What is Basal Metabolic Rate?
"Basal metabolic rate (BMR) is the minimal rate of energy expenditure per unit time by endothermic animals at rest."
"Metabolism comprises the processes that the body needs to function. Basal metabolic rate is the amount of energy expressed in calories that a person needs to keep the body functioning at rest."
"The basal metabolic rate accounts for about 60 to 75% of the daily calorie expenditure by individuals."
"BMR generally decreases with age and with the decrease in lean body mass (as may happen with aging). Increasing muscle mass has the effect of increasing BMR."
"Basal metabolism is usually by far the largest component of total caloric expenditure."
"A decrease in food intake will typically lower the metabolic rate as the body tries to conserve energy."
Fasting increases metabolism
"Most people expect that a period of fasting will leave them feeling tired and drained of energy ... the body is still being fueled— it’s just getting energy from burning fat ... it’s also because adrenaline is used to release stored glycogen and to facilitate fat-burning ... studies show that after a four-day fast, resting energy expenditure increased by 12 percent. Rather than slowing the metabolism, fasting revs it up."The Complete Guide to Fasting by Jason Fung and Jimmy Moore, page 49
Calories in, Calories out? Not that simple.
"The first law of Thermodynamics is always true, but completely irrelevant to human health. Yes, if Calories In is more than Calories Out then you will gain fat. But if you eat more Calories, you will burn more calories. If you eat less calories, you will burn less. So there is no overall change in body fatness."
Dr Jason Fung, in The Evidence for Caloric Restriction