Ramadan Fasting Lowers Insulin and Improves Insulin Sensitivity in Healthy Men: What the Research Shows

Medical disclaimer: This article summarises published research for informational purposes only. It is not medical advice and is not a substitute for guidance from a qualified health professional. Always consult your doctor before starting any fasting protocol, especially if you have an existing health condition or take medication.

Study at a Glance

What This Study Looked At

Researchers wanted to know what happens to insulin sensitivity, body composition, and appetite-regulating hormones when healthy young men fast from dawn to sunset for a full month during Ramadan. Unlike time-restricted eating protocols practiced year-round, Ramadan fasting involves no food or water for roughly 12–16 hours a day depending on season and location, followed by an eating window that often includes two larger meals. The study measured serum insulin, HOMA-IR (a standard surrogate marker of insulin resistance), body composition, and the hormones leptin and adiponectin before Ramadan began and again in the final days of the fasting month. For broader context on how fasting affects insulin, see can intermittent fasting improve insulin sensitivity? and intermittent fasting and metabolism: what science says.

Who Was Studied

Participant profile: Healthy young adult men with no diagnosed diabetes or major metabolic disease; single group followed longitudinally with no separate non-fasting control group.

How Ramadan fasting worked in this study: Participants abstained from all food and drink between dawn and sunset every day for approximately 30 consecutive days, then ate during the permitted evening and pre-dawn hours. Researchers assessed participants within three days of the start of Ramadan (baseline) and again in the final three days of the month (end-line), capturing the cumulative effect of a full month of daily fasting.

What the Researchers Found

Insulin and Insulin Resistance

Both of the two most commonly used surrogate markers of insulin sensitivity moved in the favorable direction. Falling insulin alongside a falling HOMA-IR score indicates that the body needed less insulin to manage blood glucose by the end of the fasting month — the hallmark signature of improved insulin sensitivity.

Body Composition

Weight, BMI, fat mass, and waist circumference all fell significantly, consistent with the reduced energy intake researchers documented across the month. Muscle mass also declined slightly, a common finding in short fasting studies that do not include a resistance-training component.

Appetite Hormones

Leptin, the hormone that signals fullness and is secreted by fat tissue, tracked closely with weight change: the percentage drop in leptin was significantly correlated with the percentage drop in body weight (r = 0.412, P = .037). This is expected physiologically, since leptin is produced roughly in proportion to fat mass — as fat mass fell, leptin fell with it.

What the Researchers Concluded

The authors concluded that one month of Ramadan intermittent fasting improved insulin sensitivity in healthy young men, evidenced by significant reductions in both serum insulin and HOMA-IR alongside a significant rise in QUICKI. They linked these metabolic improvements to the reduction in energy intake, body weight, fat mass, and waist circumference observed over the same period, and noted that the fall in leptin tracked proportionally with fat loss — supporting the idea that improved insulin sensitivity during Ramadan is driven substantially by reduced caloric intake and fat loss rather than fasting alone as an isolated mechanism.

What This Means If You Fast

• Insulin sensitivity can improve within a month of daily time-restricted fasting. Two independent markers — falling insulin and falling HOMA-IR — both moved in the same favorable direction over just 30 days, suggesting metabolic benefits appear relatively quickly. See can intermittent fasting improve insulin sensitivity? for more on the mechanisms involved.
• Fat loss and reduced calorie intake likely drive much of the effect. Participants ate less overall during the study, and their weight, BMI, and waist circumference all dropped significantly — a reminder that intermittent fasting and metabolism are closely intertwined with total energy intake, not just meal timing.
• A daily dawn-to-sunset fasting window is a realistic real-world model. Unlike lab-controlled clamp studies, this research captures what actually happens when healthy adults observe a month-long fasting practice in everyday life, with normal eating in the evening hours.
• Watch for muscle loss without a maintenance strategy. Muscle mass declined slightly alongside fat mass, underscoring the value of maintaining protein intake and physical activity during any extended fasting period. This is consistent with findings in intermittent fasting benefits research on preserving lean mass during fasting.
• Appetite hormones adjust alongside body composition. Falling leptin proportional to fat loss suggests the body's hunger-signaling system recalibrates as fasting continues, rather than working against the faster indefinitely.

Study Limitations

• Small sample size (27 participants), all healthy young men — findings may not generalize to women, older adults, or those with existing metabolic disease
• No separate non-fasting control group; changes are measured only within the fasting group over time, so some improvement could reflect factors other than fasting itself (e.g., general lifestyle changes during Ramadan)
• Used surrogate insulin sensitivity markers (HOMA-IR, QUICKI) rather than a gold-standard euglycemic or hyperinsulinemic clamp; a true clamp study of Ramadan fasting in non-diabetic adults could not be identified, likely because the multi-hour clamp procedure is difficult to schedule within a dawn-to-sunset fasting day
• Exact numerical mean values for insulin, HOMA-IR, and QUICKI at baseline versus end-line were not available in the accessible abstract — only direction of change and statistical significance are reported here
• One-month duration does not establish whether improvements persist after Ramadan ends or reflect a lasting change versus a temporary state tied to reduced food intake
• Weight loss and reduced energy intake are confounded with the fasting protocol itself, making it difficult to isolate fasting-specific effects from simple caloric restriction

Source

Prasetya, G., & Sapwarobol, S. (2021). Intermittent Fasting During Ramadan Improves Insulin Sensitivity and Anthropometric Parameters in Healthy Young Muslim Men. American Journal of Lifestyle Medicine, 15(2), 200–206. PMID: 33786036

Frequently Asked Questions

Does Ramadan fasting improve insulin sensitivity?

Yes. In this study of 27 healthy young men, one month of Ramadan fasting significantly reduced serum insulin (P = .005) and HOMA-IR (P = .009), while QUICKI — a marker of insulin sensitivity — significantly increased. These changes indicate the body needed less insulin to regulate blood glucose by the end of the fasting month.

Has anyone studied Ramadan fasting and insulin sensitivity using a glucose clamp?

No published human study using a formal euglycemic or hyperinsulinemic clamp to measure insulin sensitivity specifically during Ramadan fasting in non-diabetic adults could be identified. Most Ramadan fasting research relies on surrogate markers like HOMA-IR and QUICKI, likely because the multi-hour clamp procedure is logistically difficult to perform within a dawn-to-sunset fasting schedule.

Does Ramadan fasting cause weight loss?

Yes, in this study body weight, BMI, fat mass, and waist circumference all decreased significantly (P < .001 for weight and BMI) over the month, alongside a documented reduction in daily energy intake.

Can Ramadan-style fasting cause muscle loss?

This study observed a small but statistically significant decrease in muscle mass (P = .004) alongside fat loss. Maintaining adequate protein intake and physical activity during the eating window may help offset this effect, which is a common finding across fasting studies that do not include a resistance-training component.

Is Ramadan fasting similar to other forms of intermittent fasting?

Ramadan fasting is a form of extended daily time-restricted eating, but it differs from typical 16:8 protocols in that it excludes water as well as food during fasting hours and lasts a full month rather than being practiced indefinitely. This study suggests it produces insulin-sensitivity improvements consistent with other intermittent fasting research, though direct comparisons are limited by differences in study design.

Related Research and Articles

• Can intermittent fasting improve insulin sensitivity?
• Intermittent fasting and metabolism: what science says
• Does intermittent fasting cause autophagy?
• Intermittent fasting benefits: the complete science-backed guide
• What is alternate-day fasting?
• Ramadan fasting and the gut microbiome: what the research shows
• Ramadan fasting and cardiovascular risk markers: what the research shows

Want the complete guide to fasting? Get Intermittent Fasting in Practice on Amazon — and claim 3 months free on our fasting app at fastinginpractice.com/redeem.