Excretion and perception of a characteristic odor in urine after asparagus ingestion: a psychophysical and genetic study.

The urine of people who have recently eaten asparagus has a sulfurous odor, which is distinct and similar to cooked cabbage. Using a 2-alternative forced-choice procedure, we examined individual differences in both the production of the odorants and the perception of this asparagus odor in urine. We conclude that individual differences exist in both odorant production and odor perception. The biological basis for the inability to produce the metabolite in detectable quantities is unknown, but the inability to smell the odor is associated with a single nucleotide polymorphism (rs4481887) within a 50-gene cluster of olfactory receptors.

Food addiction in humans.

Most of the evidence for or against food addiction in humans focuses on similarities between food craving and drug craving. There are numerous parallels in neuroanatomy, neurochemistry, and learning. Indeed, brain mechanisms for craving probably evolved to promote seeking of natural rewards and are taken over by drugs of abuse. Healthy, normal weight individuals, by definition, do not suffer from food addiction; however, overweight and obese individuals could meet clinical criteria. Palatable foods are not responsible for the obesity problem, because even nonpalatable foods can come to be desired and potentially overconsumed. It may be the way in which foods are consumed (e.g. alternating access and restriction) rather than their sensory properties that leads to an addictive eating pattern.

Images of desire: food-craving activation during fMRI.

Food craving (defined as an intense desire to eat a specific food) is of interest because it is extremely common and because it influences obesity or nutritional status. It has also been suggested that food craving may be the evolutionary source for cravings of all kinds including cravings for drugs and alcohol. Yet, little is known about the functional neuroanatomy of food craving. We report here the first functional magnetic resonance imaging (fMRI) study to explicitly examine food craving. A two-part technique was used to produce the food cravings. Threshold was reduced through a diet manipulation (monotonous diet) and cravings were triggered during blood oxygenation level-dependent (BOLD) fMRI sessions by having subjects imagine the sensory properties of favorite foods (a cue-induction technique). Subjects were also asked to imagine the monotonous diet (which they did not crave). Diet condition had an activating effect on both behavioral (reports of craving) and fMRI measures. Craving-related changes in fMRI signal were identified in the hippocampus, insula, and caudate, three areas reported to be involved in drug craving. Thus, this work supports the common substrate hypothesis for food and drug cravings.