You'd think that genetic variation in obesity would influence fat tissue or digestive processes. Not so, say researchers. It influences our behaviour. A genetic study of more than 90,000 people revealed five out of a total of six variants linked to increased BMI affected the brain.

Genetics cannot be the whole story when it comes to weight, BMI and losing weight. If you eat rubbish and don't exercise, you'll get fatter. However skinny your genes.

Genetic traits of body shape and build were used to classify ability to exercise way before genetic testing became possible. In the 1940s psychologist William Sheldon came up with three categories of body build, each with differing physical and metabolic characteristics: endomorphic, mesomorphic and ectomorphic. His theories are considered outdated by scientists today.

Overweight people eat more fatty and sugary foods to compensate for a relative lack of enjoyment, according to a study. People that carry a genetic variant called Taq1A1, associated with having fewer dopamine receptors in the pleasure centres of the brain, have to eat more to trigger the pleasurable response of those with more dopamine receptors.

February 2008: Study claims becoming overweight as a child more likely to be the result of genes than lifestyle.

Genes are only part of the story when it comes to determining how good you are at sport. Training helps build up your endurance and fitness, and some scientists think it may even alter the proportions of fast and slow fibres in your muscles.