What Are the Benefits of Intermittent Fasting?

In 30 seconds

Intermittent fasting usually produces modest weight loss, similar to daily calorie restriction rather than greater. Effects on blood sugar and cholesterol are small and inconsistent, and very few trials last beyond a year.

• Intermittent fasting produces small weight losses similar to daily calorie restriction; only alternate-day fasting lost slightly more (about 1.3 kg), in shorter trials.
• When calories are matched, adding a time window rarely adds weight loss.
• Pooled trials show only trivial changes in fasting glucose and insulin resistance and no change in HbA1c or HDL cholesterol.
• If you have diabetes or take glucose-lowering medicines, plan any fast with your clinician; pregnancy is not the time to diet.

Does fasting help with weight?

A fasting schedule often means eating less simply because there is less time to eat, so the fair comparison is with daily calorie restriction.

Intermittent-fasting strategies produce small weight losses that are similar to daily calorie restriction; only alternate-day fasting showed a slightly larger loss (about 1.3 kg) in shorter trials.Source 11

Adding a time window to the same calorie target is a direct test of timing alone.

In a systematic review of 7 energy-matched trials, adding time-restricted eating to calorie restriction gave extra weight loss in 2 trials, but most found no added benefit; in a 12-month trial, time-restricted eating was not more effective than daily calorie restriction.Source 22Source 33

What about blood sugar and cholesterol?

Beyond weight, the changes were small.

Compared with unrestricted eating, pooled trials found only trivial declines in fasting glucose and insulin resistance and no differences in HbA1c or HDL cholesterol, and a 12-week trial of a noon-to-8 p.m. window found no significant changes in its other secondary outcomes.Source 11Source 44

Does fasting help you live longer or protect the brain?

That isn’t shown in people. Those claims come mostly from animal and lab research, while human trials have mainly measured weight and metabolic markers.

The National Institute on Aging notes that interest in the ageing and lifespan benefits of fasting stems from decades of animal research, that human studies have mostly focused on weight loss, and that more work is needed to determine which, if any, fasting diets have long-term benefits.Source 55

The same goes for autophagy, the cell recycling often linked to fasting: see autophagy fasting.

What did 99 trials find?

A network meta-analysis of 99 randomized trials in 6,582 adults found that all fasting strategies and daily calorie restriction lowered weight compared with unrestricted eating; with moderate certainty, only alternate-day fasting lost more than calorie restriction (about 1.3 kg). In trials of 24 weeks or more, fasting and calorie restriction did not differ.Source 11

What are the limits of these trials?

Trials varied in who they included, how closely people kept to the schedule and what fasting was compared with. The two main trials cited here used one fixed window, noon to 8 p.m.

Fasting trials have typically recruited adults aged 60 or younger, so the results don't necessarily apply to children or people older than 60, and long-term safety and benefits remain uncertain.Source 55

Who should get advice first?

Weight goals never justify changing a medicine on your own.

People with diabetes or who take glucose-lowering medicines face a higher risk of low blood sugar when fasting and may need planned dose changes, and anyone should talk with a healthcare provider about benefits and risks before significant changes to their eating pattern.Source 66Source 55

Talk to a qualified health professional before fasting if you are pregnant or breastfeeding, under 18, living with or recovering from an eating disorder, have diabetes, take insulin or a medicine affected by meal timing, are an older adult, or are acutely ill. Do not change the dose or timing of any medicine without your clinician. See Blimbi’s safety guide.

Related guides

• Fasting Timeline: What Happens and Why Timing Varies

  This fasting timeline explains how the body moves from meal glucose to liver glycogen, then to fat and ketones, and why the timing varies.

• How Do You Read Intermittent Fasting Research?

  Read intermittent fasting research with four checks: who took part, the comparison, the size of the difference and how long it lasted. What it shows.

• What is intermittent fasting? How it works

  Intermittent fasting means eating in planned windows and going without calories in between. How it works, the main types and what trials found.

• Does Bone Broth Break a Fast? On a Strict Fast, Yes

  Bone broth breaks a strict zero-calorie fast because its protein and fat add energy. See how chicken broth compares and what a modified fast allows.

Frequently asked questions

Does time-restricted eating lead to more weight loss than standard calorie restriction?

Not on average. When calories are matched, adding a time window rarely adds weight loss, and in a 12-month trial time-restricted eating matched 25% daily calorie restriction.Source 22Source 33

How much weight can I expect to lose with intermittent fasting?

Modest amounts on average. For example, in a 12-month trial, adults with obesity lost about 5% more body weight than a control group. No amount is guaranteed.Source 33Source 11

What are the benefits of 16:8 fasting?

Mostly modest weight loss. In a 12-month trial of eating only between noon and 8 p.m., adults with obesity lost about 4.6 kg more than a control group, and not significantly different from daily calorie restriction. No amount is guaranteed.Source 33

Is intermittent fasting safe if I have diabetes or take glucose-lowering medications?

If you have diabetes or take glucose-lowering medicines, fasting can cause low blood sugar and doses may need planned changes, so plan any fast with your clinician.Source 66

Are the long-term benefits of intermittent fasting clear?

No. Trials of 6 to 12 months show weight loss similar to daily calorie restriction, not better. Very few trials last longer than a year, so longer-term effects are uncertain.Source 11Source 33

Sources

1. 1

   Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trialsZhila Semnani-Azad et al. BMJ, June 18, 2025.DOI: 10.1136/bmj-2024-082007 · PMID: 40533200Systematic review and meta-analysis

2. 2

   Does time-restricted eating add benefits to calorie restriction? A systematic reviewArmin Ezzati et al. Wiley, April 1, 2024.DOI: 10.1002/oby.23984 · PMID: 38383703Systematic review and meta-analysis

3. 3

   Time-Restricted Eating Without Calorie Counting for Weight Loss in a Racially Diverse Population: A Randomized Controlled TrialShuhao Lin et al. American College of Physicians, July 1, 2023.DOI: 10.7326/M23-0052 · PMID: 37364268Human randomized trial

4. 4

   Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical TrialDylan A. Lowe et al. American Medical Association (AMA), November 1, 2020.DOI: 10.1001/jamainternmed.2020.4153 · PMID: 32986097Human randomized trial

5. 5

   Calorie restriction and fasting diets: What do we know?National Institute on Aging. National Institute on Aging, August 14, 2018.Official guidance

6. 6

   Fasting Safely with DiabetesMartin M. Grajower. National Institute of Diabetes and Digestive and Kidney Diseases, August 26, 2020.Official guidance

7. 7

   Weight gain in pregnancyNHS. NHS, July 6, 2022.Official guidance

8. 8

   Overview – Eating disordersNHS. NHS, January 23, 2024.Official guidance