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Head-to-head evidence comparison — which supplement is right for you?
Orlistat vs Vitamin D3: Vitamin D3 has the stronger overall evidence (7.5 vs 6/10); they're alternatives for metabolic health — the best pick depends on your goals. Take the 60-second quiz for a pick tailored to your goals.
Vitamin D3 wins 3 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Mostly mechanism / observational
Top outcomes
Verdict
Probably helps
15 of 25 studies with measurable effects showed benefit.
Top outcomes
Prescription Xenical: 120 mg three times daily (360 mg/day), taken with or up to 1 hour after each main fat-containing meal. Over-the-counter Alli: 60 mg three times daily (180 mg/day). Skip the dose if a meal is missed or contains no fat. Used alongside a reduced-calorie diet in which fat supplies roughly 30% of energy — a higher-fat meal makes the gastrointestinal side effects markedly worse, not the weight loss better.
with-meals
Xenical 120 mg capsule three times daily with meals (prescription)
2000-4000 IU daily
Morning with breakfast
D3 (cholecalciferol) softgel or liquid
Lower vitamin D absorption, with measurable falls in fat-soluble vitamin concentrations reported during orlistat treatment.
Keep taking vitamin D, but separate it from any orlistat dose by at least two hours — bedtime is the usual advice, since orlistat is taken with meals.
4–12 weeks to onset; maximal by 6–12 months
Year 2 of continuous use
Years
3–12 months
4-8 weeks
4-8 weeks
2-4 weeks
4-8 weeks
XENical in the prevention of diabetes in obese subjects (XENDOS) study: a randomized study of orlistat as an adjunct to lifestyle changes for the prevention of type 2 diabetes in obese patients.
Diabetes Care (2004) · Rct · n=3305
4-year double-blind trial randomising 3,305 obese patients (BMI ≥30) to lifestyle changes plus orlistat 120 mg or placebo three times daily
Randomised placebo-controlled trial of orlistat for weight loss and prevention of weight regain in obese patients. European Multicentre Orlistat Study Group.
Lancet (1998) · Rct · n=688
743 obese patients (BMI 28–47) entered a 4-week placebo lead-in at 15 European centres; 688 were randomised double-blind to orlistat 120 mg three times a day or placebo for 1 year on a 600 kcal/day-deficit diet, then reassigned for a second 52-week weight-maintenance period
Weight control and risk factor reduction in obese subjects treated for 2 years with orlistat: a randomized controlled trial.
JAMA (1999) · Rct · n=892
2-year randomised, double-blind, placebo-controlled trial at 18 US research centres; 1,187 obese adults (BMI 30–43) entered and 892 were randomised, with 223 placebo- and 657 orlistat-treated subjects in the intent-to-treat analysis
Vitamin D supplementation vs. placebo and incident type 2 diabetes in an ancillary study of the randomized Vitamin D and Omega-3 Trial
Nature communications (2025) · Meta analysis · n=5205
Mean body mass index (BMI) was 27.5 kg/m2 (SD = 5.3), with 51% female and 17% Black race/ethnicity.
Vitamin D Supplementation for Patients with Dysmenorrhoea: A Meta-Analysis with Trial Sequential Analysis of Randomised Controlled Trials
Nutrients (2024) · Meta analysis · n=687
TSA revealed that the current RCTs provide sufficient information.
Vitamin D and respiratory tract infections
BMJ (2017) · Meta analysis · n=11321
12% reduction in respiratory infections overall
Meta-analysis showed 12% overall reduction in respiratory infections, with greater benefits in severely deficient individuals. Daily dosing more effective than bolus. Conservative estimate assumes most users not severely deficient.
AI-estimated from published studies. Interpret as directional guidance.
Vitamin D3 has a higher evidence score (7.5/10 vs 6/10) and wins in 3 of 3 categories.
For metabolic health, Orlistat has a higher relevance score (58 vs 55).
Lower vitamin D absorption, with measurable falls in fat-soluble vitamin concentrations reported during orlistat treatment. Keep taking vitamin D, but separate it from any orlistat dose by at least two hours — bedtime is the usual advice, since orlistat is taken with meals. Consult a healthcare provider for personalized advice.
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The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.