In March 2010 an article titled Cheek swab to choose your diet plan by Jennifer Thomas of HealthDay News made headlines. The article stated that scientists at Stanford University had analysed data obtained from a study conducted in 2007, and found that the genetic profile of the participants indicated which diet would produce the most efficient and highest weight loss.
In the original study, 138 overweight or obese women were assigned for 12 months to either the Atkins diet (zero or very low carbohydrate), the Zone diet (low carbohydrate), the Ornish diet (very low fat) or a balanced slimming diet designed according to the principles of the Food Pyramid developed by the US Department of Agriculture. DNA samples were obtained from cheek swabs of all the participants and analysed to determine the women’s genotypes (Thomas, 2010).
The researchers then assigned the women in the study to a “genotype appropriate” diet tailored to their genetic makeup. The women who used what the researchers termed a “genotype appropriate” diet lost 2-3 times more weight over the period of a year than those who used a “genotype inappropriate” diet. These dramatic results were presented at a Conference on Nutrition, Physical Activity and Metabolism held in San Francisco at the beginning of March this year (Thomas, 2010).
In many ways this announcement was a dream come true for slimmers. The idea of having a genetic test done before embarking on a slimming diet so that one can select the “genotype appropriate” diet for oneself, is highly desirable.
Understandably there are now hundreds, if not thousands, of people all over the world who want their genes tested to pinpoint which diet will work the best for them and provide the best weight loss results. South Africans are no doubt also frantic to have access to such tests.
The questions that spring to mind are “Do we have such tests in SA?” and “Are these tests really so accurate?”
Genetic testing in South Africa
So what is the position in South Africa? According to Dr Maritha Kotze, one of our leading researchers in the field of genetics at the University of Stellenbosch Medical School, gene testing is well developed and available in South Africa.
Dr Kotze points out that even though individuals can take a cheek swab or finger prick sample for genetic testing in the comfort of their own home, it is advisable that a doctor or dietician is involved from the start in ordering the test.
The reasons for using this approach are as follows:
Human genetics and genetic testing are much more complex than the author of the popular article mentioned above, makes them out to be
Hundreds of genetic and environmental factors all interact with each other and will in many cases override the effect of the limited number of genes tested for the research project
Inappropriate testing and oversimplification of the meaning of the results may lead to incorrect, potentially dangerous behaviours and may cause stress when the expected weight loss is not achieved
Interpreting the results of a gene test is complicated and needs specialised knowledge
The most important reason for using trained health professionals for the interpretation of the test results and counselling, is that each person who undergoes a genetic test has the right to a meaningful genetic testing experience, says Kotze.
The one-size-does-not-fit-all nutrigenetic tests can indeed be used to better define individual nutrient requirements, similar to pharmacogenetic tests already used by doctors to help them decide whether a patient with breast cancer for example, will benefit from chemotherapy.
To provide patients with meaningful test results, Dr Kotze in collaboration with the Innovation Centre of the Medical Research Council, has developed the online GknowmixTM genetic knowledge integration system. This independent expert platform is used increasingly by healthcare practitioners to request genetic counselling and testing for their patients. Because the costs of some tests are relatively high, individuals deserve to obtain the maximum benefit from their genetic tests.
Genetic testing and slimming diets
So what about having a gene test done in South Africa to determine which diet an individual should use to lose weight in the most efficient way? The answer to this is that the cheek swab genotype-diet article by Jennifer Thomas (2010) may have raised false hopes in slimmers as the scientific facts were oversimplified.
Dr Kotze mentioned that the genetic community received notification of an article published by Nadja Popovich entitled “Genetically determined dieting? Maybe not yet”, which cautions that although the Stanford study may have improved scientific understanding of why some people react better to one diet than to another, we have as yet not reached the point where a single-focused genetic test of variations in three genes can provide one slimming solution for all.
According to Nanette Steinle, an endocrinologist at the University of Maryland Medical School, it is still “far too early to start offering this type of test to the public". (Popovich, 2010). It is only when a genetic test is performed and contextualised according to the medical history and lifestyle of the individual, that the result could be helpful to pinpoint the most appropriate slimming diet.
The GenePro Test
The Wellness Division of Molecular Diagnostic Services (MDS) in Durban is one of several South African laboratories that offer a variety of genetic tests. Samples are obtained from anywhere in South Africa and are then tested at the SANAS accredited Durban Laboratory.
According to Natalie Williams, a Medical Scientist working at the Wellness Division of MDS laboratory, their GenePro Test is probably the most popular test performed at the laboratory in Durban.
For the GenePro Test a sample obtained from the individual is tested for a panel of genes that are involved not only in the onset of obesity and response to diet, but the test results are presented in such a way that the individual is empowered to minimise the risk of developing heart disease, stroke, type II diabetes, Alzheimer’s disease and other chronic inflammatory medical conditions.
Interactions between the individual’s genetic make-up and known environmental triggers that may lead to biochemical abnormalities assessed as part of the testing process are highlighted in the report provided to the medical professional who referred the patient for testing.
What the test entails is that the patient’s finger is pricked to obtain a drop of blood which is then analysed for 16 DNA mutations in the laboratory, which makes use of the GknowmixTM software program mentioned above for report generation.
Depending on the results, the consultant physician and/or dietician will be able to advise patients which lifestyle changes and type of diet that will most likely improve their health and well-being. Because the expression of many of the genetic mutations are lifestyle and environment driven, it is possible to “switch off” negative mutations by doing simple things like taking an omega-3 supplement or eating green leafy vegetables. In some women the avoidance of hormone replacement therapy may be advisable to reduce the risk of breast cancer due to a genetic predisposition.
According to Natalie Williams, the cost of DNA tests ranges from R1 000 to R4 000*. The cost of the GenePro Test that combines several individual gene tests is R3 950. Therefore it is important that anyone who has such a comprehensive test done should be given guidance and counselling after testing to ensure that they obtain the maximum benefit.
(*Please note that prices quoted in this article are from 2010)
Dr Maritha Kotze has indicated that South Africans who have already had genetic tests done, such as the GenePro Test, in combination with dietary counselling (or will in future have such a test), can contact her if you are prepared to share your experiences and therefore contribute to our knowledge in this field.
Contact Dr Maritha Kotze on (021) 938-9324 or visit the website at www.gknowmix.com for more information.
Your details will be kept strictly confidential, but by joining the study to report on your success or failure with losing weight or lowering cholesterol based on new genetic knowledge, etc, you will be making a valuable contribution to the future of genetic testing in South Africa.
The contact details of the Wellness Division of Molecular Diagnostic Services, one of several laboratories offering genetic testing in SA, are as follows:
Tel: (031) 267-7000, Fax: (031) 267-7005
If you would like to have genetic tests done for anyone of the conditions mentioned in this article, ask your medical doctor, physician or dietician or e-mail firstname.lastname@example.org.
So while we are not yet at the point where you can have a quick genetic test done at your local pharmacy to determine which slimming diet will work best for you, genetic testing for a variety of conditions, including obesity risk management, is well developed and available in South Africa.
(References: Kotze M (2010), Personal communication. Popovich N (2010), Genetically determined dieting? Maybe not yet. 11 March 2010, www.npr.org. Thomas J (2010), Cheek swab to choose your diet plan, 4 March 2010, www.health24.com. Williams N (2010), Genepro Wellness Screen, Personal communication. )
- (March 2010)
Any questions? Ask DietDoc
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.