is the dominant whey protein in breast milk, this protein may, in part, account for an infant’s alertness and contribute to the infant’s visual tracking development.
Other possible and intriguing sources of nutritional effects on mood involve cholecystokinin (CCK), the most abundant neuropeptide in our cerebral cortex and limbic system. At "drug-level" oral doses of ~50 mg, CCK acts on sites in the brain that appear to modulate anxiety and panic behavior. One provocative approach to the management of anxiety disorders might be the use of food rich in CCK. There are few data on natural sources of CCK or similar potentially bioactive peptides, but screening common foods for this protein may be an effort that the current fascination with functional foods will support.
Observations that polyphenol-rich extracts from grape seeds, blueberries, and soy may modulate select neuroproteins and thus function as neuroprotectants in rodent models may have significant clinical implications in the management of cognitive disorders and the sordid use of psychoactive drugs through functional improvements of the nervous system.
Caffeine, one of three major methylxanthines found in our diet (theobromine and theophylline are the other two), is an integral bioactive component in the socially engaging beverage, coffee. These mood-altering compounds are also found in seasonal favorites such as chocolate and tea. These and other innate psychoactive compounds in these widely consumed products improve mental alertness and cognitive performance. Neurologically, they may act to strengthen the brain’s central information processing capabilities. Clinic-ally, they may have positive effects on sleep disorders associated with anticonvulsant therapy, and reduce the risk of Parkinson’s and Alzheimer’s disease in some population segments. For chocolate lovers, it appears that methylxanthines provide psychostimulant effects, arouse emotions, and may even evoke guilt feelings.
The beliefs of history and culture may well be validated and explicated through science. We may well be acquiring another level of appreciation of the prospects and the challenges presented by health claims for various foods. And perhaps we also are presented with a window on the future design and application of foods in health and medicine.
References for the studies mentioned above are available from the authors.
by Roger Clemens, Dr.P.H.,
by Peter Pressman, M.D.,
Attending Staff, Internal Medicine, Cedars-Sinai Medical Center, Los Angeles, Calif.