Portobello Mushroom Nutrition Calculator — Calories & Nutrition per Serving

A whole raw portobello cap (~84g) contains 18 calories — and even grilled, that cap rises to only about 24 calories. A standard slice of white bread has 79 calories. When used as a burger bun substitute, two portobello caps replace two bread slices, saving roughly 134 calories while adding potassium, selenium, and B-vitamins that bread doesn't provide ^[1].

Per 100g, raw portobello (FDC 169255) delivers 22 calories, 2.11g protein, 0.35g fat, and 3.9g carbohydrates. The fiber at 1.3g per 100g (5% DV) is modest but double that of cremini mushrooms (0.6g) — the maturation from cremini to portobello develops more structural cell wall material, which registers as dietary fiber ^[1].

At 92.8% water, portobello mushrooms are filling relative to their calorie content. The large cap size (typically 10-15cm diameter) provides visual and volumetric satisfaction on a plate — a grilled portobello looks like a substantial dish component while contributing minimal calories compared to the proteins and starches it typically accompanies ^[1].

Portobello's micronutrient strengths cluster around three standouts: niacin at 4.5mg per 100g (28% DV), selenium at 18.6mcg (34% DV), and potassium at 364mg (8% DV). A single cap (~84g) delivers 3.8mg niacin (24% DV), 15.6mcg selenium (28% DV), and 306mg potassium (7% DV) at just 18 calories ^[1].

Phosphorus at 108mg per 100g (9% DV) is another notable mineral — higher than most vegetables and comparable to eggs (86mg). Copper at 0.29mg (32% DV) is particularly high, making portobello one of the best vegetable-category sources of this trace mineral. Copper works alongside iron in supporting cellular processes tracked in nutrition research ^[1].

Pantothenic acid (vitamin B5) at 1.14mg per 100g (23% DV) rounds out the B-vitamin profile. Combined with niacin, this makes portobello a dual-B5/B3 source. The selenium content is especially relevant for plant-based eaters: most selenium in Western diets comes from wheat products and animal proteins — mushrooms offer one of the few vegetable-category alternatives ^[1][3].

A grilled portobello cap (~84g) versus a standard beef patty (~113g, 80/20 ground beef): 24 calories vs. 287 calories, 2.8g protein vs. 19.4g protein, 0.34g fat vs. 23g fat. The calorie difference is stark — portobello has 92% fewer calories — but protein drops by 86%. For calorie tracking, the trade is dramatic; for protein tracking, the gap is significant ^[1].

Where portobello competes is in micronutrient density per calorie: selenium at 0.85mcg/kcal (vs. beef's 0.07mcg/kcal), niacin at 0.20mg/kcal (vs. beef's 0.018mg/kcal), and potassium at 16.5mg/kcal (vs. beef's 1.0mg/kcal). Gram for gram on a calorie-adjusted basis, portobello outperforms beef patty in these three nutrients by 5-16x ^[1].

The practical application for meal logging: using portobello as a bun (not the patty) is the most common real-world use case — keeping the meat for protein while swapping bread for the mushroom cap. This saves 100+ calories from bread while adding ~24 calories of mushroom with meaningful selenium and B-vitamins. It's a calorie-efficient swap that preserves the burger structure ^[1].

Portobello and cremini are both *Agaricus bisporus*, but portobello's riboflavin drops to 0.13mg per 100g (10% DV) compared to cremini's 0.49mg (38% DV). This 73% decline happens because the cap opens and enlarges dramatically at maturity, diluting riboflavin concentration as cell mass increases faster than riboflavin production ^[1][3].

Niacin moves in the opposite direction — portobello's 4.5mg per 100g exceeds cremini's 3.8mg. The maturation process appears to continue niacin synthesis while riboflavin production plateaus. This means choosing between the two involves a trade-off: cremini for riboflavin, portobello for niacin. The difference matters most for people actively tracking specific B-vitamins ^[1].

Other changes from cremini to portobello: potassium drops from 448mg to 364mg (portobello's larger volume dilutes mineral concentration), fiber increases from 0.6g to 1.3g (more mature cell walls), and protein decreases slightly from 2.5g to 2.11g. For general nutrition logging, these differences are modest — but for detailed micronutrient tracking, the growth stage matters ^[1][3].

Grilled portobello is the most popular preparation. High heat for 4-5 minutes per side produces the characteristic smoky flavor while concentrating nutrients through water loss: grilled portobello reaches ~29 kcal per 100g (from 22 raw). Brush with 1 tsp olive oil before grilling and log the oil separately (~40 calories) for accurate tracking ^[1].

Stuffed portobello caps are a popular entrée — the cap serves as an edible bowl. A typical stuffing (spinach, breadcrumbs, cheese) can add 150-300 calories per cap. Log the mushroom shell separately from the filling: the baked shell contributes roughly 24 calories with 3.0mg niacin and 16mcg selenium, while the filling supplies the bulk of the meal's calories ^[1].

In salads and sandwiches, sliced portobello is typically used at 40-60g per serving. At 50g raw: 11 calories, 1.1g protein, 182mg potassium, 2.25mg niacin (14% DV), and 9.3mcg selenium (17% DV). The mushroom adds meaningful B-vitamins and minerals at virtually zero calorie cost to the dish — making it a nutrient-dense addition worth logging even in small quantities ^[1].