Dieting is the practice of eating food in a regulated and supervised fashion to decrease, maintain, or increase body weight, or to prevent and treat diseases, such as diabetes and obesity. A restricted diet is more often pursued by those wanting to lose weight. Continuous dieting is recommended by US guidelines for obese or diabetic individuals to reduce body weight and improve general health. Some people follow a diet to gain weight (usually in the form of muscle). Diets can also be used to maintain a stable body weight and improve health.
Several diets to promote weight loss have been devised: low-fat, low-carbohydrate, low-calorie, very low calorie and more recently flexible dieting. A meta-analysis of six randomized controlled trials found no difference between low-calorie, low-carbohydrate, and low-fat diets, with a 2–4 kilogram weight loss over 12–18 months in all studies. At two years, all calorie-reduced diet types cause equal weight loss irrespective of the macro nutrients emphasized. In general, the most effective diet is any which reduces calorie consumption. Several diets are effective for weight loss of obese individuals with similar results, diet success being most predicted by adherence with little effect of the type or brand of diet. Dieting appears more effective than exercise for weight loss, but combining both provides even greater long-term results.
Short-term dieting result on average in a meaningful long-term weight-loss, although more limited because of gradual 1 to 2 kg/year weight regain. For each individual, the result will be different, with some even regaining more weight than they lost, while a few others achieve a tremendous loss, so that the "average weight loss" of a diet is not indicative of the results other dieters may achieve.
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.
According to Foxcroft, the word diet comes from the Greek diaita, which represents a notion of a whole way healthy lifestyle including both mental and physical health, rather than a narrow weight-loss regimen.
One of the first dietitians was the English doctor George Cheyne. He himself was tremendously overweight and would constantly eat large quantities of rich food and drink. He began a meatless diet, taking only milk and vegetables, and soon regained his health. He began publicly recommending his diet for everyone suffering from obesity. In 1724, he wrote An Essay of Health and Long Life, in which he advises exercise and fresh air and avoiding luxury foods.
The Scottish military surgeon, John Rollo, published Notes of a Diabetic Case in 1797. It described the benefits of a meat diet for those suffering from diabetes, basing this recommendation on Matthew Dobson's discovery of glycosuria in diabetes mellitus. By means of Dobson's testing procedure (for glucose in the urine) Rollo worked out a diet that had success for what is now called type 2 diabetes.
The first popular diet was "Banting", named after the English undertaker William Banting. In 1863, he wrote a booklet called Letter on Corpulence, Addressed to the Public, which contained the particular plan for the diet he had successfully followed. His own diet was four meals per day, consisting of meat, greens, fruits, and dry wine. The emphasis was on avoiding sugar, sweet foods, starch, beer, milk and butter. Banting's pamphlet was popular for years to come, and would be used as a model for modern diets. The pamphlet's popularity was such that the question "Do you bant?" referred to his method, and eventually to dieting in general. His booklet remains in print as of 2007.
The first weight-loss book to promote calorie counting, and the first weight-loss book to become a bestseller, was the 1918 Diet and Health: With Key to the Calories by American physician and columnist Lulu Hunt Peters.
It was estimated that over 1000 weight loss diets have been developed up to 2014.
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-calorie diets usually produce an energy deficit of 500–1,000 calories per day, which can result in a 0.5 to 1 kilogram (1.1 to 2.2 pounds) weight loss per week. One of the most commonly used low-calorie diets is 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. Women doing low-calorie diets should have at least 1,000 calories per day and men should have approximately 1,200 calories per day. These caloric intake values vary depending on additional factors, such as age and weight.
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 loss of 1.5–2.5 kg (3.3–5.5 lb) per week. "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 totally fasting, after which the cycle repeats. These is some evidence that these diets results in considerable weight loss. These diets are not recommended for general use and should be reserved for the management of obesity 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.
Meals timing schedule is known to be an important factor of any diet. Recent evidence suggest that new scheduling strategies, such as intermittent fasting or skipping meals, and strategically placed snacks before meals, may be recommendable to reduce cardiovascular risks as part of a broader lifestyle and dietary change.
Religious prescription may be a factor in motivating people to adopt a specific restrictive diet. For example, the Biblical Book of Daniel (1:2-20, and 10:2-3) refers to a 10- or 21-day avoidance of foods (Daniel Fast) declared unclean by God in the laws of Moses. In modern versions of the Daniel Fast, food choices may be limited to whole grains, fruits, vegetables, pulses, nuts, seeds and oil. The Daniel Fast resembles the vegan diet in that it excludes foods of animal origin. The passages strongly suggest that the Daniel Fast will promote good health and mental performance.
Fasting is practiced in various religions. Examples include Lent in Christianity; Yom Kippur, Tisha B'av, Fast of Esther, Tzom Gedalia, the Seventeenth of Tamuz, and the Tenth of Tevet in Judaism. Muslims refrain from eating during the hours of daytime for one month, Ramadan, every year.
Details of fasting practices differ. Eastern Orthodox Christians fast during specified fasting seasons of the year, which include not only the better-known Great Lent, but also fasts on every Wednesday and Friday (except on special holidays), together with extended fasting periods before Christmas (the Nativity Fast), after Easter (the Apostles Fast) and in early August (the Dormition Fast). Members of The Church of Jesus Christ of Latter-day Saints (Mormons) generally fast for 24 hours on the first Sunday of each month. Like Muslims, they refrain from all drinking and eating unless they are children or are physically unable to fast. Fasting is also a feature of ascetic traditions in religions such as Hinduism and Buddhism. Mahayana traditions that follow the Brahma's Net Sutra may recommend that the laity fast "during the six days of fasting each month and the three months of fasting each year" [Brahma's Net Sutra, minor precept 30]. Members of the Baha'i Faith observe a Nineteen Day Fast from sunrise to sunset during March each year.
Another kind of diet focuses not on the dieter's health effects, but on its environment. The One Blue Dot plan of the BDA offers recommendations towards reducing diets' environmental impacts, by:
Weight loss diets that manipulate the proportion of macronutrients (low-fat, low-carbohydrate, etc.) have been shown to be no 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.
The Dietary Guidelines for Americans is a set of recommendations about a healthy diet written for policy makers, nutrition scientists, and dieticians and other clinicians, produced by the US Department of Agriculture, in concert with the US Department of Health and Human Services and quintannually-revised. The current guidelines are written for the period 2015 - 2020 and were used to produce the MyPlate recommendations on a healthy diet for the general public.
One of the most important things to take into consideration when either trying to lose or put on weight is output versus input. It is important to know the amount of energy your body is using every day, so that your intake fits the needs of one's personal weight goal. Someone wanting to lose weight would want a smaller energy intake than what they put out. There is increasing research-based evidence that low-fat vegetarian diets consistently lead to healthy weight loss and management, a decrease in diabetic symptoms as well as improved cardiac health.
Several diets are effective for weight loss of obese individuals with similar results, diet success being most predicted by adherence with little effect of the type or brand of diet.
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.
Some weight loss groups aim to make money, others work as charities. The former include Weight Watchers and Peertrainer. The latter include Overeaters Anonymous, TOPS Club and groups run by local organizations.
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.
A 2008 study published in the American Journal of Preventive Medicine showed that dieters who kept a daily food diary (or diet journal), lost twice as much weight as those who did not keep a food log, suggesting that if a person records their eating, they are more aware of what they consume and therefore eat fewer calories.
A 2009 review found limited evidence suggesting that encouraging water consumption and substituting energy-free beverages for energy-containing beverages (i.e., reducing caloric intake) may facilitate weight management. A 2009 article found that drinking 500 ml of water prior to meals for a 12-week period resulted in increased long-term weight reduction. (References given in main article.)
Fasting is when there is a long time interval between the meals. In dieting, long term (periodic) fasting is not recommended, instead, having small portions of food after small intervals is encouraged. Lengthy fasting can also be dangerous due to the risk of malnutrition and should be carried out only under medical supervision. During prolonged fasting or very low calorie diets the reduction of blood glucose, the preferred energy source of the brain, causes the body to deplete its glycogen stores. Once glycogen is depleted the body begins to fuel the brain using ketones, while also metabolizing body protein (including but not limited to skeletal muscle) to be used to synthesize sugars for use as energy by the rest of the body. Most experts believe that a prolonged fast can lead to muscle wasting, although some dispute this. The use of short-term fasting, or various forms of intermittent fasting, have been used as a form of dieting to circumvent the issues of long fasting.
The concept of crash dieting is to drastically reduce calories, using a very-low-calorie diet. Crash dieting can highly be dangerous because it can cause various kind of issues for the human body. Crash dieting can produce weight loss but without professional supervision all along, the extreme reduction in calories and potential unbalance in the diet's composition can lead to detrimental effects, including sudden death.
This article needs to be updated. In particular: Outdated information from primary sources and original research, consider improving this section by using newer higher quality sources such as systematic reviews and guidelines. (October 2019)
While there are studies that show the health and medical benefits of weight loss, a study in 2005 of around 3000 Finns over an 18-year period showed that weight loss from dieting can result in increased mortality, while those who maintained their weight fared the best. Similar conclusion is drawn by other studies, and although other studies suggest that intentional weight loss has a small benefit for individuals classified as unhealthy, it is associated with slightly increased mortality for healthy individuals and the slightly overweight but not obese.
Low-carbohydrate and low-fat diets perform similarly in the long term as weight maintenance depends on calorie intake, not macronutrient ration.
"The glycemic index (GI) factor is a ranking of foods based on their overall effect on blood sugar levels. The diet based around this research is called the Low GI diet. Low glycemic index foods, such as lentils, provide a slower, more consistent source of glucose to the bloodstream, thereby stimulating less insulin release than high glycemic index foods, such as white bread."
The glycemic load is "the mathematical product of the glycemic index and the carbohydrate amount".
Diets 2 and 3 lost the most weight and fat mass; however, low density lipoprotein fell in Diet 2 and rose in Diet 3. Thus the authors concluded that the high-carbohydrate, low-glycemic index diet was the most favorable.
A meta-analysis by the Cochrane Collaboration concluded that low glycemic index or low glycemic load diets led to more weight loss and better lipid profiles. However, the Cochrane Collaboration grouped low glycemic index and low glycemic load diets together and did not try to separate the effects of the load versus the index.
The Set-Point Theory, first introduced in 1953, postulated that each body has a preprogrammed fixed weight, with regulatory mechanisms to compensate. This theory was quickly adopted and used to explain failures in developing effective and sustained weight loss procedures. A 2019 systematic review of multiple weight change procedures, including alternate day fasting and time-restricted feeding but also exercise and overeating, found systematic "energetic errors" for all these procedures. This shows that the body cannot precisely compensate for errors in energy/calorie intake, countering the Set-Point Theory and potentially explaining both weight loss and weight gain such as obesity. This review was conducted on short-term studies, therefore such a mechanism cannot be excluded in the long term, as evidence is currently lacking on this timeframe.
The view of weight loss as a health goal is criticized by some who propose to rather seek health benefits, such as cardiovascular biomarkers improvements, without necessarily seeking weight loss. This hypothesis and movement is commonly named Health at Every Size, and it argues that weight loss and dieting do not reliably produce positive health outcomes, and that the benefits of lifestyle interventions are real but independent of weight loss.
There is however a considerate amount of evidence that overweight is associated with increased all-causes mortality, and significant weight loss (>10%) improves or reverses metabolic syndromes and other health outcomes.
It is estimated that about 1 out of 3 Americans is dieting at any given time. 85% of dieters are women. Approximately, sixty billion dollars are spent every year in USA on diet products, including "diet foods," such as light sodas, gym memberships or specific regimes. 80% of dieters start by themselves, whereas 20% see a professional or join a paid program. The typical dieter attempts 4 tries per year.
In sum, there is little support for the notion that diets ["severely restricting one’s calorie intake"] lead to lasting weight loss or health benefits.
'A crash diet is typically a very low-calorie diet, where you eat a very restrictively for a short period of time,' explains Registered Dietician, Helen Bond.
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