Metabolism refers to the amount of energy (calories) your body burns up in a day. The majority (approximately 70 percent) of your daily caloric expenditure goes into your Resting Metabolic Rate (RMR), which is the energy required to keep your body functioning.
Resting Metabolic Rate is how many calories one burns just sitting around, Senay explains. Different people have different Resting Metabolic Rates. There are sex differences and hormonal differences. And the size of the person and the amount of lean muscle, less or more fat also determine the RMR. If you take two people of the same sex, about the same height and weight and lean muscle, their resting metabolic rates are going to be pretty similar, Senay says.
The term high/fast metabolism refers to people who have high RMRs, meaning it takes a lot of food for their bodies to function.
A really accurate metabolic rate is calculated using a large, indirect calorimeter, which is found in labs or hospitals under strictly controlled conditions. Another way to calculate metabolisms is using the widely used Harris-Benedict formula, which calculates metabolism based on age, height, weight, gender and activity level. But it is a far less accurate measurement, especially for very overweight people.
A person only has control over about 20-30 percent of his or her total caloric expenditure. And that relates to a person's activity level.
Here are some of the things that impact your resting metabolic rate.
Weight Training - Lean muscle requires calories just to exist; fat does not. So you if have more lean muscle, your resting metabolic rate will be higher, Senay explains.
"A pound of muscle burns up to nine times the calories of a pound of fat," says Richard Cotton, a spokesperson for the American Council on Exercise. According to a study published in Medicine & Science in Sports & Exercise, when a person lifts weights, the metabolism remains in overdrive for up to two hours after the workout.
Eat Regular Meals/Snacks - By snacks, Senay does not mean potato chips. Chewing and swallowing and absorbing and digesting all require calories. So if you do that up to four times a day, 400 calories a meal, you're going to be burning calories, Senay explains.
For breakfast, try a high-fiber cereal with skim milk. Aim for two 200- to 300-calorie healthy snacks. Eat a well-balanced mix of protein and fiber: the digestive system uses more energy to break down protein and fiber. Examples of fiber-rich foods are: fruit, yogurt, and some cereals.
Avoid Stress - Stress elevates levels of the hormone cortisol, which interferes with your body's production of insulin and makes it more difficult for you to process carbohydrates.
Rest - If you're not resting, your body is not going to do a lot of things efficiently, including burning calories, Senay says. As to the amount of hours of rest, she says it depends on different people, but 7 to 8 hours a night on average is what most people need.
Avoid Certain Diets Avoid starvation diets, Senay says the more you restrict calories, the more your body starts to conserve energy and starts to find ways not to burn so many calories at rest. So starvation dieting is sort of a self-defeating cycle.
Age also has an impact on metabolism. Senay explains metabolism rates decrease when you get older because you're dropping the amount of lean muscle in your body. So if you want to keep that youthful metabolism, use weight training and aerobics to keep those youthful muscles.
Dr. Jeanine Albu Of St. Luke's-Roosevelt Hospital Center says, "For women, there's a big drop with menopause." The sex hormones affect how fat is stored and there is some loss in muscle mass.
Experts agree that as far as weight loss is concerned, trying to manipulate metabolism is not very effective. "The role of metabolism, RMR in particular, has been overrated," says Dr. Steve Smith, an assistant professor of endocrinology at the Pennington Biomedical Research Center Of Louisiana State University. "People are just not expending enough energy."