13 August 2010

Genetic testing and obesity

Thanks to the Human Genome Project we now have a much clearer picture of how our genes impact on body weight.


"Genes load the gun; lifestyle pulls the trigger!"

A statement made by Dr Daniel Meyersfeld of DNAlysis at a recent ADSA Workshop on The Genetics of Obesity and Weight Loss, emphasises the interaction between our genetic makeup and lifestyle factors.

In other words, someone who has a genetic tendency to become overweight will react to negative lifestyle factors, such as a high-fat or high-energy diet and lack of physical activity, by gaining weight.


Thanks to the Human Genome Project, an international collaboration that started in 1990 to identify the approximately 25 000 genes in human DNA at the cost of more than $3 Billion, we now have a much clearer picture of how our genes impact on body weight.

Amazingly it was found that the DNA of any two individuals in the world is 99.9% identical. So your DNA and that of your favourite film star only differ by 0.1%! But it is this very small variation in genetic material that influences how genes function which in turn determines various physiological body processes.

Based on the findings of the Human Genome Project, researchers are now studying these gene variations and how they impact on health and disease. One of the most pressing needs in modern medicine and nutrition is to determine what is causing the present Obesity Epidemic that is swamping the populations of the world, and then to find solutions that will work.

How genes contribute to obesity

Genetic factors can contribute to obesity in 4 different ways:

  • Genetic obesity, where the mutation occurs in a single gene and the person gains weight despite a non-obesogenic environment (an environment that does not encourage obesity). Only 1-5% of individuals who develop overweight or obesity have this type of mutation.
  • Strong disposition - persons who develop overweight in a non-obesogenic environment and obese individuals in an obesogenic environment (i.e. an environment that encourages obesity) 
  • Slight predisposition - persons with normal weight in a non-obesogenic environment and those that become overweight in an obesogenic environment 
  • Genetically resistant - people who maintain their normal weight even when they are exposed to an obesogenic environment.

(Joffe, 2010)

The following genetically influenced factors also determine if someone will gain weight or not:

  • Hunger and appetite
  • Eating behaviour (binge eating, overeating, etc)
  • Taste perceptions
  • Satiety (how full you feel after meals)
  • Spontaneous physical activity, such as fidgeting (fidgety movements can use up a large amount of energy)
  • Metabolic rate (the metabolic rate determines how much energy is used up to keep our bodies going and how efficiently we use up energy)
  • Thermogenesis
  • Motivation to exercise

(Joffe, 2010)

How genes determine our reaction to weight loss attempts

Genes also determine how individuals will react when they attempt to lose weight.

Studies with twins show that the human predisposition to gain or lose body fat is strongly influenced by genetics.

At present most weight loss programmes concentrate on reducing energy intake (low-energy, low-fat diet) and increasing energy expenditure (physical exercise). But unfortunately it is very evident that many people are resistant to weight loss and/or will regain all the weight they lose once they stop dieting and exercising.

One of the purposes of the investigations into the genetic components of obesity, is to determine how responsive each obese individual is to weight loss strategies.

For example, genetic studies have shown that a specific genetic variation impairs insulin sensitivity when the affected person eats a diet that is rich in saturated fats, which leads to additional weight gain and inability to lose weight as long as that person continues to eat a diet loaded with saturated fats.

Another gene mutation is specifically linked to the development of abdominal obesity, very slow weight loss, increased weight gain starting in childhood and greater weight gain during the adult years.

Genetic variations in the so-called $2-adrenoceptor cause high levels of norepinephrine in the blood that are in turn responsible for rebound weight gain after weight loss.

There are many more examples of such gene-diet/exercise interactions, but basically what current research is uncovering is that we can use genetics to determine which type of diet an individual should use to lose weight (low-energy, or low-saturated fat, or low-carbohydrate) and also what type of exercise will have to most positive effect on weight loss. Genetic information also helps to identify which patients will be resistant to weight loss and which ones will be in danger of regaining weight that they have lost.

According to Joffe (2010) "subjects on diets appropriate for their genotype (genetic makeup) achieved statistically significant average weight loss of 6.2% of body weight at one year, compared to individuals not on a diet matched to genotype (i.e. the latter only lost 2.4% of body weight in 24 months)".

Genetic training for health professionals

DNAlysis, the company launched by Yael Joffe and Dr Daniel Meyersfeld, is at present encouraging dietitians and medical doctors to complete courses in the Genetics of Weight Loss offered locally and by the NuGo organisation in the EU. The purpose of such studies is to empower South African health professionals to assist their patients to lose weight by having genetic tests done before a slimming diet and/or exercise regimen is allocated to the individual patient.

If you are interested in learning more about genetics and weight loss and obtaining an International Certificate in this field, contact Yael Joffe at: (021) 439-5813 or or Daniel Meyersfeld at: (011-268-0268) or

The nutrigenomics of weight loss

If you would like to learn more about the use of genetics to determine which diet and exercise schedules are best tailored to your genetic makeup, visit the DNAlysis website.

At present DNAlysis offer two different genetic tests to the public, namely:

The DNA Diet at a cost of R1 150 and DNA Health for R2 350 (the latter analysis is used to pinpoint genetic tendencies for developing heart disease and other diseases of lifestyle). Visit the above mentioned website to read more about such tests or ask your dietician to assist you. It is advisable to arrange these tests through an accredited dietician or a trained medical doctor, who will help you to interpret, understand and apply the results of your genetic tests to achieve improved weight loss and/or health benefits. The DNAlysis team can refer you to dieticians or medical doctors who have completed the genetic training course.

- (Dr IV van Heerden, DietDoc, August 2010)

(Meyersfeld D (2010). Nutritional genomics. Paper presented at the ADSA Workshop on ‘The genetics of obesity and weight loss’. Pretoria, 26 July 2010; Joffe Y (2010). The role of genetics in weight regulation. Paper presented at the ADSA Workshop on ‘The genetics of obesity and weight loss’. Pretoria, 26 July 2010.)

Any questions? Ask DietDoc

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