What Is Metabolism?


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Metabolism is the process by which your body converts what you eat and drink into energy. During this complex biochemical process, calories in food and beverages are combined with oxygen to release the energy your body needs to function. Even when you're at rest, your body needs energy for all its "hidden" functions, such as breathing, circulating blood, adjusting hormone levels, and growing and repairing cells.

The number of calories your body uses to carry out these basic functions is known as your basal metabolic rate (BMR) what you might call metabolism. Several factors determine your individual basal metabolic rate:

  • Your body size and composition. The bodies of people who are larger or have more muscle burn up more calories, even at rest.
  • Your sex. Men usually have less body fat and more muscle than do women of the same age and weight, burning more calories.
  • Your age. As you get older, the amount of muscle tends to decrease and fat accounts for more of your weight, slowing down calorie burning.

Energy needs for your body's basic functions stay fairly consistent and aren't easily changed. Your basal metabolic rate accounts for about 60 to 75 percent of the calories you burn every day. In addition to your basal metabolic rate, two other factors determine how many calories your body burns each day:

  • Food processing (thermogenesis). Digesting, absorbing, transporting and storing the food you consume also takes calories. This accounts for about 10 percent of the calories used each day. For the most part, your body's energy requirement to process food stays relatively steady and isn't easily changed.
  • Physical activity. Physical activity and exercise such as playing tennis, walking to the store, chasing after the dog and any other movement account for the rest of the calories your body burns up each day.
  • You can burn more calories with:
    • Regular aerobic exercise. Aerobic exercise includes activities such as walking, bicycling and swimming. As a general goal, include at least 30 minutes of physical activity in your daily routine. If you want to lose weight or meet specific fitness goals, you may need to increase your activity even more. If you can't set aside time for a longer workout, try 10-minute chunks of activity throughout the day. Remember, the more active you are, the greater the benefits.
    • Strength training. Strength training exercises, such as weightlifting, are important because they help counteract muscle loss associated with aging. And since muscle tissue burns more calories than fat tissue does, muscle mass is a key factor in weight loss.
    • Lifestyle activities. Any extra movement helps burn calories. Look for ways to walk and move around a few minutes more each day than the day before. Taking the stairs more often and parking farther away at the store are simple ways to burn more calories. Even activities such as gardening, washing your car and housework burn calories and contribute to weight loss.

English BMR Formula
Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age in years )
Men: BMR = 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height in inches ) - ( 6.8 x age in year )

Metric BMR Formula
Women: BMR = 655 + ( 9.6 x weight in kilos ) + ( 1.8 x height in cm ) - ( 4.7 x age in years )
Men: BMR = 66 + ( 13.7 x weight in kilos ) + ( 5 x height in cm ) - ( 6.8 x age in years )

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