Understanding the 5:2 Diet, Is it Effective? An Overview of Studies

Alastair Hunt
Jul 10
22 min read

Updated: Jul 12

The popular 5:2 diet - five days of normal eating and two non-consecutive days of calorie restriction each week - offers a flexible and evidence-supported approach to weight loss and metabolic health. Unlike daily calorie restriction, this form of intermittent fasting, does not require constant monitoring, which makes it appealing to those seeking a simpler structure.

We explore the diet below and - if you want to dig deeper - provide a comprehensive set of summarised studies at bottom of page.

As ever, please talk to your doctor or medical practitioner most familiar with your medical history before implementing any changes in diet, exercise or lifestyle, especially if you are under treatment.

What Studies Show

Studies consistently show that the 5:2 diet leads to meaningful weight loss - typically 3 to 9% of body weight over 8 to 16 weeks. In some trials, it outperforms continuous restriction, particularly when combined with behavioural support. Fat mass, waist circumference, and BMI tend to drop, with additional improvements seen in blood pressure, LDL cholesterol and insulin resistance.

One of its strengths lies in promoting metabolic switching during fasting periods, which helps the body burn fat more efficiently. This shift supports better glucose control and may reduce systemic inflammation, both of which are key factors in reducing chronic disease risk.

Some studies show benefits to liver health, especially in people with fatty liver conditions, but the 5:2 diet’s broader appeal lies in its versatility - it supports weight management, metabolic resilience and cardiometabolic markers, often with fewer feelings of restriction.

Unfortunately the diet is often construed as 'eat what and as much as you want' on non-fasting days, and this is its biggest failing. As a recent study (Tosti et al, 2023) found:

"In conclusion, the findings of this trial demonstrate that intermittent fasting in overweight men and women results in significant body weight and fat loss but without clinically meaningful improvements in systemic inflammatory markers or glucose-insulin metabolism, reinforcing the concept that weight reduction does not always translate into improved metabolic health"

Adherence to 5:2 is generally good in the short term, though long-term success varies without ongoing support. Hunger and compensatory eating can occur, but most participants still achieve a net reduction in energy intake. Nutritionally, the diet is safe when well planned. The 5:2 diet also performs well alongside resistance training, helping preserve lean mass and functional strength during weight loss. Learn more about the combined effects of caloric restriction and exercise here. While not suitable for everyone. - such as those with a history of disordered eating or complex medical needs - it offers a practical and sustainable alternative to more rigid dieting approaches.

For deeper insights into the background of the 5:2 diet, and how to practice it to maximise long-term health outcomes, read here.

fasting diet calorie restriction — Non-starchy vegetables play a key role in a 'fasting diet'.

Final Thoughts

In summary, the 5:2 diet is a well-tolerated, accessible option for improving weight and metabolic health. Its simplicity, flexibility and growing evidence base make it a valuable tool for those seeking long-term health benefits through non-pharmacological means.

Scroll down to read the comprehensive set of summarised studies.

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Related Studies

Tosti V., et al. (2023). When a Calorie Is Not a Calorie: Metabolic and Molecular Effects of Intermittent Fasting in Humans; Exploratory Outcomes of a Randomized Clinical Trial, AgingBio, 1, e20230013. doi: 10.59368/agingbio.20230013.

The following studies are focused on, or reference, the 5:2 diet. Do you have have a new (other) citations to share? Please add the PMID to the Comments section at bottom of page.

Khalafi M, Rosenkranz SK, Ghasemi F, Kheradmand S, Habibi Maleki A, Korivi M, Tsao JP. Efficacy of intermittent fasting on improving liver function in individuals with metabolic disorders: a systematic review and meta-analysis. Nutr Metab (Lond). 2025 Jan 6;22(1):1. doi: 10.1186/s12986-024-00885-x. PMID: 39762987; PMCID: PMC11706068.

This systematic review and meta-analysis found that intermittent fasting (IF) improves liver function in adults with metabolic disorders by reducing liver fat, steatosis, and liver enzymes such as ALT and AST. However, IF did not significantly reduce liver fibrosis, likely due to short intervention durations or participants not having advanced fibrosis. The benefits of IF were observed across various IF protocols (5:2, alternate-day fasting, time-restricted eating) and were largely independent of age, BMI, or health status—though individuals with obesity experienced additional improvements, including reduced AST and fibrosis.

Mechanistically, IF may enhance liver health by reducing hepatic fat synthesis and increasing fat oxidation, although the exact pathways are not fully understood. Weight loss, reduced visceral fat, and lower inflammation are likely contributors. While all forms of IF were effective for lowering liver fat and ALT, only the 5:2 diet reduced AST significantly.

Subgroup analyses showed consistent results across populations, but the quality of included studies varied, with many showing moderate to high risk of bias. Despite some limitations—such as study heterogeneity and a lack of long-term data—this analysis supports IF as a practical, non-pharmacological intervention to improve liver health in individuals with obesity or metabolic conditions. Further high-quality trials are recommended.

Haddad RR, Battula NS, Chay T, Patel T, Dumaru N, Maddukuri S, Khan S. Role of Fasting in the Management of Non-alcoholic Fatty Liver Disease (NAFLD): A Systematic Review of Clinical Trials. Cureus. 2025 May 16;17(5):e84259. doi: 10.7759/cureus.84259. PMID: 40525060; PMCID: PMC12168860.

This review highlights the potential of intermittent fasting (IF), including the 5:2 diet, as a viable non-pharmacological approach for managing non-alcoholic fatty liver disease (NAFLD). Among the 12 reviewed trials, four examined IF protocols, including time-restricted feeding (TRF), alternate-day fasting (ADF), and the 5:2 diet. Notably, the 5:2 diet was shown to reduce liver fat, improve liver enzymes, and lower inflammation markers within 8–12 weeks. It also matched the effectiveness of low-carb, high-fat diets in improving liver stiffness and cholesterol, with better patient adherence reported.

The 5:2 diet's success may stem from its ability to reduce visceral fat, insulin resistance, and systemic inflammation—core drivers of NAFLD. While individual studies vary in design and protocol, the overall evidence supports IF’s benefits for liver health, particularly when combined with other lifestyle strategies like low sugar intake or moderate exercise. Importantly, diet quality and meal timing both contribute to outcomes.

However, limitations such as short durations, small sample sizes, and inconsistent fasting methods reduce generalisability. Further research is needed to determine long-term effects and refine fasting protocols. Still, the 5:2 diet stands out as a practical and potentially sustainable option for improving liver function and metabolic health in NAFLD.

Wu C, Chen B, Yu J, Zhang Q, Piao C. Effect of the 5:2 Diet on Weight Loss and Cardiovascular Disease Risk Factors in Overweight and/or Obesity: A Systematic Review and Meta-Analysis. Int J Endocrinol. 2025 Feb 24;2025:6658512. doi: 10.1155/ije/6658512. PMID: 40041761; PMCID: PMC11876533.

This systematic review and meta-analysis confirms that the 5:2 diet is an effective and generally safe intervention for weight loss and cardiometabolic improvement in overweight and obese individuals. The findings show significant reductions in body weight, BMI, waist and hip circumference, fat mass, and LDL cholesterol, along with improvements in blood pressure and insulin resistance (HOMA-IR). However, the diet did not significantly reduce visceral fat or improve other glucose markers such as fasting glucose or HbA1c—possibly due to the participants' normal baseline glucose levels.

The 5:2 diet was shown to reduce fat-free mass, suggesting some muscle loss may occur, particularly in those with low protein intake or reduced activity. Middle-aged participants (45 to 59 years) experienced the greatest benefit, possibly due to higher motivation and increased fat mobilisation during fasting. While adverse effects were mild, the diet should be used cautiously in vulnerable groups and those on long-term medication.

Mechanistically, the 5:2 diet influences pathways tied to fat oxidation, inflammation reduction, gut microbiota, and circadian rhythms. Although promising, current evidence is limited by study variability, short durations, and a lack of long-term adherence data. More rigorous, longer-term studies are needed to confirm its utility in clinical and public health contexts.

Wang YY, Tian F, Qian XL, Ying HM, Zhou ZF. Effect of 5:2 intermittent fasting diet versus daily calorie restriction eating on metabolic-associated fatty liver disease-a randomized controlled trial. Front Nutr. 2024 Aug 20;11:1439473. doi: 10.3389/fnut.2024.1439473. PMID: 39229586; PMCID: PMC11368853.

This 12-week randomised controlled trial compared the effects of a 5:2 intermittent fasting (IF) diet and daily calorie restriction (CER) in adults with metabolic-associated fatty liver disease (MAFLD). Both interventions produced similar improvements in weight, liver enzymes, lipid profile, and glycaemic indices. However, the 5:2 IF diet led to significantly greater reductions in liver steatosis and fibrosis, as measured by Fibrotouch-B and ultrasound, despite similar weight loss outcomes. Notably, these liver-specific benefits appeared to occur independently of overall weight reduction.

The 5:2 diet group also showed lower CAP and LSM values and a greater shift toward mild or no fibrosis, supporting the idea that intermittent fasting may induce beneficial hepatic changes through metabolic switching between feeding and fasting states. These shifts may enhance fatty acid and ketone utilisation, reduce liver fat, and improve liver resilience without requiring continuous energy restriction.

No serious adverse events were reported, though some participants experienced minor discomfort such as hunger or fatigue. While CER led to greater reductions in fasting insulin, hs-CRP, and blood glucose, the 5:2 group demonstrated stronger histological improvements. Overall, the study supports 5:2 IF as a safe and effective dietary approach for improving liver health in MAFLD, even when weight loss is modest.

Brogi S, Tabanelli R, Puca S, Calderone V. Intermittent Fasting: Myths, Fakes and Truth on This Dietary Regimen Approach. Foods. 2024 Jun 21;13(13):1960. doi: 10.3390/foods13131960. PMID: 38998465; PMCID: PMC11241639.

This review evaluated over 50 clinical trials comparing intermittent fasting (IF), including the 5:2 diet, with continuous calorie restriction (CR). The 5:2 diet—five days of normal eating and two low-calorie days—shows modest, consistent weight loss and improvements in metabolic risk factors such as blood lipids, insulin resistance, and liver enzymes. Although IF does not clearly outperform CR, its flexible structure may improve adherence, especially in busy individuals or those with limited resources. However, dropout rates remain a concern.

The authors conclude that while IF, including the 5:2 approach, is a promising and accessible tool for weight and metabolic health management, more long-term studies are needed to confirm its safety, sustainability, and possible superiority over traditional dietary strategies.

Guo L, Xi Y, Jin W, Yuan H, Qin G, Chen S, Zhang L, Liu Y, Cheng X, Liu W, Yu D. A 5:2 Intermittent Fasting Meal Replacement Diet and Glycemic Control for Adults With Diabetes: The EARLY Randomized Clinical Trial. JAMA Netw Open. 2024 Jun 3;7(6):e2416786. doi: 10.1001/jamanetworkopen.2024.16786. PMID: 38904963; PMCID: PMC11193124.

This large, 16-week randomised clinical trial found that a 5:2 intermittent fasting meal replacement diet (5:2 MR) significantly improved glycaemic control in Chinese adults with early-stage type 2 diabetes, outperforming both metformin and empagliflozin. Participants following the 5:2 MR plan experienced greater reductions in HbA1c (−1.9%) and body weight (−9.7 kg) than those on medication, with 80% achieving HbA1c levels below 6.5%—a threshold for diabetes remission. These improvements persisted in most participants during the 8-week follow-up.

The 5:2 MR approach combined two nonconsecutive low-energy days using meal replacements with five days of regular eating and one replaced meal. Beyond glycaemic markers, the diet also led to improved blood pressure, waist circumference, triglycerides, and HDL-C levels. While improvements in insulin sensitivity were seen in all groups, they were not significantly different between the 5:2 MR and medication arms.

Adverse events were mild and comparable across groups. The study reinforces the 5:2 MR as a safe, non-pharmacological first-line intervention for early diabetes management. However, longer-term data are needed to confirm sustained effects and its role in broader populations. Still, this trial provides strong evidence supporting intermittent fasting with meal replacement as an effective alternative to early drug therapy in type 2 diabetes.

Schroor MM, Joris PJ, Plat J, Mensink RP. Effects of Intermittent Energy Restriction Compared with Those of Continuous Energy Restriction on Body Composition and Cardiometabolic Risk Markers - A Systematic Review and Meta-Analysis of Randomized Controlled Trials in Adults. Adv Nutr. 2024 Jan;15(1):100130. doi: 10.1016/j.advnut.2023.10.003. Epub 2023 Oct 10. PMID: 37827491; PMCID: PMC10831889.

This systematic review and meta-analysis found that intermittent energy restriction (IER) diets, including the 5:2 diet, time-restricted eating (TRE), and alternate-day fasting (ADF), are not superior to continuous energy restriction (CER) for weight loss or cardiometabolic risk improvements in healthy, overweight, or obese adults. While IER led to modestly greater reductions in fat-free mass and waist circumference, overall differences between IER and CER were minimal across most outcomes.

Subgroup analysis showed TRE reduced body weight and fat more than CER, and ADF improved insulin resistance (HOMA-IR), but the 5:2 diet was less effective for reducing BMI compared to CER. No significant differences were found in blood lipids, glucose, or blood pressure between any IER type and CER. This suggests that weight loss itself—rather than the dietary pattern—is the key driver of health improvements.

Differences in energy intake between groups may explain some inconsistencies in results. Studies reporting larger calorie deficits in the IER group did not show proportionately greater effects. The review notes that while IER may trigger beneficial metabolic switching via fasting periods, evidence remains limited. Overall, the findings highlight that the 5:2 diet is a viable but not superior option, and longer, well-controlled studies are needed.

Elsworth RL, Monge A, Perry R, Hinton EC, Flynn AN, Whitmarsh A, Hamilton-Shield JP, Lawrence NS, Brunstrom JM. The Effect of Intermittent Fasting on Appetite: A Systematic Review and Meta-Analysis. Nutrients. 2023 Jun 1;15(11):2604. doi: 10.3390/nu15112604. PMID: 37299567; PMCID: PMC10255792.

This meta-analysis found no clear evidence that intermittent fasting (IF) alters appetite—such as hunger, fullness, desire to eat, or prospective food consumption—any differently than continuous energy restriction (CER). These findings contrast with earlier narrative reviews suggesting IF might blunt the increase in appetite that often accompanies weight loss. The discrepancy may arise from methodological differences, as this review used a direct statistical comparison across randomised controlled trials rather than counting individual study outcomes.

Subgroup analysis revealed no difference in self-reported energy intake between IF and CER groups. While a fixed-effects sensitivity analysis did show slightly increased fullness and decreased desire to eat with IF, these effects were small and should be interpreted with caution given the medium-to-high risk of bias, largely due to the unblinded nature of behavioural interventions and the reliance on self-reported appetite.

Importantly, appetite responses may vary by time of day. One study showed a midday difference in hunger between IF and CER, suggesting circadian influences. The authors propose using ecological momentary assessment (EMA)—a real-time tracking method—as a more precise tool for measuring appetite fluctuations across the day.

In conclusion, IF does not appear to offer appetite regulation advantages over CER, but better-designed future studies using EMA may uncover more nuanced effects.

Li Z, Huang L, Luo Y, Yu B, Tian G. Effects and possible mechanisms of intermittent fasting on health and disease: a narrative review. Nutr Rev. 2023 Nov 10;81(12):1626-1635. doi: 10.1093/nutrit/nuad026. PMID: 36940184.

"Abstract The imbalance between energy intake and expenditure in an environment of continuous food availability can lead to metabolic disturbances in the body and increase the risk of obesity and a range of chronic noncommunicable diseases. Intermittent fasting (IF) is one of the most popular nonpharmacological interventions to combat obesity and chronic noncommunicable diseases. The 3 most widely studied IF regimens are alternate-day fasting, time-restricted feeding, and the 5:2 diet. In rodents, IF helps optimize energy metabolism, prevent obesity, promote brain health, improve immune and reproductive function, and delay aging. In humans, IF’s benefits are relevant for the aging global population and for increasing human life expectancy. However, the optimal model of IF remains unclear. In this review, the possible mechanisms of IF are summarized and its possible drawbacks are discussed on the basis of the results of existing research, which provide a new idea for nonpharmaceutical dietary intervention of chronic noncommunicable diseases."

van den Burg EL, van Peet PG, Schoonakker MP, van de Haar DE, Numans ME, Pijl H. Metabolic impact of intermittent energy restriction and periodic fasting in patients with type 2 diabetes: a systematic review. Nutr Rev. 2023 Sep 11;81(10):1329-1350. doi: 10.1093/nutrit/nuad015. PMID: 36888890; PMCID: PMC10494137.

This systematic review assessed intermittent energy restriction (IER) - including time-restricted eating, the 5:2 diet, and alternate-day modified fasting - and periodic fasting (PF) in people with type 2 diabetes (T2D). The findings suggest that IER and PF offer similar short-term benefits to continuous energy restriction (CER) in improving body weight, glucose regulation, and metabolic control. However, evidence on their effects on blood pressure, lipid profiles, and glucose-lowering medication dosage remains limited.

While a few studies showed that IER may reduce medication requirements, data are sparse and often not statistically robust. Adherence to IER was generally comparable to CER, though longer interventions saw declining compliance. Patient experience and treatment satisfaction were largely underreported, despite their clinical relevance. Safety concerns persist, particularly for insulin or sulfonylurea users, due to increased hypoglycaemia risk. Most studies excluded such patients, limiting generalisability. No specific IER approach can currently be recommended over another.

The review highlights a need for larger, long-term, well-controlled trials assessing medication needs, hypoglycaemia risk, and personalised responses to dietary patterns. Overall, IER and PF may offer promising alternatives or adjuncts to CER in managing T2D, but more robust evidence is needed before formal clinical recommendations can be made.

Elortegui Pascual P, Rolands MR, Eldridge AL, Kassis A, Mainardi F, Lê KA, Karagounis LG, Gut P, Varady KA. A meta-analysis comparing the effectiveness of alternate day fasting, the 5:2 diet, and time-restricted eating for weight loss. Obesity (Silver Spring). 2023 Feb;31 Suppl 1(Suppl 1):9-21. doi: 10.1002/oby.23568. Epub 2022 Nov 8. Erratum in: Obesity (Silver Spring). 2025 May;33(5):1011. doi: 10.1002/oby.24266. PMID: 36349432; PMCID: PMC10098946.

This meta-analysis found that intermittent fasting (IF) regimens—alternate-day or modified alternate-day fasting (ADF/MADF), time-restricted eating (TRE), and the 5:2 diet—achieved similar weight loss outcomes to continuous energy restriction (CER). Among the IF methods, ADF/MADF had the highest probability of ranking first for weight-loss effectiveness, though individual responses varied widely due to study heterogeneity.

Weight loss across IF protocols ranged from approximately 1% to 13% over periods of 2 to 52 weeks. The short duration of most studies (maximum 12 months) and small sample sizes limit conclusions on long-term outcomes. Mechanistically, IF regimens improve metabolic flexibility through alternating periods of nutrient availability, potentially supporting fat mobilisation and energy balance. However, adherence to IF declined after 3 months, similar to CER, suggesting that sustained compliance is a key challenge across all diets. While ADF/MADF appears promising for meaningful weight loss, further direct comparisons and long-term studies are needed to confirm superiority and assess nutritional adequacy.

Overall, IF can be considered a viable alternative to CER for weight management, provided the individual finds it acceptable and sustainable. Future research should focus on longer-duration trials, adherence metrics, and mechanistic pathways that contribute to weight and metabolic health outcomes.

Kim KK, Kang JH, Kim EM. Updated Meta-Analysis of Studies from 2011 to 2021 Comparing the Effectiveness of Intermittent Energy Restriction and Continuous Energy Restriction. J Obes Metab Syndr. 2022 Sep 30;31(3):230-244. doi: 10.7570/jomes22050. PMID: 36177730; PMCID: PMC9579470.

This meta-analysis reviewed 16 randomised controlled trials involving over 1,400 participants to compare the effects of intermittent energy restriction (IER), including 5:2 fasting, with continuous energy restriction (CER) over periods of 12 weeks or more. The findings confirm that IER produces weight loss and metabolic improvements comparable to CER, but not superior.

Across all studies, both IER and CER led to significant reductions in body weight, waist circumference, and body fat percentage. However, there were no meaningful differences between the groups. Most participants lost between 0.6 and 13.9 kg depending on the study duration and design. Blood glucose reductions were slightly better in the CER group, though results varied, and HbA1c improvements were similar across both diets. Lipid profiles improved modestly, with CER slightly favoured for triglycerides and HDL, while IER appeared marginally better for total and LDL cholesterol—though these findings were inconsistent and not robust across all subgroup analyses.

One important observation is that attrition rates were similar for both groups—roughly 25%—suggesting that intermittent fasting is not necessarily easier to stick to than daily restriction, at least during the active weight loss phase. While IER offers flexibility and may suit those who prefer structure over constant restraint, it did not result in greater adherence in practice.

In short, this meta-analysis reinforces that the 5:2 diet is a valid alternative to traditional calorie restriction. It works well for many people, but it’s not a magic solution or clearly superior. Like any diet, success depends on individual preference, support, and consistency over time.

Kord Varkaneh H, Salehi Sahlabadi A, Găman MA, Rajabnia M, Sedanur Macit-Çelebi M, Santos HO, Hekmatdoost A. Effects of the 5:2 intermittent fasting diet on non-alcoholic fatty liver disease: A randomized controlled trial. Front Nutr. 2022 Jul 26;9:948655. doi: 10.3389/fnut.2022.948655. PMID: 35958257; PMCID: PMC9360602.

This 12-week randomised controlled trial investigated the effects of the 5:2 intermittent fasting (IF) diet on patients with non-alcoholic fatty liver disease (NAFLD). Participants following the 5:2 diet—two consecutive days of 75% energy restriction and five days of normal intake—showed significant improvements in body composition, liver health, and inflammatory markers compared to a control group following their usual diet.

Patients on the 5:2 diet experienced a mean weight loss of 3.7 kg, alongside reductions in BMI, waist circumference, and fat mass. Liver steatosis and fibrosis scores significantly improved, as did liver enzymes ALT and AST. Triglyceride levels dropped by 43 mg/dL, and inflammation markers hs-CRP and CK-18 were also significantly reduced. However, the diet had no significant impact on HDL, LDL, total cholesterol, fasting glucose, insulin, HOMA-IR, or total antioxidant capacity.

These results suggest the 5:2 IF diet is a safe and effective non-pharmacological option for managing NAFLD, particularly in improving hepatic parameters and reducing adiposity and inflammation. While it may not surpass other dietary approaches, it offers a viable and practical option that can be tailored to individual needs as part of broader lifestyle intervention strategies.

Keenan SJ, Cooke MB, Hassan EB, Chen WS, Sullivan J, Wu SX, El-Ansary D, Imani M, Belski R. Intermittent fasting and continuous energy restriction result in similar changes in body composition and muscle strength when combined with a 12 week resistance training program. Eur J Nutr. 2022 Jun;61(4):2183-2199. doi: 10.1007/s00394-022-02804-3. Epub 2022 Jan 27. PMID: 35084574; PMCID: PMC9106626.

This 12-week randomised controlled trial compared the effects of 5:2 intermittent fasting (IFT) and continuous energy restriction (CERT), both combined with moderate protein intake and supervised resistance training, on body composition and strength in untrained adults. Participants in both groups experienced significant improvements in lean body mass (LBM), muscle strength, and reductions in body weight and fat mass. Specifically, LBM increased by 3.7% and fat mass decreased by 24.1%, with no significant differences between the two dietary strategies overall.

Participants in the 5:2 fasting group followed a protocol involving two non-consecutive days per week of ~70% energy restriction, supported by protein-rich meals, and ate at maintenance levels on non-fasting days. The CERT group followed a consistent daily energy deficit of ~20%. Both groups gained similar strength in upper and lower body exercises, and both reduced subcutaneous and intramuscular fat. While CERT participants showed slightly greater increases in thigh muscle surface area, IFT participants maintained or gained LBM regardless of weight loss, suggesting a potential protective effect on muscle mass.

The study concludes that 5:2 intermittent fasting is as effective as continuous restriction when paired with resistance training and adequate protein intake, offering a viable alternative for improving body composition and muscle strength.

Gao Y, Tsintzas K, Macdonald IA, Cordon SM, Taylor MA. Effects of intermittent (5:2) or continuous energy restriction on basal and postprandial metabolism: a randomised study in normal-weight, young participants. Eur J Clin Nutr. 2022 Jan;76(1):65-73. doi: 10.1038/s41430-021-00909-2. Epub 2021 May 26. PMID: 34040199; PMCID: PMC8766278.

This small, two-week randomised trial compared 5:2 intermittent energy restriction (IER) with continuous energy restriction (CER) in healthy, normal-weight young adults. Both diets produced similar short-term weight loss (~2.5 kg) and had no significant differences in postprandial insulin, glucose, free fatty acid (FFA), triglyceride (TAG) responses, or subjective appetite ratings during a 3-hour post-meal period. However, 5:2 IER significantly improved fasting blood glucose and fasting appetite ratings (composite appetite score), indicating reduced hunger and greater satiety at rest.

Although postprandial responses to a liquid meal and an ad libitum pasta meal were comparable between groups, the fasting improvements observed with 5:2 IER suggest enhanced hepatic insulin sensitivity or altered metabolic regulation in the fasting state. These benefits appeared independent of weight loss, which was similar across both groups. Importantly, the 5:2 IER group also reported better appetite control in the fasted state—potentially supporting better long-term adherence.

Overall, while 5:2 IER did not outperform CER in post-meal metabolism, it offered additional fasting-state benefits, particularly in glucose control and appetite regulation. These findings support the idea that metabolic advantages of 5:2 fasting may stem from fasting-phase mechanisms, rather than immediate postprandial effects, especially in healthy individuals.

Cook F, Langdon-Daly J, Serpell L. Compliance of participants undergoing a '5-2' intermittent fasting diet and impact on body weight. Clin Nutr ESPEN. 2022 Dec;52:257-261. doi: 10.1016/j.clnesp.2022.08.012. Epub 2022 Aug 17. PMID: 36513463.

This 28-day study evaluated compliance and outcomes of a 5:2 intermittent fasting (IF) regimen, where participants restricted energy intake to 500–650 kcal on two non-consecutive “fast” days per week. Among 52 adults (mostly female, mean age ~44), median weight loss was modest but statistically significant at 1.8 kg (2.8%), with a marked reduction in overall energy intake compared to baseline (from ~1752 to ~1288 kcal/day, p < 0.001). However, only 55.8% of participants adhered to the strict calorie targets on fast days, which is lower than reported in many previous trials. Additionally, participants consumed significantly more energy on non-fast days following a fast day (mean ~1928 kcal) compared to non-fast days not following a fast (~1316 kcal), suggesting a compensatory eating pattern. Despite this, the net energy reduction still led to weight loss.

The findings highlight that while the 5:2 IF diet can reduce energy intake and support short-term weight loss, variable compliance and rebound eating on non-fast days may limit its effectiveness for some. Long-term adherence and strategies to manage post-fast compensation remain key areas for further investigation.

Kang J, Shi X, Fu J, Li H, Ma E, Chen W. Effects of an Intermittent Fasting 5:2 Plus Program on Body Weight in Chinese Adults with Overweight or Obesity: A Pilot Study. Nutrients. 2022 Nov 9;14(22):4734. doi: 10.3390/nu14224734. PMID: 36432420; PMCID: PMC9698935.

Hajek P, Przulj D, Pesola F, McRobbie H, Peerbux S, Phillips-Waller A, Bisal N, Myers Smith K. A randomised controlled trial of the 5:2 diet. PLoS One. 2021 Nov 17;16(11):e0258853. doi: 10.1371/journal.pone.0258853. PMID: 34788298; PMCID: PMC8598045.

This 12-week retrospective cohort study examined the effects of a modified 5:2 intermittent fasting regimen—called the 5:2 Plus program—in Chinese adults with overweight or obesity. The program involved 30% of energy needs on two non-consecutive fasting days and 70% of energy needs on non-fasting days, contrasting with typical 5:2 plans that allow full intake on non-fasting days. Outcomes were compared to daily calorie restriction (CR) and CR with high-protein meal replacements (HP).

The 5:2 Plus group achieved the greatest weight loss, with an average 9.0% total weight loss, compared to 5.7% in the CR group (p < 0.001) and 8.6% in the HP group. A significantly greater proportion of 5:2 Plus participants lost over 5% (85.7%) and 10% (45.2%) of their initial body weight than those on daily CR. Improvements in BMI and body composition (increased fat-free mass ratio) were also observed in all groups.

Importantly, no serious adverse events were reported, and compliance appeared good with supportive behavioural strategies and structured follow-up. This pilot study suggests that 5:2 Plus may offer superior short-term weight loss compared to daily CR, even without meal replacements. However, long-term effects and generalisability remain to be confirmed in larger, prospective randomised trials.

This UK randomised controlled trial investigated the effectiveness of the 5:2 intermittent fasting diet compared to standard brief weight loss advice and explored whether group support could enhance adherence and outcomes. A total of 300 adults with obesity were randomly assigned to one of three groups: self-help 5:2 (5:2SH), 5:2 with weekly group support (5:2G), or standard brief advice (SBA). Over the 12-month follow-up, weight loss across all groups was modest, with participants in the 5:2SH and SBA arms losing an average of 1.9 kg and 1.8 kg respectively, while those in the 5:2G group lost 2.6 kg. These differences were not statistically significant.

By one year, 18% of participants in the 5:2SH group and 15% in the SBA group had lost at least 5% of their baseline weight, compared to 28% in the 5:2G group. However, adherence to the 5:2 diet declined substantially over time, from 74% at six weeks to 22% at one year. Despite this, participants rated the 5:2 diet more positively than standard advice, particularly in terms of helpfulness and likelihood of recommending it to others. Group support initially boosted adherence and reduced reported hunger on fasting days, but the benefits faded without continued support.

Overall, the 5:2 diet was not superior to standard advice in long-term weight outcomes, but its simplicity, favourable user ratings, and ease of delivery make it an attractive alternative for brief clinical guidance. This study suggests that the 5:2 approach may be a useful option for patients who struggle with more complex or demanding weight management strategies, though sustaining adherence remains a challenge.

Scholtens EL, Krebs JD, Corley BT, Hall RM. Intermittent fasting 5:2 diet: What is the macronutrient and micronutrient intake and composition? Clin Nutr. 2020 Nov;39(11):3354-3360. doi: 10.1016/j.clnu.2020.02.022. Epub 2020 Feb 22. PMID: 32199696.

This study investigated the macronutrient and micronutrient intake of individuals following the 5:2 intermittent fasting (IF) diet, a regimen that restricts energy intake on two days per week while allowing habitual intake on the remaining five. Data from 38 overweight or obese participants—including individuals with and without type 2 diabetes—were analysed using 4-day estimated food records at baseline and after six weeks of the diet.

The findings showed that during the IF 5:2 protocol, daily energy intake was composed of approximately 22% protein, 33% fat, and 39% carbohydrates. Notably, carbohydrate and fibre intake significantly decreased from baseline to week six, and were also lower on fasting days compared to non-fasting days. Protein intake as a percentage of energy increased on fasting days, rising from 21% to 25%.

Micronutrient analysis revealed suboptimal intake of calcium, magnesium, potassium, and zinc, while sodium intake was consistently above recommended levels. Despite the lack of imposed restrictions on non-fasting days, total energy intake declined over the six-week period, suggesting a spontaneous reduction in caloric consumption.

Overall, the 5:2 diet was found to be high in protein, moderate in fat, and low in carbohydrates and fibre. While some micronutrient intake fell below guideline levels, the diet was deemed safe and acceptable as a short-term weight-loss strategy.

Carter S, Clifton PM, Keogh JB. Effect of Intermittent Compared With Continuous Energy Restricted Diet on Glycemic Control in Patients With Type 2 Diabetes: A Randomized Noninferiority Trial. JAMA Netw Open. 2018 Jul 6;1(3):e180756. doi: 10.1001/jamanetworkopen.2018.0756. PMID: 30646030; PMCID: PMC6324303.

This 12-month randomised noninferiority trial* compared the effects of a 5:2 intermittent energy restriction (IER) diet to continuous energy restriction (CER) in adults with type 2 diabetes. A total of 137 participants were assigned to either two non-consecutive days of severe caloric restriction per week (500–600 kcal/day) or a standard daily calorie-restricted diet (1200–1500 kcal/day). Both diets aimed for a similar weekly energy deficit.

At 12 months, both groups achieved clinically meaningful reductions in HbA1c (–0.3% for IER vs –0.5% for CER), meeting the predefined margin for equivalence. Weight loss was also similar, though slightly greater in the IER group (–6.8 kg vs –5.0 kg), but the between-group difference did not meet statistical equivalence criteria. Fat mass and fat-free mass decreased in both groups, with slightly greater fat-free mass loss in the IER group. Medication use, glycemic events, and lipid profiles improved similarly between groups.

The study found that IER is a safe and effective alternative to CER for glycemic control in type 2 diabetes, with the potential for greater weight loss. It is well tolerated, but requires careful medication management for patients on insulin or sulfonylureas. Regular support was key to better outcomes, particularly during the initial phase of treatment.

*A noninferiority trial tests whether a new treatment is not significantly worse than the standard treatment by more than a set margin. It's used when the new option might offer other benefits like fewer side effects, lower cost, or easier use, even if it's slightly less effective.

Harvie MN, Pegington M, Mattson MP, Frystyk J, Dillon B, Evans G, Cuzick J, Jebb SA, Martin B, Cutler RG, Son TG, Maudsley S, Carlson OD, Egan JM, Flyvbjerg A, Howell A. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes (Lond). 2011 May;35(5):714-27. doi: 10.1038/ijo.2010.171. Epub 2010 Oct 5. PMID: 20921964; PMCID: PMC3017674.

A six-month randomised trial published in International Journal of Obesity compared intermittent energy restriction (IER)—a 5:2 style approach—with continuous energy restriction (CER) in overweight premenopausal women. Both diets aimed to create the same overall energy deficit. The study found that IER and CER produced comparable weight loss, with women in the IER group losing an average of 6.4 kg, and those in the CER group losing 5.6 kg. Around one-third of women in each group achieved a 10% reduction in body weight—an amount associated with clinically meaningful improvements in health.

Crucially, both groups saw reductions in fat mass, waist circumference, blood pressure, cholesterol, triglycerides, and inflammatory markers. However, the IER group showed greater improvements in fasting insulin and insulin resistance, suggesting that short, intense fasting periods may offer additional metabolic benefits. These improvements were still present five days after the fasting days had ended, hinting at longer-lasting effects on glucose control.

Adherence was slightly lower in the IER group, and some participants reported hunger or difficulty fitting the protocol into their routines. Nonetheless, most continued with at least one fasting day per week by the end of the trial. Importantly, there was no evidence of rebound overeating on non-fasting days.

This study supports the 5:2 diet as a flexible and effective option for weight loss and metabolic health, with benefits at least equal to daily calorie restriction.