Intermittent fasting (IF) is any of various meal timing schedules that cycle between voluntary fasting (or reduced calorie intake) and non-fasting over a given period. Methods of intermittent fasting include alternate-day fasting, periodic fasting, such as the 5:2 diet, and daily time-restricted eating. Intermittent fasting has been studied to find whether it can reduce the risk of diet-related diseases, such as metabolic syndrome. It may improve several health outcomes in overweight or obese adults; its effect on lowering blood pressure appears to be less pronounced than that of continuous energy restriction. There is preliminary evidence that intermittent fasting is generally safe. Adverse effects of intermittent fasting have not been comprehensively studied, leading some academics to point out its risk as a dietary fad. The United States National Institute on Aging states that current research is limited and inconclusive; they do not recommend intermittent fasting to the general public. The New Zealand Ministry of Health states that intermittent fasting may aid weight loss but is not recommended for people with insulin-dependent diabetes and can cause low energy and hunger. Fasting exists in various religious practices, including Buddhism, Christianity, Hinduism, Islam, Jainism, and Judaism.
History Fasting is an ancient tradition, having been practiced by many cultures and religions over centuries. Therapeutic intermittent fasts for the treatment of obesity have been investigated since at least 1915, with a renewed interest in the medical community in the 1960s after Bloom and his colleagues published an "enthusiastic report". Intermittent fasts, or "short-term starvation periods", ranged from 1 to 14 days in these early studies. This enthusiasm penetrated lay magazines, which prompted researchers and clinicians to caution about the use of intermittent fasts without medical monitoring.
Types
There are multiple methods of intermittent fasting.
Time-restricted eating involves eating only during a certain number of hours each day, often establishing a consistent daily pattern of caloric intake within an 8–12-hour time window. This schedule may align food intake with circadian rhythms (establishing eating windows that begin after sunrise and end around sunset). One-meal-a-day fasting is consuming all daily macronutrients within a single 1-2 hour eating window, with only water or non-caloric beverages, vitamins, minerals and medication allowed to be taken during the remaining hours. Alternate-day fasting involves alternating between a 24-hour "fast day" when the person eats less than 25% of usual energy needs, followed by a 24-hour non-fasting "feast day" period. There are two subtypes: Complete alternate-day fasting is total intermittent energy restriction (IER vs. CER = continuous energy restriction), where no calories are consumed on fasting days. Modified alternate-day fasting (mADF) involves partial intermittent energy restriction which allows the consumption of up to 25% of daily calorie needs on fasting days instead of complete fasting. This is akin to alternating days with normal eating and days with a very-low-calorie diet. 5:2 diet is a type of periodic fasting (that does not follow a particular food pattern) which focuses entirely on calorie content. In other words, two days of the week are devoted to consumption of approximately 500 to 600 calories, or about 25% of regular daily caloric intake, with normal calorie intake during the other five days of the week. It was first documented in a 2011 article co-authored by Michelle Harvie, Mark Mattson, and 14 additional scientists. It was later published in the UK and Australia by Michael Mosley through the 2012 BBC documentary Eat, Fast and Live Longer (where he learned about the 5:2 diet from Mark Mattson). It also became common in Australia. Periodic fasting or whole-day fasting involves intermittent periods of water fasting longer than 24 hours. The science concerning intermittent fasting is preliminary and uncertain due to an absence of studies on its long-term effects. Preliminary evidence indicates that intermittent fasting may be effective for weight loss, may decrease insulin resistance and fasting insulin, and may improve cardiovascular and metabolic health, although the long term sustainability of these effects has not been studied.
Research Intermittent fasting may improve several health outcomes in overweight or obese adults. It may reduce waist circumference, fat mass, low-density lipoprotein cholesterol, triacylglycerols, total cholesterol, and fasting insulin. It may also slightly lower systolic blood pressure and increase high-density lipoprotein cholesterol and fat-free mass. Its effect on lowering blood pressure appears to be less pronounced than that of continuous energy restriction.
Body weight and metabolic disease risk There is limited evidence that intermittent fasting produces weight loss comparable to a calorie-restricted diet. Most studies on intermittent fasting in humans have observed weight loss, ranging from 2.5% to 9.9%. The reductions in body weight can be attributed to the loss of fat mass and some lean mass. For time restricted eating the ratio of weight loss is 4:1 for fat mass to lean mass, respectively. Alternate-day fasting does not affect lean body mass, although one review found a small decrease. Alternate-day fasting improves cardiovascular and metabolic biomarkers similarly to a calorie restriction diet in people who are overweight, obese or have metabolic syndrome. As of 2021, it remains uncertain whether intermittent fasting could prevent cardiovascular disease. Intermittent fasting has not been studied in children, elderly, or underweight people, and may be harmful in these populations. Intermittent fasting is not recommended for people who are not overweight, and the long-term sustainability of intermittent fasting is unknown as of 2018. A 2021 review found that moderate alternate-day fasting for two to six months was associated with reductions of body weight, body mass index, and cardiometabolic risk factors in overweight or obese adults.
… excerpt ends here. Continue reading the full article.
