ieting is the practice of eating food in a regulated fashion to achieve or maintain a controlled weight. In most cases dieting is used in combination with physical exercise to lose weight in those who are overweight or obese. Some athletes, however, follow a diet to gain weight (usually in the form of muscle). Diets can also be used to maintain a stable body weight. Diets to promote weight loss are generally divided into four categories: low-fat, low-carbohydrate, low-calorie, and very low calorie. A meta-analysis of six randomized controlled trials found no difference between the main diet types (low calorie, low carbohydrate, and low fat), with a 2–4 kilogram weight loss in all studies.[1] At two years, all calorie-reduced diet types cause equal weight loss irrespective of the macronutrients emphasized. The first popular diet was “Banting”, named after William Banting. In his 1863 pamphlet, Letter on Corpulence, Addressed to the Public, he outlined the details of a particular low-carbohydrate, low-calorie diet that had led to his own dramatic weight loss. Low-fat diets involve the reduction of the percentage of fat in one’s diet. Calorie consumption is reduced because less fat is consumed. Diets of this type include NCEP Step I and II.
A meta-analysis of 16 trials of 2–12 months’ duration found that low-fat diets (without intentional restriction of caloric intake) resulted in average weight loss of 3.2 kg (7.1 lb) over habitual eating. Low carbohydrate diets such as Atkins and Protein Power are relatively high in protein. Low-carbohydrate diets are sometimes ketogenic (i.e. they restrict carbohydrate intake sufficiently to cause ketosis). Low-calorie diets usually produce an energy deficit of 500–1,000 calories per day, which can result in a 0.5 kilogram (1.1 lb) to 1 kilogram (2.2 lb) weight loss per week. Amongst some of the most commonly used low-calorie diets include DASH diet, Diet to Go, and Weight Watchers. The National Institutes of Health reviewed 34 randomized controlled trials to determine the effectiveness of low-calorie diets. They found that these diets lowered total body mass by 8% in the short term, over 3–12 months. Very low calorie diets provide 200–800 calories per day, maintaining protein intake but limiting calories from both fat and carbohydrates. They subject the body to starvation and produce an average weekly weight loss of 1.5–2.5 kilograms (3.3–5.5 lb). “2-4-6-8”, a popular diet of this variety, follows a four-day cycle in which only 200 calories are consumed the first day, 400 the second day, 600 the third day, 800 the fourth day, and then the cycle repeats.
These diets are not recommended for general use as they are associated with adverse side effects such as loss of lean muscle mass, increased risks of gout, and electrolyte imbalances. People attempting these diets must be monitored closely by a physician to prevent complications. Detox diets claim to eliminate undesirable “toxins” from the human body rather than claiming to cause weight loss. Weight loss typically involves the loss of fat, water and muscle. Overweight people, or people suffering from obesity, typically aim to reduce the percentage of body fat. Additionally, as muscle tissue is denser than fat, fat loss results in increased loss of body volume compared with muscle loss. Reducing even 10% body fat can therefore have a dramatic effect on a person’s body shape. To determine the proportion of weight loss that is due to decreased fat tissue, 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. Those on low-carbohydrate diets, and those doing particularly strenuous exercise, may wish to increase their 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. Excessive protein intake, though not connected to declined kidney functioning in healthy individuals, may be harmful to those with certain kidney diseases. There is no conclusive evidence that moderately high protein diets in healthy individuals are dangerous; it has only been shown that these diets are dangerous in individuals already suffering from kidney and liver problems. The Basal Metabolic Rate, which is the amount of calories the body expends at rest, meaning without performing any physical activity, is influenced by the person’s total weight and total amount of muscle. The more muscle, the more calories a person can burn naturally. When the amount of muscle is increased, then more calories can be ingested without gaining weight. Conversely, if the amount of fat is increased, increasing the number of calories ingested will only add weight. Normally, when people lose weight, they lose a combination of fat and muscle. If the diet plan includes a daily caloric intake greater than the basal metabolic rate (BMR), the person will most likely lose fat. In contrast, if the person follows a diet that includes a lower caloric intake than the BMR, this person will lose fat but also a higher percentage of muscle.[citation needed] Severe diets may make people lose 50% fat and 50% muscle weight thus affecting their metabolism because by losing muscle the BMR is affected. Maintaining muscle mass while losing fat is therefore a key factor to reach both the ideal weight and body composition. To achieve this goal, experts advise not to reduce carbohydrates aggressively. Fat can be lost by reducing the calorie intake by 20% of daily needs for two days.
This reduced calorie intake, even in the presence of 100% carbohydrate consumption, allows for reduction of fat without muscle loss because the glycogen in the muscle is properly replenished. Exercising on days when the highest amount of carbohydrates is consumed, 1.5 to 2 hours after eating, is also helpful to achieve a balanced fat reduction in the absence of muscle loss. Within this window of time, sugar and insulin levels are undergoing a slow decline. When insulin levels start dropping, the pancreas then produces the hormone glucagon while releasing nutrients stored in the fat cells to the blood to be turned into energy. Conversely, if blood sugar levels suffer a high increase, insulin feeds the muscle cells and deposits excess into fat cells. Furthermore, if insulin levels decrease too much, the muscle cells do not receive the appropriate amount of food they require. There should always be a meal left during the day after exercising to allow the muscles to recover from exercise. The energy intake 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, while efficiency of utilization is affected by a variety of factors, including age, gender, body weight, hormone levels, and many more. Chewing, especially in the elderly, has been shown to increase the intake of micronutrients. However, the effect of chewing on the intake of macronutrients, such as sugars, fats, and proteins has not been observed. Food provides nutrients from six broad classes: proteins, fats, carbohydrates, vitamins, dietary minerals, and water. Carbohydrates are metabolized to provide energy. Proteins provide amino acids, which are required for cell construction, especially for the construction of muscle cells. Essential fatty acids are required for brain and cell membrane construction. Vitamins and trace minerals helps to keep good electrolyte balance and are used for metabolic processes. Dietary fiber also affects one’s health, although it’s not digested into the body.
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. Vitamin E supplements have been found in some studies to increase mortality, congenital heart defects in offspring and an increased risk of stroke. Most people can obtain their nutritional needs from their diet. In any event, a multivitamin taken once a day will suffice for the majority of the population. Weight loss diets that manipulate the proportion of macronutrients (low-fat, low-carbohydrate, etc.) have not been shown to be any more effective than diets that maintain a typical mix of foods with smaller portions and perhaps some substitutions (e.g. low-fat milk, or less salad dressing). Extreme diets may, in some cases, lead to malnutrition.
Besides the importance of eating a balanced diet that includes all the necessary nutrients, other factors also contribute to healthy nutrition. As well, drinking sufficient amounts of water can help eliminate toxins and fat.[citation needed] Heavily processed and fried foods as well as sweets, junk foods, and alcohol should also be avoided in a healthy diet. Also a topic of great importance discussed among nutritionists as well as psychologists is the attitude to weight-loss and the consumption of food in general. Voicing ideas such as “it’s just one burger” during and after weight loss regimes is discouraged, and often is said on the part of an insecure individual who has reached the unfortunate conclusion that nothing can be done any longer and that any effort to do so is futile. The advice given is, avoid reaching such a conclusion, as not only does it change one’s perception of the effect of excessive amounts of food on the body, but also encourages a ‘lack-lustre’ lifestyle and approach to life as a whole.
Nutritionists also agree on the importance of avoiding fats, especially saturated fats, to reduce weight and to be healthier. They also agree on the importance of reducing salt intake because commercial foods such as snacks, biscuits, and bread, among others, already contain salt, thus contributing to an excess of salt daily intake. MyPyramid Food Guidance System is the result of extensive research performed by the United States Department of Agriculture to revise the original Food Guide Pyramid. It offers a wide array of personalized options to help individuals make healthy food choices. It also provides advice on physical activity. But how the body eliminates fat? All body processes require energy in order to function properly. When the body is expending more energy than it is consuming (e.g. when exercising), the body’s cells rely on internally stored energy sources, such as complex carbohydrates and fats, for energy.
The first source to which the body turns is glycogen (by glycogenolysis). Glycogen is a complex carbohydrate, 65% of which is stored in skeletal muscles and the remainder, in the liver (totaling about 2,000 kcal in the whole body). It is created from the excess of ingested macronutrients, mainly carbohydrates. When glycogen is nearly depleted, the body begins lipolysis, the mobilization and catabolism of fat stores for energy. In this process, fats, obtained from adipose tissue, or fat cells, are broken down into glycerol and fatty acids, which can be used to generate 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. Many teens are quite aware that they have a weight problem but are unsure how the problem occured or how to reverse it. If you are an overweight teenager you have a big advantage over most overweight adults. You are still young, so your metabolism is higher and you will burn that fat off quicker once you start dieting and exercising. Few teenagers are aware that their daily calorie requirements are so much higher than anyone else. For example, a very active 17 year old boy will on average require 3300 calories a day.
So anyone playing competitive sports, involved in martial arts, athletics or gymnastics will need a lot more calories than active adults or their less active friends. This is 850 calories a day more than 17 year olds that do no exercise. For teenage girls the difference is also significant. Between the ages of 14 and 18 the average sedentary girls and young women (i.e. those that do not exercise) require around 1750 calories a day. However, very active young women need 2400 calories a day, 650 calories a day more. This is one of the reasons why so often we here young women saying “my friend eats all the time and never gains weight“. It is usually because she is much more active and her metabolism is burning 650 calories more every day. Many people are concerned that calorie restrictive diets are unsafe. There are so many horror stories about people starving themselves while trying to lose weight or people becoming anorexic that many people avoid even mentioning the word “diet” to teenagers.
But dieting is essential and the only sure way to lose weight is to reduce calories. As a general rule of thumb you need to have a calorie deficit of 1000 calories per day to lose 2 pounds per week. This means eating 1000 calories less than your daily recommended amount. Reducing calories to around 1250 per day may help you achieve this. However, good nutrition is absolutely essential. For teenagers, whether they are maintaining weight or trying to lose weight, it is very important to have a varied diet that is very nutritious. Ideally staple foods (bread, pasta, rice, potatoes) should be controlled well so that a lot of energy comes from a wide variety of fresh fruits, vegetables and pulses, as well as healthy proteins (fish, poultry, pulses) and healthy fats (oily fish, olive oil, seeds). Here below we report you some real examples of people before and after dieting.
