Diet
From Atkinspedia
Dieting is the practice of eating (and drinking) in a regulated fashion to achieve a particular, short or long-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 without 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.
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Types of Diets
There are several kinds of diets:
- Weight-loss diets restrict the intake of specific foods, or food in general, to reduce body weight. What works to reduce body weight for one person will not necessarily work for another, due to metabolic differences and lifestyle factors. Also, it's important to note that short-term dieting does not necessarily 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 crash 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.
History of Targeted Dieting
The practice of dieting in order to lose weight is ancient. Throughout the 17th and 18th centuries, physicians and patients regulated their food carefully, in order to prevent disease. In the 19th century, as the scientific classification of foods took shape, doctors and scientists began experimenting with targeted diets.
William Banting is one of the first people known to have successfully lost weight by developing a targeted diet, circa 1863, by targeting carbohydrates.
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, climbing stairs instead 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.
Actual energy obtained from food
The energy humans get from food is limited by the efficiency of digestion and the efficiency of utilization. The efficiency of digestion is largely dependent on the type of food being eaten. Poorly chewed seeds are poorly digested. Refined sugars and fats are absorbed almost completely. Despite the claims of certain popular diets, chewing and digesting does not use a substantial amount of the energy offered by any food (that anyone would want to eat). Even celery, known for being low in caloric value, contains enough sugars (including sucrose, glucose and galactose) to easily compensate for the cost of (energy invested in) chewing it. (See Food & Nutrition Information Center.}
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.
Proper nutrition
Humans require essential nutrients from 5 broad classes: proteins, fats, carbohydrates, vitamins and minerals. Essential amino acids (protein) are required for cell, especially muscle, construction. Essential fatty acids are required for brain and cell wall construction. Vitamins and minerals are essential for many functions.
Any diet that fails to meet minimum nutritional requirements can threaten general health (and physical fitness in particular). If a person is not well enough to be active, weight loss and good quality of life will be unlikely.
The National Academy of Sciences and the World Health Organization publish guidelines for dietary intakes of all known essential nutrients.
Sometimes dieters will ingest excessive amounts of vitamin and mineral supplements. While this is usually harmless, some nutrients are dangerous. Men (and women who don't menstruate) need to be wary of iron poisoning. Retinol (oil-soluble vitamin A) is toxic in large doses. As a general rule, most people can get the nutrition they need from foods (there are specific exceptions; vegans often need to supplement vitamin B-12). In any event, a multivitamin taken once a day will suffice for the majority of the population.
A sensible weight-loss diet is a normal balanced diet; it just comes with smaller portions and perhaps some substitutions (e.g. low-fat milk, or less salad dressing). Extreme diets may lead to malnutrition, and are less likely to be effective at long-term weight loss in any event.
How the body gets rid of fat
All body processes require energy to run properly. When the body is expending more energy than it is taking in (e.g. when exercising), body cells rely on internally stored energy sources, like complex carbohydrates and fats, for energy. The first source the body turns to is glycogen, which is a complex carbohydrate created by the body. When that source is nearly depleted, the body begins lipolysis, the metabolism of fat for energy. In this process, fats, obtained from fat cells, are broken down into glycerol and fatty acids, which can be used to make energy. The primary by-products of metabolism are carbon dioxide and water; carbon dioxide is expelled through the respiratory system.
Fats are also secreted by the sebaceous glands (in the skin).
Psychological aspects of weight-loss dieting
Diets affect the "energy in" component of the energy balance by limiting or altering the distribution of foods. Techniques that affect the appetite can limit energy intake by affecting the desire to overeat.
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. Even those who are overweight to the point that it will impact their long-term health are unlikely to benefit from complete fasting or radical changes.
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
There exist both profit-oriented and non-profit weight loss organizations who assist people in their weight loss efforts. Examples of the former include Weight Watchers and Jenny Craig; examples of the latter include Overeaters Anonymous, as well as a multitude of non-branded support groups run by local churches, hospitals, and like-minded individuals.
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.
Yo-yo dieting
Yo-yo dieting is defined by alternating periods of feast and famine (that the dieter deliberately undertakes). It is a particularly ineffective method of sustaining weight loss.
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.
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)
While anyone can lose weight by fasting (temporarily stopping one's food intake), it is a dangerous practice. When concentration camp survivors, who involuntarily suffered famine as a result of horrendous living conditions, were examined by doctors, what little weight they had was mostly fat, with practically no muscle.
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 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, commonly called "hitting the wall" or bonking.)
Because fasts, very low calorie diets (VLCD), and low-carbohydrate diets restrict the intake of carbohydrates, glucose must be obtained from protein. In the event 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). This type of diet is possible when dietary protein is sufficient to meet the body's glucose needs via gluconeogenesis conversion, thus sparing muscle protein. 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) per day prevented the loss of body protein. A somewhat "safer" intake of 0.8 to 1.2 grams of protein per pound of LBM per day is often recommended. Thus, a 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. A PSMF is sometimes used by bodybuilders for "cutting" (losing fat to expose muscle) just before competitions.
See also
- Healthy eating
- Appetite suppressant
- Body image
- Body fat percentage
- Overeaters Anonymous
- Underweight
- Vegetarianism
- General Fitness Training
External links
- Directory of diet info
- U.S. government site on dieting
- U.K. government site on dieting
- Michael Ryan - Thermoregulation
- American Heart Association - High-Protein Diets
- Overeaters Anonymous website
- Not-for-profit Organisation fighting the diet mentality
- Some excellent video lectures at the Harvard School of public health
- A PBS Frontline interview with Prof. Walter Willett, Chair of Harvard's nutrition department
- Harvard School of Public Health "Nutrition Source" website
- Registered charity researching dieting
Sources
- Dansinger, M.L., Gleason, J. L., Griffith, J.L., et al., "One Year Effectiveness of the Atkins, Ornish, Weight Watchers, and Zone Diets in Decreasing Body Weight and Heart Disease Risk", Presented at the American Heart Association Scientific Sessions November 12, 2003 in Orlando, Florida.)
- American Dietetic Association. 2003. Position paper on vegetarian diets. J Am Diet Assoc. 103:748-765.
- Davis, B. and Melina, V. 2000. Becoming Vegan. pg. 22.
Categories: Diets | Nutrition | Obesity
