Summer squash: a watery vegetable with one warning worth knowing

The most practical number on summer squash comes from a hospital kitchen. In a Brazilian study where 68 heart patients on potassium-restricted diets rated the dishes, zucchini cooked under pressure held 93.62 mg potassium per 3.5 oz (100 g), one of the lowest values among the vegetables tested. The randomization in that study applied to the tasting, the potassium came from lab analysis, and the raw starting level of that squash was not given. For comparison, 8 raw zucchini samples analyzed by USDA averaged 226 mg. The squash itself is about 95% water. A cup of raw green slices, 115 g, has about 20 calories and 20.6 mg vitamin C. The warning is taste. A French case report describes a 66-year-old woman admitted with bloody diarrhea and colitis after eating bitter zucchini, and she recovered on intravenous fluids within two days. It is one case, and the authors treat the bitter taste as the key sign of this poisoning.

Every statement here is tied to a source. The badge says what kind of evidence stands behind it: A is a meta-analysis or systematic review, E is the position of an expert body without its own analysis. How we verify →

The numbers, per 3.5 oz (100 g)

USDA entry	kcal	Protein	Fat	Carbs	Fiber
Squash, summer, zucchini, includes skin, raw	17	1.21 g	0.32 g	3.11 g	1 g
Squash, summer, all varieties, cooked, boiled, drained, with salt	20	0.91 g	0.31 g	4.31 g	1.4 g
Squash, summer, all varieties, cooked, boiled, drained, without salt	20	0.91 g	0.31 g	4.31 g	1.4 g
Squash, summer, all varieties, raw	16	1.21 g	0.18 g	3.35 g	1.1 g
Squash, summer, crookneck and straightneck, canned, drained, solid, without salt	13	0.61 g	0.07 g	2.96 g	1.4 g
Squash, summer, crookneck and straightneck, cooked, boiled, drained, with salt	19	1.04 g	0.39 g	3.79 g	1.1 g
Squash, summer, crookneck and straightneck, cooked, boiled, drained, without salt	19	1.04 g	0.39 g	3.79 g	1.1 g
Squash, summer, crookneck and straightneck, frozen, cooked, boiled, drained, with salt	25	1.28 g	0.2 g	5.54 g	1.4 g
Squash, summer, crookneck and straightneck, frozen, cooked, boiled, drained, without salt	25	1.28 g	0.2 g	5.54 g	1.4 g
Squash, summer, crookneck and straightneck, frozen, unprepared	20	0.83 g	0.14 g	4.8 g	1.2 g
Squash, summer, crookneck and straightneck, raw	19	1.01 g	0.27 g	3.88 g	1 g
Squash, summer, green, zucchini, includes skin, raw	16	0.98 g	0.2 g	3.27 g	0.75 g

All 22 USDA entries for summer squash (10 more)

USDA entry	kcal	Protein	Fat	Carbs	Fiber
Squash, summer, scallop, cooked, boiled, drained, with salt	16	1.03 g	0.17 g	3.3 g	1.9 g
Squash, summer, scallop, cooked, boiled, drained, without salt	16	1.03 g	0.17 g	3.3 g	1.9 g
Squash, summer, scallop, raw	18	1.2 g	0.2 g	3.84 g	1.2 g
Squash, summer, yellow, includes skin, raw	19	0.89 g	0.14 g	4.39 g	0.96 g
Squash, summer, zucchini, includes skin, cooked, boiled, drained, with salt	15	1.14 g	0.36 g	2.69 g	1 g
Squash, summer, zucchini, includes skin, cooked, boiled, drained, without salt	15	1.14 g	0.36 g	2.69 g	1 g
Squash, summer, zucchini, includes skin, frozen, cooked, boiled, drained, with salt	14	1.15 g	0.13 g	2.97 g	1.3 g
Squash, summer, zucchini, includes skin, frozen, cooked, boiled, drained, without salt	17	1.15 g	0.13 g	3.56 g	1.3 g
Squash, summer, zucchini, includes skin, frozen, unprepared	17	1.16 g	0.13 g	3.58 g	1.3 g
Squash, summer, zucchini, italian style, canned	29	1.03 g	0.11 g	6.85 g	— g

These are the USDA entries that are summer squash, not foods made from it; they differ in cut, part, pack or preparation. Linked names have a page with the full profile and per-portion figures.

As people eat it, per 3.5 oz (100 g)

As eaten	kcal	Protein	Fat	Carbs	Fiber
Squash, summer, casserole with tomato and cheese	85	3.48 g	4.32 g	8.87 g	1.4 g
Squash, summer, casserole, with cheese sauce	92	3.69 g	4.71 g	9.28 g	1.2 g
Squash, summer, casserole, with rice and tomato sauce	83	2.32 g	1.66 g	14.9 g	1.1 g
Squash, summer, souffle	125	4.65 g	8.94 g	6.87 g	0.7 g
Summer squash, cooked, as ingredient	21	1.31 g	0.35 g	4.11 g	1.2 g
Summer squash, green, raw	17	1.21 g	0.32 g	3.11 g	1 g
Summer squash, yellow or green, NS as to form, cooked	47	1.27 g	3.33 g	3.99 g	1.1 g
Summer squash, yellow or green, canned, cooked, fat added, NS as to fat type	35	0.6 g	2.6 g	2.86 g	1.3 g
Summer squash, yellow or green, fresh, cooked with butter or margarine	44	1.28 g	2.91 g	3.99 g	1.1 g
Summer squash, yellow or green, fresh, cooked with oil	51	1.26 g	3.75 g	3.98 g	1.1 g
Summer squash, yellow or green, fresh, cooked, fat added, NS as to fat type	47	1.27 g	3.33 g	3.99 g	1.1 g
Summer squash, yellow or green, fresh, cooked, no added fat	21	1.3 g	0.35 g	4.1 g	1.2 g

All 17 (5 more)

As eaten	kcal	Protein	Fat	Carbs	Fiber
Summer squash, yellow or green, frozen, cooked with butter or margarine	40	1.19 g	2.35 g	4.42 g	1.3 g
Summer squash, yellow or green, frozen, cooked with oil	46	1.18 g	3.06 g	4.4 g	1.3 g
Summer squash, yellow or green, frozen, cooked, fat added, NS as to fat type	43	1.18 g	2.71 g	4.41 g	1.3 g
Summer squash, yellow or green, frozen, cooked, no added fat	21	1.21 g	0.16 g	4.54 g	1.3 g
Summer squash, yellow, raw	19	1.01 g	0.27 g	3.88 g	1 g

USDA Food and Nutrient Database for Dietary Studies (FNDDS, release 2024-10-31): summer squash as it is prepared and served, from the recipes behind the national dietary survey, rather than a single laboratory sample.

How much is actually in it

Across 8 USDA-analyzed samples of zucchini with skin, folate ranged from 20 to 147 mcg per 3.5 oz (100 g) and vitamin C from 10.4 to 19.3 mg. — USDA Foundation Foods Squash, summer, green, zucchini, includes skin, raw, 8 samples (n = 8 samples) Evidence E source
Per 100 g mean (range): vitamin C 15.0 mg (10.4-19.3); folate 71.0 mcg (20.0-147.0); potassium 225.8 mg (182.5-284.0); fiber 0.75 g (0.61-0.96); water 95.01 g
Yellow summer squash in 8 USDA samples averaged 17 mg vitamin C and 36 mcg folate per 3.5 oz (100 g), with about 94% water. — USDA Foundation Foods Squash, summer, yellow, includes skin, raw, 8 samples (n = 8 samples) Evidence E source
Per 100 g mean (range): vitamin C 17.0 mg (12.7-25.7); folate 36.0 mcg (13.0-46.0); potassium 220.5 mg (153.0-281.0); fiber 0.96 g (0.71-1.17); water 94.05 g

What a real portion looks like

USDA survey data put one cup of raw sliced green summer squash at 115 g and about 20 calories, with 20.6 mg vitamin C, and a whole squash weighs about 7.1 oz (200 g). — FNDDS Summer squash, green, raw (FDC 2709808) (n = 1 record) Evidence E source
Per 100 g: 17 calories, vitamin C 17.9 mg; per cup (115 g): 19.6 calories, vitamin C 20.6 mg; whole (200 g): 34 calories, vitamin C 35.8 mg; slice 10 g
Cooked summer squash without added fat is 180 g per cup in USDA survey data, about 38 calories, because cooking collapses the slices. — FNDDS food code 75233011 Summer squash, yellow or green, fresh, cooked, no added fat (FDC 2709991) (n = 1 record) Evidence E source
Per 100 g: 21 calories; per cup (180 g): 37.8 calories; cup mashed 240 g; whole 200 g: 42 calories

What cooking and storage change

By the USDA retention table for boiled and drained vegetables, summer squash keeps about 65% of its folate and 75% of its vitamin C, and 90% of its potassium. — USDA R6 retention code 3775, Vegetables group, VEG,OTHER,BLD,WATER COVER,DRAINED (n = 1 record) Evidence E source
Retained: folate 65%, vitamin C 75%, thiamin 80%, niacin 85%, vitamin B6 85%, potassium 90%, riboflavin 90%, calcium 95%, iron 95%, magnesium 95%

What it does to your health

In 12 obese insulin-resistant women, a meal with zucchini deep-fried in extra-virgin olive oil gave a lower late C-peptide response than grilled zucchini with raw oil. — 12 obese insulin-resistant women (BMI 32.8) and five lean subjects; 150 g zucchini, 60 g pasta, 25 g oil (n = 17) Evidence B source
C-peptide AUC lower after fried meal at 120-180 min (P = .0020 to .0039) in obese women; no difference in lean
In three US cohorts, eggplant and summer squash ranked among the top five vegetables and fruits for favorable cardiometabolic biomarkers. — 41,714 participants for biomarkers; 207,241 followed for 32 y (HPFS, NHS, NHSII) (n = 207241) Evidence C source
High-metabolic-quality FV share, highest vs lowest quartile: HR 0.84-0.89 for major chronic disease

Safety, limits and interactions

A case report describes a 66-year-old woman hospitalized with bloody diarrhea and colitis after eating bitter zucchini containing cucurbitacins. — one 66-year-old female patient (n = 1) Evidence D source
Tachycardia, hypotension, hemorrhagic colitis; recovered after IV fluids within 2 days
Over 22 years at a French poison center, plants of the squash family caused 3.3% of 2197 cases where a toxic plant was eaten by mistake for food. — 2197 food confusion events, Marseille Poison Control Centre, 2002-2023 (n = 2197) Evidence C source
Cucurbitaceae 3.3% of events, second after Nerium oleander 13.1%; severe poisonings overall 0.5%
A case report describes zucchini allergy caused by an allergen that survives heat and digestion, so cooking may not make it safe for such patients. — one middle-aged male patient (n = 1) Evidence D source
Mono-sensitization to a heat- and pepsin-stable zucchini allergen

Who this works differently for

In a trial with 68 heart patients rating the dishes, pressure-cooked zucchini had one of the lowest potassium contents, 93.62 mg per 3.5 oz (100 g). — 68 patients, Institute of Cardiology, Porto Alegre, Brazil; potassium-restricted diets (n = 68) Evidence D source
Potassium after pressure cooking: zucchini 93.62 mg/100 g, spinach 74.85 mg/100 g, squash 237.83 mg/100 g
A case report describes food protein-induced enterocolitis syndrome from zucchini in a child, who later tolerated it on a repeat food challenge. — one child with FPIES (n = 1) Evidence D source
First oral food challenge positive; second tolerated
In 60 UK infants, those weaned at 6 months ate more of a new vegetable if they had first been given a variety pack including zucchini rather than carrot alone. — Sixty parent-infant dyads, South Birmingham, UK; 9-day exposure (n = 60) Evidence C source
Interaction of weaning age and exposure group on pea intake; single-taste group weaned at 6 months ate significantly less

The bottom line

The nutrients vary more than a single table value suggests. Across 8 USDA samples of zucchini with skin, folate ran from 20 to 147 mcg per 3.5 oz (100 g), a sevenfold spread, and vitamin C from 10.4 to 19.3 mg. Yellow squash in 8 samples averaged 17 mg vitamin C and 36 mcg folate. Boiling and draining, by a 1975 USDA factor for vegetables in general, keeps about 65% of folate, 75% of vitamin C and 90% of potassium. A cooked cup packs down to 180 g and about 38 calories. Health research on squash alone is sparse. In three US cohorts, eggplant and summer squash were counted as one item among the top five of 52 fruits and vegetables linked with favorable heart and metabolic markers. That is an association for a group of foods, and it does not isolate squash. In 12 obese insulin-resistant women, a meal of 5.3 oz (150 g) zucchini deep-fried in extra virgin olive oil gave a lower C-peptide response than grilled zucchini with raw oil. The difference lay in the oil, and the study is small. Who should be careful. Over 22 years at the Marseille poison center, plants of the squash family made up 3.3% of 2197 cases where a toxic plant was eaten by mistake for food, a count for the whole family. One case report describes a man allergic to a zucchini protein that survives heat and digestion, so cooking may not help people with that allergy. Another describes a child with food protein-induced enterocolitis from zucchini who tolerated it at a later challenge. For babies, one UK study of 60 infants found that those weaned at 6 months ate more of a new vegetable after a variety pack of zucchini, parsnip and sweet potato than after carrot alone, and the abstract does not say how groups were assigned. We found no studies on squash in pregnancy.

Related foods

Squash: thin evidence and one bitter warning

More from the same food group (vegetables and vegetable products)

Sources

ssq-r6-03 · USDA Foundation Foods, dataset
Squash, summer, green, zucchini, includes skin, raw (Foundation, 8 samples): Vitamin C, total ascorbic acid 15.0 mg, range 10.4-19.3; Folate, total 71.0 µg, range 20.0-147.0; Potassium, K 225.8 mg, range 182.5-284.0; Fiber, total dietary 0.7525 g, range 0.61-0.96; Water 95.01 g per 100 g
USDA FoodData Central Foundation Foods, release 2026-04-30, Squash, summer, green, zucchini, includes skin, raw · checked 2026-09-30
ssq-r6-04 · USDA Foundation Foods, dataset
Squash, summer, yellow, includes skin, raw (Foundation, 8 samples): Vitamin C, total ascorbic acid 17.0 mg, range 12.7-25.7; Folate, total 36.0 µg, range 13.0-46.0; Potassium, K 220.5 mg, range 153.0-281.0; Fiber, total dietary 0.9563 g, range 0.71-1.17; Water 94.05 g per 100 g
USDA FoodData Central Foundation Foods, release 2026-04-30, Squash, summer, yellow, includes skin, raw (FDC 2685569) · checked 2026-09-30
ssq-r6-01 · USDA FNDDS, dataset
Summer squash, green, raw (FDC 2709808): 1 slice = 10 g; 1 whole = 200 g; 1 cup = 115 g; per 100 g: Energy 17 kcal; Vitamin C, total ascorbic acid 17.9 mg; per 1 cup: 19.6 kcal, vitamin C 20.6 mg; per 1 whole: 34.0 kcal, vitamin C 35.8 mg
USDA FNDDS (FoodData Central survey 2024-10-31), Summer squash, green, raw (FDC 2709808) · checked 2026-09-30
ssq-r6-02 · USDA FNDDS, dataset
Summer squash, yellow or green, fresh, cooked, no added fat (FNDDS 75233011, FDC 2709991): 1 slice = 10 g; 1 whole = 200 g; 1 cup = 180 g; 1 cup, mashed = 240 g; per 100 g: Energy 21 kcal; per 1 cup: 37.8 kcal
USDA FNDDS (FoodData Central survey 2024-10-31), food code 75233011 (FDC 2709991) · checked 2026-09-30
ssq-r6-05 · USDA R6 retention factors, dataset
USDA-RETN-R6:3775 VEG,OTHER,BLD,WATER COVER,DRAINED (Vegetables and Vegetable Products, group 11): folate_total_ug 65%; vitamin_c_mg 75%; thiamin_mg 80%; niacin_mg 85%; vitamin_b6_mg 85%; phosphorus_mg 90%; potassium_mg 90%; riboflavin_mg 90%; calcium_mg 95%; iron_mg 95%; magnesium_mg 95%
USDA Table of Nutrient Retention Factors, Release 6 (2007), code 3775 · checked 2026-09-30
ssq-r6-07 · RCT
Meal A was composed of 60 g of pasta made from wheat flour and 150 g of grilled courgettes with 25 g of uncooked oil. Meal B included 15 g of oil in the 150 g of deep-fried courgettes and 10 g of oil in the 60 g of stir-fried pasta.
J Med Food, 2011 · checked 2026-09-30
ssq-r6-12 · cohort
Of 52 FV items, 19 were identified as high-metabolic quality (top 5: apples/pears, iceberg/head lettuce, raw spinach, alfalfa sprouts, and eggplant/summer squash).
Am J Clin Nutr, 2024 · checked 2026-09-30
ssq-r6-08 · case report
A 66-year-old female patient was admitted to the emergency department following bitter zucchini ingestion. ... Bitter taste is essential to diagnose cucurbitacin intoxications.
Dtsch Med Wochenschr, 2020 · checked 2026-09-30
ssq-r6-09 · retrospective review
Over 22 years, 2197 food confusion events were managed with 321 different species. The most frequently involved plant was Nerium oleander (289 cases, 13.1%), then Cucurbitaceae genus (3.3%), Colchicum autumnale (3.3%), Prunus amygdalus (3%), Mahinot esculenta (3%), Cytisus laburnum (2.6%), Aesculus hippocastanum (2.5%) and Narcissus Jonquilla (2%).
Toxins (Basel), 2024 · checked 2026-09-30
ssq-r6-10 · case report
A case of mono-sensitization to a heat- and pepsin-stable allergen in zucchini is described.
Eur Ann Allergy Clin Immunol, 2012 · checked 2026-09-30
ssq-r6-06 · laboratory analysis
The vegetables with the lowest potassium values were spinach (74.85 mg/100 g) and zucchini (93.62 mg/100 g), both cooked under pressure.
Clin Nutr ESPEN, 2025 · checked 2026-09-30
ssq-r6-11 · case report
We report an unusual case of FPIES due to zucchini. During the follow-up. Two oral food challenges (OFC) were carried out to evaluate tolerance to the food involved. RESULTS: The first OFC was positive and in the second the child tolerated the food without problems.
Allergol Immunopathol (Madr), 2021 · checked 2026-09-30
ssq-r6-13 · clinical trial
During the exposure period half of each age group was given carrot every day, and the other half was given a variety pack of courgette, parsnip and sweet potato.
Appetite, 2014 · checked 2026-09-30

Review. Reviewed on 2026-09-30 for evidence level, dose and population context, and claims a reader could misread. Bioma Learn has no human medical reviewer at this time, and we say so rather than invent one. Methodology. This is information, not medical advice.