How can basal metabolic rate affect energy balance?

The basal metabolic rate in humans is elevated during the first 36-60 (perhaps 72 or more) hours of fasting in humans, declining afterwards (substantially, in the case of prolonged fasting). Noradrenaline and growth hormone production are also elevated during early fasting, declining afterwards.

Therefore, not eating for a day or two (or merely skipping breakfast) should make a person more energetic and active. Many, however, report nearly the opposite effect of fasting.

Psychological conditioning may be at play, as well as hormonal imbalances.

There is a common myth that skipping meals (especially breakfast) slows down metabolism (or, the other claim of breakfast "revving up" metabolism). They have no basis in reality whatsoever.