How does the body lose weight?

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The body can only lose weight if it is in a negative energy balance. What this means is you must take in less energy (calories, food) than you need on a regular and consistent basis. Your body is constantly burning energy. It requires 100's and 100's of calories a day no matter who you are. The average adult body requires 1800 calories - 2200 calories a day just to break even. We have to eat less than this to lose weight. Consult with a trainer, nutritionist, or your physician to determine your energy needs and then eat less than this and pursue an exercise program that fits into your goal set. Every human being that wants too or needs too can lose weight. It is just a matter of energy management.

Weight loss hinders on the scientific energy balance equation (Law of Thermodynamics): calories consumed versus calories burned in activity. If you have a calorie deficit, you will be losing weight, and you must burn an extra 3500 calories (in excess of what you eat) to lose a pound. Burning an extra 500 calories per day will enable you to lose 1 pound per week.

The body loses weight (bodyfat) by burning more calories than what is consumed or eaten. The human body burns a certain amount of calories in order to perform metabolic processes necessary to sustain life. This is called resting metabolism. An individual may increase their resting metabolism by performing resistance training that increases muscle density. This allows an individual to burn even more calories (including stored bodyfat) at rest. An individual may enhance the weight loss process by continuing a regimen of resistance and cardiovascular training on a routine basis and by eating nutrient dense foods in portions that do not exceed the amount of calories being burned.
Alberta Scruggs
Nutrition & Dietetics

The body loses weight by causing a caloric deficit. This can be done by expending more energy than you ingest (increased physical activity) or eating less energy or kcalories than you need (reduced caloric intake). Kcalories in food are energy. If you require 1,800 kcalories each day to remain at your current weight and you consume 1,800 kcalories every day, your weight will remain stable. If you consume 2,000 kcalories every day, eventually weight gain will occur. If you consume less than 1,500 kcalories everyday eventually, weight loss will occur.

The body loses weight according to the laws of thermodynamics. Weight gain and loss is centered around your energy balance. When your body is in a negative energy balance, this means you are expedning more calories than you are taking in. When this happens, the body must rely on its stores of fat, glycogen and muscle as fuels. The result is a loss of body mass.
Kat Barefield, MS, RD
Nutrition & Dietetics
The body loses weight when fewer calories are taken than the body uses for our metabolism activity and digesting food. This forces the body to tap into its stored energy for fuel, that being adipose tissue, fat, stored carbohydrates called glycogen and protein or lean body mass. Simply put, if food does not supply the calories our body needs we use our stored calories and lose weight.
Our bodies require a certain amount of energy (think of it like fuel for a car). We run on this fuel, and we need to replenish it when it is low. Our hunger is like the gas light on a car, telling you it is time to refuel. However, if you put too much fuel in a car, it will simply spill out of the gas tank. Not so with us. When we eat too much – meaning more than our body needs - we are able to store it. Our bodies have an unlimited potential to store fat. So we can overeat, continuously for a long time, and keep storing more fat. Scientists call this an energy imbalance. Which means we have eaten more than we need. In order to lose this fat, once accumulated, we must eat less than we need. We still need nutrients, because they body can’t survive on stored fat alone. We need to provide slightly less energy than our body needs, so it uses our stored body fat to make up the difference. Over time this “reserve tank” will get smaller and smaller as we achieve a healthier weight. We measure this fuel in calories – whether we are measuring the input side (the foods we eat) or the output side – the energy our body pays out to meet its daily needs. To successfully lose weight, you must pay out more than you put in, or put in less than you put out.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.