If both your parents are obese you have a 70% chance of obesity too, compared with less than 20% if both parents are lean. But it’s not just your genes that are at fault; family eating habits, activity patterns and attitudes to food also help to dictate your weight. Researchers have found, for example, that girls are 10 times more likely to become overweight if their mothers are obese, while overweight fathers are 6 times more likely to have obese sons.