Does a ketogenic diet cause gallstones?

No study has directly tested a standard ketogenic diet for this, so there's no trial that says 'keto causes stones.' What the evidence does show is that rapid, substantial weight loss, regardless of how the calorie restriction is achieved, raises gallstone risk. Keto may be linked to this risk indirectly, to the extent it speeds up weight loss; there's no evidence the diet itself forms stones through some separate mechanism.

Does ursodiol actually work?

In a 1995 trial of 1,004 people published in Annals of Internal Medicine, 28% of the placebo group on a 520-calorie-a-day diet program developed gallstones within 16 weeks; in the group taking 600 mg/day of ursodeoxycholic acid (ursodiol), that fell to 3%. The difference was statistically significant. This is a prescription drug and isn't routinely recommended for everyone — it's an option to discuss with a doctor if you're entering an aggressive rapid weight-loss program and are at higher risk.

Does keto's high fat content make it safer or riskier?

The literature disagrees here. A small 1998 study in the International Journal of Obesity found a 54.5% stone rate on a low-fat (about 3g/day) very-low-calorie diet versus zero stones on a higher-fat (about 12g/day) version, suggesting fat protects by keeping the gallbladder emptying regularly. But a larger study the same year in Digestive Diseases and Sciences found no significant difference in stone rates between 16g and 30g of daily fat (17.0% versus 11.2%, p=0.18). So the idea that fat is protective is plausible and has one study's strong backing, but it isn't settled.

If I'm on a weight-loss injection and keto, does the risk multiply?

In that case two separate risk factors stack. A 2022 meta-analysis in JAMA Internal Medicine, pooling 76 randomized trials and about 103,000 participants, found GLP-1 drugs (like semaglutide and liraglutide) raised gallbladder and biliary disease risk by about 37% overall, rising to about 129% in trials where the drugs were used for weight loss specifically. Add an aggressive diet that also drives rapid weight loss, and two independent risk mechanisms are active at once; anyone with a prior history of gallbladder trouble should discuss this combination with their doctor.

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Gallstone Risk on Keto: How Much Is Rapid Weight Loss to Blame?

9 min read · Health Guide · November 4, 2026

There's a complaint that keeps surfacing in keto forums around the same point every cycle: pain in the upper right abdomen after a fatty meal, sometimes radiating to the back or right shoulder blade. The first question people ask is "I'm eating this much fat, could I have developed a gallstone?", and the answer usually comes from a forum comment or a one-line warning with no source attached. There's actually real clinical data on this, it just comes from a different place than you'd expect: no study has directly tested a ketogenic diet, but several fairly solid studies have tested rapid weight loss. This piece looks at that data, gives the actual numbers, and separates what can honestly be said about keto specifically from what can't.

In a 1995 trial of 1,004 people on a 520-calorie-a-day diet program, 28% developed gallstones within 16 weeks; among those taking 600 mg/day of ursodeoxycholic acid, that fell to 3%. But this trial tested a very-low-calorie liquid diet program, not a standard ketogenic diet — a distinction that matters later in this piece.

Why Does the Gallbladder Come Under Pressure During Weight Loss?

Bile is produced in the liver, stored in the gallbladder, and keeps cholesterol, bile acids, and phospholipids dissolved in a particular ratio. During rapid weight loss, more cholesterol gets released from fat tissue into circulation, and the liver shunts some of it into bile — but bile acid and phospholipid production don't rise at the same rate. The result is bile that becomes supersaturated with cholesterol, meaning cholesterol that should stay dissolved starts to crystallize instead. A second mechanism compounds this: when calorie intake, and especially fat intake, drops sharply, the gallbladder contracts and empties less often, so bile sits longer (stasis). Stagnant, cholesterol-supersaturated bile is close to an ideal setup for stone formation. None of this is specific to keto — the same physiology applies to any diet that drives fast, substantial weight loss.

What Do the Numbers Say? The Ursodiol Trial

The strongest evidence here comes from a multicenter, placebo-controlled trial published in 1995 in Annals of Internal Medicine. It enrolled 1,004 people with a body mass index (BMI) of 38 or higher who had a normal gallbladder on baseline ultrasound; everyone followed a 520-calorie-a-day liquid protein commercial diet program (Health Management Resources) for 16 weeks. Participants were randomized into four groups: placebo, or 300 mg, 600 mg, or 1,200 mg of ursodeoxycholic acid (ursodiol) per day.

By week 16, 28% of the placebo group (95% CI 22-35%) had developed new gallstones. That dropped to 8% in the 300 mg group, 3% in the 600 mg group, and 2% in the 1,200 mg group. The researchers concluded that 600 mg/day was highly effective at preventing stone formation. This is still the clearest numerical evidence cited on this topic today — but note what was actually tested: not a ketogenic diet, a 520-calorie liquid protein program. A standard ketogenic diet usually doesn't involve this degree of calorie restriction.

Real-World Evidence: A Swedish Cohort Study

A study published in 2013 in the International Journal of Obesity looks at this with real-world data. Adults enrolled at 28 commercial weight-loss centers in Sweden between 2006 and 2009 were followed; one group did a 3-month, 500-calorie-a-day very-low-calorie diet (VLCD), the other a milder 1,200-1,500-calorie-a-day diet (LCD), after which both groups entered a 9-month weight-maintenance phase. Researchers pulled gallstone-related hospitalization and surgery (cholecystectomy) data from national health registries.

Over 6,361 person-years of follow-up, gallstone events requiring hospital care occurred at a rate of 152 per 10,000 person-years in the VLCD group versus 44 in the LCD group — a hazard ratio of 3.4 (95% CI 1.8-6.3, p<0.001). Cholecystectomy events showed a similar gap, with a hazard ratio of 3.2. Adjusting for the amount of weight lost in the first 3 months shrank the difference somewhat but didn't erase it (hazard ratio for gallstones: 2.5). What makes this study valuable is that it's registry-verified data from a real commercial weight-loss program, not a lab setting. It's not randomized, though — people chose their own program, which could influence the result to some degree.

Is Fat Content Protective? The Literature Disagrees

The biggest difference between a ketogenic diet and other standard low-calorie diets is its high fat content, and some researchers think that could actually cut gallstone risk rather than raise it — because dietary fat is the main trigger that makes the gallbladder contract and empty regularly. A small 1998 study in the International Journal of Obesity supports this idea: 32 stone-free obese people were randomized to one of two very-low-calorie diets (one with about 3 grams of fat a day, the other about 12 grams), and 22 completed the study. In the low-fat group, 6 of 11 people (54.5%) developed asymptomatic stones; in the higher-fat group, none did. The authors suggested that adequate fat intake may prevent stone formation by preserving gallbladder emptying.

But a much larger study published the same year in Digestive Diseases and Sciences found something different. 272 obese people were randomized to one of two 900-calorie liquid diets containing either 16 or 30 grams of fat a day, with a repeat ultrasound after 13 weeks. The stone rate was 17.0% in the 16-gram-fat group and 11.2% in the 30-gram-fat group — not a statistically significant difference (p=0.18). In other words, this study found that fat amount didn't meaningfully change stone formation. The two studies contradict each other: one shows a strong protective effect from fat (but a small sample, 11 people per arm), the other finds no significant difference (a larger, if still moderate, sample). Bottom line: the idea that fat content is protective is plausible and has strong support from one study, but the literature hasn't settled it.

An Extra Layer for Anyone on a Weight-Loss Injection

More people have started combining GLP-1 drugs (like semaglutide and liraglutide) with keto in recent years, and that adds a second factor to the risk picture. A 2022 systematic review and meta-analysis in JAMA Internal Medicine, pooling 76 randomized trials and roughly 103,000 participants, found that GLP-1 receptor agonists raised gallbladder and biliary disease risk by about 37% overall (relative risk 1.37). The effect was larger in trials where the drugs were used for weight loss (relative risk 2.29) than in trials for diabetes treatment (relative risk 1.27) — so dose and purpose of use matter.

This means that when both the drug and an aggressive diet are driving rapid weight loss at the same time, two independent risk mechanisms are active together. We covered how keto affects muscle mass while on a weight-loss injection in a separate article; a similar principle applies here — when you stack two powerful interventions, each one's individual risks add up rather than cancel out.

Who Should Be More Careful?

Women and people over 40 — gallstones are already more common in women and with age in the general population; combined with rapid weight loss, that baseline risk can climb further.
Anyone targeting fast, large weight loss — programs aiming for more than 1.5 kg a week sit closer to the risk profile seen in the studies above; a standard, ad-libitum (not calorie-counted, satiety-driven) ketogenic diet is usually far less aggressive than that.
Anyone on a very-low-calorie clinical protocol like VLCKD — the kind we detailed in our PCOS article, limited to 600-800 calories a day, sits much closer to the conditions in the ursodiol trial above; it's worth discussing the ursodiol option with a doctor if you're on one of these.
Anyone on a weight-loss injection — given the extra risk layer described above, especially if you have a prior history of gallbladder trouble, this combination is worth discussing with your doctor.
Anyone with a previous gallstone or gallbladder inflammation episode — recurrence risk runs higher than in the general population.

Symptoms and When to See a Doctor

Most gallstones stay silent and never cause symptoms. When they do, the typical picture is pain that shows up especially after a fatty meal, starting in the upper right abdomen or below the breastbone and sometimes radiating to the back or right shoulder blade, lasting anywhere from 30 minutes to a few hours (called biliary colic); nausea can come with it. If fever, chills, or yellowing of the skin or eyes (jaundice) joins the pain, that can point to gallbladder inflammation or a blocked bile duct, which needs urgent evaluation. If you start having this kind of pain after beginning keto, don't write it off as "keto flu" or a passing digestive issue — get it checked.

What Does This Mean in Practice?

The real risk factor these studies point to isn't keto itself, it's the degree of calorie restriction and the speed of weight loss. A standard ketogenic diet that isn't calorie-counted, that runs on satiety rather than a fixed deficit, and that loses weight at a more moderate pace, say 0.5-1 kg a week on average, sits physiologically quite far from the 500-900-calorie liquid diet protocols tested in these studies. The idea that fat supports gallbladder emptying has strong backing in one study, so eating adequate fat at regular meals, rather than skipping meals and then eating one very fatty one, is a theoretically sound approach. If you're going on a genuinely aggressive, very-low-calorie protocol, or combining a weight-loss injection with keto, planning that with your doctor and discussing the ursodiol option if needed is a concrete, evidence-backed step based on what's covered here.

Limitations

None of the studies cited here directly tested a standard ketogenic diet; they all look at very-low-calorie, mostly liquid or formula-based diet programs, so reading these numbers as "the risk for someone doing ad-libitum keto at home is exactly this" would be a mistake. The ursodiol trial and the Swedish cohort were conducted between the 1990s and 2013 and may not map neatly onto today's eating patterns. The 1998 fat-comparison study was completed with only 22 people, too small a sample to draw a strong conclusion from on its own. The Swedish cohort isn't randomized — it follows people who voluntarily joined a commercial program, which raises the possibility of selection bias. The risk ratios in the GLP-1 meta-analysis are a general estimate for the drug class and may not apply identically to every drug or dose. In short: the evidence that rapid weight loss raises gallstone risk is solid, but how much of that applies to a standard ketogenic diet specifically is a question that hasn't been directly tested yet.

Sources: Shiffman ML et al., "Prophylaxis against gallstone formation with ursodeoxycholic acid in patients participating in a very-low-calorie diet program", Annals of Internal Medicine (1995) · Johansson K et al., "Risk of symptomatic gallstones and cholecystectomy after a very-low-calorie diet or low-calorie diet in a commercial weight loss program: 1-year matched cohort study", International Journal of Obesity (2014) · Festi D et al., "Gallbladder motility and gallstone formation in obese patients following very low calorie diets. Use it (fat) to lose it (well)", International Journal of Obesity (1998) · Hutton LC et al., "Similarity in gallstone formation from 900 kcal/day diets containing 16 g vs 30 g of daily fat", Digestive Diseases and Sciences (1998) · He L et al., "Association of Glucagon-Like Peptide-1 Receptor Agonist Use With Risk of Gallbladder and Biliary Diseases: A Systematic Review and Meta-analysis of Randomized Clinical Trials", JAMA Internal Medicine (2022)

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