An old joke from my medical school days asks, “How many psychiatrists does it take to change a light bulb?” Only one, but the light bulb must want to change. How many weight-loss programs does it take before you lose that weight for good? Only one, but… Where does the fat go when you lose weight dieting? Metabolic reactions convert it to energy, water, and carbon dioxide, which weigh less than fat. Most of your energy supply is used to fuel basic life-maintaining physiologic processes at rest, referred to as resting or basal metabolism. Basal metabolic rate (BMR) is expressed as calories per kilogram of body weight per hour. Even at rest, a kilogram of muscle is much more metabolically active than a kilogram of fat tissue. So muscular lean people sitting quietly in a room are burning more calories than are fat people of the same weight sitting in the same room. The major determinants of BMR are age, sex, and the body’s relative proportions of muscle and fat. Heredity plays a lesser role. Energy not used for basal metabolism is either stored as fat or converted by the muscles to physical activity. Most of us use about 70 percent of our energy supply for basal metabolism and 30 percent for physical activity. Those who exercise regularly and vigorously may expend 40–60 percent of their calorie intake doing physical activity. Excess energy not used in resting metabolism or physical activity is stored as fat. If you want to lose excess weight and keep it off, you must learn the following equation:
The energy you eat,
minus the energy you burn in metabolism and activity,
determines your change in body fat.
Or, more succinctly:
Energy Intake minus Energy Expenditure Equals Change in Energy Stores
This is the Energy Balance Equation.
Energy is measured in calories. For example, if you eat 2,000 calories of energy daily, but burn up 2,300 calories daily, you will have a negative energy balance and your fat stores will go down. That is, you lose weight. Now, a pound of body fat contains 3,500 calories, so you have a way to go before you lose a pound on the bathroom scale. Overweight and obesity result from an imbalance between energy intake and expenditure.
It’s just that simple. The degree of this imbalance is quite small. Over the course of a year, you will gain three and a half pounds of fat just by adding a teaspoon of butter to your dinner roll every day, assuming all other variables are unchanged. Simply avoid a 10 minute walk daily for a year and you will gain five and a half pounds. Taking the walk and avoiding the teaspoon of butter sound easy, and they are, but if not done you will gain 35 pounds over the course of five years. While we don’t have much control over our basal metabolic energy requirements (roughly 1,200–1,500 calories daily), many of us are able to adjust food intake and activity levels to strike a happy balance in the energy equation, minimizing unwanted fat. For a lucky few, that desirable balance is automatic and unconscious. The rest of us have to think about it, work at it, make it a priority at times. Right now your balance is tipped in favor of excess energy stores (fat). It will soon be tipped in the other direction. You will convert fat to energy and lose weight in the process. Once you achieve your goal weight, the energy equation must be balanced again. There is no doubt that the energy balance equation applies to you. People who swear they can’t lose weight on extreme low-calorie diets have been locked up (with consent) in university medical center metabolic wards with access to food strictly controlled by staff. On appropriate calorie-restricted diets, everyone loses weight. When an exercise program is added, they lose more weight.
All matters regarding your health require supervision by a personal physician or other appropriate health professional familiar with your current health status. Always consult your personal physician before making any dietary or exercise changes.