Mushrooms are one of the lowest-carb vegetables you can eat. A one-cup serving of raw white button mushrooms (about 96 grams) contains just 3 grams of total carbohydrates and 1 gram of fiber, bringing the net carb count to roughly 2 grams. That’s alongside 3 grams of protein and only 21 calories.
Carb Counts by Mushroom Variety
Not all mushrooms are created equal when it comes to carbs, though the differences are modest. White button mushrooms and portobellos sit at the low end, while shiitake and oyster mushrooms carry a bit more. Here’s how they compare per one-cup raw serving:
- White button: 3 grams total carbs, 1 gram fiber (about 2 grams net carbs)
- Portobello (diced): 3 grams total carbs per cup, or about 3 grams per whole cap
- Oyster: roughly 6 grams total carbs
- Shiitake: roughly 7 grams total carbs
The gap between varieties comes down partly to density. Shiitake and oyster mushrooms have meatier, more substantial flesh, so a cup of them packs more plant material by weight. Per 100 grams, raw white button mushrooms contain about 2.7 grams of carbohydrate, while oyster mushrooms come in closer to 6 grams.
What Makes Up Those Carbs
The carbohydrates in mushrooms are mostly fiber and complex polysaccharides, not the simple sugars or starches found in bread or fruit. A significant portion of mushroom fiber comes from beta-glucans, a type of soluble fiber found in fungal cell walls. Beta-glucans are the dominant polysaccharide in mushrooms and have been studied for their effects on blood sugar regulation and immune function. This means the small amount of carbohydrate you get from mushrooms behaves very differently in your body than the same number of grams from, say, white rice.
On a dry weight basis, the fiber and carbohydrate content of mushrooms is actually substantial. But since fresh mushrooms are roughly 90% water, you’d need to eat a very large quantity before the carbs added up to anything meaningful.
Fresh vs. Canned vs. Dried
How mushrooms are processed changes the nutritional picture. Canning can slightly shift the carbohydrate content in either direction depending on the variety. Research comparing fresh and canned button mushrooms found that canning reduced total carbohydrates modestly (from about 47 to 42 grams per 100 grams of dry weight). For oyster mushrooms, the opposite happened: canned versions had higher carbohydrate content than fresh (66 vs. 61 grams per 100 grams dry weight). Canned mushrooms may also contain added sodium or preservatives worth checking on the label.
Dried mushrooms are the biggest change. Removing the water concentrates everything, so gram for gram, dried mushrooms contain far more carbohydrates than fresh. A small handful of dried shiitake reconstituted for a stir-fry won’t dramatically change your carb intake, but if you’re measuring by weight rather than volume, keep in mind that dried mushrooms are roughly ten times more carb-dense than fresh ones.
Mushrooms on a Low-Carb or Keto Diet
With 2 to 7 grams of total carbs per cup depending on variety, mushrooms fit comfortably into a ketogenic diet, which typically caps total carbs at 50 grams per day. You would need to eat around 6 cups of white button mushrooms in a single day just to hit 18 grams of carbs from mushrooms alone. In practical terms, it’s hard to overdo it.
The main thing to watch for is preparation. Sautéing mushrooms in butter or olive oil doesn’t add carbs, but breading them, stuffing them with grain-based fillings, or using sweetened sauces changes the equation quickly. Packaged mushroom products like cream of mushroom soup or mushroom-based snack chips often contain added starches and sugars that bump the carb count well beyond what the mushrooms themselves contribute. Always check the nutrition label on anything that isn’t plain mushrooms.
Full Nutritional Picture
Mushrooms punch above their weight nutritionally for something so low in calories and carbs. That one-cup serving of white button mushrooms delivers 3 grams of protein alongside its 3 grams of carbs, with virtually no fat (about 0.2 grams per 100 grams). They’re also a notable source of B vitamins, potassium, selenium, and, when exposed to UV light, vitamin D.
Because they’re low in carbs, calories, and fat simultaneously, mushrooms are one of the few foods that fit into nearly every dietary framework, from keto to low-fat to calorie-restricted eating plans. Their savory, umami-rich flavor also makes them a practical substitute for higher-carb ingredients in dishes like tacos, pasta sauces, and burger patties.