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An extensive review of the literature reveals no consensus on the relationship between food and mood. The numerous contradictory findings are likely due to differences in methodologies in a research area for which few objective endpoints have been identified. Studies have used many different dietary, psychologic, and biologic measures. A few studies have attempted to use objective physiologic and psychologic endpoints; most have used self-reported mood and diet parameters. Some reports of negative findings may have resulted from insufficient numbers of subjects and inadequate study designs. Not surprisingly, few conclusions and recommendations can be made with certainty in this complex and confusing area.

Nonetheless, several foods and nutrients have been hypothesized to influence mood via physiologic pathways. For example, because tryptophan is a precursor of serotonin, which has been shown to improve mood consumption of tryptophan has been suggested to improve mood by increasing brain serotonin synthesis. Consequently, tryptophan supplementation has been used to treat many neuropsychiatric disorders, with variable success." The data in healthy subjects are also equivocal, perhaps owing to differences in methodologies and populations studied. Some shortterm studies in healthy people have shown no effect of altered blood tryptophan levels on mood, whereas others have shown tryptophan depletion to lower mood in healthy males. Genetic factors might influence the response to tryptophan depletion. For example, in a recent double-blind, placebo-controlled crossover study, depletion of blood tryptophan levels by 89% through administration of a tryptophan-deficient amino acid mixture resulted in a depressed mood in six out of 20 healthy men with a family history of psychiatric illness, but had no effect in controls.

Wurtman and Wurtman hypothesize that carbohydrate consumption improves mood by increasing tryptophan transport into the brain. This is suggested to occur because tryptophan and other neutral amino acids, such as the branched-chain amino acids (BCAAs), are transported into the brain by the same transport system. As a result, tryptophan uptake into the brain increases when the ratio of circulating tryptophan to BCAAs is increased. A carbohydrate-rich, protein-poor meal stimulates insulin secretion, which causes a preferential uptake of BCAAs into muscle cells. This would lower the blood levels of BCAAs and remove them as competitors for transport into the brain. Wurtman and Wurtman hypothesize that this results in increased brain tryptophan levels, with subsequent increased serotonin synthesis.

Studies on the effects of carbohydrate consumption on mood yield inconsistent results. Increased carbohydrate consumption had no effect on mood in obese women on a 950 kcal weight loss diet.60 Meals high in both simple carbohydrates and complex carbohydrates improved mood within 30 minutes of consumption in young women, but similar effects were also seen with a low-carbohydrate meal. Neither a 40 g nor a 100 g sucrose beverage affected mood in young women and men. Conversely, a high-carbohydrate beverage (47.5 g dextrose and maltodextrin) expected to increase blood tryptophan levels improved mood 90 to 180 minutes after consumption in women with PMS.64 In female athletes, supplementation with a beverage containing 4 g carbohydrate/kg/day reduced postpractice psychologic fatigue, but did not influence any other psychologic variables.

Although a high-fat meal reduced alertness and responses to stimuli in a sustained-attention task in males, other studies have shown minor or no effects of a high-fat meal on mood in either males or females. Higher than usual consumption of either fat or carbohydrate at lunch increased feelings of drowsiness and confusion in males and females, although subjects felt less tense after the high-carbohydrate meal and more tense and less cheerful after the high-fat meal.

It has been suggested that chocolate consumption may elevate mood because it contains several biologically active compounds. These include caffeine and theobromine (both generally considered to stimulate the central nervous system), phenylalanine and tyrosine, which are precursors to norepinephrine and dopamine, and the biogenic amines tyramine and phenylethylamine. Phenylethylamine, a neurotransmitter-like substance similar in structure to amphetamine, improves mood when administered to certain depressed patients. The antidepressant buproprion, similar in structure to phenylethylamine, has been shown to eliminate chocolate craving.

Although chocolate contains several bioactive substances, the effects of consuming chocolate itself on mood are unknown. Most of the evidence on chocolate and mood is anecdotal, with very little scientific data showing that chocolate consumption actually exerts pharmacologic effects. Caffeine levels are low in milk chocolate (10 mg/1.55 ounces), and theobromine (86 mg/1.55 ounces) is only a weak central nervous system stimulant. In addition, higher levels of other bioactive substances are found in foods such as cheddar cheese, salami, and pickled herring.

Some individuals reportedly use carbohydrate or chocolate to self-medicate for depression. For example, both food intake and mood are altered, supposedly via serotoninergic pathways, in psychologic syndromes such as PMS and seasonal affective disorder (SAD). Because depressive patients with PMS or SAD respond to serotoninergic drugs with reduced carbohydrate craving and improved mood, some scientists speculate that increased carbohydrate consumption may have the same effect as the drug.

Countering this self-medication hypothesis are observations that many healthy women who crave sweets tend to have negative rather than positive mood reactions to satisfying the craving. Weingarten and Elston found in their study of college students that 82% of the men but only 57% of the women reported a positive response to fulfilling their cravings. Hetherington and Macdiarmid reported similar findings in women. Thus, although men feel generally good after acting on their food cravings, many women have negative feelings. In another study, self-described chocolate "addicts" were more depressed and tense than normal women; chocolate consumption in this group resulted in increased guilt with no improvement in mood.

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