It's true -- the more you eat, the more calories you'll burn. That doesn't mean you'll lose weight by piling your plate at mealtime, however. While your body will expend energy digesting the food, the boost won't come close to making up for the increase in caloric consumption, which is why you'll ultimately gain weight by adding more calories to your diet.
In a nutshell, metabolism is the process of converting food into usable energy. Your body needs that energy for vital functions such as breathing and pumping blood, as well as for activities such as typing, walking or playing sports. Your metabolic rate refers to the speed at which you burn calories, which varies from person to person. Factors such as body size, hormone levels and body composition all determine your metabolic rate. On average, however, moderately active men burn 2,400 to 2,800 calories per day, and moderately active women burn 1,800 to 2,200 calories per day.
The Food Factor
The process of breaking down, absorbing and transporting food requires energy. Thus, digestion accounts for some of the calories you expend each day. You burn about 10 calories for every 100 calories you consume, according to the University of Illinois' McKinley Health Center, so it takes 300 calories to digest 3,000 calories' worth of food. While you'll technically have a faster metabolism eating 3,000 calories than 2,000 calories, you'll also have consumed a net of 900 calories at the end of the day.
Calories and Your Weight
Despite the slight metabolism boost, increasing caloric intake will lead to weight gain, not loss, for the average person. You gain weight when you consume more calories than you burn, causing your body to store the excess as body fat. Conversely, you lose weight by eating fewer calories than you burn. Only highly active people will burn 3,000 calories per day; for most, such a diet will lead to a wider waistline.
To boost your metabolism without compromising your weight, turn to muscle-building activities such as lifting weights, practicing yoga or doing push-ups, crunches and squats. Muscle tissue burns more calories per hour than fat, so your metabolism will run faster day and night as you develop this lean mass. You should also perform cardiovascular activities, such as jogging, hiking or swimming, most days of the week for optimal weight management. Although these activities won't necessarily build muscle for a lasting boost, they will increase calorie burning as you perform them.