Your eating pattern is one of the first things that I ask about when I meet with a new weight loss client. With young people, the week's eating pattern can be completely different from the weekend. They go out clubbing and dancing and come home in the early hours and can become very, very hungry. As a result, they buy a takeaway on the way home, or go the supermarket and load up with pies, cakes, crisps and other calorie-dense foods. In the morning they regret this because they know it is promoting weight gain.

The dynamics of weight gain are quite complex but when we get overhungry, we overeat. This is a primeval response, to protect ourselves from the risk of starvation by building up fat stores to see us through another hard time.

Clubbing involves lack of normal sleep. Research shows that sleep deprivation down-regulates leptin, the hormone which gives you sensations of food satisfaction and up-regulates the appetite-stimulating hormone ghrelin. So sleep deprivation actually makes you feel more hungry. Most young people going out at the weekend have already eaten the contents of the fridge, so there is nothing healthy to eat when they get home, so the takeaway is an obvious choice.

Our normal circadian rhythm - our body clock - is to be awake during the day and asleep at night. The hormone melatonin is produced as light dims in the evening and helps us to sleep. (So if you are a poor sleeper, dim the lights for 2 hours before bed.) We disrupt melatonin production with bright lights and when we take the decision to stay awake through the night. Research has shown that this disruption affects our body at the system, tissue, and cellular levels and in the longer term is associated with diabetes and obesity.