Does eggplant cause gas? Portion, sorbitol and the frying oil

Rarely, at a normal portion. Monash University’s FODMAP researchers rate 1 cup of eggplant as low in FODMAPs, the poorly absorbed carbs that gut bacteria ferment into gas, and only bigger servings turn moderate, then high, in sorbitol. If eggplant reliably bloats you, check the serving size and the cooking fat before you blame the vegetable.

Start with the fat. Raw eggplant has 0.18 g of fat per 100 g. The USDA’s survey entry for battered or breaded fried eggplant has 12.82 g, about 70 times as much (our arithmetic). Its recipe, per 100 g, is 38 g of cooked eggplant, 50 g of batter and 12 g of oil, so the government’s fried eggplant is mostly not eggplant. NIDDK, the US institute for digestive diseases, says some people get more gas symptoms from high-fat foods, which can increase bloating. Whether oil belongs on a plant-based plate at all is a different argument, and we make it in our piece on eating oil on a plant-based diet. For gas, the point is narrower: a plate of fried eggplant puts two suspects in front of you, and the vegetable is only one of them.

What in eggplant can cause gas?

Gas from food comes from carbohydrates that the stomach and small intestine do not fully digest. When they reach the large intestine, bacteria break them down and make gas in the process. Eggplant brings two of these: fiber and sorbitol.

Sorbitol is a polyol, one of the sugar groups Monash’s team describes as not completely digested or absorbed. Polyols move slowly through the small intestine and pull water in with them, then bacteria in the large intestine ferment them and produce gas. Monash says the extra gas and water stretch the intestinal wall, and that in people with IBS, whose gut is highly sensitive, the stretching causes exaggerated pain and discomfort. The same sorbitol is sold as a sweetener, and NIDDK lists candy and gum with sweeteners ending in “-ol” among the things that can lead to excess gas. Eggplant simply grows its own.

Then there is the fiber. Raw eggplant has 3 g per 100 g, and the USDA weighs a cup of cubes at 82 g, so a cup carries about 2.5 g (our arithmetic). A whole unpeeled eggplant of about 1¼ lb weighs 548 g in the same entry, which works out to roughly 16 g of fiber (our arithmetic). The Daily Value for fiber on US labels is 28 g, so one whole eggplant is more than half of it before anything else on the plate counts. NIDDK notes that some people have more gas when they take in too much fiber.

NIDDK’s own list of gassy foods names apples, peaches and pears, cruciferous vegetables such as broccoli and kale, beans and lentils, dairy, whole wheat and drinks sweetened with high-fructose corn syrup. Eggplant is not on it. Anyone who has sat through the aftermath of a three-bean chili will not be shocked by who made the list.

How much eggplant is too much?

Monash rates foods with traffic lights by serving size. In a 2016 post, two of its research dietitians gave eggplant as their example of a food that is green at 1 cup, amber at larger quantities because of a moderate amount of sorbitol, and red, or high in sorbitol, at very large amounts. The same post asks whether 1 cup of eggplant, half a cup of sweet potato and half a cup of red cabbage can go into one meal, each green on its own, and says that for the vast majority of people with IBS on a low FODMAP diet it will be tolerated. Even past the green limit, the dietitians write, most people manage amber and the lower end of red servings.

A dish built from a whole eggplant is where the numbers climb. Monash’s own low FODMAP smoky eggplant dip uses a single large eggplant of 700 g and divides it into 8 servings, which is about 88 g, or 3 oz, of eggplant per person (our arithmetic). Eat the whole bowl yourself on a Friday night and you have had 8 of Monash’s servings in one sitting, with a dip spoon as your only witness.

That recipe has a second detail worth stealing. It flavors the dip with 1½ tbsp of garlic-infused olive oil instead of garlic cloves. Garlic contains fructans, which dissolve in water and not in oil, according to Monash’s piece on cooking with onion and garlic. A baba ganoush made the usual way, with crushed raw garlic stirred through, has a second FODMAP in the bowl, and the eggplant tends to get the blame for both.

Is it because eggplant is a nightshade?

This is the claim the old version of this page leaned on, and the evidence behind it is thin. Eggplant, like its relatives the potato and the tomato, makes glycoalkaloids, compounds plants use to defend themselves against pests. In 2020 the European Food Safety Authority assessed them. For potato glycoalkaloids, its panel found that acute toxic effects in humans include nausea, vomiting and diarrhea, and set the lowest dose at which it saw adverse effects at 1 mg of total potato glycoalkaloids per kg of body weight per day. For eggplant and tomato glycoalkaloids, the panel could not characterize the risk at all, citing a lack of occurrence data and limited toxicity data.

Here is the nightshade case at full strength. Plenty of people say they feel worse after nightshades, and a regulator admitting it lacks data on eggplant is not the same as a regulator clearing eggplant. If your gut reacts to every nightshade on the menu but shrugs at a big bowl of lentils, the fiber-and-sorbitol explanation fits that pattern poorly, and something else may be going on.

Nothing we read for this article measured eggplant’s glycoalkaloids against gas at a dinner-sized portion, and nothing covered the lectins and salicylates the old version also blamed, so its advice to peel your eggplant to dodge them is gone. The way to test a nightshade suspicion is the one NIDDK describes for any food: keep a diary of what you eat and drink and when the symptoms come, and take it to a doctor or dietitian.

What to change before you give up eggplant

Cut the fat before you cut the vegetable. The USDA’s entry for cooked eggplant with fat added has 2.92 g of fat per 100 g, against 0.19 g with no added fat, and the breaded fried version sits at 12.82 g. Roasting halves with a light brush of oil, or grilling slices, gets you the smoky flavor without asking your gut to handle a sponge of oil.

Keep the portion near a cup if you know you are sensitive, since that is where Monash’s green rating sits, and bulk the dish out with other vegetables rather than more eggplant. NIDDK’s habit changes apply here too: eat slowly, sit down to eat, and have smaller, more frequent meals instead of large ones.

If bloating comes back with many foods besides eggplant, the low FODMAP diet is the structured version of all this. Monash says it is intended for people with medically diagnosed IBS, is best followed with a dietitian, and starts with 2 to 6 weeks of high restriction before foods come back in stages. NIDDK describes trying it for a few weeks to see whether it helps IBS symptoms. The old version of this page also suggested peppermint pills. The NIH’s complementary health center says peppermint oil in enteric-coated capsules may improve IBS symptoms in adults, and lists heartburn, nausea, abdominal pain and dry mouth as possible side effects, so that is a conversation for your doctor rather than a fix for one dinner.

NIDDK says studies suggest people pass gas 8 to 14 times a day on average, and experts consider up to 25 times a day normal. NIDDK advises talking to a doctor if gas symptoms bother you, if they change suddenly, or if they come with abdominal pain, constipation, diarrhea or weight loss.

The part we are least sure about is the nightshade question, because the regulator that looked could not answer it either. If you are someone who reacts to every member of the family, tell us what your food diary showed. And if the issue is less how much gas than how it smells, that is a different mechanism, covered in our piece on vegan gas and bloating.