More than two thirds of the processes that make people gain weight are controlled by their diet, while less than one in five is hereditary, according to research.

Scientists explored how the chemical reactions in a person's gut – mainly caused by what they eat – affect the way fat develops in their body.

They also pinpointed what causes fat to accumulate at the waist, which could help to combat type 2 diabetes.

The risk of developing the condition is known to be higher among people who have more visceral fat – abdominal fat which surrounds the vital organs.

Researchers from King's College London say the findings could lead to personalised treatment for obesity and other chronic diseases, such as smart toilet paper.

They say understanding how different chemical reactions in the gut change the way the body handles fat means people could change their diet or medication to control their body weight.

One researcher said the study is 'exciting work' and 'opens up many ways to use food as medicine.'

More than 600,000 people were admitted to hospital for conditions related to obesity in the UK last year

The study says just 17.9 per cent of gut processes which control fat storage are caused by hereditary factors, suggesting the vast majority of people can control their weight with their diet and lifestyle.

Meanwhile, 67.7 per cent of gut activity is controlled by the 'environment' in the gut – primarily the food and drink people consume.

Changes in this environment lead to changes in the way the body digests and stores fat, the researchers say.

A quarter of the world's population to be obese by 2045

The team's findings come less than a week after experts warned nearly 25 per cent of the world's population will be obese by 2045.

About 32 per cent of people in Britain are already obese, as well as 39 per cent of Americans – the world's expanding waistline has been labelled a crisis.

Scientists behind this study at King's College hope their findings will pave the way for personalised obesity treatments using people's food to improve their health.

'This opens up ways to use food as medicine'

Head of the King's College London's Twin Research Group, Professor Tim Spector said: 'This exciting work in our twins shows the importance to our health and weight of the thousands of chemicals that gut microbes [bacteria] produce in response to food.

'Knowing that they are largely controlled by what we eat rather than our genes is great news, and opens up many ways to use food as medicine.

'In the future these chemicals could even be used in smart toilets or as smart toilet paper.'

How the research was carried out

The study was conducted by analysing the faeces of 500 pairs of twins to look at changes in their gut bacteria based on what they eat.

They analysed the stool samples to find out how changes in gut bacteria affected how the body deals with fat.

The analysis revealed biomarkers – a molecule, gene or characteristic – which caused fat to build up at the waist.

OBESITY: ADULTS WITH A BMI OVER 30 ARE SEEN AS OBESE Obesity is defined as an adult having a BMI of 30 or over. A healthy person's BMI - calculated by dividing weight in kg by height in metres, and the answer by the height again - is between 18.5 and 24.9. Among children, obesity is defined as being in the 95th percentile. Percentiles compare youngsters to others their same age. For example, if a three-month-old is in the 40th percentile for weight, that means that 40 per cent of three-month-olds weigh the same or less than that baby. Around 58 per cent of women and 68 per cent of men in the UK are overweight or obese. The condition costs the NHS around £6.1billion, out of its approximate £124.7 billion budget, every year. This is due to obesity increasing a person's risk of a number of life-threatening conditions. Such conditions include type 2 diabetes, which can cause kidney disease, blindness and even limb amputations. Research suggests that at least one in six hospital beds in the UK are taken up by a diabetes patient. Obesity also raises the risk of heart disease, which kills 315,000 people every year in the UK - making it the number one cause of death. Carrying dangerous amounts of weight has also been linked to 12 different cancers. This includes breast, which affects one in eight women at some point in their lives. Among children, research suggests that 70 per cent of obese youngsters have high blood pressure or raised cholesterol, which puts them at risk of heart disease. Obese children are also significantly more likely to become obese adults. And if children are overweight, their obesity in adulthood is often more severe. As many as one in five children start school in the UK being overweight or obese, which rises to one in three by the time they turn 10. Advertisement

By isolating these characteristics scientists hope they can change what happens in a person's digestive system to reduce fat build up.

Chemicals in the gut revealed that less than a fifth of digestive processes could be attributed to hereditary traits, while over two thirds were caused by a person's diet.

This means that important changes can be made to the way someone's body distributes fat by changing their their diet or using drugs to alter the way their gut works.

The team's findings were published in the journal Nature Genetics.

'Risk of developing fat round the waist can be modified with drugs or diets'

Lead investigator Dr Cristina Menni said: 'This study has really accelerated our understanding of the interplay between what we eat, the way it is processed in the gut and the development of fat in the body, but also immunity and inflammation.

'By analysing the faecal metabolome, we have been able to get a snapshot of both the health of the body and the complex processes taking place in the gut.'

More than 600,000 people were admitted to hospital in the UK last year because of problems linked to obesity.

Being severely overweight increases a person's risk of heart disease, stroke and cancer and the NHS spends billions of pounds every year treating obese people.

Dr Jonas Zierer, first author of the King's College study added: 'This new knowledge means we can alter the gut environment and confront the challenge of obesity from a new angle that is related to modifiable factors such as diet and the microbes in the gut.

'This is exciting, because unlike our genes and our innate risk to develop fat around the belly, the gut microbes can be modified with probiotics, with drugs or with high fibre diets.'