The 5:2 Diet: What the Trials Actually Show

What Is the 5:2 Diet?

The 5:2 diet means eating normally five days a week and eating very little, commonly 500 to 600 kilocalories, roughly 25% of normal energy needs, on two non-consecutive days. It differs from alternate-day fasting, which restricts every other day rather than two days a week, and from 16:8 or OMAD, which restrict the hours food is eaten every day, not which days. This is a different schedule from a complete 24-hour fast done weekly, which does not allow any calories on fast days.

The two low-calorie days are typically non-consecutive, for example Monday and Thursday, with normal, ad-lib eating on the other five days. See what is fasting for how the 5:2 pattern fits the wider landscape of fasting types, and how to start intermittent fasting for how 5:2 compares to other schedules someone might choose between.

Trial-by-Trial Evidence

The table below lists each trial discussed on this page: who was studied, the design and duration, what it found, and what it did not find or could not show, tagged supports, limited evidence, no effect found, or contradicts.

Does the 5:2 Diet Work for Weight Loss?

Yes, people lose weight on the 5:2 diet, often several kilograms over months. But randomized trials comparing it against daily calorie restriction or standard dieting advice mostly find no advantage: the largest dedicated trial, 300 adults with obesity over one year, found near-identical weight loss on 5:2-style advice and standard dieting advice, and three further trials found the same.

In that largest trial, people randomized to a 5:2 self-help booklet or to standard brief weight-management advice lost similar, modest amounts of weight at 6 months (-1.8 vs -1.7 kg) and at 12 months (-1.9 vs -1.8 kg), with no significant difference between the two; adherence to the 5:2 pattern fell from 74% at 6 weeks to only 22% at one year, and a third group given 5:2 plus six weekly support sessions lost more than the self-help group at 6 weeks but not significantly more by one year (Hajek et al., 2021) [1]. A 50-week trial that explicitly tested "the 5:2 diet" against daily calorie restriction and a no-advice control found a slightly greater weight loss with 5:2 at 12 weeks (-7.1% vs -5.2%, P=0.053, not significant) that had closed by week 50 (-5.2% vs -4.9%, not significant); the authors' own conclusion was that the 5:2 pattern "may be equivalent but not superior" to daily restriction (Schübel et al., 2018) [2]. A one-year trial in adults with abdominal obesity found equal weight loss between a 2-day/week reduced-calorie pattern and daily calorie restriction (8.0 vs 9.0 kg, not significant); see the hunger section below for this trial's one significant between-group finding (Sundfør et al., 2018) [3]. A small 6-month pilot trial in obese men found both a 5:2 pattern and a standard energy-restricted diet produced similar weight loss (5.5% vs 5.4%, not significant) (Conley et al., 2018) [4].

A separate 8-week trial in 40 older adults with insulin resistance found the 5:2 pattern produced greater weight loss than a "healthy living diet" comparator, with comparable effects on most brain-aging and blood biomarkers measured; that trial is cited in full, with its brain-imaging findings, on fasting research facts (Kapogiannis et al., 2024).

Is the 5:2 Diet Better Than Daily Calorie Restriction?

Mostly no. Four separate randomized trials comparing a 5:2-style pattern against daily calorie restriction, or in one case standard dieting advice, found no significant difference in weight loss. Two found a modest edge for the 5:2 pattern on insulin sensitivity or fat loss specifically, not on total weight lost.

The four null trials above, Hajek et al., 2021 [1], Schübel et al., 2018 [2], Sundfør et al., 2018 [3], and Conley et al., 2018 [4], found no weight-loss advantage for 5:2 over daily calorie restriction (three trials) or standard dieting advice (Hajek et al., 2021). Against that, a trial from one research group, the Genesis Breast Cancer Prevention Centre in Manchester, found equal weight loss but a modestly greater reduction in fasting insulin and insulin resistance with the intermittent pattern than with daily restriction (P=0.04) (Harvie et al., 2011) [5]; a later trial from the same group found greater body-fat reduction (-3.7 kg vs -2.0 kg) and greater insulin-sensitivity improvement with an intermittent, carbohydrate-restricted version than with daily restriction (Harvie et al., 2013) [6]. A larger trial from a different research group found no significant difference between the two patterns in circulating metabolic biomarkers (Schübel et al., 2018) [2], so the Harvie-group metabolic edge stands as two trials from one group, not a general finding.

Pooled meta-analyses that combine 5:2 with alternate-day fasting and time-restricted eating, cited in full on alternate-day fasting, add more context than support: one found the 5:2 diet reduced BMI less than daily calorie restriction (Schroor et al., 2024), and another found pooling all three intermittent patterns together showed only a 0.26 kg non-significant difference against continuous restriction overall (Elortegui Pascual et al., 2023). Across dedicated 5:2 trials, weight loss is comparable to daily calorie restriction, not clearly better; any metabolic edge seen is specific to insulin sensitivity or fat distribution in two trials from one research group, not a general finding.

Does the 5:2 Diet Cause More Hunger Than Dieting Every Day?

One year-long randomized trial found people following the 5:2-style pattern reported significantly higher hunger than people on daily calorie restriction (4.7 vs 3.6 on a numeric rating scale, P=0.002), despite losing a similar amount of weight.

That trial randomized 112 adults with abdominal obesity to 2 days a week of 400 to 600 kilocalories or to daily calorie restriction for one year. Weight loss was equal between groups (8.0 vs 9.0 kg, not significant), and the groups also showed similar favorable changes in waist circumference, blood pressure, triglycerides, and HDL cholesterol. The only significant between-group difference the authors reported was hunger: people on the 2-day/week pattern reported higher hunger scores than people on daily calorie restriction (Sundfør et al., 2018) [3]. See hunger during intermittent fasting for the fuller discussion of hunger and appetite hormones across fasting patterns generally; this page states the one trial's finding rather than re-explaining the hunger mechanics.

What Happens to Cholesterol, Blood Pressure, and Blood Sugar?

Several of the trials above measured cardiometabolic markers alongside weight. A trial in young overweight women found comparable reductions in LDL and total cholesterol, triglycerides, and blood pressure between the 2-day/week and daily-restriction groups, no advantage either way (Harvie et al., 2011) [5]. A one-year trial found favorable improvements in waist circumference, blood pressure, triglycerides, and HDL cholesterol, with no difference between the 2-day/week and daily groups (Sundfør et al., 2018) [3]. A pilot trial in obese men found no significant change in diastolic blood pressure, fasting glucose, or blood lipids in either diet group (Conley et al., 2018) [4].

A meta-analysis pooling 20 randomized trials of the 5:2 diet specifically, not combined with alternate-day fasting or time-restricted eating, found the 5:2 diet reduced LDL cholesterol and systolic blood pressure versus pooled comparators, alongside weight, BMI, waist circumference, fat mass, fat-free mass, and HOMA-IR, with no significant difference in visceral fat, total cholesterol, triglycerides, HDL cholesterol, diastolic blood pressure, insulin, fasting glucose, HbA1c, or heart rate (Wu et al., 2025) [7]. It also found fat-free mass fell more on the 5:2 diet than in the comparison groups, and that participants reported mild physical and psychological side effects on fasting days that resolved on their own. The comparison group across those 20 pooled trials is described only as "control", and the abstract does not state that every pooled trial used daily calorie restriction as the comparator, so this meta-analysis shows the 5:2 diet reduces several markers versus the mix of comparators pooled into it, not that it beats calorie-restriction dieting specifically; the dedicated trials above carry that comparison.

A secondary analysis of the same 112 participants as the one-year trial above measured the enzyme Sirtuin1. The direct comparison between the two diets found no significant between-group difference at one year (P=0.98), while within the intermittent-restriction group median Sirtuin1 rose from baseline (P=0.041), most markedly in men, which the authors read as a stronger effect of intermittent restriction; this is a secondary biomarker analysis of an existing cohort, not a second, separate study (Opstad et al., 2021) [8].

How Does the 5:2 Diet Compare to Alternate-Day Fasting and 16:8?

The 5:2 diet and alternate-day fasting both restrict which days a person eats close to normally, while 16:8 and OMAD restrict the hours of the day food is eaten, every day. Pooled analyses cited in full on alternate-day fasting rank alternate-day fasting ahead of 5:2 on weight reduction in one network meta-analysis (Elortegui Pascual et al., 2023); a dedicated head-to-head randomized trial of 5:2 against alternate-day fasting was not found in this search.

Who Should Talk to a Clinician First

Talk to a clinician before trying the 5:2 diet if you are pregnant, under 18, have a history of an eating disorder, or manage diabetes or blood pressure with medication. The trials cited above were not designed to test the 5:2 pattern as a treatment for diabetes; trials of 5:2-style eating as a treatment for diagnosed type 2 diabetes are a separate area and are not summarized on this page. Get clinician guidance either way.

Authors and Funding of the Cited Studies

• Hajek et al., 2021 [1]: Disclosure: "The authors have declared that no competing interests exist."
• Schübel et al., 2018 [2]: No conflict-of-interest statement available in the retrieved record.
• Sundfør et al., 2018 [3]: No conflict-of-interest statement available in the retrieved record.
• Conley et al., 2018 [4]: No conflict-of-interest statement available in the retrieved record.
• Harvie et al., 2011 [5]: Michelle Harvie (Genesis Breast Cancer Prevention Centre, Manchester) is first author. Disclosure: "None of the authors have any conflicts of interest."
• Harvie et al., 2013 [6]: Michelle Harvie (Genesis Breast Cancer Prevention Centre, Manchester) is first author; same research group as Harvie et al., 2011 [5]. Disclosure: "The authors declare no conflict of interest."
• Wu et al., 2025 [7]: Disclosure: "The authors declare no conflicts of interest."
• Opstad et al., 2021 [8] (a secondary analysis of the same cohort as citation 3): Disclosure: "Declaration of competing interest None."
• Disclosures are listed where the full text of the paper was available to us; a study not listed here is not a statement that its authors have no ties.

Safety and Cautions

This is general information, not medical advice. The evidence disagrees on whether the 5:2 diet outperforms daily calorie restriction: four dedicated trials found no weight-loss advantage over daily calorie restriction or standard dieting advice, while two trials from one research group found a modest edge on insulin sensitivity or fat distribution specifically, not on total weight lost (Hajek et al., 2021 [1]; Harvie et al., 2011) [5]. One trial found people on the 5:2 pattern reported more hunger than people on daily calorie restriction despite losing a similar amount of weight (Sundfør et al., 2018) [3]. Talk to a clinician before trying the 5:2 diet if you are pregnant, under 18, have a history of an eating disorder, or manage diabetes or blood pressure with medication. Stop and seek care for any severe or concerning symptom.

Related Reading

New to intermittent fasting generally, and deciding between schedules? See how to start intermittent fasting for how the 5:2 pattern compares to 16:8, OMAD, and alternate-day fasting side by side.