29 September 2004

More on gene tests and your diet

Genetic factors influence how we react to various treatments. In this article, DietDoc takes a look at further examples of gene-diet interactions.

Genetic factors influence how we react to various treatments. In this article, DietDoc takes a look at further examples of gene-diet interactions.

Do you have high cholesterol?
You may be an individual who has raised blood cholesterol levels. You have followed a low-fat diet for a while, but your blood cholesterol levels have not responded. So what can your dietician do to help you?

She can send a sample of your cells to the GeneCare laboratory in Cape Town for genetic classification. When the dietician receives the results of this analysis, she will be able to give you much more accurate advice about your diet, or refer you to a medical doctor for medication because you may be a ‘diet non-responder’.

Heart disease is still one of the main causes of death and disability in certain sectors of the South African population. Raised blood cholesterol levels are indicators of an increased risk of heart disease. The logical treatment would, therefore, be to put a patient with high blood cholesterol levels on a low-fat, low-cholesterol diet.

Many patients react well to such diets and their blood cholesterol levels decrease favourably, but there are some patients who can eat a ‘zero cholesterol’ diet and still have high blood levels and still be exposed to the risk of heart disease.

How genes play a role
The reason for this anomaly lies in the patient’s genes. Research in South Africa has shown that certain genes which are common in our white population, make individuals more prone to develop heart disease.

The so-called Apo lipoprotein E4 gene, is associated with greater risk of heart disease in general, greater risk of heart disease in smokers, as well as high blood cholesterol levels if the diet has a high saturated fat content.

The good news is that patients with this type of genetic makeup also respond well to a low-fat, low-cholesterol diet. They respond so well that most of these patients can control their blood cholesterol levels by diet alone without having to use statins and other cholesterol-lowering medications.

Another group of South Africans has the so-called E2 gene, which provides them with genetic protection against high cholesterol. These individuals have much lower blood fat levels and are less prone to develop heart disease.

On the other hand, people with other combinations of this specific gene will not respond to dietary intervention and need to control their blood cholesterol levels by means of medications (e.g. statins).

It is evident that patients with blood cholesterol and heart problems will benefit greatly from having a gene test to determine if they are going to respond to diet, or medication, or a combination of both.

GSTs and cancer
Another fascinating genetic difference in human beings is how effectively a specific group of enzymes called glutathione-S-transferases (GSTs) react.

GSTs are involved in the detoxification of the body. Some people can be exposed to much greater levels of toxins in their diet and environment, and suffer little or no damage to their body or health. Other people will develop diseases such as cancer when they are exposed to relatively low levels of toxins.

Researchers now believe that this difference in human susceptibility to toxins is in part determined by their GSTs, which are in turn determined by the individual’s genetic makeup.

People with a specific gene which influences how effectively the GST enzymes detoxify harmful substances in the body, will have a much lower tendency to develop certain cancers when exposed to toxins such as alcohol and tobacco smoke.

Other people who lack efficient GST enzymes will require dietary interventions to protect them against the dangers of environmental toxins. The latter group has to eat more fruit and vegetables to compensate for their genetic inability to produce efficient GSTs. Such people need to eat plenty of vegetables particularly from the Brassica family (cabbage, cauliflower, Brussels sprouts, broccoli), and the Allium family (onions, shallots, garlic) to obtain the benefits of the antimutagenic (anticancer) compounds found in these vegetables.

It could save your life
Once again, knowledge of your genetic makeup could save your life. If you happen to be genetically prone to low GST levels, then you can prevent cancer by increasing your dietary intake of Brassica and Allium vegetables in particular, and vegetables and fruit in general. In other words, it is nowadays possible to compensate for genetic variations by means of dietary manipulations.

Research studies have also indicated that populations can reduce their risk of developing cancer of the bladder, lung, prostate and breast by increasing dietary intake of Brassica vegetables, reducing their intakes of red meat, especially char-grilled meat, limiting intakes of smoked and cured meat, reducing alcohol intake and avoiding smoking. Scientists now believe that the protective effects of such dietary and lifestyle changes work through the genes. – (Dr Ingrid van Heerden, DietDoc)


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