Most people who drink olive oil daily experience no side effects at all. When effects do occur, they're almost always mild digestive adjustments — loose stools, mild nausea, or stomach gurgling — that resolve within 3 to 7 days as your body adapts to the concentrated fat and bile response. Starting with 1 teaspoon and building up to a full tablespoon over a week prevents nearly all of it. Serious adverse effects from dietary olive oil are not documented in the medical literature.
Key Facts
- Most side effects are mild and temporary — typically resolving in 1–3 days as your digestive system adjusts
- Most common side effect: loose stools in the first few days, caused by bile stimulation, not illness
- Calorie content: 120 calories per tablespoon (15 mL)
- No documented serious adverse effects from dietary olive oil consumption in the clinical literature, including the 7,447-person PREDIMED trial (Estruch et al., NEJM, 2018)
- Best practice: start with 1 teaspoon and increase gradually over 1 week rather than jumping straight to a full tablespoon
What Are the Side Effects of Drinking Olive Oil?
The most commonly reported side effects of drinking olive oil are digestive: loose stools, mild stomach cramping, occasional nausea (especially on an empty stomach), and — much less commonly — a peppery throat sensation from high-polyphenol oils. These effects are almost always mild, short-lived, and tied to your body adjusting to a concentrated dose of fat rather than any sign of harm.
The mechanism behind most of these effects is bile. Drinking olive oil straight triggers a rapid release of bile from your gallbladder to help digest the concentrated fat. That surge in bile accelerates intestinal motility in people who aren't used to it — the same physiological response responsible for olive oil's reputation as a natural remedy for constipation. Once your digestive system adapts, usually within a week, this effect fades.
| Side Effect | Likelihood | Severity | Typical Duration | How to Prevent |
|---|---|---|---|---|
| Loose stools | Common | Mild | 3–7 days | Start with 1 tsp; increase gradually |
| Nausea (empty stomach) | Uncommon | Mild | Resolves same day | Take with food; chase with citrus |
| Calorie-related weight gain | Uncommon | Mild | Ongoing if not managed | Replace other fats rather than adding on top |
| Throat irritation (oleocanthal "sting") | Common with high-polyphenol EVOO | Mild, brief | Seconds to 1–2 minutes | Chase with water or citrus; not a sign of a problem |
| Allergic reaction | Extremely rare | Potentially serious | Immediate onset | Discontinue and seek care if hives, swelling, or breathing difficulty occur |
Can Drinking Olive Oil Cause Diarrhea?
Loose stools (not true diarrhea for most people) can occur in the first few days, particularly if you start with a full tablespoon on an empty stomach. This happens because a concentrated dose of fat triggers a strong bile release, which speeds up movement through the intestines. It's the same mechanism that makes olive oil a folk remedy for constipation.
The fix is dosing, not avoidance: start with 1 teaspoon taken with food, and increase gradually over 3–5 days. Most people report the effect fully resolves within a week as their digestive system adjusts to the routine.
Is It Safe to Drink Olive Oil Every Day?
Yes, for the large majority of healthy adults. The strongest evidence here comes from the PREDIMED trial (Estruch et al., New England Journal of Medicine, 2018, n=7,447), in which participants consumed more than 4 tablespoons of extra virgin olive oil daily for nearly five years as part of a Mediterranean diet, with improved — not worsened — cardiovascular and metabolic outcomes. Olive oil has been a daily dietary staple across Mediterranean populations for centuries at volumes far exceeding a single daily tablespoon.
The exceptions are people with active gallstone attacks, biliary disease, fat malabsorption disorders, or those preparing for surgery (see "Who Should Not Drink Olive Oil" below) — these groups should check with a doctor before starting a shot routine.
How Much Olive Oil Is Too Much?
There's no established toxic dose of dietary olive oil. The practical ceiling comes from calories and digestive tolerance, not toxicity. The PREDIMED trial used 4+ tablespoons daily with positive health outcomes, while FDA qualified health claims are based on roughly 1.5 tablespoons (about 20g) per day. Signs you've overshot your personal tolerance include persistent loose stools, unintended weight gain, or an uncomfortable sense of fullness — all of which resolve by scaling the dose back down.
Does Olive Oil Cause Weight Gain?
Only if it's added on top of your existing calorie intake rather than replacing other fats. At 120 calories per tablespoon, olive oil is calorie-dense, but in the PREDIMED trial, participants assigned to the higher olive-oil-intake group did not gain more weight than the control group — and some analyses found modest weight loss, likely because oleic acid promotes a satiety signal (oleoylethanolamide) that can reduce overall food intake. The practical takeaway: use olive oil to replace butter, seed oils, or other fats in your diet, not as an addition on top of your normal eating pattern.
What Happens the First Week of Drinking Olive Oil?
Who Should Not Drink Olive Oil
- People experiencing an active gallstone attack or acute biliary disease — concentrated fat triggers a strong gallbladder contraction that can worsen an attack
- Those with fat malabsorption disorders (chronic pancreatitis, unmanaged celiac disease, short bowel syndrome)
- Children under 12 — limited pediatric research exists on concentrated daily doses
- People preparing for surgery — olive oil has mild blood-thinning properties; most clinicians suggest pausing 1–2 weeks pre-procedure
Quick-Start Protocol to Avoid Side Effects
- Days 1–3: 1 teaspoon with food
- Days 4–7: 2 teaspoons with food
- Week 2: 1 tablespoon (full dose)
- Week 3+: Experiment with timing — morning, evening, or with meals — based on personal preference
Frequently Asked Questions
What are the side effects of drinking olive oil?
Most people have none. When side effects occur, they're typically mild and temporary digestive adjustments — loose stools, mild nausea on an empty stomach, or a peppery throat sensation from high-polyphenol oils — resolving within 3–7 days as the body adapts.
Can drinking olive oil cause diarrhea?
It can cause loose stools in the first few days, especially at a full tablespoon dose on an empty stomach, due to bile stimulation speeding up intestinal motility. Starting with 1 teaspoon and increasing gradually over a week prevents this in most people.
Is it safe to drink olive oil every day?
Yes, for most healthy adults. The PREDIMED trial had 7,447 participants consume 4+ tablespoons of EVOO daily for nearly five years with improved cardiovascular outcomes. Exceptions include people with active gallbladder disease, fat malabsorption disorders, or those about to have surgery.
How much olive oil is too much?
There's no established toxic dose. Practical limits come from calories (120 per tablespoon) and digestive tolerance. The PREDIMED trial used 4+ tablespoons daily safely; signs of overdoing it include persistent loose stools or unwanted weight gain.
Does olive oil cause weight gain?
Not when it replaces other fats in your diet rather than adding to your existing calorie intake. PREDIMED participants on higher olive oil intake did not gain more weight than controls, likely aided by oleic acid's satiety effect.
What happens the first week of drinking olive oil?
Days 1–2 may bring mild loose stools as bile release increases; days 3–5 are an adjustment window; by days 6–7 digestion typically normalizes; week 2 onward, most people notice no further digestive effects and begin building toward longer-term benefits.
The Bottom Line
Olive oil's side effects are mild, temporary, and almost entirely preventable through gradual dosing and taking it with food. The documented benefits — from the PREDIMED trial's cardiovascular findings to oleocanthal's anti-inflammatory activity (Beauchamp et al., Nature, 2005) — accumulate over months and years, while any digestive adjustment resolves within a single week.
- Estruch R, Ros E, Salas-Salvadó J, et al. "Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra-Virgin Olive Oil or Nuts." New England Journal of Medicine, 2018;378:e34. n=7,447.
- Beauchamp GK, Keast RSJ, Morel D, et al. "Ibuprofen-Like Activity in Extra-Virgin Olive Oil." Nature, 2005;437:45–46.
- U.S. Food and Drug Administration. Qualified Health Claim: Monounsaturated Fatty Acids from Olive Oil and Reduced Risk of Coronary Heart Disease.
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