Just as we are born with the colour of our eyes, we can be born with
a tendency to put on weight. And just as we do not blame anyone for
the colour of their eyes, we shouldn’t blame people who are
genetically predisposed to gain weight.
Some of the first clues of a link between genes to obesity came in
1952 from a group of researchers from the University of Michigan. They
carried out a study involving 81 pairs of twins from mostly local high
schools. The twins were measured in many ways including foot length,
forearm length and even nose height.
The measurements enabled the researchers to figure out how likely it
was that these different traits had been inherited from their parents
– this is called heritability. Out of all the different traits that
the researchers measured, they found that the traits with the highest
heritability rate were body weight and waist circumference.
Many similar studies have been carried out since, which also compared
twins that have not grown up together. Identical twins were equally
similar in weight, regardless of whether they have been raised
together or raised apart from birth. This shows the power of genes
over environment in determining body weight. Together, these findings
provide indisputable evidence that genetics play a central role in
obesity. Some evidence suggests that the genetic contribution is
between 40 and 70 percent. This means that the genes you inherit from
your parents may increase your risk of developing obesity.
40 - 70 %
Genetics play a central role in obesity, with some evidence
suggesting the genetic contribution to be between 40 to 70 percent.
-Waalen J., The genetics of human obesity
How do genes affect weight?
The research in this field is ongoing. But what we do know, is that
How much food we tend to eat at a sitting
respond to the sensation of fullness
How much enjoyment we
get from certain types of food
How much energy we need to
run our body’s basic functions
How and where excess
calories are stored as fat in our bodies
We now know that these things might have less to do with our
personalities and lifestyle choices and more to do with our genes.
Our environment has changed, but our genes have not
But if that’s the case, why there were very few people with obesity a
hundred years ago? As the geneticist Francis Collins puts it:
“Genetics loads the gun, and environment pulls the trigger”.
Our genes haven’t changed over the last hundred years. In fact, they
have remained largely unchanged over the last 50,000 years. What has
changed is our environment. And just as some of us develop allergies
in certain environments, some of our genes can be activated and
changed by the environment too.
We now live in a different environment, with different types of
stress, food and technology. They interact with our genes in a new
way. Obesity is part of the result.
Genetics make some people more at risk of obesity in today’s environment
Professor Joseph Proietto, a researcher and clinician specialising in
obesity, explains the genetic basis of obesity by asking us to think
about two pots. They have different sizes: one pot holds five litres
while the other pot holds fifty. The pots stand in the rain overnight,
and in the morning both are full of water.
It’s no surprise that the larger pot is holding more water than the
smaller pot. Professor Joseph Proietto explains that this is because
the bigger pot was made to hold more water. “In other words,
you need both your genetic make-up (how the pot was made) and the
environment (the rain) to develop obesity,” he says.
“You need both your genetic make-up and the environment to develop obesity”
-Professor Joseph Proietto, University of Melbourne
Find a weight management strategy that matches you
So, how can we use this information? After all, we can’t change our
genes. But our individual genetic differences can make us more or less
at risk of developing obesity. So, the more we know about our genes,
the more information we have to make informed decisions about weight
management. For example, we can try to minimise our exposure to
environmental factors that increase the risk of developing obesity.
And because of our individual genetic make-up, we may respond
differently to different types of treatment. What works for one
person, might not work for another. That’s why we each need an
individual approach to weight management.
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Proietto J. Body Weight
Regulation. Essential Knowledge to lose weight and keep it off.
Your Body Mass Index (BMI) is a number calculated from your weight and
height. It’s not a precise calculation of percentage of body fat, but it
is an easy way to determine where your weight falls in the range from
healthy to unhealthy.