Do & # 39; bad genes & # 39; you to gain weight?

With obesity on the rise, the food and weight loss industry is increasing, which is currently estimated at US $ 70 billion in the US alone. But most of us are still confused about the factors that lead to weight gain. Three commonly attributed factors are our genes, our microbiome (gut bacteria) and our energy intake (kilojoules). So let's look at the debt of each of them.

It is official: Australia and New Zealand have the fastest growing excess weight on earth

A new worldwide study of international obesity figures has sketched a tasteless picture of Australasia, which is now the fastest growing region in the world. Since 1980, the obesity rates in Australia and New Zealand have risen from 16 percent to as much as 29 percent. In Australia, an estimated 11 million adults are now overweight, along with almost a quarter of our children.

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Genes are involved at species level. But for individuals, genes do not have as much effect as we might think. Let me explain.

In comparison with our cousins ​​of primates, we humans are the "fat monkey". We store more energy supplies in the form of body fat than gorillas, chimpanzees or orangutans. So the idea is that we have evolved to put more fat energy away to supply our larger brains with energy.

For an individual, however, genes can not play such a big role. Approximately 100 genes to date are linked to body weight, but together they account for less than 3% of the variation in body mass index (BMI).

The largest contributing gene, identified from genome-wide association studies, was the very logically named fat mass and the obesity-associated gene (FTO). The BMI-increasing FTO variant is relatively common, present in a maximum of 42% of the population and can add an extra kilogram of body weight.

This FTO gene, however, only explains 0.3% variation in BMI. The better news is that people with this variant can lose weight just as easily by eating less and exercising more.

It is therefore good to remember that genes do not work in isolation, but in cahoots with the food we eat and the physical activity we do.

Bowel bugs

It is a rather strange thought that we share our body with 30 trillion bacteria. That is about one mistake for each of our human cells. Many of these insects live in our guts and their effect on various disorders, including obesity, is intensively studied.

Probiotic supplements contain live bacteria, such as Lactobacillusand prebiotics are a type of fiber that can improve gut health by promoting the growth of more bowel-friendly bacteria varieties.

A summary of 13 studies found that taking probiotic supplements to three months reduced body weight by an average of 0.6 kg. Another recent summary of 18 studies combining data from treatments with prebiotics and / or probiotics came to a similar conclusion. That is, there was only an average decrease of 0.6 kg in body weight.

Another, perhaps less pleasant, way to improve the profile of our intestinal bones is by poop transplants. However, we have to wait for large systematic studies on poop transplants for weight loss before we can say whether they help or not.


We often hear about energy intake, also called calories, but the unit of measurement is the joule, with one calorie of 4.2 kilojoules.

In theory, if you reduce the kilojoule you consume by 10%, you lose 10% of your body weight.

This theory was put to the test and proved to be accurate by a survey of 117 healthy participants over two years.

Conversely, increased energy intake predicted weight gain in 253 participants followed for two years. The energy intake had to be measured carefully and objectively, because self-reporting underestimated the energy intake by 35%.

If a kilojoule is a kilojoule, you should also be able to lose weight in the same way as the kilojoule comes from fat or carbohydrates, as long as there are fewer kilojoules in total. And that is virtually everything that was found in a summary of 32 controlled feeding studies, in which different ratios of fat to carbohydrate were compared, but had the same reduced energy intake.

Our genes and intestines can therefore influence the weight gain, but the effects are relatively modest. Kilojoules, on the other hand, keep the master key in the regulation of body weight. Weight gain occurs when more kilojoules are consumed as food than are used as fuel.

The conversation

Andrew Brown, professor, school for biotechnology and biomolecular sciences, UNSW

This article has been republished in The Conversation under a Creative Commons license.

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