Modified alternate-day fasting

What it is

Modified alternate-day fasting alternates a fast day, when about a quarter of usual energy needs is eaten, with a feed day. In the largest year-long trial, participants ate 25% of energy needs on fast days and 125% on alternating feast days.

What the research says

Modified ADF leads to weight loss compared with no diet change. An umbrella review rated this high quality for BMI over 1 to 2 months. Compared with ordinary daily calorie restriction, the only year-long RCT found similar weight loss and no advantage. In that trial dropout was higher, participants struggled to hit fast-day targets, and LDL cholesterol rose relative to daily restriction by 12 months.

Evidence grade: Well established.

The schedule

• Pattern: weekly
• Fast days per week: 3.5
• Calorie limit on fast days: about 25% of energy needs (often one meal of about 500 kcal) on fast days, alternating with unrestricted or 125% 'feast' days

Why people choose it

Modified ADF allows a small meal on fast days, which may be easier to tolerate than a full fast. It has the strongest evidence of any intermittent fasting type for short-term weight loss compared with a regular diet: an umbrella review rated one BMI result high quality. But in a year-long trial against daily calorie restriction, it gave no better adherence, weight loss or heart-risk markers, and more people dropped out (38% vs 29%).

Cautions

• Older adults and people at risk of sarcopenia: A meta-analysis of ADF trials found lean mass fell, and its authors warn this could worsen muscle loss. (Source 1)
• People with raised LDL cholesterol or heart disease risk: In the year-long trial, LDL cholesterol was higher by month 12 with modified ADF than with daily calorie restriction. (Source 2)
• People with diabetes, pregnant or breastfeeding women, and people with a history of eating disorders or disordered eating: The Academy of Nutrition and Dietetics does not recommend intermittent fasting for these groups. (Source 3)
• People taking insulin: A Johns Hopkins fasting researcher warns of unsafe hypoglycaemia during fasting periods for people on insulin with type 1 diabetes. (Source 4)
• Anyone taking medicines: The Academy of Nutrition and Dietetics advises discussing fasting with a doctor first, especially when medicines may need adjusting. (Source 3)

What goes wrong

Dropout was highest with modified ADF: 38%, against 29% with daily calorie restriction and 26% in controls. (Source 2)

• Randomized trial, Certainty not rated.
• Size: 100 adults.
• Who: Metabolically healthy adults with obesity.
• How long: 12 months.
• Result: Dropout 13 of 34 (38%) ADF vs 10 of 35 (29%) daily restriction vs 8 of 31 (26%) control.
• Funding: independent: NIH grants listed in the Europe PMC record.

Among the 100 participants (86 women and 14 men; mean [SD] age, 44 ¹¹ years), the dropout rate was highest in the alternate-day fasting group (13 of 34 [38%]), vs the daily calorie restriction group (10 of 35 [29%]) and control group (8 of 31 [26%]).

Participants on modified ADF ate more than prescribed on fast days and less than prescribed on feast days, while the daily restriction group mostly met its targets. (Source 2)

• Randomized trial, Certainty not rated.
• Size: 100 adults.
• Who: Metabolically healthy adults with obesity.
• How long: 12 months.
• Result: Fast-day energy targets not met (figures not in abstract)
• Funding: independent: NIH grants listed in the Europe PMC record.

Participants in the alternate-day fasting group ate more than prescribed on fast days, and less than prescribed on feast days, while those in the daily calorie restriction group generally met their prescribed energy goals.

By month 12, LDL cholesterol was significantly higher with modified ADF than with daily calorie restriction. (Source 2)

• Randomized trial, Certainty not rated.
• Size: 100 adults.
• Who: Metabolically healthy adults with obesity.
• How long: 12 months.
• Result: LDL cholesterol +11.5 mg/dL (95% CI 1.9 to 21.1) vs daily restriction.
• Funding: independent: NIH grants listed in the Europe PMC record.

Limit of this finding: HDL rose at 6 months (6.2 mg/dL) but not at 12 months.

Mean low-density lipoprotein cholesterol levels were significantly elevated by month 12 among the participants in the alternate-day fasting group (11.5 mg/dL [95% CI, 1.9-21.1 mg/dL]) compared with those in the daily calorie restriction group.

In that trial, two participants had mild headaches in week 1, one had constipation, and one dropped out because they could not stick to the diet. (Source 5)

• Randomized trial, Certainty not rated.
• Size: 32.
• Who: Normal-weight and overweight adults.
• How long: 12 weeks.
• Result: 2 mild headaches, 1 constipation, 1 dropout for non-adherence.
• Funding: independent (University of Illinois departmental grant)

Two subjects experienced mild headaches during week 1 of the trial, which may or may not be related to dietary treatment.

A meta-analysis of alternate-day fasting RCTs (mostly 25%-energy designs) found a significant reduction in lean mass. (Source 1)

• Meta-analysis, Certainty not rated.
• Size: 7 RCTs, 269 participants.
• Who: Adults.
• How long: short-term.
• Result: Lean mass p = 0.002 vs control.
• Funding: independent: National Natural Science Foundation of China, Taishan Scholars Program, Beijing Municipal Administration of Hospitals.

Limit of this finding: Most pooled trials used 25%-energy fast days; the authors call the evidence low in rigour.

We found a significant reduction in lean mass in the ADF group. This serves as a caution for patient populations at risk for sarcopenia because ADF could exacerbate muscle loss.

What the evidence supports

An umbrella review rated modified ADF for 1 to 2 months as high-quality evidence for a moderate reduction in BMI compared with a regular diet. This was the only association in the review graded high quality. (Source 6)

• Review of reviews, High certainty.
• Size: 11 meta-analyses of 130 RCTs.
• Who: Healthy adults and adults with overweight, obesity or non-alcoholic fatty liver disease.
• How long: 1 to 2 months.
• Result: Moderate reduction in BMI (effect size not given in the abstract)
• Funding: not stated.

Limit of this finding: The comparator was a regular diet, not calorie restriction, and the result covers only 1 to 2 months.

One significant association (1%) supported by high-quality evidence was modified alternate-day fasting for 1 to 2 months, which was associated with moderate reduction in body mass index in healthy adults and adults with overweight, obesity, or nonalcoholic fatty liver disease compared with regular diet.

The umbrella review also linked modified ADF with improvements in LDL cholesterol, total cholesterol, triglycerides and blood pressure over 2 to 12 months, compared with regular diet. (Source 6)

• Review of reviews, Certainty not rated.
• Size: 11 meta-analyses of 130 RCTs.
• Who: Adults.
• How long: 2 to 12 months.
• Result: Associations with lower LDL-C, total cholesterol, triglycerides and blood pressure.
• Funding: not stated.

Limit of this finding: In the Trepanowski trial, LDL rose relative to daily calorie restriction at 12 months.

MADF was also found to be associated with improvement of several cardiometabolic risk factors in the first 2 to 12 months including LDL-C, total cholesterol, triglycerides, and blood pressure.

In non-obese adults, 12 weeks of modified ADF was followed by weight and fat-mass loss in the ADF group, and the authors concluded ADF is effective for weight loss; they called for larger trials. (Source 5)

• Randomized trial, Certainty not rated.
• Size: 32 randomised, 30 completed.
• Who: Normal-weight and overweight adults (BMI 20 to 29.9)
• How long: 12 weeks.
• Result: Within the ADF group: weight -5.2 kg (6.5%), fat mass -3.6 kg, fat-free mass unchanged; these are changes in the ADF arm, not between-group differences from control; fast-day adherence 98%.
• Funding: independent (University of Illinois departmental grant)

Limit of this finding: Small and short; the comparison group was controls, not calorie restriction. The authors call for larger trials.

These findings suggest that ADF is effective for weight loss and cardio-protection in normal weight and overweight adults, though further research implementing larger sample sizes is required before solid conclusion can be reached.

What the evidence does not support

In a one-year RCT, modified ADF gave no better adherence, weight loss, weight maintenance or heart-risk markers than daily calorie restriction. (Source 2)

• Randomized trial, Certainty not rated.
• Size: 100 adults (86 women, 14 men)
• Who: Metabolically healthy adults with obesity, aged 18 to 64, mean BMI 34.
• How long: 12 months (6 months weight loss, 6 months maintenance)
• Result: Weight -6.8% vs -6.8% at 6 months; -6.0% (95% CI -8.5% to -3.6%) vs -5.3% (-7.6% to -3.0%) at 12 months, relative to control.
• Funding: independent: NIH grants listed in the Europe PMC record.

Limit of this finding: A single-centre trial, mostly in women.

Alternate-day fasting did not produce superior adherence, weight loss, weight maintenance, or cardioprotection vs daily calorie restriction.

In the same trial, blood pressure, glucose, insulin, insulin resistance and CRP did not differ between modified ADF and daily restriction. (Source 2)

• Randomized trial, Certainty not rated.
• Size: 100 adults.
• Who: Metabolically healthy adults with obesity.
• How long: 12 months.
• Result: No significant differences at months 6 or 12.
• Funding: independent: NIH grants listed in the Europe PMC record.

There were no significant differences between the intervention groups in blood pressure, heart rate, triglycerides, fasting glucose, fasting insulin, insulin resistance, C-reactive protein, or homocysteine concentrations at month 6 or 12.

A Cochrane review that included modified alternate-day fasting trials found little to no difference in weight loss compared with regular dietary advice. (Source 7)

• Systematic review, Low certainty.
• Size: 21 studies, 1,430 participants.
• Who: Adults with overweight or obesity.
• How long: 6 to 12 months.
• Result: MD -0.33 percentage points (95% CI -0.92 to 0.26)
• Funding: independent (no dedicated funding)

Limit of this finding: The review pools all intermittent fasting types and reports no separate modified-ADF result in its abstract.

Compared to regular dietary advice, intermittent fasting may result in little to no difference in percentage from baseline weight loss (MD -0.33, 95% CI -0.92 to 0.26; 21 studies, 1430 participants; low-certainty evidence due to risk of bias).

What official bodies say

The Academy of Nutrition and Dietetics states that some modified fasting studies saw more weight loss than traditional diets, but the difference was not significant. (Source 3)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: General public.
• How long: not applicable.
• Result: not applicable.
• Funding: not stated.

Limit of this finding: Consumer page reviewed by Academy staff in July 2025.

Participants in some modified fasting weight loss studies lost more weight than those on traditional weight-loss diets, although the difference was not significant.

Where the research disagrees

Whether modified ADF is a better weight-loss approach

• Patikorn and colleagues (umbrella review, 2021), umbrella: The evidence supports intermittent fasting, especially modified ADF, as a weight-loss approach; its BMI benefit over a regular diet was the only high-quality result. (Source 6)
• Trepanowski and colleagues (1-year RCT, 2017), rct: Compared with daily calorie restriction, modified ADF gave no better adherence, weight loss or cardioprotection. (Source 2)

A common belief, and what the research shows

The belief: Because modified ADF has the strongest evidence among fasting types, it must beat ordinary dieting.

What the research shows: The strong evidence compares it with a regular diet over 1 to 2 months. Against daily calorie restriction over a year, weight loss was the same (-6.0% vs -5.3%) and more people dropped out.

References

1. Frontiers in Nutrition. Health Effects of Alternate-Day Fasting in Adults: A Systematic Review and Meta-Analysis. 2020. PMID 33330587, DOI 10.3389/fnut.2020.586036. Read the source
2. JAMA Internal Medicine. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. 2017. PMID 28459931, DOI 10.1001/jamainternmed.2017.0936. Read the source
3. Academy of Nutrition and Dietetics (eatright.org). What is Intermittent Fasting? (Barbara Gordon, RDN, LD; reviewed by Academy staff RDNs, July 21, 2025). 2025. Read the source
4. Johns Hopkins Medicine. Intermittent Fasting: What Is It, And How Does It Work? (expert Q&A with Mark Mattson, PhD). Read the source
5. Nutrition Journal. Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. 2013. DOI 10.1186/1475-2891-12-146. Read the source
6. JAMA Network Open. Intermittent Fasting and Obesity-Related Health Outcomes: An Umbrella Review of Meta-analyses of Randomized Clinical Trials. 2021. PMID 34919135, DOI 10.1001/jamanetworkopen.2021.39558. Read the source
7. Cochrane Database of Systematic Reviews. Intermittent fasting for adults with overweight or obesity. 2026. PMID 41692034, DOI 10.1002/14651858.CD015610.pub2. Read the source