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Those who can't resist a tempting snack might have previously been labelled weak-willed.

Now, they can blame their genes, as new research has revealed DNA plays a 'significant' role in obesity, the Daily Mail reports.

Genes can explain why some people are more likely to put on extra pounds – and why they might put on weight around their middle, scientists found.

In fact, more than a fifth of the differences between people's weight can be explained by 'obesity genes', they said.

These obesity genes seem to work by changing how the brain regulates appetite and energy use, rather than changing the body's metabolism.

Elizabeth Speliotes, a genetic epidemiologist at the University of Michigan, and senior author of the paper, told The Guardian: 'Looking at obesity, we didn't necessarily expect to see genes that work in the brain.

'In retrospect, it's not that surprising that appetite and feeding pathways have a big role.'

Studying the genes that affect whether people become fat could help explain why some people develop diseases such as diabetes and high cholesterol, she added, and could possibly lead to ways of treating these diseases in future.

Scientists also discovered certain variation in genes which mean some people are more likely to become obese, but are protected against diabetes and heart disease at the same time.

This means it might be possible to be both overweight and healthy.

The researchers analysed samples from more than 300,000 people to study obesity and body fat distribution.

They sifted through the data to find genes that hand an effect on body mass index (BMI).

They identified 97 regions on the genome that influence obesity, triple the number previously known about.

They concluded weight is influenced by a large number of genes each having a small effect.