Diet & your brain: appetite

Part 1-chemicals that control appetite
Recently, at a Symposium on “Changing Paradigms in Clinical Nutrition”., a booklet which was called “Nutrition and Brain”, published by Nestle, was made available to delegates. One of the most fascinating articles in this booklet describes how dietary factors and so-called monoamine neurotransmitters control our appetite.

A complex process
The control of appetite in humans is a highly complex process. The human nervous system transmits messages in the form of electric signals through the brain and nerves. Although this system is similar to electric wiring, nerve ends are not connected to each other. To transmit the message from one nerve ending to another, a so-called neurotransmitter chemical has to be released.

Some of the best known neurotransmitter chemicals are serotonin (5HT), dopamine and norepinephrine. Researchers have been studying these neurotransmitters for years to discover how message transmission can be selectively changed to produce specific results, for example to control appetite.

Appetite-suppressing drugs
Drugs have been developed to influence the three abovementioned neurotransmitters in an attempt to control appetite and combat overeating which leads to obesity.

  • Selective enhancement of serotonin release or activity of 5HT will suppress appetite (Example: sibutramine which is a selective serotonin or 5HT reuptake inhibitor)
  • Selective enhancement of dopamine release will suppress appetite (Example: amphetamine)
  • Selective enhancement of norepinephrine will suppress appetite (Example: phentermine)

Pharmaceutical appetite suppressants, which include these 3 monoamines, can all have a wide variety of side-effects. To be safe you should only take these appetite suppressants under medical supervision and stop immediately if you develop any negative side effects.

Manufacturing our own monoamine chemicals
Research has also shown that the so-called monoamines are manufactured in the human body from amino acids:

  • the amino acid tyrosine is used by our bodies to synthesize dopamine and norepinephrine, which can suppress appetite
  • the amino acid tryptophan is used to synthesize serotonin or 5HT, which can suppress appetite

An important factor in the manufacture of monoamines is availability of substrate or basic material from which these chemicals are produced in our bodies. It is, therefore, theoretically possible to boost the concentrations of these appetite-suppressing monoamines in our bodies by dietary manipulation.

Dietary factors that boost monoamine synthesis
If we need the amino acids tyrosine and tryptophan to produce dopamine, norepinephrine and serotonin or 5HT, then it is logical that increasing the amount of tyrosine and tryptophan in the body will boost their production and possibly cause appetite suppression.

To increase the availability of these two amino acids, research has indicated that we need to do the following:

Boosting tryptophan
Contrary to expectation, levels of the amino acid tryptophan are not by eating very high-protein diets. To boost your brain levels of tryptophan and thereby increase the manufacture of serotonin or 5HT you need to eat a carbohydrate-rich diet.

Because serotonin is the brain chemical that makes us feel more positive and happy, this also explains why people get carbohydrate cravings. Readers often ask what they can do to control their irresistible urges to eat sugar, sweets and processed starches. One of the reasons why they have these urges is probably that their brain levels of serotonin are low. By eating sugar, sweets and starches they boost their brain tryptophan levels, which in turn boost serotonin or 5HT production and makes them feel more positive.

The urge to eat carbohydrates is a signal from your body that you either have a problem with serotonin production, or that your basic intake of carbohydrate is too low (for example slimmers who eat low-carbohydrate diets often get depressed and crave carbohydrates). To remedy this situation you need to ensure that you are eating sufficient unprocessed or minimally processed carbohydrates (e.g. unsifted maize meal, high-bran cereals, brown rice, potatoes, samp, crushed wheat, wholewheat bread). The high-carbohydrate diet must also contain moderate amounts of low-fat protein such as lean meat, fish, eggs, and low-fat milk and dairy products to provide tryptophan to the body.

Boosting dopamine and norepinephrine
To boost the production of these 2 monoamines humans require a high-protein diet. This is also the reason why high-protein diets give slimmers a “high”. The use of high-protein diets is associated with many risks. The risks include too high an intake of saturated fat and cholesterol which can have a negative effect on blood fat levels, development of acidosis and ketosis with damage to the kidneys, coma and death, constipation and a variety of other negative effects.

If you want to boost your intake of tyrosine, it may be safer to use an amino acid supplement which is low in fat together with a normal diet, rather than a diet overloaded with fatty proteins. Once again, it is not a good idea to overdo this supplementation. Use the amino acid supplements as described on the container and don’t think that if the prescribed dose may suppress your appetite, then taking double and treble the dose will give better results. If you find that you start getting depressed, then increase your intake of unprocessed carbohydrates to boost tryptophan and serotonin levels in the brain.

It is evident that the control of appetite is a very complex process and that interfering with the brain chemicals that control appetite can be potentially dangerous. So be careful what you take to suppress your appetite and never overdo the intake of one category of food.

If you have any diet queries, post a question or message on The Message Board. I am here to assist you with your Diet and Food Choices, so let’s interact. (Dr I.V. van Heerden, registered dietician)

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