VoltraIntermittent fasting: does it work better than just eating less?
Not better; about the same. In a 12-month trial, people who ate only between 8 am and 4 pm lost 8.0 kg, and people on the same calorie target at any time of day lost 6.3 kg, a difference that wasn't significant [1]. Another 12-month trial found no significant difference between eating from noon to 8 pm and cutting calories by 25% [2].
Across 99 trials, time-restricted eating gave only a trivial 1.72 kg more loss than eating freely, and in trials of 24 weeks or longer, fasting methods did no better than cutting calories every day [3]. As Australia's government health service puts it, the benefits may come from eating fewer calories, and the timing may not make a difference [4].
What it is
Intermittent fasting means eating only in set hours or on set days. The best known is 16:8: you eat within an 8-hour window and fast for the other 16 hours [4]. Other versions are alternate-day fasting and fasting for whole days [3].
What the trials show
| Trial | What people did | Result |
|---|---|---|
| 12 months, 139 people with obesity [1] | Ate 8 am to 4 pm on a calorie target, or the same target at any time | −8.0 vs −6.3 kg; no significant difference |
| 12 months [2] | Ate noon to 8 pm without counting, or cut calories by 25% a day | −4.61 vs −5.42 kg against a control group; no significant difference |
| 12 weeks [5] | Ate noon to 8 pm, or ate throughout the day | No significant difference between the groups |
A 2025 analysis of 99 trials compared each method with eating freely [3]:
| Method | Extra weight lost |
|---|---|
| Alternate-day fasting | 3.40 kg |
| Whole-day fasting | 2.36 kg |
| Cutting calories every day | 2.11 kg |
| Time-restricted eating, such as 16:8 | 1.72 kg |
Most of those trials were short, a median of 12 weeks, and two-thirds of the people in them were women [3].
What about muscle?
In the 12-week trial, the fasting group lost more lean mass in the arms and legs than the group eating throughout the day [5], and a review of 130 trials linked intermittent fasting with a drop in fat-free mass [6]. The International Society of Sports Nutrition found no advantage of intermittent over daily calorie restriction for body composition [7]. If you fast, keep your protein up and keep lifting; our cutting guide covers how.
Who shouldn't fast
Australia's government health service says not to do intermittent fasting if you [4]:
- are underweight
- have, or have had, an eating disorder
- are pregnant or breastfeeding
- are a child or teenager, or an older adult
- take daily medicine that must be taken with food.
If you take diabetes medicines or are having cancer treatment, ask your doctor first [4]. Fasting may raise the risk of low blood sugar in people with type 2 diabetes on glucose-lowering medicines, and in type 1 diabetes [8]. Saudi Arabia's Deputy Minister of Health for Population Health said heart patients, people with diabetes (especially on insulin), older and frail people, people with a history of eating disorders, and pregnant and breastfeeding women should consult a doctor before fasting [9].
The heart-death headline
A study linking eating within less than 8 hours a day with more deaths from heart disease was first presented at an American Heart Association meeting in 2024 [9]. In its 2025 published version, eating within less than 8 hours was linked with a higher risk of cardiovascular death (hazard ratio 2.35) than eating over 12 to 14 hours, but not with more deaths overall [10]. That's an association, and the authors say more research is needed to know whether the short eating window itself or other factors explain it [10]. Saudi Arabia's deputy health minister said the results of intermittent fasting are similar to those of continuous calorie restriction [9].
What guidelines say
England's NICE found that alternate-day fasting and time-restricted eating improved a few outcomes but not most, so it made no recommendation on them and called for better trials [11].
In Voltra
Voltra doesn't time your fast. What moves the scale is calories, so if a shorter eating window helps you eat less, log your meals on the Eat tab as usual; your daily calorie target works with any eating window.
Frequently asked
Does intermittent fasting work for weight loss?
About as well as cutting calories every day, but not better: in year-long trials the difference wasn't significant.
Does intermittent fasting burn muscle?
It can. A 12-week trial found more lean-mass loss than eating throughout the day, and a review of 130 trials linked fasting with a drop in fat-free mass. Eat enough protein and keep strength training.
Who shouldn't do intermittent fasting?
People who are underweight, have had an eating disorder, are pregnant or breastfeeding, children and teenagers, older adults, and anyone whose daily medicine must be taken with food. Ask a doctor first if you take diabetes medicines.
Does intermittent fasting cause heart disease?
That hasn't been shown. A study linked eating within less than 8 hours a day with more heart deaths, but it shows an association, and its authors say more research is needed.
Sources
- Liu D, Huang Y, Huang C, et al. (2022). Calorie restriction with or without time-restricted eating in weight loss. N Engl J Med 386(16):1495–1504. Abstract.
- Lin S, Cienfuegos S, Ezpeleta M, et al. (2023). Time-restricted eating without calorie counting for weight loss in a racially diverse population: a randomized controlled trial. Ann Intern Med 176(7):885–895. Abstract.
- Semnani-Azad Z, Khan TA, Chiavaroli L, et al. (2025). Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials. BMJ 389:e082007. Abstract and results.
- healthdirect Australia (Australian Government) (2025). Intermittent fasting (last reviewed December 2025). Examples, benefits and safety sections.
- Lowe DA, Wu N, Rohdin-Bibby L, et al. (2020). Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA Intern Med 180(11):1491–1499. Abstract.
- Patikorn C, Roubal K, Veettil SK, et al. (2021). Intermittent fasting and obesity-related health outcomes: an umbrella review of meta-analyses of randomized clinical trials. JAMA Netw Open 4(12):e2139558. Abstract.
- Aragon AA, Schoenfeld BJ, Wildman R, et al. (2017). International Society of Sports Nutrition position stand: diets and body composition. J Int Soc Sports Nutr 14:16. Abstract, point 7.
- Mozaffarian D, Agarwal M, Aggarwal M, et al. (2025). Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory. Am J Clin Nutr 122(1):344–367. Use of specific dietary patterns.
- صحيفة اليوم (٢٠٢٦). وكيل الصحة: لا دليل علميًا على زيادة وفيات القلب بسبب الصيام المتقطع. In Arabic. Statements by Saudi Arabia's Deputy Minister of Health for Population Health, 28 July 2026.
- Chen M, Xu L, Van Horn L, et al. (2025). Association of eating duration less than 8 h with all-cause, cardiovascular, and cancer mortality. Diabetes Metab Syndr 19(7):103278. Abstract.
- NICE (2025). Overweight and obesity management (NG246): rationale and impact, intermittent fasting in adults. Intermittent fasting in adults (no recommendations).
Sources checked on 30 September 2026.
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