Some of the most common constipating foods are refined grains, high-fat dairy, fried foods, and unripe bananas. These foods slow digestion through different mechanisms, from absorbing water in the colon to reducing intestinal muscle contractions. If you’ve noticed a pattern between what you eat and how often you go, the culprits likely fall into a few well-studied categories.
Refined Grains and White Bread
Refined grains like white bread, white rice, and regular pasta have had their bran and germ stripped away during processing. That removal takes most of the fiber with it. Fiber is what gives stool its bulk and softness, and it speeds up the time food takes to move through your colon. Without it, everything slows down.
A study of women with functional constipation found that eating white rice for four weeks actually increased the time food spent in the digestive tract, while brown rice and whole wheat diets both reduced transit time significantly. The difference was measurable: women on brown rice saw their transit time drop by about 16.5 hours on average, while those on white rice saw it climb by nearly 7 hours. That’s a swing of almost a full day just from switching between two versions of the same grain.
Most adults need 28 to 34 grams of fiber per day, roughly 14 grams for every 1,000 calories. A diet built around white bread, regular pasta, and white rice makes that target very hard to hit. Swapping even one serving per meal to a whole grain version (brown rice, whole wheat bread, oatmeal) can make a noticeable difference within a few days.
Dairy Products
Dairy is one of the more complicated constipating foods because it doesn’t affect everyone equally. For some people, especially children, the proteins in cow’s milk slow bowel movement and can increase resting pressure in the muscles of the lower digestive tract. This makes it physically harder to pass stool. The combination of high dairy intake and low fiber intake is a well-documented recipe for constipation in kids.
Cow’s milk allergy plays a significant role here, particularly in children under seven. In clinical trials, removing cow’s milk from the diet resolved constipation in 28% to 78% of children studied, depending on the trial. One study found that among children who improved on a milk-free diet, over 86% were under age seven, the age group where sensitivity to milk proteins is most common. Full-fat cheese and ice cream tend to be the worst offenders because they pair those proteins with high fat content, which independently slows digestion.
If you suspect dairy is contributing to your constipation, a two-week elimination trial (cutting out all cow’s milk products) is a straightforward way to test it. Many people tolerate fermented dairy like yogurt and kefir better because the fermentation process partially breaks down the proteins involved.
Fried and High-Fat Foods
Fried foods delay digestion in a very direct way. When researchers compared identical meals prepared either fried or unfried, the fried version took an average of 317 minutes to empty from the stomach, compared to 227 minutes for the unfried version. That’s an extra hour and a half just at the stomach stage. Participants also reported longer-lasting feelings of fullness and epigastric heaviness after the fried meal.
This delay cascades through the rest of the digestive tract. When food sits longer in the stomach, the colon has more time to absorb water from whatever arrives next, producing harder, drier stools. Fast food, deep-fried snacks, and heavily buttered dishes all fall into this category. The issue isn’t fat itself in moderate amounts. It’s the high concentration of fat in fried foods that overwhelms the digestive system’s ability to process it at a normal pace.
Unripe Bananas
Bananas are unusual because their effect on your gut depends entirely on ripeness. Green, unripe bananas are high in resistant starch and tannins, both of which can slow digestion and worsen constipation. Resistant starch is difficult for the body to break down, and tannins have an astringent effect that can reduce the secretion of fluid in the intestines.
As bananas ripen and turn yellow (and eventually spotted), that resistant starch converts into simple sugars. A ripe banana is actually easier to digest and contains enough soluble fiber to help move things along. So if you’re prone to constipation, skip the green bananas but don’t fear the ripe ones.
Persimmons and Tannin-Rich Foods
Persimmons, particularly the astringent varieties eaten before they’re fully ripe, contain large amounts of soluble tannin. When these tannins meet stomach acid, they can form a dense, rubbery mass that is harder than other plant-based clumps and very difficult for the body to break down. In extreme cases, this leads to a bezoar, a solid mass that can cause obstruction in the stomach or small intestine.
You don’t need to avoid persimmons entirely. Fully ripe, soft persimmons have much lower tannin levels. The risk comes from eating large quantities of unripe or partially ripe fruit, especially on an empty stomach. Other tannin-rich foods like strong black tea, red wine, and some unripe fruits can have a mildly constipating effect for the same reason, though rarely as dramatic as persimmons.
Alcohol
Alcohol contributes to constipation through dehydration. It suppresses a hormone called antidiuretic hormone (ADH), which normally signals your kidneys to hold onto water. With less ADH circulating, you urinate more and lose fluid faster. When your body is short on water, the colon compensates by pulling more moisture out of stool as it passes through, leaving it harder and more difficult to pass.
This effect is dose-dependent. A single beer is unlikely to cause problems, but regular or heavy drinking creates a chronic state of mild dehydration that compounds over time. Mixing alcohol with caffeinated mixers makes the effect worse, since caffeine is also a mild diuretic. If you drink regularly and notice constipation, increasing your water intake alongside (not instead of) reducing alcohol is the most practical first step.
Calcium and Iron Supplements
Supplements are easy to overlook as a cause of constipation because they don’t feel like “food,” but calcium and iron are two of the most common culprits. Calcium carbonate, the form found in most over-the-counter calcium supplements, is particularly associated with constipation, flatulence, and bloating. In a large, five-year study tracking 92,000 adverse events, constipation rates were noticeably higher in the group taking 1,200 mg of calcium carbonate daily compared to placebo.
Iron supplements are similarly notorious. The unabsorbed iron that passes into the colon can harden stool and slow motility. If you need to take either supplement, calcium citrate tends to cause fewer digestive side effects than calcium carbonate. For iron, taking it with vitamin C can improve absorption so less unabsorbed iron reaches the colon. Taking these supplements with meals rather than on an empty stomach also helps.
Patterns That Matter More Than Single Foods
Most constipation isn’t caused by one food in isolation. It’s the overall pattern that matters. A diet that’s simultaneously high in refined grains, cheese, fried foods, and red meat while low in fruits, vegetables, and water creates the perfect conditions for slow transit. Each of these foods removes a piece of what your colon needs to function: fiber for bulk, water for softness, and the natural stimulation that comes from plant-based foods moving through the system.
If you’re trying to identify your personal triggers, it helps to change one category at a time rather than overhauling everything at once. Swap refined grains for whole grains for a week. Then add more water. Then reduce fried food frequency. This approach makes it easier to pinpoint which changes actually make a difference for your body, since individual responses to these foods vary considerably.