A figure of about 2000 kcal a day is often quoted as amount of food energy a typical adult human needs to eat to have a healthy life. This corresponds to a 8400 kJ per day, a power consumption of about 100 W. It would be possible to live on less, but it could become difficult to undertake the activities required to ‘survive’.
The rate needed for your body to just continue working is called your Basal Metabolic Rate (BMR)- this is the energy you need to stay warm, keep your bloody pumping, digest food and do all the other things that we don’t need to think about.
BMR differs, depending on a range of things like your age, your height if you’re a boy or girl and how fit you are.
A VERY rough guide is that females need 2000 calories a day and males need 2500 calories a day . This is roughly the same amount of energy as it takes to run 8-10 fluorescent lightbulbs