Why We Gain Weight – Is It Genetics or Lifestyle?

By Jiri Kaloc

The easiest way to give up responsibility for your weight and health is to say that genetics are at fault. But what if it’s true? How much weight gain can be attributed to genetics and how much is down to our lifestyle? Let’s take a look at the science.

How genetics affect weight

The first thing to note is that the strength of the genetic influence on how easily your weight changes varies a lot from person to person. Research suggests that for some people, genes account for just 25% of the predisposition to be overweight, while for others the genetic influence is as high as 70%. Now, before you start thinking that you’re probably in the 70% camp and there’s simply nothing you can do, you should consider epigenetics.

Epigenetics is the king

Epigenetics is the study of how your environment and your habits can affect the way your genes work. It shows that changing your lifestyle can modify even the most unfavourable epigenomic profile. Since you can’t really change your genes, all you’re left with is changing how you live. And research into specific lifestyle interventions is showing that you’re actually in charge of a lot! Here are a few examples that show how powerful the right lifestyle choices can be.

Sleep improvements

A 2015 study looked at women who were put on a low-calorie diet for 2 months. Those who slept fewer than 6 hours daily had the highest body mass index and the highest levels of visfatin, a protein secreted by fat cells, compared with women who were instructed to increase their sleep to more than 6 hours per day. And it seems like good sleep doesn’t only help you prevent weight gain. According to a 2010 study, it can help you lose fat and maintain muscle mass. In this 2-week trial, 10 adults with excess weight followed a low-calorie diet. Those who only slept 5,5 hours per night lost 55% less body fat and 60% more muscle mass than those who slept 8,5 hours per night.

Sleeping woman
A good sleep makes everything else better.

Stress management

High levels of stress hormones in the body can also negatively affect weight according to a 2018 study. They have been shown to increase hunger and your desire for highly palatable, calorie-dense foods. A trial in obese patients from 2014 also suggests that people with obesity have higher levels of stress hormones than those with normal weight. Chronic stress can not only drive but also reinforce excess weight.

Introduction of whole foods

A trial from 2019 tested what happens when you give adults with normal stable weight either a diet of ultra-processed foods or a diet of whole foods for 2 weeks. The ultra-processed-food group ended up gaining 0,3 kg in those two weeks while the whole-food group lost 0,9 kg. Choosing whole or minimally processed foods can be one of the most impactful decisions in weight management.

Another example of this would be a different study from 2019 that included 19.363 participants and found that those who ate the most ultra-processed foods were 32% more likely to be obese than those who ate the least of such foods.

And whole foods can be a powerful tool for weight loss as well. A 2018 study divided 609 adults with excess weight into groups that followed either a low-fat or low-carb diet for 12 months. Both groups were instructed to eat a lot of vegetables, restrict added sugars, trans fats, and refined carbohydrates. This was a push towards whole foods. The results showed that both groups lost similar amounts of weight of 5,4 kg and 5,9 kg. This is yet another reason to focus not on macronutrient ratios but on the quality of your diet.

It’s clear that despite genetics do affect weight there is a lot we can do to influence our weight. In the next article of this series, we will put it all together to give you a set of recommendations for weight management.