A few minutes of relatively strenuous exercise can dramatically change a person’s DNA, experiments have revealed. The changes affect the chemicals which activate, silence and crank up genes and their actions. In the case of muscle, exercise appears to crank up the genes needed to burn fat and sugar and support the body. Just 20 minutes of pedalling flat  out on an exercise bike makes  a difference, the journal Cell Metabolism reports. Researcher Juleen Zierath, of the Karolinska Institute in Stockholm, said: ‘We often say that you are what you eat. Well, muscle adapts to what you do. ‘If you don’t use it, you lose it and this is one of the mechanisms that allows this to happen.’ Professor Zierath and colleagues from Denmark and Dublin began with two experiments in which healthy men who didn’t take exercise regularly were  put through their paces on an exercise bike. After they stopped, slivers of muscle were taken from their thigh and the DNA analysed for chemical changes. This revealed that changes occur after just minutes. However, gentle exercise won’t do. The person needs to be out of breath and, while able to speak, to have difficulty in carrying on a conversation. Further experiments on cells in the test-tube linked the changes to the contraction of muscle. Coffee had a similar effect. But, unfortunately for those who would choose a cappuccino over a trip to the gym, it takes 50 to 100 strong coffees to mimic the effect of exercise on muscles.