The foods that cause the worst-smelling farts are those high in sulfur: red meat, eggs, cruciferous vegetables like broccoli and cauliflower, garlic, onions, and dried fruits. The smell of flatulence comes almost entirely from sulfur-containing gases, not from the volume of gas itself. That distinction matters, because some foods that make you gassy (like beans) don’t necessarily make your gas smell terrible, while a small amount of gas from a steak dinner can clear a room.
Why Some Gas Smells and Some Doesn’t
Flatulence is really two separate problems: volume and odor. The bulk of any fart is made up of odorless gases like hydrogen, nitrogen, and methane. These come from fermenting carbohydrates, which is why high-fiber foods can make you bloated and gassy without producing much smell at all.
The smell comes from an entirely different source: sulfur gases, particularly hydrogen sulfide, the same compound responsible for the rotten-egg stink of sewers and hot springs. Gut bacteria produce hydrogen sulfide in two main ways. Some species break down sulfur-containing amino acids (the building blocks of protein) from food. Others, notably bacteria in the Desulfovibrio genus, convert sulfate compounds found in certain foods and drinking water directly into hydrogen sulfide. About half of all people harbor significant populations of these sulfate-reducing bacteria, which helps explain why the same meal can affect two people very differently.
Red Meat, Eggs, and High-Protein Foods
Protein-rich animal foods are the single biggest dietary driver of smelly gas. Red meat, in particular, is loaded with sulfur-containing amino acids like cysteine and methionine. When these reach the large intestine, bacteria ferment them into hydrogen sulfide and other sulfur compounds. A controlled human feeding study found that fecal sulfide concentrations increased more than fifteenfold when participants went from eating no meat to eating 600 grams per day. The relationship between meat intake and sulfide production was direct and significant.
Eggs are another major offender, especially the yolks, which are rich in the same sulfur-containing amino acids. Whey protein shakes and protein bars can compound the problem, particularly when they contain added sugar alcohols like sorbitol or xylitol. These sweeteners ferment in the gut and can worsen both the volume and the odor of gas.
Cruciferous Vegetables
Broccoli, cauliflower, Brussels sprouts, cabbage, and kale belong to the Brassica family, and they pull double duty when it comes to gas. They contain raffinose, a carbohydrate humans can’t fully digest, which increases gas volume. But they also contain sulfur-based compounds called glucosinolates and S-methyl cysteine sulfoxide derivatives, which gut bacteria convert into sulfur gases. That combination of more gas plus smellier gas is why cruciferous vegetables have such a strong reputation.
Garlic and onions work through a similar mechanism. Both are rich in organosulfur compounds that break down in the gut and contribute directly to hydrogen sulfide production.
Beans: Gassy but Not Always Smelly
Beans are famous for causing flatulence, but the gas they produce is mostly odorless. The primary culprit is raffinose, which passes undigested into the colon where bacteria ferment it into hydrogen and methane. Since the fermentation is carbohydrate-based rather than protein-based, the resulting gas tends to be high in volume but low in sulfur content.
That said, beans aren’t completely off the hook. They do contain some sulfur compounds, and when combined with other sulfur-rich foods in a meal, they can amplify the overall smell simply by increasing the total amount of gas pushing those sulfur molecules out. The good news is that your gut adjusts. Studies have found that after three to four weeks of regularly eating beans, flatulence levels return to normal as your gut bacteria adapt to the increased fiber.
Dairy Products and Lactose Intolerance
If you’re lactose intolerant, dairy can cause dramatic bloating and gas, but the gas itself is technically odorless. Undigested lactose ferments in the colon, producing hydrogen and carbon dioxide rather than sulfur compounds. The smell of flatulence comes from protein breakdown, not carbohydrate fermentation. So while a glass of milk might leave you uncomfortably gassy, the gas from lactose alone won’t smell particularly foul. Cheese and other high-protein dairy products are a different story, since they deliver both lactose (in varying amounts) and sulfur-containing amino acids.
Dried Fruits and Sugar Alcohols
Prunes, apricots, and other dried fruits contain sorbitol, a naturally occurring sugar alcohol that humans absorb poorly. Sorbitol ferments in the large intestine and can increase both gas volume and odor. The same goes for sugar-free gums and candies sweetened with sorbitol, xylitol, or mannitol. Apples, pears, and peaches also contain natural sorbitol, though in smaller amounts than their dried counterparts.
How to Reduce Smelly Gas
Since volume and odor have different causes, they need different strategies. Enzyme supplements like alpha-galactosidase (sold as Beano) can reduce the volume of gas from fermentable carbohydrates like beans and high-fiber foods. They work by breaking down raffinose before it reaches the colon. However, these enzymes don’t address sulfur gas production, so they won’t necessarily make your gas smell better.
To reduce odor specifically, the most effective approach is moderating your intake of sulfur-rich foods: cutting back on red meat, eggs, garlic, onions, and cruciferous vegetables, or at least not eating them all in the same meal. Spreading protein intake across the day rather than loading it into one large serving also helps, because smaller amounts of sulfur-containing amino acids reaching the colon at once means less substrate for bacteria to convert into hydrogen sulfide.
If you’re increasing fiber or plant intake, introduce it gradually. Adding large amounts of fiber suddenly overwhelms your gut bacteria, but a slow ramp-up over three to four weeks gives your microbiome time to adjust, reducing both volume and the fermentation byproducts that contribute to smell.