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Dieting
Dieting is the practice of eating (and drinking) in a regulated fashion to achieve a particular, short-term objective. This is distinct from the more basic concept of "diet," which addresses the longer-term and more generic habit of nutritional consumption. For example, a vegan eats a diet completely devoid of animal products, including milk; but while this is a diet, it is not "dieting."
The most common objective of dieting is loss of excess body fat. Some dieting is prescribed to achieve particular medical objectives, such as sodium-free diets, bland diets and soft food diets, while some dieting is actually designed to increase body fat and/or muscle weight gain.
There are several kinds of diets:
Weight-loss diets restrict the intake of specific foods, or food in general, to reduce body weight. Reduction of body weight is the target of most, if not all, "fad diets." There is a (sometimes confusing) multitude of weight loss techniques, many of which are ineffective. What works for one person will not necessarily work for another, due to metabolic differences and lifestyle factors. Also, it's important to note that dieting does not actually lead to weight loss in the long term. Reducing the body's food supply causes it to stockpile excess fat as a starvation response once normal eating is resumed - meaning dieting leads to small short term weight loss, then an increase in weight shortly afterwards.
Many professional athletes impose weight-gain diets on themselves. For example, wrestlers may overeat in order to achieve a higher weight class. American football players may try to "bulk up" through weight-gain diets in order to gain an advantage on the field with a higher mass.
Medical conditions often require the following of special diets. Each of these diets will specifically include or exclude or regulate certain chemicals (and the foods that contain them). For example, a person who has diabetes is often on a diet designed to carefully manage his or her blood sugar level. Epileptics are often put on the Ketogenic Diet. Sufferers of celiac disease must follow a gluten-free diet, the lactose-intolerant are advised to omit milk products, and people with kidney disease must follow a strict low-sodium diet to ease the strain on their kidneys. Treatment of mild hypertension includes adhering to a diet rich in fruits and vegetables and low in fat and sodium. This diet may be tailored to focus on weight loss if that is necessary to control blood pressure.
Scientific principles of weight loss
A successful weight-loss diet requires that energy expenditure exceeds energy intake (from food). In theory, one must burn 3,500 Calories (14,644 kilojoules) more than one consumes to lose one pound (0.45 kilograms) or burn 9000 Calories (37,656 kilojoules) more than one consumes to lose one kilogram. (disputed — see talk page)
Actual numbers are a bit less, since fat tissue is not 1000.000000at, so burning 9000 Calories will make one lose a bit more than 1Kg. But 9000Kcal per Kg is a good rule of thumb.
Thermoregulation
According to the principles of thermoregulation, humans are endotherms. We expend energy to maintain our blood temperature at body temperature, which is about 37 °C (98.6 °F). This is accomplished by metabolism and blood circulation, by shivering to stay warm, and by sweating to stay cool.
In addition to thermoregulation, humans expend energy keeping the vital organs (especially the lungs, heart and brain) functioning. Except when sleeping, our skeletal muscles are working, typically to maintain upright posture. The average work done just to stay alive is the basal metabolic rate, which (for humans) is about 1 watt per kilogram of body mass. Thus, an average man of 75 kilograms who just rests (or only walks a few steps) burns about 75 watts (continuously), or about 6,500 kilojoules (1,500 Calories) per day.
Physical exercise (with an example)
Physical exercise is an important complement to dieting in securing weight loss. Aerobic exercise is also an important part of maintaining normal good health, especially the muscular strength of the heart. To be useful, aerobic exercise requires maintaining a target heart rate of above 50 percent of one's maximum heart rate for 30 minutes, at least 3 times a week. Brisk walking can accomplish this.
The ability of a few hours a week of exercise to contribute to weight loss can be overestimated. To illustrate, consider a 100-kilogram man who wants to lose 10 kilograms and assume that he eats just enough to maintain his weight (at rest), so that weight loss can only come from exercise. Those 10 kilograms converted to work are equivalent to about 350 megajoules. (We use an approximation of the standard 37 kilojoules or 9 Calories per gram of fat.) Now assume that his chosen exercise is stairclimbing and that he is 20 percent efficient at converting chemical energy into mechanical work (this is within measured ranges). To lose the weight, he must ascend 70 kilometers. A man of normal fitness (like him) will be tired after 500 meters of climbing (about 150 flights of stairs), so he needs to exercise every day for 140 days (to reach his target).
The minimum safe dietary energy intake (without medical supervision) is 75 percent of that needed to maintain basal metabolism. For our hypothetical 100-kilogram man, that minimum is about 5,700 kilojoules (1,300 Calories) per day. By combining daily aerobic exercise with a weight-loss diet, he would be able to lose 10 kilograms in half the time (70 days). Of course, the described regime is more rigorous than would be desirable or advisable for many persons. Therefore, under an effective but more manageable weight-loss program, losing 10 kilograms (about 20 pounds) may take as long as 6 months.
There are also some easy ways for people to exercise, such as walking rather than driving, climing stairs istead of taking elevators, doing more housework with fewer power tools, or parking their cars farther and walking to school or the office.
Fat loss versus muscle loss (and the importance of exercise and protein intake)
It is important to understand the difference between weight loss and fat loss. Weight loss typically involves the loss of fat, water and muscle. A dieter can lose weight without losing much fat. Ideally, overweight people should seek to lose fat and preserve muscle, since muscle burns more calories than fat. Generally, the more muscle mass one has, the higher one's metabolism is, resulting in more calories being burned, even at rest. Since muscles are more dense than fat, muscle loss results in little loss of physical bulk compared with fat loss. To determine whether weight loss is due to fat, various methods of measuring body fat percentage have been developed.
Muscle loss during weight loss can be restricted by regularly lifting weights (or doing push-ups and other strength-oriented calisthenics) and by maintaining sufficient protein intake. According to the National Academy of Sciences, the Dietary Reference Intake for protein is "0.8 grams per kilogram of body weight for adults."
Those on low-carbohydrate diets, and those doing particularly strenuous exercise, may wish to increase their protein intake. However, there may be risks involved. According to the American Heart Association, excessive protein intake may cause liver and kidney problems and may be a risk factor for heart disease [1]. There is no conclusive evidence that moderately high protein diets in healthy individuals are dangerous, however. It has only been shown that these diets are dangerous in individuals who already have kidney and liver problems.
Source: Wikipedia |
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