Diets and 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 purist 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. There are also special religious diets - observant Jews, for example, must not eat certain foods during Passover when special dietary rules are in effect; and other religious-based dietary restrictions apply throughout the year to Jews, Muslims, and Hindus, among others. Some diets are prescribed for particular medical reasons, such as sodium-free diets, bland diets and soft food diets. Some dieting is actually designed to promote increase of body fat and/or of muscular weight gain.
Types of DietsThere are several kinds of diets:
Weight-loss diets restrict the intake of specific foods, or food in general, or reduce body weight. This is what "fad diets" are marketed for. 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.
William Banting is one of the first people known to have successfully lost weight by dieting, circa 1863, by targeting carbohydrates. The low carbohydrate diet, sometimes marketed today as the Atkins Diet, remains popular today.
Scientific principles of weight loss:
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):
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.
Fat loss versus muscle loss (and the importance of exercise and protein intake)
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 .
Actual energy obtained from food
The efficiency of energy utilization by skeletal muscles is around 20 percent. That is, of the chemical energy used, 20 percent does work and 80 percent creates heat.
How the body gets rid of fat
Psychological aspects of weight-loss dieting:
Consumption of low-energy, fiber-rich foods, such as non-starchy vegetables, is effective in obtaining satiation (the feeling of "fullness"). Exercise is also useful in controlling appetite. (Extreme physical fatigue, such as experienced by soldiers and mountain climbers, can make eating a difficult chore.)
The use of drugs to control appetite is (potentially) dangerous. Stimulants are often taken as a means to ignore (normal, healthy) hunger by people who are not actually overweight.
Habitual or emotional eating is a common problem. Sufferers often turn to self-help books, hypnosis and group therapy. While these sources can sometimes be of assistance, dieters must beware. Some "diet gurus" are charlatans, others are well-meaning but focus on psychology or philosophy at the expense of practical solutions. Diets designed to appeal to people emotionally are often either very difficult to follow (i.e., too strict) or useless (i.e., too lenient).
Weight loss groups:
These organizations' customs and practices differ widely. Some groups are modelled on twelve-step programs, while others are quite informal. Some groups advocate certain prepared foods or special menus, while others train dieters to make healthy choices from restaurant menus and while grocery-shopping and cooking.
Most groups leverage the power of group meetings to provide counseling, emotional support, problem-solving, and useful information.
Popular Weight-Loss diets:
Most popular diets experience short-lived popularity, partly because new diet books are continuously being published.
Judging the effectiveness (and nutritional merit) of popular diets can be especially difficult. Diet proponents often locate medical professionals to back up their work. And some diets are so controversial that they divide the medical community.
Many popular diets advocate the combination a specific technique (such as eliminating a certain food, or eating only certain combinations of foods) with reduced caloric intake, with the goal being to accelerate weight loss. Others ignore traditional science altogether.
Unfortunately, the general public came to believe, partly due to information from low-fat diet proponents, that carbohydrates were "energy food" and that only fat made people fat. This led to excessive consumption of low-fat foods rich in refined carbohydrates (notably corn syrup), which lead some people to gain more weight.
Some low-fat diets were healthier, focusing on consumption of whole grains, vegetables and lean meats. (See Pritikin diet.) But even these diets did not recognize the importance of essential fatty acids.
Atkins (low-carbohydrate diet):
Atkins discourages refined carbohydrate intake and encourages protein intake, especially in the form of meat. The diet encourages the consumption of fruits and non-starchy vegetables for the provision of fiber and nutrients; it takes a somewhat neutral stand on fat intake.
Many people experience rapid initial weight loss on Atkins, some of which is due to depletion of glycogen stores in the liver. (Glycogen in the body is associated with several times its weight in water.)
Low carbohydrate diets have been shown to reduce the fasting levels of triglycerides. Elevated triglycerides are a demonstrated risk factor for heart disease. (Low-fat diets also reduce fasting levels of triglycerides.)
A low-carbohydrate diet may not be suitable as a weight-maintenance diet (long-term). The products of fat metabolism (lipolysis) and protein metabolism (gluconeogenesis) include ketones.
According to the American Dietetic Association, "Vegetarians have been reported to have lower body mass indices than nonvegetarians, as well as lower rates of death from ischemic heart disease; vegetarians also show lower blood cholesterol levels; lower blood pressure; and lower rates of hypertension, type 2 diabetes, and prostate and colon cancer."
Vegans on average weigh 10 percent less than non-vegetarians. And in a year-long study comparing Dean Ornish's vegetarian diet to Weight Watchers, The Zone Diet, and The Atkins Diet, subjects on Dean Ornish's diet achieved the most weight loss (on average).
Very Low Calorie Diet:
There are risks to this diet. A patient who drinks more formula than allowed can get too much iron and selenium. Constipation is a problem: extra water and (fiber) laxatives may be required. Immune response may be compromised.
VLCD should only be used for dieting when a patient's body mass index exceeds 30. The diet requires regular consultation between patient and doctor.
VLCD can be very successful when used over a 6-12 week period. As with all starvation diets, metabolism will fall. A sensible diet-and-exercise plan must follow cessation of VLCD, or weight will be gained back.
Dangers of weight loss dieting
Some drugs enable short-term weight loss, usually with unpleasant and potentially dangerous side effects. The drugs include (physiologically active) herbal products available at health food stores, as well as over-the-counter (OTC) and prescribed medications provided by doctors and pharmacists.
Typically these drugs fall into two classes: diuretics to induce water-weight loss and stimulants (such as ephedrine) to increase heart rate and reduce appetite. Both classes of drugs can cause kidney and liver damage, and stimulants can cause sudden heart attacks and addiction.
The human body responds to starvation by decreasing metabolism. When food is again available, it is stored immediately as fat. This survival mechanism, while a useful response to genuine food scarcity, leaves the yo-yo dieter feeling lethargic and fatigued (and defeated).
Metabolism can be restored to a higher level with exercise and a sensible weight-loss diet. This diet is defined by the minimum safe daily caloric intake of 75 percent of the basal metabolic rate or 4200 kilojoules (1000 Calories), whichever is greater. (Those eating less should do so only under medical supervision. Parents and guardians should consult medical professionals before placing their children on any type of diet.)
Once an ideal weight is attained, a weight-maintenance diet is essential. This requires limiting excess caloric intake and making small changes in caloric intake in response to physical observations (of one's weight and appearance).
Scientific analysis of the dangers of fasting (and discussion of partial fasting with protein supplementation)
The muscle loss is partly due to the fact that the brain cannot rely completely on fat for fuel. The brain usually reserves ketones for lipid synthesis but will use ketones (from fat) for some energy once levels rise during carbohydrate shortages or starvation, but it must get at least 15 percent of its energy from glucose, and it takes a much greater percentage than this early in a fast before the switch to ketones for most energy needs. Glucose can only be synthesized from proteins, glycerol and carbohydrates.
The body stores carbohydrates as fat and as glycogen in the muscles and the liver; glycogen is used to make glucose. Glycogen stores (from carbohydrates) can only last a couple days (during starvation). (In fact, marathon runners experience a shortage of easily-available glycogen after only 2 hours: they speak of "hitting the wall".)
Because fasts, very low calorie diets (VLCD), and low-carbohydrate diets restrict the intake of carbohydrates, glucose must be obtained from protein. If dietary protein is insufficient, internal sources will be obtained: autolysis and muscle wasting occurs. (The conversion of amino acids to glucose is called gluconeogenesis.)
A very low calorie diet that restricts all carbohydrates and non-essential fats, while providing just enough dietary protein to prevent muscle loss, is termed a "protein sparing modified fast" (PSMF).
After experimentation, it was found that a protein intake of 1 to 1.5 grams of protein per kilogram of ideal bodyweight (lean body mass or LBM) prevented the loss of body protein. A somewhat "safer" intake of .8 to 1.2 grams of protein per pound of LBM is often recommended. (More active persons and those taking less protein must compensate by consuming at least some carbohydrates.)
Thus, PSMF allows for rapid fat loss due to the severe caloric deficit that is created when nearly all carbohydrates and fats are removed from the diet. This extreme dieting technique has many potential hazards, such as hormonal changes and rapid metabolic slowdown. PSMF is sometimes used by bodybuilders to "get cut" (lose fat to expose muscle) just before competitions.
Information about specific Diet:
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