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Updated 28 August 2013

The physiology of food cravings

Are you plagued by food cravings? An imbalance in hormonal and chemical substances in your brain could be to blame.

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Are you plagued by food cravings? Are these cravings hampering your weight-loss efforts?
While some food cravings have psychological causes, others can be physiological or biochemical in origin, and could be caused by hormonal and chemical imbalances in your brain and nervous system.

This is a relatively new field of research, and there are many things we don't yet know about body chemicals and their effect on food cravings. New chemicals and hormonal substances are constantly being discovered, and there's still a lot of uncertainty about which chemical triggers affect food intake.

The biochemistry of food intake is also very complex and much more research is required before we can completely solve the problem of food cravings.

Serotonin

It seems likely that a neurotransmitter (a chemical that transmits messages in the brain and nervous system) called serotonin plays an important role in the control of eating patterns.

  • Serotonin participates in the regulation of mood and impulsive behaviours. Many studies have identified links between mood changes, low serotonin levels and food cravings. When serotonin levels in the brain drop, or are deficient, we develop cravings for carb-rich foods. Many people "self-medicate" when they experience low serotonin by eating foods like sugar, sweets, cake and chocolate.
  • Depressed serotonin levels are associated with conditions such as seasonal affective disorder (SAD, characterised by depression, especially in winter), carbohydrate craving obesity (CCO) and premenstrual syndrome (PMS).  Other conditions, such as atypical depression, anorexia, bulimia and binge-eating disorder, are also associated with low serotonin.
  • In some of these conditions, the low serotonin levels lead to excessive food intake, particularly of highly refined carbohydrates (e.g. bulimia and binge-eating disorder), while in anorexia the disordered serotonin biochemistry causes cravings that the patient doesn't satisfy with food.
  • Drinking alcohol increases serotonin. Certain alcoholics crave carbohydrates when they're unable to drink. One study found that when these “carbohydrate cravers” were given a low-carb diet, they suffered from pronounced mood changes and low serotonin. When deprived of alcohol, this type of alcohol-dependent person might binge on carbs in an attempt to boost serotonin levels.
  • Many women experience food cravings at certain times of the month, particularly for sugar, sweets or sugar-sweetened drinks. Research indicates that fluctuations in food intake occur over the menstrual cycle, with a drop just before ovulation and a peak just after ovulation. In some cases, the daily changes in food intake can be as much as 2 500kJ. These hormone-induced changes could contribute to excessive energy intake and weight gain.
Solutions

  • In view of the central role played by serotonin in regulating cravings for sweet carbohydrate foods, mood swings and depression, the question is how we can influence our serotonin levels without overeating. Any treatment that increases serotonin may help to curb carbohydrate cravings.
  • Carbohydrates and foods that contain the amino acid tryptophan boost brain serotonin levels. To increase your tryptophan intake, make sure you get enough protein: fat-free milk, yoghurt and cottage cheese, lean meat, fish or eggs.
  • You may be able to control your cravings by making sure you eat a diet rich in carbs. However, these should not be loaded with additional fat, or be excessively high in energy. This excludes all chocolates, cakes, pastries, cookies, tarts, biscuits, desserts and sugar-sweetened cold drinks.
  • Concentrate on eating carbohydrates with a high fibre content and which are minimally processed, e.g. high-fibre bran cereals, oats, plenty of fruit and starchy vegetables and unprocessed grains such as brown rice and wholegrain wheat.
  • Whenever you experience food cravings, try some fat-free yoghurt, a wholewheat cracker or dried/fresh fruit.
  • Ask your doctor about medical treatment if you feel your food cravings are out of control.

Sources: Moorhouse (2000); Wurtman (1988, 1990, 1993); Wallins & Rissanen (1994); Buffenstein (1995); Moller (1992)

Dr Ingrid van Heerden is a registered dietician and holds a doctoral degree in Nutrition and Biochemistry. She believes that "we are what we eat" and offers free nutrition and weight loss advice via her DietDoc service on Health24.com. Read more of her articles.

 
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