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Food craving is often defined as an intense desire for a particular food or type of food." Although the term "food craving" is widely cited in the lay press, a scientific definition for it does not exist. In fact, scientists argue over the utility of such a subjective, ill-defined term.

Craving is most often self-reported and, as such, is influenced by a subject's own view of the intensity of the craving. Objective attempts to measure craving have included amount and speed of food consumption and psychobiologic measures, such as heart rate and skin conductance. Each measure has numerous limitations and is difficult to interpret. In addition, scientists find it difficult to compare studies that use different measurement tools. Despite these methodologic problems, the concept of craving remains important to the understanding of food intake.

Food cravings are quite common. In a study of college students, 68% of men and 97% of women reported having experienced food cravings. Both sexes reported that the frequency of their cravings was one to four times per month, and 85% of both men and women reported satisfying their cravings more than 50% of the time.

The most frequently reported food craving among young women is for chocolate. In the previously mentioned study of college students, 39% of women craved chocolate compared with 14% of men. In men, the prevalence of chocolate craving was similar to the craving for pizza.

Numerous biologic factors are postulated to cause food craving. Evidence exists that food deprivation, including self-imposed restriction such as dieting, leads to cravings. However, decreased cravings have occurred in obese people on low-calorie or very-low-calorie diets." Food cravings have also been attributed to a requirement for a specific nutrient lacking in the diet. For example, a craving for chocolate has been attributed to its magnesium content and craving for dairy products to their calcium content. Although it is appealing to speculate that cravings reflect a biologic need, scientific experiments do not generally support this view. Weingarten and Elston critically analyzed this hypothesis, noting that if it were true, the nutrient itself, as well as other concentrated food sources, should satisfy the craving. In addition, individuals with micronutrient deficiencies should crave foods high in the deficient nutrient. Neither of these expected observations has been found to be true.

It has also been suggested that certain foods are craved because they contain substances that influence brain neurochemistry to create a feeling of well-being. Two of these bioactive substances are tryptophan and carbohydrate, both thought to increase brain serotonin levels. Chocolate contains several biologically active compounds, including the methylxanthines caffeine and theobromine, the neurotransmitter precursors phenylalanine and tyrosine, and the biogenic amines phenylethylamine and tyramine. The presence of bioactive substances in foods is well documented, but little scientific evidence exists that they satisfy cravings when consumed in the foods themselves. The effect of these substances on mood will be discussed in more depth in the next section.

Many clinicians, researchers, and women speculate about the physiologic basis of craving, but only one study has been published in which researchers directly tested this hypothesis. Michener and Rozin" gave male and female chocolate cravers one of the following: a milk chocolate bar; a white chocolate bar (containing cocoa butter but no cocoa and thus providing the energy, sweetness, and texture of chocolate without the pharmacologic compounds); capsules containing cocoa (providing the minerals and pharmacologic compounds without the flavor); capsules containing white chocolate plus cocoa (providing all of the ingredients of chocolate without the flavor); placebo capsules containing flour; or no treatment.

Only consumption of chocolate itself fully satisfied the craving. These results strongly suggest that chocolate craving is due to its sensory properties, such as aroma, sweetness, and texture, or to psychologic attributions associated with it, rather than its pharmacologic effects. Observations that foods other than chocolate cannot satisfy most people's chocolate cravings support this. After evaluating the literature in this area, Rogers commented that serious reviews have found little support for the hypothesis that chocolate craving is related to psychoactive constituents.

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