Site: http://www.weightlossforgood.co.uk/basal_metabolic_rate.htm

Summary:

Did you know that your basal metabolic rate, or BMR, is the minimum calorific requirement needed to sustain life in a resting individual? So obviously with weight loss and dieting in mind, your Basal Metabolic rate could prove to be a key factor.

Your BMR can also be looked at as being the amount of energy (measured in calories) expended by the body to remain in bed asleep all day! BMR can be responsible for burning up to 70% of the total calories expended, but this figure varies due to different factors (see below).