The physiology behind food cravings


Chocolate, sweets, popcorn, crisps… Are you constantly plagued by food cravings that are hampering your weight-loss efforts?

While some cravings have psychological causes, others can be physiological or biochemical in origin, and could be caused by an imbalance in hormonal and chemical substances in your brain and nervous system.

This is a relatively new field, which means that there are many things we don't yet know about body chemicals and their effect on food cravings. However, good progress is being made…

Research shows that a so-called neurotransmitter called serotonin (also referred to as 5HT) may play an important role in the control of food intake.

It looks as if serotonin regulates carbohydrate intake, while tryptophan (one of the common amino acids) increases serotonin release from the brain. When brain serotonin levels drop, or are deficient, we develop cravings for carbohydrate-rich foods.

Any treatment that can increase brain serotonin levels will help to counteract this effect, and may help to curb carbohydrate cravings. However, most people "self-medicate" a drop in brain serotonin levels by eating carbohydrate-rich foods like sugar, sweets, cake and chocolate. This could inevitably lead to weight gain.

The serotonin-alcohol connection
Alcohol may also increase brain serotonin levels. This means that people who have an alcohol addiction may crave carbohydrates when they're unable to drink.

One study looked at alcohol-dependent subjects who were either carbohydrate cravers or non-carbohydrate cravers. The researchers found that when the carbohydrate cravers were given a low-carbohydrate diet, they suffered from pronounced mood changes and had low serotonin levels.

This would explain why this type of alcohol-dependent person would crave and possibly binge on carbohydrates when deprived of alcohol. It's simply an attempt to boost serotonin levels.

Serotonin, mood disorders and cravings
Many studies have identified a link between mood changes, low serotonin levels and food cravings.

Researchers from the Massachusetts Institute of Technology (MIT) have published extensively on the association between depressed serotonin levels and conditions such as seasonal affective disorder (characterised by bouts of depression, especially in winter), carbohydrate craving obesity (CCO), and premenstrual syndrome (PMS).

It’s also been suggested that atypical depression, anorexia, bulimia and binge eating disorder are associated with low serotonin levels and food cravings.

In some of these conditions (e.g. depression, bulimia and binge eating disorder), the low serotonin levels lead to excessive food intake, particularly of highly refined carbohydrates. In anorexia, the disordered serotonin biochemistry causes cravings that the patient doesn't satisfy with food.

Food cravings and PMS
Many women experience food cravings (especially for sugar and sweets) at certain times of their menstrual cycle.

A team of South African researchers found that cyclical fluctuations in food intake occurred in women at various time during the menstrual cycle, with a drop in food intake just before ovulation and a peak just after ovulation. In some cases, the changes in food intake in response to changes in the hormones produced by the ovaries amounted to as much as 2500kJ per day.

These researchers suggest that the hormone-induced changes in food intake could contribute to excessive energy intake and weight gain.

In addition to the influence exerted by the ovarian hormones, a study from Denmark found that serotonin helps with the regulation of mood and impulsive behaviours, including food cravings. It also governs eating patterns.

In view of the central role played by serotonin in regulating cravings for sweet carbohydrate foods and mood swings associated with depression, SAD, CCO and PMS, the question is how we can influence our serotonin levels without overeating and gaining weight as a result.

There are a number of potential solutions:

Many antidepressant medications contain so-called selective serotonin re-uptake inhibitors, which increase the levels of serotonin in the brain and which help keep these levels steady.

If you suffer from depression associated with weight gain (a common combination) or SAD, CCO or PMS, it may be a good idea to ask your doctor about the use of selective serotonin re-uptake inhibitors that control the serotonin levels in the brain.

Dietary interventions
We know that carbohydrates and foods that contain the amino acid tryptophan boost brain serotonin levels.

If you suffer from food cravings due to low brain serotonin levels, you may be able to control your cravings by making sure you eat a diet that's rich in carbs. However, the carbs you eat shouldn’t 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, which are minimally processed, e.g. high-fibre bran cereals, oats, plenty of fruit and starchy vegetables (especially sweet potatoes) and unprocessed grains such as brown rice and wholegrain wheat.

To boost your tryptophan intake, you need to have some protein, such as milk, yoghurt and cottage cheese, lean meat, fish or eggs.

Whenever you experience food cravings, try having some fat-free yoghurt, a wholewheat cracker or dried/fresh fruit.

- (Dr I.V. van Heerden, registered dietician)

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