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There are 3500 calories per pound of body fat. In order to lose just one pound of stored fat we obviously need to burn off 3500 extra calories, sounds simple yet so many dieters claim to cut enough calories but hardly lose any fat.
Calories will never add up easily when losing weight!
If daily calorie intake is cut by more than the body requires it seems logical the fat stores will supply the additional energy requirements, after all fat is stored for later use when needed. However energy metabolism is complex and can be very different between individuals.
Which fuel the body uses depends on many factors; fitness levels, present energy stores, motivation levels, type of exercise chosen, genetic predisposition and nutritional state are just a few.
A calorie reduction will always help burn some fat for energy because that's partly its role. The problem is that fat is not the best source of energy for cells. Muscle cells need a constant supply of oxygen in order to burn fat continuously. At rest enough oxygen can easily be supplied but resting hardly uses any calories at all, we may only burn 50 calories an hour. Remember we need to burn 3500 extra calories per pound so activity is required to increase the total calories burned, now this is where things can get complicated!
Exercising obviously burns many more calories but because many overweight people tend to have lower fitness levels they cannot supply enough oxygen to enable the millions of active cells to continue burning fat for energy. The cells must use another fuel, preferably a quick-burning fuel that requires no oxygen - the role of carbohydrates!
The result is carbohydrates and fats are BOTH used to supply the cells energy with carbs being the predominant fuel. The proportion of carbohydrate to fat used depends on factors associated with each individual and the type or intensity of exercise performed.
The fact that total energy burned is a combination of carbs, fats and even protein helps explain the errors in many calculations of calories, dieters reduce intake in calories without realizing that body fat alone cannot make up ALL the deficit in energy. The main point here is that we need to burn a far greater number of calories to burn off one pound of fat!!
Q. Is this why low carb diets work well, by limiting carbs to cells they use more fat?
A. Well, to a small degree yes!
Low carb diets can help some people lose weight however most of the loss will not be fat especially in the initial stages when weight loss is rapid. Remember I said cells cannot use all fat for energy because they need to be supplied with sufficient oxygen to burn it, also overweight people tend to have lower fitness levels than lean people thus their body cannot always keep up with the necessary oxygen demands when exercising.
Our body has a clever mechanism for energy metabolism, if carbs are limited it simply burns more protein by converting it to carbs in the liver, a process known as Gluconeogenesis. Gluconeogenesis actually goes on all the time but if carbs are restricted the process is accelerated especially during exercise or even light activities. More protein lost from cells results in increased fluid loss from the body!
As we have an abundance of protein in the body simply cutting carbs wont transform the body into a lean fat-free machine!!
Remember the body always burns a combination of fats, carbohydrates and protein and there is more reliance on the latter two fuels when movements demand more effort and oxygen. To burn off enough calories per pound of fat we need to take into account the number of calories that come from carbs and protein, not just fat!
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