Exercise & Weight Loss
To lose weight you must exercise! The energy cost of
physical activity must exceed the energy supplied by your food intake. Weight
loss is directly equated to physical work, not food deprivation. Weight loss
means fat-burning. Most weight loss dieters experience increased-efficiency as
calories are restricted. In healthy experimental subjects, a daily deficit of
1500 calories produced a maximum weight loss at 24 weeks, when a new equilibrium
was established. No significant weight loss may be seen in a sedentary obese
person until energy intake has dropped below 800 calories per day.
Weight loss is directly equated to physical work; not just food deprivation.
The jogger or swimmer is losing weight. Even the walker is losing weight,
although more slowly.
Hunger must be restored as a normal, welcome feeling. There
is nothing wrong with hunger! In order to establish new healthy eating patterns
it is essential to practice being comfortably hungry for periods as long as 4-6
hours before eating. A normal rhythm might be 4 hours between meals. The less
you move, the longer you have to be hungry; another way of looking at weight
Long sustained exercise burns fat. Short bursts of activity burn sugar
derived from your food, and leave the fat stores intact. The cyclist who trains
2-3 hours a day with sustained exertion becomes the leanest person in town, by
slowly, progressively burning up fat stores.
Human action is an expression of biological energy derived from food.
Food-derived energy allows us to move, to do work by muscle contraction, and to
keep warm. Body heat is generated by the metabolic activity of every cell.
Nutrient molecules supply the fuel for our metabolic processes. Carbohydrates
and fats are the principle sources of energy, although amino acids may be
utilized as energy. The amount of energy in food is expressed as calories. Not
all food calories are metabolically equivalent. The energy requirement of any
individual is determined by physical activity. Our energy balances shift with
variations in food intake and activity level. A healthy, active adult will
usually spend 1000-3500 cal per day of food energy (or approximately 33 cal/Kg).
Daily physical exercise is beneficial and tends to promote normal body
weight, with energy intake matching output. With food restriction, increased
metabolic efficiency allows the body to do better with less. This increased
efficiency, induced by caloric restriction, tends to frustrate people seeking to
lose weight. The basic equation of energy requirement is:
Energy Required = Basal Metabolic Rate + Work Energy + Metabolic Overhead
Body weight remains constant when this equation is balanced. Metabolic
overhead is the amount of energy consumed by digestion and absorption of food,
plus the work done to synthesize the thousands of compounds we need to stay
alive. A basal energy requirement (Basal Metabolic Rate) for a healthy adult
with no other energy expenditure would be in the range of 1000-1500 cal/day.
Excess food energy may be stored as fat at the rate of 7900 cal/Kg of fat.
Food energy is also expressed as heat. As caloric intake increases, heat
production also increases. Heat production accounts for 8-18% of food intake.
There is a relationship between body heat and appetite. An increase in body
temperature depresses feeding behaviors, and visa versa.
This discussion of the role of exercise in weight management is continued in
Eating and Weight Management
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