What Determines Our
Body Weight
Energy Intake vs. Energy
Expenditure
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Calories-in vs. Calories-out
As a living, changing thing, our body can
gain or lose weight depending on circumstances. This process of weight gain
or weight loss is determined by the energy-intake / energy expenditure
equation - otherwise known as calories-in, calories-out.
Weight and Energy Intake
Energy in this case is measured in units
called calories. We take in energy by eating or drinking anything that
contains calories. If we eat a bagel containing 200 calories, our energy
intake is 200 calories.
Weight and Energy Expenditure
Energy expenditure is made up of three
things. 1) Our Basal Metabolic Rate (BMR). On average this accounts for
about 60 percent of all energy expenditure, and is the amount of energy or
calories our body consumes on basic body processes alone, without any
additional physical activities. BMR varies according to several factors,
especially the fat-muscle ratio of our body and the amount of exercise we
take, but on average, our basal metabolic rate burns about 11 calories of
energy per pound of body weight (women), or 12.2 calories per pound of body
weight (men). 2) Physical Activity. On average this accounts for about 30
percent of energy expenditure. 3) Dietary Thermogenesis. This is the energy
or calories we burn as we eat and digest food. It accounts for about 10
percent of the total energy we expend.
Weight - The Energy Intake vs.
Energy Expenditure Balance
Like a see-saw, if our energy (calorie)
intake balances our energy (calorie) expenditure, our weight remains stable.
If we take in more energy (calories) than we use up, we gain weight. If we
take in less energy (calories) than we burn, we lose weight. This is the
basic law of weight gain and weight loss.
Weight Gain and Energy Intake/
Expenditure
If, as above, we take in more energy
(calories) than we burn, this surplus energy (calories) is stored as body
fat. Although different foods are metabolised and processed in the body in
different ways, fat cells are the ultimate destination for all nutrients
your body does not need for immediate use.
Weight Loss and Energy Intake/
Expenditure
If, as above, we take in less energy
(calories) than we burn, our body re-converts some of it's stored body fat
back into energy. Over time, this leads to weight loss.
Weight - Hormones, Steroids and
Environment
Obesity expert Jules Hirsch wrote in the
British Medical Journal: "The balance of food intake and energy expenditure
that maintains constant energy storage is determined by the metabolism of
muscle, liver, pancreas and intestine. The balance is regulated by the
adrenal and sex steroids as well as adipose tissue itself, which together
create a complex set of signals [which affect] energy dissipation and food
intake. Hovering over this complex system are potent psychosocial and
behavioral factors."
In other words, even though the relationship between energy intake and
energy expenditure is clearly marked, it is affected by a huge number of
bodily and mental processes.
Energy Intake/ Expenditure - A
Useful Guide to Weight Control
Although there are a number of complex
factors that influence the energy-intake vs. energy-expenditure equation, no
one seriously challenges the basic equation between calories-in and
calories-out. So if you want to lose fat and keep your weight under control,
aim to reduce your calorie-intake below your calorie expenditure. This is
best achieved by a combination of sensible diet and regular exercise.
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