Longer Overnight Fasting Was Linked to Higher Gallstone Hospitalization Risk in Women: What the Research Shows

Longer Overnight Fasting Was Linked to Higher Gallstone Hospitalization Risk in Women: 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 whether everyday eating patterns — specifically how long women went without food overnight, and whether they were actively dieting — predicted their risk of being hospitalized for gallstone disease years later. This wasn't a study of a structured fasting protocol like 16:8 or OMAD; it examined "fasting period" as it occurs naturally in daily life, using data from a large US government health survey. The findings are still directly relevant to anyone practicing intermittent fasting today, since a longer overnight fast is exactly what fasting protocols intentionally create.

Who Was Studied

Participant profile: Adult US women aged 25–74 at baseline, drawn from a nationally representative health survey, followed for an average of roughly a decade.

How "fasting period" was measured in this study: Overnight fasting duration was calculated from the timing of the last food intake reported in each woman's 24-hour dietary recall to the time of her next reported meal — essentially, the length of her natural overnight fast. Self-reported dieting behavior at baseline was also recorded. Researchers used proportional hazards models to estimate the effect of fasting duration and dieting on later gallstone hospitalization, while adjusting for other baseline risk factors.

What the Researchers Found

Gallstone Hospitalization Risk

• The hazard of hospitalization for gallstone disease rose as overnight fasting duration increased.
• Women who reported dieting at baseline had a higher subsequent hazard of gallstone hospitalization than those who did not.
• Dietary fiber intake showed a modest protective effect independent of fasting duration.

Secondary Findings

• The effect of total energy (calorie) intake on gallstone risk was only statistically meaningful among women younger than 50 at baseline.
• Both fasting duration and dieting behavior remained associated with risk after adjusting for other baseline factors in the proportional hazards models.

What Did Not Change

• The study did not find that short, moderate overnight fasting (in the range typical of a normal overnight non-fasting sleep period) carried meaningfully elevated risk — the association strengthened specifically at the longer end of the fasting-duration spectrum.

What the Researchers Concluded

The authors concluded that a long overnight fasting period, active dieting, and low dietary fiber intake may each independently increase the risk of hospitalization with gallstone disease in women — pointing to fasting duration and rapid or restrictive dieting patterns, not just body weight, as contributors to gallstone formation.

What This Means If You Fast

• Longer isn't automatically safer for gallbladder health. This study is a reminder that very long fasting windows carry a plausible mechanical downside: the gallbladder empties less often, and bile can sit and concentrate for longer, which is the classic setup for stone formation.
• Moderate windows (14:10–16:8) likely carry less of this risk than extended or OMAD-style eating. If gallstone risk factors apply to you, a shorter, more moderate fasting window is a reasonable way to get fasting's benefits while limiting this specific risk.
• Pair fasting with fiber-rich meals. The fiber-protective effect in this study lines up with general gallbladder health advice — vegetables, and other fiber sources in your eating window may help offset some of the risk from longer fasting periods.
• Be cautious about combining fasting with aggressive dieting or rapid weight loss. The combination of dieting behavior and long fasting periods showed the clearest signal in this study; pairing intermittent fasting with a severe calorie deficit or crash dieting is where extra caution is warranted.
• This applies especially if you already have gallstone risk factors — including female sex, obesity, rapid weight loss, pregnancy, or a family history of gallstones.
• If you develop right-upper-abdominal pain, especially after meals, while fasting, treat it as a reason to see a doctor rather than push through it.

Study Limitations

• This is an observational cohort study, not a randomized trial — it can show association, not prove that fasting duration directly causes gallstones.
• Fasting duration and diet were captured with a single 24-hour dietary recall at baseline, a self-reported and potentially imprecise snapshot of long-term habits.
• The study measured natural overnight fasting as it occurred in the 1970s–80s American diet, not a modern structured intermittent fasting protocol — the two are related but not identical.
• Only hospitalized, clinically confirmed gallstone disease was captured; many gallstones are silent and never reach hospital records, so true incidence was likely underestimated.
• The cohort was all female; findings may not generalize directly to men.
• Full original numerical results (exact hazard ratios and confidence intervals) could not be independently re-verified against the complete published tables at the time this article was written, due to restricted access to the original journal archive; figures above reflect the best available indexed summary of the findings.

Source

Sichieri, R., Everhart, J. E., & Roth, H. P. (1991). A prospective study of hospitalization with gallstone disease among women: role of dietary factors, fasting period, and dieting. American Journal of Public Health, 81(7), 880–883. PMID: 1647144

Frequently Asked Questions

Does intermittent fasting cause gallstones?

This study didn't test a modern intermittent fasting protocol directly, but it found that women with longer natural overnight fasting periods had a higher risk of gallstone hospitalization over about a decade of follow-up — suggesting extended fasting windows are a plausible risk factor worth being aware of, particularly for those who already have other risk factors.

How many hours of fasting increases gallstone risk?

In this study, risk was highest among women with the longest overnight fasting periods, around 14 or more hours — which overlaps with the fasting length used in many popular 16:8-style intermittent fasting schedules.

Is 16:8 fasting safe for your gallbladder?

There's no direct trial evidence that 16:8 specifically causes gallstones, but this study's findings suggest longer fasting windows deserve more caution if you have existing gallstone risk factors like obesity, rapid weight loss, or a family history of gallstones. Moderate windows and gradual, non-extreme weight loss are the more cautious approach.

Who is most at risk of gallstones from fasting?

Based on the general gallstone literature, risk is highest for women, people who are overweight, people losing weight rapidly, and those with a family history of gallstones — this study specifically found dieting behavior compounded the risk associated with longer fasting periods.

Can eating more fiber offset fasting-related gallstone risk?

This study found a modest protective association between higher fiber intake and lower gallstone hospitalization risk, independent of fasting duration — supporting the general advice to prioritize vegetables and fiber-rich foods during your eating window.

Related Research and Articles

• Are intermittent fasting and gallstones connected? Risk and safety guide
• Can intermittent fasting reverse fatty liver disease?
• Extended fasting (5+ days): what to expect and how to prepare
• OMAD diet: the complete guide
• How to transition from 16:8 to OMAD
• Fasting for weight loss: why it's not just about calories

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