05 January 2006

Genes, diet and disease

Genetic factors influence how we react to various treatments such as folic acid supplementation and low-fat diets for heart disease. DietDoc explains.

Genetic factors influence how we react to various treatments such as folic acid supplementation, low-fat diets for heart disease and diets to enhance the GST enzymes that protect us again cancer.

The basic principle of "nutrigenomics" is that patients who do not react to standard diet therapy can have gene tests done to determine why they are not responding and/or to determine if they are at increased risk of developing certain potentially dangerous conditions.

Genes and haemochromatosis
Haemochromatosis (HC) is a genetically determined condition where the body absorbs and stores iron too efficiently so that iron is deposited in organs. Progressive damage to the liver, pancreas, heart and other organs can occur. HC is a relatively common disease in South Africa with nearly three out of every 1000 whites suffering from iron overload.

Ironically the symptoms of iron-overload in HC are similar to the symptoms of iron deficiency. Patients with HC may develop fatigue, weakness, chronic abdominal pain, aching joints, impotence and menstrual irregularities. As the disease progresses it can lead to serious problems, such as enlarged liver, liver cirrhosis, skin pigmentation, diabetes, arthritis, cancer, heart disease and deterioration of the sexual organs.

Researchers have identified the so-called HFE gene that predisposes individuals to HC. Forty to 60% of people with this gene will have increased body iron levels. Men and post-menopausal women are at greatest risk. It is, therefore, essential that patients who have increased body iron levels should have their genes checked to see if this condition is due to accidental causes, such as an increased iron intake, particularly by means of supplements, or if it is caused by a hereditary disposition.

Treatment of HC involves drawing blood regularly and restricting dietary intakes of iron (liver, kidneys, red and other types of meat, fish, egg yolk, iron-fortified cereals and bread, dried fruit and of course all mineral supplements that contain iron).

Increasing the patient’s intake of vegetables, grains and legumes will also help to lower body iron stores. Alcohol should be avoided and fruit intake should be restricted because the vitamin C content of fruit will increase iron absorption from other foods. Vitamin supplements containing vitamin C should also be avoided. Tea, coffee and soy products can help to lower body iron stores. Certain compounds such as carbonates, oxalates, phosphates and phytates, as well as other so-called chelating agents, can also be used to bind excess iron.

An important thing to keep in mind is that if you, or any member of your family, are diagnosed with hereditary (not accidental) iron overload and HC, then other members of the family should have genetic tests done to determine if they also have the HFE gene.

Other gene-diet interactions
There are many other gene-diet interactions where identification of the genetic makeup of the patient can assist dieticians to tailor diets to their specific needs, for example:

  • A gene that increases the patient’s tendency to develop cancer which can be counteracted by ensuring that the diet is rich in vitamins C and E. This is a situation where the use of vitamin and mineral supplements with high vitamins C and E contents can protect bearers of this gene from developing breast cancer and other types of cancer.
  • A gene that predisposes individuals to high blood pressure, but makes these hypertension sufferers sensitive to salt intake. They can control their blood pressure to a great extent by restricting salt in the diet. Other patients with high blood pressure will not respond to salt restriction, but will react positively to losing weight. This is a good example of how nutrigenomics can explain why certain hypertensives can lower their blood pressure by restricting their salt intake while others can eat a salt-free diet and not change their blood pressure at all.
  • A gene that predisposes people to developing osteoporosis. If these individuals can be identified by gene testing at an early age, they can increase their calcium and vitamin D intakes as a preventative measure.
  • Gene variations which determine why some people will react positively to omega-3 fatty acids, while others will not.
  • A gene that predisposes certain individuals to deep vein thrombosis.

Genes and athletic performance
Gene testing can also be used to determine how well an athlete will perform in certain sports.

If we keep in mind that genes are responsible for 50% of the variation in physical performance, then it is understandable why countries with intensive sports promotion programmes such as Australia are using gene testing to determine which athletes should do which sport.

Some experts regard the genetic makeup of the individual as even more important as the training. Research indicates that some athletes who participate in weight training will suffer from enlarged heart muscles. It is becoming important to test the genes of individuals who intend doing serious weight training to prevent heart damage.

How to have your genetic makeup tested
The GeneCare Laboratory in Cape Town offers gene-testing services. You can either ask your doctor or dietician to have a sample of your cells tested for a variety of gene-linked diseases and conditions (cancer, heart disease, haemochromatosis, osteoporosis, hypertension), or contact GeneCare at Tel: (021) 480-6503.

- (Dr Ingrid van Heerden, DietDoc)

Any questions? Ask DietDoc


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