Intermittent fasting
Atomic claims
Intermittent fasting is a family of eating patterns that alternate periods of little or no energy intake with periods of normal intake.
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Intermittent fasting focuses on meal timing rather than food composition.
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Randomized trials generally show that intermittent fasting produces weight loss comparable to conventional calorie restriction.
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Whether intermittent fasting has benefits beyond reduced calorie intake remains unresolved.
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The long-term effect of intermittent fasting on mortality remains unresolved.
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Intermittent fasting focuses on when a person eats rather than how much or what the person eats.
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Intermittent-fasting regimens can confine food intake to specified hours of the day or days of the week.
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Intermittent-fasting regimens are commonly grouped into alternate-day fasting, the 5:2 diet, and time-restricted eating.
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A proposed mechanism of intermittent fasting is called metabolic switching.
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During fasting, glucose stores decline.
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During fasting, the liver converts fatty acids into ketones for fuel.
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Ketones appear roughly 8–12 hours into a fast.
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A 2025 network meta-analysis pooled 99 randomized trials.
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The 2025 network meta-analysis included 6,582 adults.
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Participants in the 2025 network meta-analysis had a mean age of 45 years.
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Trials in the 2025 network meta-analysis lasted between 3 and 52 weeks.
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Every intermittent-fasting strategy evaluated in the 2025 network meta-analysis produced a small reduction in weight compared with unrestricted eating.
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Alternate-day fasting was the only intermittent-fasting approach in the 2025 network meta-analysis that had an advantage over continuous calorie restriction.
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A 12-month trial conducted in China enrolled 139 patients with obesity.
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The 12-month Chinese trial randomized participants to calorie restriction with eating limited to 8 a.m.–4 p.m. or to calorie restriction alone.
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The difference in weight loss between the two groups in the Chinese trial was not statistically significant.
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The TREAT trial randomized 116 adults with overweight or obesity.
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The TREAT trial compared 16:8 time-restricted eating with three structured meals per day.
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The TREAT trial lasted 12 weeks.
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A one-year trial of alternate-day fasting and daily calorie restriction enrolled 100 adults.
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The alternate-day-fasting arm had the highest dropout rate in the one-year trial.
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A Johns Hopkins controlled-feeding trial tested whether time-restricted eating causes weight loss independently of calorie reduction.
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The Johns Hopkins controlled-feeding trial found no additional weight-loss benefit from time-restricted eating when calorie intake was matched.
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A 2024 conference abstract analyzed about 20,000 U.S. adults.
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The 2024 conference abstract associated an eating window shorter than 8 hours with 91% higher cardiovascular mortality than a 12–16 hour eating window.
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The 2024 conference abstract had not been peer reviewed when it was presented.
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The peer-reviewed version of the eating-window analysis reported 135% higher cardiovascular mortality for eating durations shorter than 8 hours.
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The peer-reviewed eating-window analysis reported no association between eating duration and all-cause mortality.
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Intermittent fasting can create a risk of hypoglycemia for people taking diabetes medication.
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A secondary summary of Johns Hopkins guidance states that intermittent fasting is not considered safe for people under 18.
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The calorie-matched Liu 2022 trial found no significant weight advantage for time-restricted eating.
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BMJ authors noted that some benefits of structured diets may come from professional support rather than the eating pattern itself.
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The cited evidence on long-term cardiovascular safety includes an observational association derived from NHANES data.
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Participants in the NHANES eating-window analysis chose their own eating patterns.
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Reverse causation is a possible explanation for the observed association between short eating windows and cardiovascular mortality.
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Cancer-related appetite loss was cited as an example of a mechanism that could produce reverse causation in the eating-window analysis.
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Eating duration in the conference analysis was estimated from two days of dietary recall.
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Salk Institute scientists sent a letter to the American Heart Association concerning the time-restricted-eating mortality report.
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The Salk Institute scientists' letter objected to publicity being given to the data before it had been vetted.
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A separate NHANES analysis found that eating windows of 8 hours per day or less were associated with higher all-cause mortality.
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The Mao et al. finding on all-cause mortality is inconsistent with the Chen et al. finding of no association with all-cause mortality.
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Mark Mattson has said that intermittent fasting can prevent diabetes.
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Human randomized evidence on intermittent fasting consists mainly of short-term trials examining weight and risk markers.
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How far animal findings on intermittent fasting translate to humans is disputed.
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Time-restricted eating is a common form of intermittent fasting.
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Alternate-day fasting is a common form of intermittent fasting.
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Periodic fasting, such as the 5:2 pattern, is a common form of intermittent fasting.
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Human trials indicate that intermittent fasting can produce modest weight loss.
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Much of the benefit of intermittent fasting appears to be related to reduced energy intake.
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Evidence that intermittent fasting is superior to conventional continuous calorie restriction is limited.
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Intermittent fasting describes a family of eating schedules rather than a single standardized diet.
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Periodic fasting is a major variant of intermittent fasting.
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Circulating glucose declines during fasting.
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Declining circulating glucose and insulin during fasting promote greater reliance on fatty-acid oxidation.
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The fasting-induced transition toward fatty-acid oxidation and ketone production is sometimes described as 'metabolic switching'.
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Randomized trials show that intermittent-fasting regimens can produce weight loss in adults with overweight or obesity.
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Weight loss from intermittent-fasting regimens occurs particularly when the fasting schedule reduces overall caloric intake.
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Trepanowski et al. (2017) was a randomized trial lasting one year.
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In the Trepanowski et al. (2017) trial, alternate-day fasting did not produce significantly greater weight loss than daily calorie restriction.
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The Liu et al. (2022) trial ran for 12 months.
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The TREAT trial was a randomized trial published in 2020.
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The TREAT trial tested a 16:8 time-restricted eating regimen.
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In the TREAT trial, 16:8 time-restricted eating did not significantly outperform a control meal schedule for weight loss.
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Some clinical studies report improvements in insulin sensitivity during intermittent fasting.
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Cardiometabolic results of intermittent fasting studies vary by study population.
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Circadian timing of eating may matter independently of fasting duration.
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Experimental studies of early time-restricted feeding have reported metabolic improvements in the absence of major weight loss.
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Experimental studies of early time-restricted feeding have generally been relatively small.
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Animal studies provide substantial evidence that fasting can alter cellular stress responses.
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The magnitude in humans of fasting's effects on cellular stress responses, nutrient-sensing pathways, and autophagy-related processes remains uncertain.
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Intermittent fasting can produce hunger as an adverse effect.
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Intermittent fasting can involve difficulty adhering to the fasting schedule.
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Adverse effects of intermittent fasting occur particularly during the initial adaptation period.
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In people using glucose-lowering medications, reducing food intake can change the risk of hypoglycemia.
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Evidence on the long-term effects of intermittent fasting on cardiovascular events in humans is insufficient.
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Much of the mechanistic literature on intermittent fasting derives from animal models or short-term human studies.
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Intermittent fasting is often presented as metabolically superior to ordinary calorie restriction.
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Several direct comparisons have found similar weight loss with intermittent fasting and calorie restriction when total energy restriction is comparable.
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Fasting influences autophagy-related pathways in experimental organisms.
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The fasting duration required to produce clinically meaningful autophagy in humans is not well established.
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The health effects of fasting-induced autophagy in humans are not well established.
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Caloric restriction extends lifespan in several laboratory organisms.
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No long-term randomized trial has demonstrated that intermittent fasting increases human lifespan.
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Longer trials are needed to confirm the reported advantage of alternate-day fasting.
Further research on residual confounding in the eating-window analysis is needed.
People taking diabetes medication are advised to consult a clinician before beginning intermittent fasting.
Diabetes-medication doses may need adjustment during intermittent fasting.
Liu's trial result should be judged by the size of the observed difference rather than by statistical significance alone.
Fasting in people using glucose-lowering medications can require medical supervision.
External references: Wikidata Q1666254