Health & Safety

Does OMAD Increase Your Risk of Gallstones?

A long daily fast changes how your gallbladder works — and after 50, that's worth understanding properly rather than ignoring or panicking about.

Your gallbladder stores bile and releases it when you eat, particularly when a meal contains fat. That release is what keeps bile moving and cholesterol dissolved. Go a long stretch without eating — as you do most of the day on OMAD — and the gallbladder simply doesn't get that regular trigger. Bile sits for longer, and the liver keeps releasing cholesterol into it regardless, so it can become more concentrated. That combination is the actual mechanism behind fasting-related gallstone risk, not fasting itself in isolation.

Why the length of the fast matters

This is a dial, not a switch. Shorter eating windows like 16:8 leave two meals a day to trigger gallbladder emptying, so the effect is small for most people. OMAD's 23-hour-or-so fast leaves only one trigger a day, which is where the research on fasting and gallstones actually points its concern — particularly when a long fast is combined with rapid weight loss, which is the strongest known risk factor of all.

Why this is worth knowing specifically over 50

Gallstones already become more common with age, and more common in women, especially after the menopause. If you're carrying more weight going in, have a family history of gallstones, or have had gallbladder trouble before, that background risk stacks on top of whatever effect the fasting pattern itself adds. None of this means OMAD is unsafe for you — it means it's a genuine factor to weigh, not a footnote.

How to fast sensibly if this applies to you

• Make sure your one meal includes a reasonable amount of fat — a very low-fat meal gives the gallbladder little reason to empty properly either, which is its own trap
• Avoid stacking OMAD with a very low-calorie or crash-diet approach; steady weight loss is meaningfully safer for your gallbladder than rapid loss
• Stay well hydrated across the fasting hours — concentrated bile is more likely to form stones, and adequate fluid helps keep things moving
• Keep half an eye on your weight trend — losing and regaining repeatedly ("weight cycling") carries its own added risk, separate from the pace of any single attempt

Signs to stop and get checked

Occasional mild discomfort isn't unusual when you change eating patterns, but some symptoms warrant stopping and speaking to a doctor rather than waiting it out: persistent pain in the upper right abdomen, especially after your meal; pain that spreads to your back or right shoulder; nausea or vomiting alongside the pain; or fever and yellowing of the skin or eyes, which needs same-day medical attention.

The bottom line

OMAD does change gallbladder behaviour, and that's a real, sensible thing to plan around — not a reason to be frightened off. Keep some fat in your one meal, avoid crash-dieting on top of the fast, stay hydrated, and get any persistent upper-right abdominal pain checked rather than pushed through. For most people over 50 with no existing gallbladder history, that's enough to fast comfortably and safely.