Palm oil is unlikely to cause diarrhea for most people. In fact, the evidence points in the opposite direction: palm oil tends to produce firmer, harder stools rather than loose ones. That said, large amounts of any fat can overwhelm your digestive system, and heavily processed forms of palm oil can irritate the gut lining in ways that may lead to digestive trouble.
Palm Oil Typically Firms Up Stools
The best clinical data on palm oil and stool quality comes from infant nutrition research, where palm olein (the liquid fraction of palm oil) is a common ingredient in formula. A meta-analysis of nine randomized clinical trials found that infants fed palm-based formulas had significantly harder stools compared to infants fed formulas without palm oil. Stool frequency, however, was the same between the two groups. So palm oil changed consistency without changing how often infants had bowel movements.
The reason comes down to chemistry. Palmitic acid, the main fatty acid in palm oil, sits in a position on the fat molecule that makes it harder to absorb. When unabsorbed palmitic acid reaches the lower gut, it binds with calcium to form what researchers call “fatty acid soaps,” which are essentially insoluble compounds that harden stool. One study found that palmitate soaps and calcium were the dominant factors determining stool hardness in both formula-fed and breastfed infants. This soap-forming tendency is a well-documented effect of palm oil and works against diarrhea, not toward it.
Why Large Amounts Could Upset Your Stomach
Palm oil is roughly 50% saturated fat, and saturated fats are absorbed more slowly than unsaturated fats. In animal studies, the more saturated fraction of palm oil (palm stearin) took over 300 minutes to reach 50% absorption, compared to about 240 minutes for soybean oil. When you eat more fat than your body can process efficiently, the unabsorbed portion pulls water into the intestines through osmosis, which can loosen stools or cause cramping.
High saturated fat intake also increases the concentration of bile acids your liver releases to help with digestion. Those bile acids have a direct antimicrobial effect on gut bacteria, favoring bile-tolerant species while reducing overall microbial diversity. This shift in your gut microbiome has been linked to a higher risk of gastrointestinal disturbances. The effect isn’t unique to palm oil. Coconut oil, butter, and other high-saturated-fat foods trigger the same pattern. But palm oil is one of the most widely used fats in processed foods, so it’s easy to consume more of it than you realize.
Processed Palm Oil Is Harder on the Gut
Not all palm oil behaves the same way in your body. Interesterified palm oil, a chemically modified form used in many packaged foods to replace trans fats, appears to be particularly damaging to the intestinal lining. A study in Food Research International found that mice fed interesterified palm oil, even at normal fat levels, developed flattened intestinal lining, shorter villi (the finger-like projections that absorb nutrients), and fewer mucus-producing cells. Their guts showed increased inflammation markers and higher oxidative stress.
More concerning, the interesterified palm oil group had increased intestinal permeability, sometimes called “leaky gut,” where the tight junctions between intestinal cells loosen. Bacteria from the gut translocated into the blood, liver, and lungs of these animals. The researchers noted that interesterified fat added to a normal diet was in some ways more harmful than simply eating a high-fat diet with unmodified oil. A compromised intestinal barrier can lead to a range of digestive symptoms, including loose stools and diarrhea, because the gut loses its ability to regulate fluid absorption properly.
Who Might Be More Sensitive
People with irritable bowel syndrome or other functional gut disorders may react more strongly to palm oil than the general population. High-fat foods are a well-known trigger for IBS symptoms, and palm oil appears on lists of potential triggers alongside chocolate, dairy fat, and artificial sweeteners. If you already have a sensitive digestive system, the combination of slow-absorbing saturated fats and bile acid changes could be enough to provoke symptoms.
People who have had their gallbladder removed are another group to consider. Without a gallbladder to regulate bile release, a sudden influx of saturated fat can cause bile to flood the intestines, leading to cramping and diarrhea. This isn’t specific to palm oil, but palm oil’s high saturated fat content makes it a more likely culprit than oils like olive or canola.
The Practical Takeaway
If you’re experiencing diarrhea and suspect palm oil, context matters more than the oil itself. A moderate amount of palm oil in cooking is unlikely to cause loose stools and may actually do the opposite. The situations where palm oil could contribute to diarrhea involve eating large quantities of high-fat processed foods (where interesterified palm oil is common), having a pre-existing digestive condition, or consuming more total fat than your body can efficiently absorb at once. Checking ingredient labels for “interesterified fat” or “interesterified palm oil” can help you identify the more processed form, which has a stronger link to gut irritation than standard refined palm oil.