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Intermittent Fasting
Intermittent fasting (IF), intermittent energy restriction (IER) or intermittent calorie restriction, is an umbrella term for various diets that cycle between a period of fasting and non-fasting during a defined period. Intermittent fasting may produce weight loss comparable to long-term calorie restriction. Benefits with regard to brain function and cancer treatment have also been observed by researchers. Scientists recognize that more research needs to be done in order to determine the long-term health effects of intermittent fasting in different population groups.

Practice and Variants
Intermittent fasting can be a viable strategy to reduce caloric intake, body weight, body fat mass, and improve insulin sensitivity. Intermittent fasting protocols can be grouped into two categories: whole-day fasting and time-restricted feeding.


 * Whole-day fasting involves regular one-day fasts. The strictest form would be alternate day fasting (ADF). This involves a 24-hour fast followed by a 24-hour non-fasting period. The alternate day modified fasting (ADMF) and 5:2 diets—the latter defined as five days per week not fasting and two days per week either total fasting or modified fasting—both allow the consumption of approximately 500–600 calories on fasting days.
 * Time-restricted feeding (TRF) involves eating only during a certain number of hours each day. A common form of TRF involves fasting for 16 hours each day and only eating during the remaining 8 hours, typically on the same schedule each day. A more liberal practice would be 12 hours of fasting and a 12 hour eating window, or a stricter form would be to eat one meal per day, which would involve around 23 hours of fasting per day.

Recommendations vary on what can be consumed during the fasting periods. Some would say only water, others would allow tea or coffee (without milk or sugar) or zero-calorie drinks with artificial sweeteners. Fasting may increase a risk of dehydration. Variants include modified fasting, such as ADMF, with limited caloric intake (20% of normal) during fasting periods rather than none at all, in order to improve tolerance and mood. Intermittent fasting has a different duration (up to 48 hours) than periodic fasting (two or more days).

Scientists advocate for more research to be done about the specific benefits of the variants of intermittent fasting.

Religious Fasting
Forms of intermittent fasting for religious reasons have been practiced for centuries in various groups across the world. Religious fasting regiments include, but are not limited to, Ramadan fasting (Islam), Yom Kippur fasting (Judaism), Orthodox Christian fasting, and Buddhist fasting. Certain religious fasting practices, like Buddhist fasting, only require abstinence from certain foods, while others, like the Jewish fast on Yom Kippur, last for a short period of time and would cause negligible effects on the body. Islam is the only major religion that engages in a fasting practice reflective of intermittent fasting in terms of both food consumption and diet consistency. The duration of the Ramadan fast is between 28 and 30 days depending on the year and consists of not eating or drinking from sunrise until sunset. During the holiday, Muslims eat twice per day: once in the morning before dawn and once in the evening after dusk. A meta-analysis on the health of Muslims during Ramadan shows significant weight loss during the fasting period of up to 1.51 kilograms, but this weight was regained within about two weeks of Ramadan ending. The analysis concluded that "Ramadan provides an opportunity to lose weight, but structured and consistent lifestyle modifications are necessary to achieve lasting weight loss." In addition to weight loss, studies have also found that Ramadan fasting, like non-religious intermittent fasting, reduces oxidative stress and inflammation. Negative effects of Ramadan fasting include increased risk of hypoglycemia in diabetics as well as inadequate levels of certain nutrients.

Fasting Trends
In a secular context, intermittent fasting (specifically the 5:2 diet) became popular in the UK in 2012 after the BBC2 television Horizon documentary Eat, Fast and Live Longer. Via sales of best-selling books, it became widely practiced. In the United States, intermittent fasting has become a trend among Silicon Valley entrepreneurs. In the UK, the tabloid press reported on research claiming the 5:2 diet could reduce the risk of breast cancer, improve brain and immune functions, or extend lifespan, but there is inadequate evidence for such statements. Following the popularity boom of IF diets, the United Kingdom's National Health Service spoke out about the lack of research regarding the benefits of intermittent fasting. A news item in the Canadian Medical Association Journal expressed concern that promotional material for the diet showed people eating high-calorie food such as hamburgers and chips, and that this could encourage binge eating since the implication was that "if you fast two days a week, you can devour as much junk as your gullet can swallow during the remaining five days."

Commercialization and Technology
The popularity of intermittent fasting has caused various technology companies to arise aimed to help those on IF diets. Platejoy, Hvmn, and other Silicon Valley-based start-ups offer a range of products and services, such as diet coaching apps, IF-specific nutritional supplements, and full meal packages. These companies have been criticized for offering products or services that are too expensive and not backed by robust enough science.

Weight Loss
A 2018 review of intermittent fasting in obese people showed that reducing calorie intake one to six days per week over at least 12 weeks was effective for reducing body weight on an average of 7 kg. Intermittent fasting was equally effective as continuous fasting over short periods for obese people to lose weight. A 2014 review described that intermittent fasting has not been studied in children, the elderly, or the underweight, and could be harmful in these populations.

In other preliminary research, alternate day fasting was effective for weight loss on a scale similar to calorie restriction. Weight loss was observed in both obese and normal weight people. Preliminary evidence indicates that improvements in several cardiovascular and metabolic biomarkers (such as body fat, LDL cholesterol, triglycerides, insulin sensitivity, blood pressure) occurred. Alternate day fasting did not affect lean body mass.

Effects on Aging
Various laboratory studies on rodents and monkeys and evolutionary evidence from humans have shown that intermittent fasting can sustain brain function and lessen age-related cognitive degeneration. Additionally, researchers have observed improved lifespans in laboratory animals; scientists attribute these positive effects to lower oxidative stress, resulting in less damage to cells. Stress resistance has also been cited by researchers as a reason why intermittent fasting improves lifespan. When an organism is subjected to a period of time without adequate food, a mild stress response is triggered and over time, a resistance is built up to this stress, eventually reducing the amount of stress-induced damage on cells. This mild stress response triggers the production of neurotrophic factors (e.g. BDNF, GDNF) which increase the development and growth of brain tissue, especially in the hippocampus. Humans begin to experience the neuroprotective effects of intermittent fasting after not eating for 10-16 hours. At this point, the body runs out of glucose reserves and starts using fat reserves, called ketones, for energy. Once in the bloodstream, ketones have "been shown to protect memory and learning functionality... as well as slow disease processes in the brain" according to a review article in the Canadian Medical Association Journal. In addition to aging, stress resistance from intermittent fasting is also a factor in reducing cancer rates.

There has also been research done to show a correlation between the effects of inflammatory processes and age-related cognitive degeneration in the development of diseases like Alzheimers. Intermittent fasting changes production levels of cytokines that cause inflammation and laboratory studies demonstrate that these changes can positively impact cognitive aging.

Cancer
Intermittent fasting has been observed by scientists to aid in the treatment of cancer, both in a lab with mice and in human trials. In trials with rodents, intermittent fasting had a similar effect to chemotherapy in terms of slowing tumor growth for certain cancers and the pairing of chemotherapy with intermittent fasting augmented these results. Positive effects of this combination include lower levels of side effects from chemotherapy as well as a reduction in the recurrence rate of the cancer. However, the anticancer effects of intermittent fasting only occur when there is a net reduction in energy consumption as compared to normal eating; if the calories lost from a fast were compensated for at another time, no positive effects resulted, a review article noted.

In small observational and randomized control studies, intermittent fasting improves reactions to chemotherapy in humans as well, specifically women with breast cancer. A 2016 study observed that the combination of intermittent fasting with chemotherapy reduced damage to DNA after treatment. Another 2016 study demonstrated that rates of relapse for breast cancer decreased when patients practiced intermittent fasting. Scientists caution that research about the role of intermittent fasting in cancer treatment is currently limited and more work needs to be done before intermittent fasting is confirmed as a viable approach to helping treat cancer.

Other Effects
Intermittent fasting may reduce rapid eye movement sleep, but other effects on brain function remain undetermined.

Evolutionary Significance and Reasoning
Proponents of intermittent fasting like neuroscientist and aging-researcher Mark Mattson point to evolutionary evidence as to why intermittent fasting may have an impact on the brain. Before access to on-demand food, humans regularly experienced intermittent fasting naturally because time periods between meals could be lengthy. Mattson and his collaborators surmise that in order to find food efficiently, people needed their brains to be performing at a high level when they had not been able to eat for periods of time. They point to evidence that through the process of natural selection, environmental pressures selected for mutations that allowed for a high level of physical and neural performance during times when food was scarce.

Concerns and Risks
Researchers have expressed concerns about the practicality and viability of maintaining intermittent fasting diets. One review article noted that in certain studies about intermittent fasting, dropout rates from participants were as high as 40 percent. Critics have noted that IF diets may be unattainable for many due to the high levels of self-control required to go for long periods without eating. There have also been concerns about binge eating at the end of fasting periods, especially with unhealthy foods, although research in this area has been minimal. After long periods of not eating, hormones in the brain create intense sensations of hunger, and this may be difficult to overcome. The culture in the United States of eating calorie-dense foods is also a reason why intermittent fasting may not achieve widespread success.

Scientists have called for more studies on the long-term implications of intermittent fasting and its effect on depression and binge eating disorder, of which little is known.

Kseses14 (talk) 17:30, 5 October 2018 (UTC)