Ramadan fasting

What it is

During the lunar month of Ramadan, Muslims do not eat or drink between dawn and sunset for about 30 days in a row. The length of each daily fast depends on the season and the country; one case report describes an average of 14 hours a day. People who are ill, including some people with diabetes, may be exempt, but many fast anyway.

What the research says

The evidence is mostly before-and-after observational studies pooled in meta-analyses, with no randomised comparison possible. It shows small, short-lived drops in body weight and fat, lower blood pressure after Ramadan in most groups except people with chronic kidney disease, little change in glucose, insulin and insulin resistance in healthy people, about an hour less sleep per night, more hypoglycaemia in people with type 2 diabetes taking sulfonylureas, no measurable effect on birth weight when pregnant women fast, but associations with poorer health in children and adults who were exposed in the womb. Evidence on heart attacks and strokes in people with diabetes is insufficient.

Evidence grade: Limited evidence.

The schedule

• Pattern: religious

Why people choose it

Ramadan fasting is chosen for religious reasons rather than for health, so the question for most people is how to fast safely rather than whether to fast. Meta-analyses of studies measuring people before and after Ramadan found a small drop in body weight (about 1 kg on average) and fat mass, mostly in people with overweight or obesity, but weight and body composition moved back towards pre-Ramadan values within 2 to 5 weeks. For people with diabetes, the IDF-DAR 2021 guidelines sort people into high, moderate and low risk groups before Ramadan.

Cautions

• People with diabetes classed as high risk under the IDF-DAR 2021 score: The IDF-DAR 2021 guidelines define high risk as the group where fasting is probably unsafe, moderate risk where safety is uncertain, and low risk where fasting is probably safe. (Source 1)
• People taking insulin or sulfonylureas: The guidelines flag people on both insulin and a sulfonylurea, or on three or more medicines, as at increased risk of hypoglycaemia; a systematic review found more hypoglycaemia with sulfonylureas than other medicines. (Source 1)
• People taking SGLT2 inhibitors (for example dapagliflozin): A case report describes euglycaemic diabetic ketoacidosis in a 51-year-old man taking dapagliflozin and metformin who fasted about 14 hours a day during Ramadan. (Source 2)
• Pregnant women: Birth weight did not differ, but a life-course meta-analysis found associations with poorer child and adult health, with the first trimester as a sensitive period. (Source 3)
• People with type 1 diabetes: An NIDDK clinician interview notes higher risk of dehydration and diabetic ketoacidosis in type 1 compared with type 2 diabetes. (Source 4)
• People with chronic kidney disease: The blood pressure fall seen in other groups was not seen in people with chronic kidney disease; the IDF-DAR score gives high points for low kidney function. (Source 5)

What goes wrong

Part of the weight lost during Ramadan was fat-free (lean) mass, and this loss was statistically significant. (Source 6)

• Meta-analysis, Certainty not rated.
• Size: 2,947 participants from 70 publications.
• Who: Healthy non-athlete adults.
• How long: About one month.
• Result: Fat-free mass loss was significant and about 30% smaller than the loss of absolute fat mass.
• Funding: not stated.

Limit of this finding: Uncontrolled pre-post data; bioimpedance and other methods varied between studies.

Loss of fat-free mass was also significant between pre-Ramadan and post-Ramadan, but was about 30% less than loss of absolute fat mass.

During Ramadan, total sleep time fell by about an hour a night (a moderate pooled effect); daytime sleepiness scores rose by nearly one point, but the pooled effect on daytime sleepiness was negligible. (Source 7)

• Meta-analysis, Certainty not rated.
• Size: 646 participants in 24 studies (median age 23.7 years, 73% men)
• Who: Mostly young adults in 12 countries.
• How long: Ramadan month.
• Result: Total sleep time 7.2 h before vs 6.4 h during Ramadan (Hedges' g -0.43, 95% CI -0.64 to -0.22; K = 22, N = 571); Epworth Sleepiness Scale 6.1 vs 7.0, a negligible pooled effect (Hedges' g -0.06, 95% CI -0.43 to 0.28; K = 9, N = 362)
• Funding: not stated.

Limit of this finding: Participants were mostly young men; older adults are under-represented.

During the month of Ramadan, there is approximately a 1 hour reduction in TST and nearly a 1 point increase in the ESS score.

In people with type 2 diabetes who fasted during Ramadan, medicines other than sulfonylureas were linked to fewer hypoglycaemic events than sulfonylureas. (Source 8)

• Systematic review, Certainty not rated.
• Size: 68 studies (35 RCTs and 33 observational studies)
• Who: Adults with type 2 diabetes who fasted during Ramadan.
• How long: Ramadan month.
• Result: Non-sulfonylurea medicines showed fewer hypoglycaemic events than sulfonylureas (no pooled estimate given in the abstract)
• Funding: not stated.

Non-sulfonylureas hypoglycemic medications showed superior effects in lowering the incidence of HE over sulfonylureas hypoglycemic medications.

A later meta-analysis found that being in the womb during Ramadan was associated with poorer health in childhood and especially adulthood, even though no effects were seen at birth. (Source 3)

• Meta-analysis, Low certainty.
• Size: 31 studies (several million subjects); 22 studies in the meta-analyses.
• Who: People whose mothers were pregnant during Ramadan.
• How long: Life course, from birth to adulthood.
• Result: Birth weight MD -3 g (95% CI -18 to 11); cognitive tests -3.10% of an SD (95% CI -4.61 to -1.58); height-for-age z-score -0.03 (95% CI -0.06 to -0.00); hearing disability OR 1.26 (95% CI 1.09 to 1.45); first trimester a sensitive period.
• Funding: not stated.

Limit of this finding: Built on observational (natural-experiment) studies; the authors call for more high-quality studies to improve certainty. Exposure is to Ramadan during pregnancy, not confirmed maternal fasting in every study. The authors rate the quality of evidence low to moderate across outcomes.

Ramadan during pregnancy is associated with adverse offspring health effects in childhood and especially adulthood, despite an absence of observable effects at birth.

What the evidence supports

Across 70 before-and-after publications, Ramadan fasting was followed by a significant drop in body fat percentage in people with overweight or obesity, but not in people of normal weight. (Source 6)

• Meta-analysis, Certainty not rated.
• Size: 2,947 participants in 90 comparison groups from 70 publications.
• Who: Healthy non-athlete adults who were not given diet or activity advice.
• How long: About one month of Ramadan, with follow-up 2 to 5 weeks after in some studies.
• Result: Fat percentage -1.46% (95% CI -2.57 to -0.35), p = 0.010 in people with overweight or obesity; -0.41% (-1.45 to 0.63), p = 0.436 in normal weight.
• Funding: not stated.

Limit of this finding: Pre-post comparisons without randomisation or control groups; the authors say the usual quality filters for randomised or observational studies could not be applied.

Consistently, there was a significant reduction in fat percentage between pre-Ramadan and post-Ramadan in people with overweight or obesity

A second meta-analysis of 85 studies found a significant but small reduction in body weight of about 1 kg with Ramadan fasting. (Source 9)

• Meta-analysis, Certainty not rated.
• Size: 4,176 people aged 16 to 80 years in 85 studies from 25 countries.
• Who: Healthy non-athletic people aged 16 and over.
• How long: Ramadan month; studies from 1982 to 2019.
• Result: Hedges' g -0.360 (95% CI -0.405 to -0.315), I2 = 45.6%; about -1.022 kg (95% CI -1.164 to -0.880 kg)
• Funding: not stated.

RDIF may confer a significant small reduction in body weight in non-athletic healthy people aged 16 years and above

In a London cohort and a meta-analysis of 33 studies, systolic and diastolic blood pressure were lower after Ramadan than before it. (Source 5)

• Meta-analysis, Certainty not rated.
• Size: 3,213 participants in 33 studies; plus 85 participants in the LORANS cohort.
• Who: Adults observing Ramadan, including healthy people and people with hypertension, diabetes or chronic kidney disease.
• How long: Measured before Ramadan and in the last 2 weeks of Ramadan or first 2 weeks after.
• Result: Pooled SBP -3.19 mm Hg (-4.43 to -1.96, I2 48%), DBP -2.26 mm Hg (-3.19 to -1.34, I2 66%); LORANS SBP -7.29 mm Hg, DBP -3.42 mm Hg.
• Funding: not stated.

Limit of this finding: Pooled studies were observational before-and-after designs; PROSPERO registered (CRD42019159477).

SBP and DBP after/before Ramadan were lower by 3.19 mm Hg (-4.43 to -1.96, I²=48%) and 2.26 mm Hg (-3.19 to -1.34, I²=66%), respectively.

What the evidence does not support

The weight and body composition changes did not last: 2 to 5 weeks after Ramadan, measurements had moved back towards or to pre-Ramadan values. (Source 6)

• Meta-analysis, Certainty not rated.
• Size: 2,947 participants from 70 publications.
• Who: Healthy non-athlete adults.
• How long: Follow-up 2 to 5 weeks after Ramadan.
• Result: At 2 to 5 weeks after the end of Ramadan, there was a return towards, or to, pre-Ramadan measurements in weight and body composition.
• Funding: not stated.

there was a return towards, or to, pre-Ramadan measurements in weight and body composition

The drop in blood pressure was not seen in people with chronic kidney disease. (Source 5)

• Meta-analysis, Certainty not rated.
• Size: Subgroup of the 33 pooled studies.
• Who: People with chronic kidney disease who fasted during Ramadan.
• How long: Ramadan month.
• Result: No lower blood pressure in the chronic kidney disease subgroup.
• Funding: not stated.

lower blood pressures were observed in the groups who are healthy or have hypertension or diabetes but not in patients with chronic kidney disease

Across 22 studies of more than 31,000 pregnancies, birth weight was not affected when mothers fasted during Ramadan, but evidence on other outcomes was insufficient. (Source 10)

• Meta-analysis, Certainty not rated.
• Size: 31,374 pregnancies in 22 studies (18,920 exposed to fasting)
• Who: Pregnant Muslim women.
• How long: Ramadan during pregnancy.
• Result: Birth weight SMD 0.03 (95% CI 0.00 to 0.05); preterm delivery OR 0.99 (95% CI 0.72 to 1.37); placental weight lower in fasting mothers (dominated by one large study); no data on perinatal mortality.
• Funding: not stated.

Limit of this finding: Mostly observational studies, assessed with ROBINS-I.

Birth weight was reported in 21 studies and was not affected by maternal fasting

Where the evidence is mixed

In healthy people, Ramadan fasting made a very small difference to fasting glucose and no significant difference to insulin, insulin resistance (HOMA-IR), leptin or adiponectin; the authors concluded it had no adverse metabolic impact. (Source 11)

• Meta-analysis, Certainty not rated.
• Size: 3,134 participants in 72 studies from 22 countries.
• Who: Healthy, non-athletic Muslims.
• How long: Ramadan month; studies from 1982 to 2020.
• Result: Fasting glucose Hedges' g -0.102 (95% CI -0.194 to -0.01); insulin 0.030 (-0.165 to 0.226); HOMA-IR -0.012 (-0.274 to 0.250); leptin -0.010 (-0.243 to 0.223); adiponectin 0.034 (-0.227 to 0.296)
• Funding: not stated.

Limit of this finding: Confidence intervals for insulin, HOMA-IR, leptin and adiponectin cross zero, so these are null results.

RDIF imposes no adverse metabolic impacts, and might help in improving some glucometabolic markers in healthy subjects.

A systematic review found insufficient evidence to link Ramadan fasting with more or fewer cardiovascular events in people with type 2 diabetes, with some indication that stroke risk may be increased. (Source 12)

• Systematic review, Certainty not rated.
• Size: 22 studies (5 on cardiovascular events, 17 on risk factors)
• Who: People with type 2 diabetes who fasted during Ramadan.
• How long: Ramadan month.
• Result: Inconsistent findings on risk factors; insufficient evidence on events.
• Funding: not stated.

There is insufficient evidence to link Ramadan fasting with increased or reduced incidence of cardiovascular events in people with diabetes, though there were some indication stroke risk may be increased.

What official bodies say

The IDF and DaR International Alliance guidelines (2021) state that people on three or more diabetes medicines, especially both insulin and a sulfonylurea, should be considered at increased risk of hypoglycaemia during Ramadan. (Source 1)

• Official position, Certainty not rated.
• Size: Not applicable.
• Who: People with diabetes who choose to fast during Ramadan.
• How long: Not applicable.
• Result: Risk stratification into high (fasting probably unsafe), moderate (safety uncertain) and low (probably safe) risk, using points for factors such as insulin regimen, sulfonylurea type, recent hypoglycaemia, kidney function, pregnancy, frailty and age over 70 without support.
• Funding: not stated.

Limit of this finding: Held by the International Diabetes Federation and the Diabetes and Ramadan International Alliance, published 2022 (dated 2021).

Individuals on 3 or more drug combinations, especially those on both insulin and SU should be considered at an increased risk of hypoglycaemia.

Where the research disagrees

Whether Ramadan fasting during pregnancy harms the child

• Glazier et al. 2018 meta-analysis, meta-analysis: Birth weight and preterm delivery were not affected; evidence on other perinatal outcomes was insufficient. (Source 10)
• Pradella et al. 2024 meta-analysis, meta-analysis: No effect at birth, but associations with poorer cognitive scores, shorter height and more hearing disability later in life. (Source 3)

Cardiovascular effects of Ramadan fasting

• Al-Jafar et al. 2021 (LORANS and meta-analysis), meta-analysis: Blood pressure was lower after Ramadan, and the authors describe Ramadan fasting as safe with respect to blood pressure. (Source 5)
• Almulhem et al. 2020 systematic review, systematic-review: Insufficient evidence on cardiovascular events in people with type 2 diabetes, with some indication of increased stroke risk. (Source 12)

A common belief, and what the research shows

The belief: Fasting through Ramadan leads to lasting weight loss.

What the research shows: Meta-analyses found an average loss of about 1 kg, including some lean mass, and weight and body composition moved back towards pre-Ramadan values within 2 to 5 weeks.

References

1. Diabetes Research and Clinical Practice; International Diabetes Federation (IDF) and Diabetes and Ramadan (DaR) International Alliance. Diabetes and Ramadan: Practical guidelines 2021. 2022. DOI 10.1016/j.diabres.2021.109185. Read the source
2. Journal of Medical Case Reports. Euglycemic diabetic ketoacidosis induced by sodium-glucose cotransporter 2 inhibitor in the setting of prolonged fasting: a case report. 2022. DOI 10.1186/s13256-022-03347-1. Read the source
3. Human Reproduction Update (Oxford University Press). Ramadan during pregnancy and offspring health outcomes over the life course: a systematic review and meta-analysis. 2024. PMID 39178355, DOI 10.1093/humupd/dmae026. Read the source
4. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), US National Institutes of Health. Fasting Safely with Diabetes (Diabetes Discoveries & Practice blog, interview with Dr. Martin M. Grajower). 2020. Read the source
5. Journal of the American Heart Association. Effect of Religious Fasting in Ramadan on Blood Pressure: Results From LORANS (London Ramadan Study) and a Meta-Analysis. 2021. PMID 34619991, DOI 10.1161/JAHA.120.021560. Read the source
6. Nutrients (MDPI). Effect of Ramadan Fasting on Weight and Body Composition in Healthy Non-Athlete Adults: A Systematic Review and Meta-Analysis. 2019. PMID 30813495, DOI 10.3390/nu11020478. Read the source
7. Sleep and Breathing (Springer). Effect of diurnal fasting on sleep during Ramadan: a systematic review and meta-analysis. 2020. PMID 31832984, DOI 10.1007/s11325-019-01986-1. Read the source
8. Frontiers in Endocrinology. Impact of Ramadan Diurnal Intermittent Fasting on Hypoglycemic Events in Patients With Type 2 Diabetes: A Systematic Review of Randomized Controlled Trials and Observational Studies. 2021. PMID 33763029, DOI 10.3389/fendo.2021.624423. Read the source
9. European Journal of Nutrition (Springer). A systematic review, meta-analysis, and meta-regression of the impact of diurnal intermittent fasting during Ramadan on body weight in healthy subjects aged 16 years and above. 2020. PMID 32157368, DOI 10.1007/s00394-020-02216-1. Read the source
10. BMC Pregnancy and Childbirth. The effect of Ramadan fasting during pregnancy on perinatal outcomes: a systematic review and meta-analysis. 2018. PMID 30359228, DOI 10.1186/s12884-018-2048-y. Read the source
11. Diabetes Research and Clinical Practice (Elsevier). A systematic review, meta-analysis, and meta-regression of the impact of diurnal intermittent fasting during Ramadan on glucometabolic markers in healthy subjects. 2020. PMID 32446800, DOI 10.1016/j.diabres.2020.108226. Read the source
12. Diabetes Research and Clinical Practice (Elsevier). The effect of Ramadan fasting on cardiovascular events and risk factors in patients with type 2 diabetes: A systematic review. 2020. PMID 31711857, DOI 10.1016/j.diabres.2019.107918. Read the source