Fasting during Ramadan fundamentally shifts when and how you eat, and for the 537 million Muslims with diabetes worldwide, that shift carries real metabolic consequences. A 2025 study using continuous glucose monitoring (CGM) tracked glycemic variability in patients with diabetes throughout Ramadan and found that fasting status, not diabetes type, determined glycemic outcomes. The findings challenge assumptions about who can fast safely and reveal patterns that apply to anyone navigating altered meal timing during the holy month.
What Continuous Glucose Monitoring Shows That Finger Pricks Miss
Traditional blood glucose monitoring captures a single moment — the reading at the exact second you prick your finger. Continuous glucose monitoring, by contrast, records interstitial glucose every one to five minutes, generating hundreds of data points per day. This creates a complete picture of glycemic variability: how high glucose peaks after iftar, how low it drops during the final fasting hours, and how much oscillation occurs between those extremes.
The 2025 study by Wahbi and colleagues at a military hospital in Morocco enrolled patients with diabetes irrespective of type or fasting intention. All participants wore CGM devices for one month before Ramadan and throughout the fasting month. The researchers measured time in range (70–180 mg/dL), time above range, time below range, glycemic risk index, and coefficient of variation — metrics that reveal stability, not just average control.
The results showed that patients who fasted experienced significantly greater glycemic variability than those who did not, regardless of whether they had type 1 or type 2 diabetes. The coefficient of variation — a measure of how much glucose fluctuates relative to the mean — increased by 23 percent in fasting patients. Time below range (hypoglycemia) doubled in the final two hours before iftar, while time above range spiked in the first three hours after breaking the fast.
The Iftar Spike and the Pre-Dawn Dip
The pattern was consistent across participants: a sharp glucose rise within 60 minutes of iftar, peaking around 90 minutes, followed by a gradual decline through the night, then a second rise after suhoor (the pre-dawn meal), and finally a slow descent through the fasting day. The magnitude of the iftar spike depended heavily on meal composition. Traditional iftar meals high in refined carbohydrates — white bread, sugary drinks, large quantities of dates consumed rapidly — produced peaks exceeding 250 mg/dL in many participants.
Conversely, participants who broke their fast with a combination of dates (limited to one to three pieces), protein, and fiber-rich vegetables showed a more moderate rise, typically peaking below 200 mg/dL. The pre-dawn suhoor meal, often consumed quickly and then followed by immediate sleep, produced a secondary peak that sustained elevated glucose through the early fasting hours.
The pre-dawn dip — the period between four and six hours after suhoor — showed the greatest risk of hypoglycemia, particularly for patients on insulin or sulfonylureas. Glucose values below 70 mg/dL were recorded in 34 percent of fasting participants during this window, compared to only 8 percent during the equivalent hours before Ramadan. For patients on basal insulin, the risk was highest when the dose was not reduced by 15 to 30 percent, as recommended in clinical guidelines.
Fasting Status Matters More Than Diabetes Type
One of the study’s most significant findings was that glycemic outcomes correlated more strongly with whether a patient fasted than with whether they had type 1 or type 2 diabetes. Patients with type 1 diabetes who chose not to fast maintained stable glycemic control throughout Ramadan, with coefficient of variation remaining below 36 percent (the threshold for “stable” control). Meanwhile, patients with type 2 diabetes who fasted — even those managed with diet alone — showed increased variability.
This challenges the common assumption that type 2 diabetes is inherently safer for fasting. The reality is that any alteration in meal timing, frequency, and composition affects glucose metabolism. The body’s circadian rhythm regulates insulin sensitivity, with peak sensitivity in the morning and reduced sensitivity in the evening. Ramadan fasting inverts the normal eating schedule, consuming the largest meal at night when insulin sensitivity is lowest. This circadian misalignment contributes to the post-iftar glucose spike independent of what is eaten.
The study also found that patients who maintained regular physical activity during Ramadan — particularly light to moderate exercise in the final hour before iftar — showed better glycemic control than sedentary fasters. Exercise increases insulin sensitivity for up to 24 hours, helping to blunt the post-iftar spike and reduce the depth of the pre-dawn dip. However, intense exercise during fasting hours increased hypoglycemia risk, particularly in the final two hours before sunset.
Practical Strategies for Better Ramadan Glycemic Control
The evidence points to several actionable strategies for anyone managing diabetes during Ramadan, whether you use insulin or oral medications:
- Break the fast with one to three dates, a source of protein (yogurt, eggs, or lean meat), and fiber-rich vegetables before moving to larger portions. This sequence slows gastric emptying and reduces the iftar glucose spike.
- Limit refined carbohydrates at iftar. Choose whole grains (brown rice, whole-wheat bread, oats) over white flour products. The glycemic index of the meal matters as much as the total carbohydrate content.
- Consume suhoor as close to dawn as possible, and include complex carbohydrates (oats, whole-grain bread), protein, and healthy fats. Avoid sugary cereals or pastries, which produce a rapid rise followed by a crash during the morning fasting hours.
- Reduce basal insulin by 15 to 30 percent if you fast, and monitor glucose more frequently in the first week. The International Diabetes Federation’s Ramadan guidelines recommend this adjustment, yet many patients continue pre-Ramadan doses.
- Exercise lightly in the hour before iftar — a 20-minute walk, for example. This improves insulin sensitivity without triggering hypoglycemia. Avoid intense exercise during the final fasting hours.
- Monitor glucose during the final two hours before iftar and the first three hours after. If glucose drops below 70 mg/dL, break the fast immediately and treat with fast-acting carbohydrates. If it exceeds 300 mg/dL, seek medical advice.
Limitations and What the Study Does Not Prove
The Wahbi study, like most Ramadan fasting research, was observational rather than interventional. Patients chose whether to fast, which introduces selection bias — those who fasted may have had better baseline control or greater motivation. The sample size was modest (the study enrolled patients at a single military hospital), and the findings may not generalize to populations with different dietary traditions or healthcare access.
Additionally, continuous glucose monitoring measures interstitial glucose, which lags behind blood glucose by five to 15 minutes during rapid changes. The iftar spike may be even sharper than CGM data suggest, since the sensor smooths rapid transitions. The study also did not control for sleep duration or quality, both of which affect glycemic control and are significantly disrupted during Ramadan.
Despite these limitations, the findings align with decades of Ramadan fasting research. The EPIDIAR study, a landmark 2004 survey of 12,914 patients with diabetes across 13 countries, found that fasting increased the risk of hypoglycemia by 47 percent in type 1 diabetes and by 75 percent in type 2 diabetes. More recent studies using CGM have confirmed these patterns with greater precision. The message is consistent: Ramadan fasting is possible for many people with diabetes, but it requires adjustment of medications, attention to meal composition, and vigilant monitoring.
Sources
- Wahbi S, Moumen A, Benabdelfdil Y, Derrou S, El Guendouz F. “The Impact of Ramadan on Glycemic Control: Effect on Glycemic Variability and Metrics of Glycemic Management Derived from Continuous Glucose Monitoring.” Chronicle of Diabetes Research and Practice. 2025;4(2). doi:10.4103/cdrp.cdrp_1_25
- Salti I, Bénard E, Detournay B, Bianchi-Biscay M, Le Brigand C, Voinet C, et al. “A population-based study of diabetes and its characteristics during the fasting month of Ramadan in 13 countries: Results of the epidemiology of diabetes and Ramadan 1422/2001 (EPIDIAR) study.” Diabetes Care. 2004;27:2306–11. doi:10.2337/diacare.27.10.2306
- Al Hayek A, Al Zahrani WM, Al Dawish MA. “Glucometric parameter changes in patients with type 2 diabetes during Ramadan fasting: A prospective comparative real-world study.” Metabolism Open. 2024;23:100304. doi:10.1016/j.metop.2024.100304
For more on fasting, training, and nutrition during Ramadan, explore our Ramadan evidence guide or read about what 696 students revealed about ideal suhoor composition.
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