Scientists at Cambridge University have shown a genetic variant increases a person's preference for high-fat food.
In the study, 54 volunteers were given unlimited access to chicken korma and Eton mess, a sweet dessert. The volunteers consisted of three categories of bodyweight: lean, obese, and those who were obese due to a variant in the melanocortin-4 receptor gene (MC4R).
MC4R, which codes for a protein found in the brain, is one of a number of genes which have been found to affect propensity for weight gain. One in 1000 people have the MC4R gene variant which makes them more likely to gain weight.
In the first experiment, the volunteers had access to three identical-tasting korma dishes with a fat content of 20 percent, 40 percent, or 60 percent. Although the volunteers all ate a similar amount, those with the MCR4 variant ate significantly more of the high-fat content dish than the lean and obese groups.
In the second experiment, volunteers could sample three identical-tasting Eton mess dishes with a sugar content of eight percent, 26 percent, or 54 percent. Lean and obese people ate the more of the highest sugar dish, while those with the MC4R gene variant ate more of the low sugar Eton mess.
Professor Sadaf Farooqi from the Wellcome Trust–Medical Research Council Institute of Metabolic Science at the University of Cambridge, who led the research team, said: 'Our work shows that even if you tightly control the appearance and taste of food, our brains can detect the nutrient content. Most of the time we eat foods that are both high in fat and high in sugar. By carefully testing these nutrients separately in this study, and by testing a relatively rare group of people with the defective MC4R gene, we were able to show that specific brain pathways can modulate food preference.'
The researchers suggest obese individuals with the MC4R variant could prefer high-fat food without realising it, which would contribute to weight problems.
They believe that these pathways may have evolved to help cope with times of famine.
Professor Farooqi explains: 'When there is not much food around, we need energy that can be stored and accessed when needed: fat delivers twice as many calories per gram as carbohydrates or protein and can be readily stored in our bodies. As such, having a pathway that tells you to eat more fat at the expense of sugar, which we can only store to a limited extent in the body, would be a very useful way of defending against starvation.'
She also emphasises that our genetic make-up does not make it compulsory to follow urges and that eating healthily and exercising are important for maintaining a healthy weight.
The study was published in Nature Communications.