ALTHOUGH it has been known for over a century that fat is the principal storage form of energy, only in the past two decades have the physiologic mechanisms for its deposition and mobilization been partially clarified. Benedict,¹ in his classic study on Mr. L., a normal man who over 50 years ago fasted experimentally for 30 days, noted that fat provided more than 75 per cent of the calories utilized after the first few days of food deprivation. He also observed a progressive decrease in daily urinary nitrogen excretion that suggested an increasing conservation of body protein. In this review . . .