Is weight determined by genetics?How much can it influence my weight?

Obesity has reached the scale of a true global pandemic. It affects people all around the globe, regardless of their race, socioeconomic status, gender or nationality and it almost looks as if anyone can get affected. This led many to question whether obesity is actually directly related to our genetic makeup and the studies conducted seem to confirm this hypothesis. So while genetics aren’t the sole contributing factor to obesity, they definitely do play a role in shaping our body throughout the years.

What’s on this page?

Prevalence of obesity in the UK

Ever since the 1960s, the prevalence of obesity in the UK has been on a constant rise. From the negligible 2% in 1960, it has reached a staggering 28% today which means that almost a third of the UK’s population is overweight. However, at the same time, these statistics clearly indicate that genes cannot be the only culprit for this rise. Changes in genetic makeup always take years to manifest and become prominent and 60 years is nowhere near enough time for the change of this.

This clearly shows that there are other contributing factors to the prevalence of obesity including physical inactivity and the increased calorie-count in the modern foods, both of which are trends that are on a steady rise during the same period of time. Then again, not everybody living unhealthy lifestyle will become obese. So, what’s the catch here?

Why are some people more likely to be overweight than others?

If we oversimplify the bio-physics of weight change in humans, we can say that the total weight of an individual is determined by three distinct aspects:

• Number of calories consumed
• Number of calories stored by the body
• Number of calories burnt off as fuel

But, each of these aspects can be influenced by our genes and our environment at the same time, thus leading to a number of possible outcomes.

So, while genes certainly play a part in an individual’s predisposition to developing certain body types by influencing the way their body converts food to energy and distributes and stores fat, environmental factors can play a crucial role in determining the final outcome.

Gene variants associated with obesity

As the science of genetics advances, the experts in the field have more and more success in identifying the specific gene variants that can be attributed to a particular disease with a high degree of certainty. However, most conditions are fairly complex and it is not as easy to identify their genetic causes. The same is true for obesity.

A gene variant is a scientific term used to describe small changes in the structure of DNA, closely linked to single-nucleotide polymorphism. Most commonly, gene variants are directly related with various health conditions or at least predisposition to developing certain conditions.

When it comes to obesity, the scientists have discovered relevant gene variants in chromosomes 16 and 18. The people having these genes do have 20 to 30% chance of becoming obese, although this doesn’t necessarily have to happen. Thus, scientists concluded that in a vast majority of cases, obesity is linked not to one type of gene (a property of the condition usually called monogenic) but is instead influenced by a complex interaction of a number of genes (polygenic) as well as by environmental factors.

The Thrifty Gene hypothesis

The Thrifty Gene hypothesis, as it is often called, claims that our ancestors survived the times of famine by evolving a specialised gene which allowed the body to store fat more effectively, using the stored supplies to fuel the body until food is available again. Survivors of these tough times managed to pass on their ‘thrifty’ gene through the next generations all the way to the present day. Of course, as the need to hunt and gather food disappeared, this specific gene started working in an unexpected way, storing more and more fat despite the lack of need to do so.

How much control our genes have over our weight?

With more than 400 genes playing some part in determining our weight, it might often seem as though our options are fairly limited, but that is not always the case. It is however true that there are many regions of the human genome which have been identified as contributing to body mass index (BMI), mostly through affecting different aspects such as:

• Appetite
• Metabolism
• Satiety
• Body fat distribution
• Psychological reaction to food
• Food cravings
• Sedentary tendency

On top of this, it would seem that there are vast individual differences when it comes to the exact impact of genetic predispositions on the actual weight of an individual, with the exact number fluctuating from 25% to 80%.

Is my weight currently controlled by genes or not?

No, without expensive and rather complicated DNA profiling, the chances are more than slim that you will be able to know if your genes are controlling your weight. However, there are some indicators that it might be the case:

• You have one or more direct relatives that is also overweight
• One or both of your parents are overweight
• Weight loss methods seem to work with lower efficiency for you
• You have been overweight for most of your life

Individuals who are ‘sabotaged’ by their own genetic makeup in their weight loss efforts might have to get medical assistance in successfully losing weight.

However, while it seems easy to simply assume that your genes are responsible for your weight, in reality it is very rare that only one specific gene causes a specific and fixed set of issues. Much more commonly, a combination of multiple genes will interact with lifestyle choices and environmental factors in order to determine your weight.

Genetics and obesity: Future perspectives

As our understanding of the role that genes play in developing obesity increases, so will the therapeutic perspectives of this knowledge. There are some indications that this might lead to the development of more effective therapeutic strategies that can be even personalised to such extent so they target the individual’s specific gene variant that seems to be causing the problem. At least theoretically, this should provide us with the most effective means of reversing or avoiding obesity.