In order to understand how we lose weight or body fat it is first necessary to understand how the body's energy systems function. Everything we eat is used to produce energy or stored for eventual use. This energy is measured in calories. Calories are nothing more than a unit of heat used to express the energy value of food. The amount of calories we need every day are determined by three things (Wardlaw, GM, 1990) :
For the average person (non-athletic) basal metabolism represents the largest use of calories. Basal metabolism is defined by the minimal energy requirements to sustain the body's functions in the waking state (Wardlaw, GM, 1990).
The second largest expenditure of energy for the average person is that used in activity. The fuel needed for activity can vary greatly depending on how much daily activity is taken by the individual (Wardlaw, GM, 1990). Of course an athlete could easily burn enough calories to make this the largest expense of energy.
The third, and perhaps the most insiginificant expense of energy, is that of the thermic effect of food. The heat generated due to the food we eat can account for about 10% to 15% of our daily energy requirements (Powers, SK & Howley, ET, 1990). The process of digesting, absorbing, and assimilating the various nutrients actually require energy for calories. However, this dietary-induced thermogenesis reaches a maximum within 1 hour after a meal depending on the type of food eaten (Brehm, BA, 1988). It is thought that protein produces the highest effect (15%) when compared to carbohydrates (8%) or fat (2%). Although this thought may have some validity and has certainly been used for dieting, other factors must be considered-including the harmfulstrain on liver and kidney function that can be brought on by excessive protein intake. For a person who exercises with dieting, the thermic effect of food is a very small and perhaps almost insignificant part of the total daily energy expenditure (Katch, FI & McArdel WD, 1993).
Now the calorie concept or energy balance explanation for weight loss and weight gain should be very simple to understand. If you take in more calories or energy than you expend, you will gain weight. If you expend more than you take in, you will lose weight. To maintain your body weight, caloric input and output must be equal or balanced (Powers, SK & Howley, ET, 1990; Wardlaw, GM, 1990; Williams, M, 1992; Katch, FI & McArdel WD, 1993).
How is this explained? Well it is thought by most that human metabolism energy systems are governed by the same laws of physics that rule all energy transformations. The First Law of Thermodynamics. This law says that in any process, the total change in energy of the system, is equal to the heat absorbed by the system minus the work done by the system (Masterson et al.,1981). Because a calorie is a unit of energy, and because the Law of Conservation of Energy states that energy sources can neither be created or destroyed, those calories we eat must be either expended in some way or conserved in the body. To date there has been NO evidence to disprove the caloric theory (Williams, M, 1992).
So what happens when we eat too many calories? It is stored in the adipose and the energy conserved for future use. What happens when we eat too few calories to support our daily needs for basal metabolism, activity, and thermogenesis? We have to get into these adipose stores to maintain energy balance. Regardless, the human body MUST maintain an equal energy balance or homeostasis. However, there are several things that effect homeostasis. This will be discussed in part 2.
As discussed earlier in part 1, the caloric concept is what actually determines whether we lose or gain weight. The body must maintain a balanced energy balance or gains or loses will take place. If calories are restricted through what ever means, the body will do what ever is necessary to reach an equal energy balance or homeostasis. However, as I said, there are certain things that may influence this process.
When calories are restricted, the body must break down other nutrients stored in the body to compensate for the lack of energy. Remember, the body must have an energy balance. Now, the body doesn't just selective burn one nutrient and preserve the others. It burns all. So this means that when energy is not available, the body not only breaks down adipose stores of fat, but it also breaks down stores of protein and stores of carbohydrates (Williams, M, 1992). Obviously, the greater the caloric restriction, the more of these stores must be consumed to reach energy balance.
Of course, we all know that much of the fat we break down comes from adipose stores. Unfortunately, the protein needs come muscle stores. Thus, the body must chemically break down muscle to provide the necessary protein for energy. Carbohydrates are also needed. So the body breaks down muscle glycogen stores for energy needs. Now obviously, the human body can't keep breaking down muscle for ever. So in order to conserve this loss of protein, the body starts an effort to conserve energy. Thus, the basal metabolism is reduced. Now the body needs less energy to function at a wakening state (Neiman, DC, 1990). So as you can see, now the restricted amounts of calories that once were causing us to lose fat are not doing the trick. That is why science has suggested that dieting alone may not be the best method to lose fat stores.
What's even worse is the person what has only restricted the diet and lost some weight returns to normal eating patterns, the fat returns even quicker that before. This is because the basal metabolism is much lower than before and now it takes even less calories that before to meet the three energy needs (Wardlaw, 1993). So the extra calories are once again, stored as fat.
Activity also effects the energy balance. By taking physical activity, the BMR increases, so the daily energy needs increase. Activity also increases the lean muscle mass in the body, which is also responsible for increased energy needs (Oscai et al., 1973; Powers & Howley, 1994). It is widely accepted that a combination of caloric restriction and exercise is perhaps the soundest method of weight loss. Exercise plus diet results in regulation of appetite, less lean body mass loss and a proportional greater fat loss than diet alone (Oscia, et al. 1972). However, it must be remembered that body composition changes must take place slowly in human exercise studies, and the magnitude of the change is small. Wilmore (1983), showed the average decreases in percent body fat to be only 1.6% with fitness programs ranging in duration from 6 to 104 weeks.
While the intensity of the exercise may play an important part in appetite suppression, the primary factor involved in weight lose is the total work accomplished. Thus, low-intense, long duration exercise is as good as high-intensity, short duration exercise in burning calories (Wardlaw, 1993).
Many have tried to influence thermogenesis by manipulating the ratios of food we consume. As reported earlier. This in theory may have some validity, but in reality, the thermic effects of these manipulations are a very small percent of out total daily expenses. So, while this is practice is not out of the question, activity is perhaps the best selection for burning calories.
As reported by Wardlaw (1993), major nutrient manipulations have been used for many years. One method is to reduce the amount of carbohydrates taken in. When carbohydrates are reduced in the diet or almost eliminated, of course weight loss will occur. Why? As I have mentioned before, 1 g of carbohydrates require 2.7 g of water for storage (Williams, 1992). Obviously, when carbohydrates are restricted from the body, not only are large amounts of carbohydrate stores released to meet energy demands, but also even larger amounts of water lost during this process. In addition to the water and carb stores that are lost during this or any other type of diet, lean tissue will also be lost. The caloric value of the lean tissue is only about 1/3 that of any fat lost. I can be assumed that for every three pounds of fat lost, there will also be about 1 pound of lean tissue or muscle lost. Even when carbs are restricted (Barnard et al., 1969).
Low-carbohydrate and low-calorie diets promote ketosis, the production of short-chain fatty acids, which may act to suppress the appetite These diets, as you can see, cause rapid weight loss. Unfortunately, this weight loss is due to carbohydrate depletion and a diuresis associated with the need to excrete the ketones. Low-carbohydrate diets can cause weakness, apathy, fatigue, vomiting, dehydration, and postural hypotension (Itallie, 1979; Vasselli, et al., 1984).
Of course these low-carbohydrate diets are nothing new. They have been in vogue many times before. Some of these diets include:
Wardlaw (1993), reports that while low-calorie intakes may decrease the appetite due to ketosis, the real reason for any fat loses are the restriction of calories. Warldaw also states that 3 to 5 pounds of weight can be lost per week through these type of diets (although men lose at a higher rate than women), however, most of this weight will be due to the decreases in water and carbohydrate stores. Weight regain and long term adaptation to this type of diet seem to be the nagging problem with this type of therapy.
Wardlaw (1993) also reports that low-carbohydrate intakes force the liver to perform gluconeogenesis. This is the process of producing new glucose. Since carbohydrates are the best source for glucose production, protein must be used as the next best source of carbons for gluconeogenesis. Thus, low-carbohydrate diets result in protein tissue loss, as well as urinary loss of essential ions, such as potassium. Since protein tissue is mostly water, the person loses weight very rapidly (Neiman, 1990; Williams, 1990; Wardlaw, 1993,; Powers & Howley 1994). When normal diet is resumed, the protein tissue is rebuilt an the weight is regained. However, it should be remembered that fat is stored much quicker than the protein is rebuilt. So larger fat gains will no doubt accompany.
There is nothing special about low-calorie approaches in the term of weight loss. If the diet is also low in calories, then it is likely to result in weight loss (although the content is questionable). But a low-carbohydrate diet by itself does not result in more fat loses than any other type of diet (Wardlaw, 1993).
In summary, the caloric concept is what actually determines whether we lose or gain weight. The body must maintain a balanced energy balance or gains or loses will take place. While manipulations in caloric intake, activity, and nutrient intakes all effect the energy balance. It has been adequately demonstrated that caloric restriction and increases in activity are the two most important factors for losing that fat. Nutrient manipulations regardless of their significance, will not make any difference if the energy balance is not altered.