Is struggling with weight your destiny?
Thursday, November 9, 2017. Author Dr. Haran Sivapalan
Thursday, November 9, 2017. Author Dr. Haran Sivapalan
“I can’t help eating junk food, we’re evolutionarily hardwired to eat high-calorie foodstuffs”
“My parents are overweight, so I’ll be overweight too”
“I’m destined to be fat, it’s in my genes”
Apart from being overly pessimistic, the above statements all have something in common. They are all guilty of the false doctrine of genetic determinism. Sometimes called ‘biological determinism’ or ‘genetic essentialism’, genetic determinism suggests that our physical and behavioural characteristics are fully determined by our genes.
Under this view, we are but the ineluctable product of our genes. If you carry the ‘fat gene’ (the risk ‘A’ allele of the FTO gene), you’re going to be obese. If you’re blessed with the R allele of the ACTN3 gene (the so-called ‘gene for speed’), then you better get warmed up: you’re going to be an Olympic sprinter.
Of course, such conjectures are pure nonsense. Just ask the editor of this blog and our newsletter, our very own Martin Cheifetz. Martin has two copies of the A allele of the FTO gene. Dubbed the ‘obesity gene’, carrying two copies of the A allele is linked to an increased appetite, greater cravings for fatty foods and a 70% increased risk of obesity (compared to carriers of two copies of the T allele). Yet, as I can personally (and perhaps sycophantically) attest, Martin has a healthy BMI and is in prime shape. Clearly then, when it comes to body composition, he has not been fatalistically constrained by his DNA sequence.
The problem with genetic determinism, to quote the late New York sociologist, Dorothy Nelkin, is it ‘reduces the self to a molecular entity, equating human beings, in all their social, historical, and moral complexity, with their genes’. In reality, we are much more than our genes – here’s why:
You’ll probably notice that tall people also tend to have tall parents. As you may have guessed, a person’s height has a strong genetic component. Using studies of twins, scientists can estimate how much of the difference in height between individuals is due to differences in genes. We call this figure heritability. Studies suggest that the heritability of height is, in line with our intuitions, quite high - between 70 and 90%.
So, genes play an important role in influencing height. But, even if you were the lovechild of tennis player Maria Sharapova (6 ft 2 in) and basketball player Yao Ming (7 ft 6 in), you would probably not grow up to be very tall if you were fed a poor diet. Environmental factors (in this case diet and nutrition) also heavily influence physical and behavioural traits/characteristics (in this case, height).
What’s true for height is also true for body weight and composition. Martin, our in-house case study, is a self-confessed ‘exercise junkie.’ His active lifestyle, an environmental factor, has overwhelmed any genetic proclivity towards being overweight or obese.
An ardent genetic determinist may counter here, claiming that Martin’s penchant for exercise was also encoded by his genes. Viewed this way, his healthy bodyweight has still been fully genetically determined.
There’s two replies to this. Firstly, there is no strong evidence to suggest that there are specific genes for preferring exercise over other rewarding activities. Secondly, even if you had genes that make you seek out exercise, your particular environment is still crucial in determining the frequency and types of exercise you can do, or whether you can exercise at all.
Consider the case of PKU (phenylketonuria). This is an inherited disease that causes an inability to metabolise the amino acid phenylalanine (found in most protein-rich foods, including fish, meats, nuts, and eggs). In turn, a build-up of phenylalanine can lead to intellectual disability and other negative health outcomes. PKU is ‘caused’ by inheriting two mutant copies of the PAH gene – there is a strong genetic influence. Yet, as the philosopher Daniel Dennett has pointed out, even if you inherit both mutant copies, you can still avoid any physical health issues if you live in an environment where there is no phenylalanine in your diet.
In short, then, your environment and lifestyle matter. A lot.
Very rarely can a single gene have a massive, and relatively immutable effect on physical traits. For example, inheriting a mutant form of the HTT gene will likely lead to the development of Huntington’s disease, a progressive, neurodegenerative disorder.
By contrast, complex things such as athletic ability, the capacity to build muscle, and tendency towards being overweight are influenced by multiple genes acting in concert with the environment. We say they are complex, polygenic traits.
On this note, your bodyweight is affected by lots of interacting factors, e.g. your metabolism, appetite, circadian rhythm, all of which are influenced by lots of different genes. Given this complexity, one cannot simply look at versions of a single gene (e.g. FTO gene) and proclaim, “Well, I’m destined to be fat.” However, knowing you have “the fat gene” or a predisposition to overeat does help answer questions about your own behaviour and gives you information that helps you make intelligent lifestyle choices.
Smoking causes lung cancer. Say this, and someone, somewhere, will invariably retort, “But my grandad smoked 30 cigarettes a day for years and he didn’t get cancer.” Such grandads do exist (but they are few and far between) – not everyone who smokes will get cancer. Of course, when we say, “smoking causes lung cancer”, we really mean, “smoking significantly increases the risk of developing lung cancer.” Genes work in a similar fashion.
Consider breast cancer. A typical woman has a 12.5% chance of developing breast cancer in their lifetime. For women with mutations of the BRCA1 gene or BRCA2 gene, this risk is much higher (65-85% and 40-85% respectively). Nevertheless, not everyone with BRCA1 or BRCA2 mutations will go on to get cancer, and it’s impossible for us to predict who will. To use genetic lingo, we say that these genes have an incomplete penetrance – not everyone with a particular genetic change will develop the associated physical trait.
Genes which increase the risk of being overweight or obese are also incompletely penetrant. In fact, with the exception of rare obesity syndromes (e.g. Prader Willi syndrome), most obesity-related genes have a low-moderate penetrance – people who carry them do not overwhelmingly become obese. Again, think of Martin with his two A alleles of the FTO gene – having an increased genetic risk of being overweight doesn’t inevitably condemn you to a lifelong battle against the bulge.
Or as our CEO Dr. Dan said in this radio interview discussing the psychological battle of weight loss:
"Two thirds of the Western World are significantly overweight, and when you do a DNA test on the people who are obese and they realize that there may be an underlying reason contributing to their obesity or to their weight management problems, all of a sudden there’s a burden lifted off their shoulders. They lose that discomfort and that bad feeling about being overweight and it prompts them to do something about it.
They understand their weight is not entirely their fault, but they also understand that there is something they can do about it, so from a psychological perspective, a DNA test can have a massive impact on a person who has been struggling and who has never been able to engage in a lifestyle that enables them to lose weight."
Without wanting to get mired in further philosophical discussion about free will, many scientists would agree that we are not merely the puppets of our DNA or our evolutionary hardwiring. If a box of cookies was put in front me, I’d definitely have cravings to devour the whole lot in one sitting. Back in the Pleistocene era (between 2.5 million to 12,000 years ago), a preference for high-calorie foods might have helped my ancestors survive in an environment that was scarce in food. The genes underlying this preference have probably passed down to me. Nevertheless, I possess the will-power and agency to resist any genetically-influenced drive to eat the whole box of cookies. Alternatively, I could choose to hide the cookies, thereby altering my immediate environment to modify the risk of gorging on the whole pack. Please read this great blog from my colleague Geraldine on controlling your cravings.
This is where FitnessGenes excel. By analyzing both your personal genetic make-up and lifestyle, FitnessGenes creates workout routines and nutritional plans (both environmental factors) to ensure you get the optimum fitness benefits.
For example, someone who is at a higher risk of overeating, due to both their genes and lifestyle, might benefit from increasing protein intake at breakfast to promote satiety and help with weight loss.
I hope you enjoyed this article. Please read my other blogs:
Related stories on obesity not mentioned above:
Dennett, D. C. (2004). Freedom evolves. Penguin UK.
Nelkin, D., & Lindee, M. S. (1995). The DNA mystique: the gene as cultural icon. WH Freeman and Co..
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