Craving sugar is a common problem as sugar is required by all cells in the body (including a great demand from brain cells) for proper functioning. One suggestion is that this craving results from decreased levels of serotonin, a neurotransmitter that is known to induce feelings of contentment and is therefore a target for several antidepressant medications. Serotonin is biochemically synthesized from the amino acid tryptophan and sugar may significantly increase tryptophan absorption. This means that eating something sweet may genuinely make you feel happier.
Approximately 80% of the human body's total serotonin is located in the enterochromaffin cells in the gut, where it is used to regulate intestinal movements. The remaining 20% is synthesized in serotonergic neurons in the central nervous system where it functions to regulate mood, appetite, sleep, memory and muscle contraction. It is easy to see why any stimulation of serotonin production could lead to significant feelings of reward. Some research suggests that carbohydrates in general help to raise serotonin levels and higher glycemic index carbohydrates (ie white bread) have a greater effect in this regard than lower glycemic index foods (ie peaches).
Chocolate is an interesting food in this discussion because not only does it usually contain significant levels of sugar, but it also contains alkaloids that may raise brain serotonin levels. In addition, dark chocolate has other constituents such as anandamines, caffeine and phenylethylamine which could act as powerful mood enhancers.
Insulin resistance is another common reason for sugar craving. If cells constantly receive excessive levels of sugar from carbohydrates they may eventually become resistant to the insulin which transports sugar from the blood stream into the cells. If you find yourself wanting a nap or craving carbohydrates (ie cakes, sweets, pastries) after a meal, it may be due to insulin resistance as the body attempts another approach to generate energy production.
Another possible reason for sugar cravings is low adrenal function. The adrenals are hormone glands that sit above the kidneys and they secrete a variety of hormones including adrenaline (which stimulates energy production) and cortisol (which relieves inflammation). They also replace the function of the ovaries in the production of the female hormones oestrogen and progesterone when women approach the menopause. An overload of physical or emotional stress can eventually lead to reduced adrenal function as the adrenals have simply been asked to give too much for too long. At this point the body demands more sugar in an attempt to boost energy production (a similar process can occur with excess caffeine intake).
Craving salt can also be a symptom of adrenal exhaustion, especially in people who live highly stressful lives. Aldosterone belongs to a class of hormones called mineralocorticoids that are produced by the adrenal glands. Aldosterone helps maintain blood pressure, water and salt balance in the body by helping the kidneys retain sodium and excrete potassium. When aldosterone production falls too low through reduced adrenal function the kidneys are not able to regulate water and salt balance, leading to a drop in both blood volume and blood pressure, and a corresponding craving for salt. The three major electrolytes are sodium (salt), potassium and chloride. They dissolve in water and carry an electrical charge which makes them absolutely essential for healthy cellular function.
Another reason for craving salt is that the body needs the additional minerals found in natural salt that have been filtered out of our regular table salt. In this case eating salty food will only satisfy your craving temporarily until your body realizes it is still missing the extra minerals.
Craving dairy products is also very common. Cow’s can produce morphine in their bodies and this may induce a calming effect in their young. Milk also contains casein, a protein which can release particular opiates (casomorphins) during digestive breakdown and which has a much higher concentration in cheese than in milk. This leads to speculation that some people may receive a chemical high from dairy products.
Researchers have also uncovered some evidence that certain foods stimulate the release of dopamine, another neurotransmitter associated with motivation and pleasure.
Psychological issues are obviously another very relevant factor in certain food cravings and this requires an exploration of indicividual life circumstances, emotional responses and behaviour patterns.
It is also important to mention that many genes are now known to be associated with variations in weight through their expression in appetite regulating centres of the brain.