Balancing Energy

You’ve heard the energy balance equation expressed before in practical terms: "Eat less and exercise more, and you will lose weight." But how does this apply in real life? Can you just eat less and lose weight? What if you just increased your physical activity and ate the same amount of food - what would happen? Finding the right balance to the energy equation is a challenge, and what works for one person, may not for another. One thing is clear: if you want to change your body weight, you’ve got make a change in either your intake of food, your output of energy, and according to scientific evidence, doing both works best in the long run.

Weight Change = Total energy intake - Total energy expended

That’s the basic equation, and that is what gets out of balance when weight gain occurs.

Total energy intake is simply the food you eat. Total energy expended includes all the things your body does that require energy. About 60% of the energy your body burns (measured as calories) is for maintaining basic body functions like keeping your body at a constant temperature, internal organ function, keeping your heart beating, and the chemical processes your body performs every day just to stay alive. So, if you need 2,000 calories to maintain your body weight, 1200 of those calories would go to these basic body functions. Then, another 10% of your calorie needs are used just to digest food (thermic effect of food). Adding this up, about 70% of the energy expended by your body is just for staying alive and maintaining your body weight. For the most part, this part of the energy balance equation is outside of your control. That leaves 30% of your calorie needs left for physical activity, or moving your body. This is the part of the energy expended side of the equation that is in your control, the part that you can do something about, the part that is affected by how much and how often you consciously move or don’t your body throughout the day.

By cutting down on your intake of food by 500-750 calories each day, this can reduce your body weight by 1 to 1-1/2 pounds a week by itself. Reducing your food intake any further than that can be very difficult to maintain - too little food, too much hunger and deprivation - that’s very tough to do long enough to have a real effect on your body weight. Besides that, it has been shown that eating a very low calorie diet doesn’t cause any more weight loss than eating a moderately reduce calorie plan over time, so why do that? So, in order to lose weight faster, instead of eating less, you can move your body more. 
An increase of 500 calories expended per day will add another 1 pound of weight loss per week.

Evidence that physical activity really makes a difference can be shown in two ways. Low levels of physical activity are associated with weight gain in both men and women. And, the reverse is true: increased levels of physical activity are associated with lower levels of body fat and lower levels of weight gain over time.

Does exercise by itself work in weight loss?

While increased physical activity increases loss of body fat and helps to maintain healthy body weight by suppressing weight gain, just increasing physical activity by itself, without cutting down on food intake is probably not enough for most people to cause a satisfying weight loss. That’s why doing both works best.