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Weight Loss and Metabolism


Intentional weight loss means the loss of total body mass in an effort to improve health and appearance.

Our body weight depends on the amount of energy we consume with food and the amount of energy we expend in the activities.

Metabolism is blamed when people put on pounds or encounter difficulty when trying to lose weight. But you can learn how to speed up your metabolism.

Metabolism is the complex biochemical process by which your body converts what you eat and drink into energy. During metabolism calories in food are combined with oxygen to release the energy necessary for body functioning, such as breathing, circulating blood, adjusting hormone levels, and growing and repairing cells.

The primary components of energy expenditure include basal metabolic rate (BMR), the thermic effect of food, and physical activity energy. BMR accounts for 60% to 70% of the total energy output, whereas thermic effect of food and physical activity together account for 25-40%.

Basal Metabolic Rate

Our bodies constantly burn calories, even when we’re doing nothing. The number of calories the body uses to carry out its functions while at rest is known as your basal metabolic rate.

Several factors determine the individual basal metabolic rate:

Body composition - amount of lean muscle tissue. Muscle burns more calories than fat does. Muscles are about 3 times more metabolically active than fat. Muscle requires a standard amount of calories each day to keep its maintenance. A higher percentage of lean body weight (muscles) results in a higher metabolism.

Body size. The higher the body weight the greater the caloric expenditure.

Height-weight ratio. The greater your body surface area, the higher your BMR. A tall person expends more calories than a short person of equal weight.

Age. BMR reduces with age. After age 20, it drops about 2% per decade. Aging in particular has a noticeable impact on the metabolism, due to changes in hormone balance.

Growth. Infants and children have higher energy requirements due to the energy demands needed for growth.

Gender. Generally, men have faster metabolisms than women.

Body temperature. For every increase of 0.5 degree C in internal temperature of the body, the BMR increases by about 7%. The chemical reactions in the body actually occur more quickly at higher temperatures.

Environmental temperature. If the environmental temperature is very low or high, the body has to work harder to maintain its normal body temperature. Exposure to cold temperature causes the body to create the extra heat needed to maintain the body's internal temperature. This increases the BMR. Prolonged exposure to heat can also raise BMR.

Hormones. Many hormones influence BMR. The thyroid hormone thyroxine regulates the basal metabolic rate. The adrenal glands, which secrete epinephrine (adrenalin), can significantly alter BMR as well.

Diet. Starvation or dramatic calorie-reduction can significantly reduce BMR by up to 30%. Crash dieting leads to loss of lean muscle tissue, which further contributes to the drop in BMR.

Drugs. Some drugs, such as caffeine or nicotine, can increase the BMR.

Muscle burns calories more efficiently than fat; the more muscle you have in relation to your body fat, the higher your metabolism will be.

High-intensity exercise delivers a bigger, longer increase in resting metabolic rate than low- or moderate-intensity workouts.

Thermic Effect of Food

The thermic effect of food (TEF) is the energy required for the digestion, absorption, transport, metabolism and storage of food. The metabolism goes up after you start eating and peaks two to three hours later. It stays up for about 5 hours to process the nutrients, digest them, metabolise and deliver to the needing tissues.

This may explain why eating smaller, more frequent meals throughout the day helps to maintain a healthy weight.

Fat is very easy to metabolize and it has very little thermic effect of 3%.

Carbohydrates have a thermic effect of about 7%. However, the thermic effect of fibrous vegetables is 20%.

Proteins have the highest thermic effect of about 30%. Lean protein foods such as chicken, turkey, and fish not only do have the highest thermic effect, but also are the most satiating foods.

Hot spicy foods (e.g. chilli, horseradish and mustard) can also have a significant thermic effect.

The thermic effect of food plays only a minor role in your total calorie expenditure, about 10% of your total needs.

Physical Activity

Energy used during physical activity is the only form of energy expenditure that you have any control over. The more sedentary the person is, the lower the effect of physical activity.

Physical activity includes the calories you burn during normal daily activities, such as walking, vacuuming, or washing the car, as well as the calories you burn during exercise such as aerobics, swimming, dancing, or running. The amount of calories people burn in physical activity varies widely.

The amount of energy used during various activities (kJ/kg/h)

energy expenditure

Your total daily energy expenditure is the sum of these three components. If it is less than your energy intake, you will gain weight. If it is more than your energy intake, you will use some body stores of energy and lose weight.



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