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What’s the link between genetics and weight?

We know all too well that weight loss can be a huge struggle for so many people. A lifetime of going on and off diets, attempting to shift weight and failing to do so can be frustrating and incredibly heart breaking.

While there are a multitude of reasons and arguments about why this is so common in our society, one emerging trend that is offering a glimmer of hope is the new world of nutrigenetics.

We know for sure that your genetics play a huge role in your body composition and your health in general. But can knowing your specific genotype help you to establish an eating pattern that will help you lose weight?

We have put together the latest evidence around how genetics could be influencing weight and weight loss, and if knowing your genotype (an individual’s collection of genes) could in fact help you to lose weight.

Do genetics control your weight?

While it is undeniable that a long-term positive energy balance is what fundamentally contributes to weight gain, our ability to lose weight is also influenced to some extent by our genetic code.

This helps to explain why certain people respond differently to different diets. For example, researchers who have conducted diet studies found that the way people metabolise identical meals is different, even amongst subjects with similar physiques.

How much do genetics influence weight?

In 2003, the human genome (the entirety of our genetic material) was fully sequenced by researchers. The project took 13 years to complete, leading to advances in medicine and inciting further research.

Since then, the science has moved quickly, and multiple genes have been associated with overweight and obesity. So far however, only a handful of these are thought to play a major role in weight, most notably the best studied fat mass and obesity associated FTO gene.

Genome-wide association studies (studies which scan many people’s DNA to look for associations between genetic variations and disease) have suggested that certain single nucleotide polymorphisms (SNPs, which refer to one singular difference in one tiny section of DNA) are now thought to be involved with the pathway to obesity.

However the strength of genetic influence varies for each individual, and having a genotype associated with a greater health risk does not always predict future health.

Does the interaction between genotype and diet affect weight loss?

More recently researchers have started to explore the interaction between genotypes and macronutrients (carbohydrates, proteins and fats) and how this impacts weight loss.

A recent review of the evidence was undertaken by Bayer and others, who found that the results of the studies to date were inconclusive. But this is not to say it doesn’t (or does) have an effect. The authors acknowledge the inability to prove or disprove an effect may be due to the lack of large-scale studies, and inconsistencies in how the studies were conducted.

Future of nutrigenetics – what could it look like?

The dietary advice or personalised nutrition prescribed to you by a qualified health professional is based on your individual goals, health, preferences, tolerances and lifestyle to name a few.

However more recently, personalised nutrition has been increasingly associated with dietary advice based on individual genotypes and genetic variances.

Some of the potential benefits to knowing this type of information are listed below:

  • Improve someone’s clinical outcomes through providing precise treatment.
  • Inform new and innovative approaches to treating diet related chronic diseases.
  • Motivate someone to proactively improve their lifestyle if they are pre-disposed to a particular condition.
  • Help to reduce uncertainty and worry in someone’s life around a genetic health condition of concern.

But can knowing your genotype do more harm than good?

A recent study was performed on two-hundred participants to investigate what the impact of simply telling people they had a specific genotype associated with poorer exercise capacity could have.

The researchers found that after individuals learned they had the risk associated genotype, their physiological ability to run reduced, and total run time and perceived exertion increased when compared to the participants own baseline (performed prior to knowing their genotype).

The twist was that some individuals were deceived into thinking they had the risk genotype and still exhibited the negative outcomes. Even more alarming was that the effect of the perceived risk was often higher than the effect associated with the actual risk genotype itself.

What does this mean for me now, and should I get a genetic test?

There are an increasing number of commercially available, direct to consumer (DTC) genetic tests being marketed in Australia.

The problem with DTC tests is they currently have no robust scientific evidence to support them. They also exhibit varying levels of quality and insight (may just test for one gene or many) which raises another concern, being able to understand what the results mean.

Some tests bypass the need to speak to a medical professional and certain companies have been found to interpret the same results differently.

You also need to consider the protection of privacy around information ownership – who does this information belong to? Results are often held by an overseas based third party, which can then be sold on to other parties under certain policies.

The National Health and Medical Research Council (NHMRC) also note that the results of genetic testing often need to be disclosed when purchasing insurance. So, depending on your results, it may have an impact on obtaining appropriate cover.

In an NHMRC statement to medical professionals and consumers, the council advise that in the absence of robust evidence and clinical validation, consumers should exercise caution prior to undertaking DTC genetic testing.

Take home messages

Weight loss is a very complex process involving many genetic and environmental factors. To illustrate just how complex weight is, scientists have mapped the factors known to contribute to obesity (take a look at https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/296290/obesity-map-full-hi-res.pdf).

Although there is promising potential for a greater insight into nutrition, the science around the interactions between SNPs and food and how this affects body weight is still emerging.

As stated by the Academy of Nutrition and Dietetics, the application of nutritional genomics will require an evidence-based approach to validate personalised dietary recommendations that result in health benefits and do not cause harm. Rest assured, a qualified health professional already takes into consideration your family history and risk factors as part of traditional personalised nutrition advice.

In summary, simply knowing your genotype will not make you lose weight. The current research shows that it is not the treatment (diet) that determines long-term weight loss, but adherence to it (in addition to physical activity and behaviour change).

The best evidence still suggests that we eat a nutritionally balanced diet from a wide variety food that comes mostly from wholegrains, vegetables, fruits, lean meat and alternatives, and some dairy and/or dairy-free alternatives.

If you have weighed up the pros and cons of genetic testing and still wish to go ahead, please talk to your GP about identifying a clinical need. Your doctor can then discuss with you the clinically valid options that have been accredited to Australian medical testing standards.

If you have undertaken a DTC test and are worried about your results, please make an appointment to speak to a health professional (medical practitioner, clinical geneticist or genetic counsellor).

Resources

NHMRC statement to medical professionals and consumers: https://www.nhmrc.gov.au/about-us/publications/direct-consumer-genetic-testing-statement#block-views-block-file-attachments-content-block-1

Position of the Academy of Nutrition and Dietetics: https://pubmed.ncbi.nlm.nih.gov/24439821/

Bayer scientific literature review on genotype-diet interactions and weight loss: https://pubmed.ncbi.nlm.nih.gov/32971836/