Zucchini (Courgette): Nutrients, What Research Shows and Safety

Zucchini, also called courgette (Cucurbita pepo), is a summer squash in the gourd family (Cucurbitaceae). The whole fruit is eaten, skin included, raw or cooked, and it is picked young while the skin is still soft. People eat it because it is light, low in calories and a source of vitamin C, potassium and the plant pigment lutein. This page covers zucchini as a food and keeps it apart from supplements and from hype.

Read this first

• Bitter zucchini: do not eat it. Rarely, a zucchini contains high levels of natural bitter toxins (cucurbitacins) and can cause vomiting, diarrhea and dehydration. Germany's food-risk body (BfR) says to taste a raw piece first and not use the vegetable if it tastes bitter. [12][13]
• Allergy: any food can cause an allergic reaction. For trouble breathing or swelling of the face or throat, call 911. See food allergy basics and emergency signs.
• Potassium and kidneys: zucchini has a moderate amount of potassium, which matters for people on certain medicines or with kidney disease (details below). [6]
• Evidence in one line: zucchini has not been studied much on its own. Most health findings come from studies of vegetables as a group, and those are observational (they cannot prove cause).

What is in it (USDA values)

USDA FoodData Central, zucchini with skin, raw, SR Legacy item 169291. [1] The serving is the USDA household portion of 1 cup chopped (124 g).

% Daily Value uses the FDA 2016 Daily Values; values vary with variety, ripeness and storage. Serving columns are our arithmetic from the USDA per-100 g values.

Zucchini is about 95% water, which is why it has so few calories. [1] Its main measured plant pigments are the carotenoids lutein and zeaxanthin; USDA lists 2,125 µg per 100 g, and only 120 µg of beta-carotene. [1] Lutein is found in the macula, the center of the retina, and has been studied for eye health, mostly as a supplement (see below). The other compounds in zucchini, including cucurbitacins, are covered under safety. We did not read a source that measured other plant compounds in zucchini, so we do not describe them.

What research says

People who eat more vegetables also differ from others in income, exercise, smoking and the rest of their diet, so an association is not proof that any one vegetable is the cause. [8]

Eaten as food vs taken as a supplement or extract. The lutein trials above used capsules or tablets, not zucchini. [9][11] Lutein from a supplement and lutein from food are not the same exposure, and zucchini has not been tested in these trials. Zucchini extracts or powders are not covered here.

How much is a normal serving

• USDA household portions: 1 cup chopped is 124 g, 1 cup sliced is 113 g, 1 medium zucchini is 196 g. [1]
• Official figures: the NHS counts 80 g of fresh, canned or frozen vegetables as one portion of its 5 A DAY. [2] The World Health Organization says at least 400 g of fruits and vegetables a day for people older than 10. [3] These figures are information, not a prescription.
• Cooking and storage: MedlinePlus says long cooking or storage can lower vitamin C in produce, and that raw produce is the best source. [4] In a lab comparison of eight other fruits and vegetables (zucchini not included), frozen produce had vitamin content comparable to fresh. [16] We did not find a zucchini-specific study of cooking and nutrients. See fresh, frozen and canned produce.

Safety, allergy and medicines

• Bitter zucchini (cucurbitacin poisoning, sometimes called toxic squash syndrome): cultivated zucchini is normally mild. BfR explains that the bitter taste comes from naturally occurring bitter toxins in the plant, which, depending on variety and growing conditions, can sometimes be present in higher amounts. BfR advises treating an unusually bitter taste as a warning sign and not using the vegetable. [12] A fatal poisoning from bitter zucchini was in the news when BfR issued this notice in 2015. [12] A German case report describes a 66-year-old woman who ate a bitter zucchini and arrived at hospital with fast heartbeat, low blood pressure, drowsiness, diarrhea with blood, nausea and vomiting, and dehydration; her bowel inflammation resolved on its own and she recovered after intravenous fluids. [14] A French poison-center series of 353 people poisoned by bitter squash found diarrhea, vomiting and stomach pain in 58%, with no deaths; 4% were of moderate severity, and the authors recommend throwing away any squash with a bitter taste. [13] Over half of those squash had been bought in a store, and a quarter came from a garden. [13] The same family of toxins has caused severe bleeding of the stomach and some deaths from very bitter bottle gourd juice in India, mostly in older people, which shows the toxins can be serious. [15] A 2022 Canadian case report is titled "Toxic squash syndrome" [17] (we could read only the title). What to do: taste a small raw piece before cooking, and spit it out and discard the zucchini if it is bitter. If someone has vomiting, bloody diarrhea, dizziness or fainting after eating a bitter squash, get medical help. See toxic herbs and plant poisoning. Sources we read did not say whether cooking removes the bitterness, so cooking should not be relied on.
• Potassium, kidney disease and medicines: MedlinePlus lists poor kidney function, ACE inhibitors, ARBs and potassium-sparing diuretics (such as spironolactone) among causes of too much potassium in the blood, which can disturb heart rhythm; it says people with kidney problems, especially on dialysis, may need to limit potassium-rich foods and should talk to their provider. [6] A cup of zucchini provides 7% of the Daily Value, so it is not among the highest-potassium vegetables by this measure. [1] The sources we read gave no zucchini-specific advice for kidney disease; ask your kidney team. See foods in kidney disease: potassium and oxalates.
• Vitamin K and warfarin: zucchini has 4.3 µg of vitamin K per 100 g, a low amount (4% of the Daily Value per cup). [1] The sources we read did not name zucchini as a concern for warfarin; for general advice see foods and medicine interactions.
• Allergy: the sources we read did not give data on zucchini allergy or on cross-reaction with other plants, so we make no claim about how common it is. Treat any reaction like any food reaction; see when to seek medical help after a food reaction.
• Pregnancy: the sources we read gave no special caution for zucchini as food. The bitter-toxin warning applies to everyone.
• Pesticide residues: Proper evidence not found; we could not read a USDA Pesticide Data Program or similar source for zucchini this session.
• Gas and bloating, FODMAPs: Proper evidence not found in the sources we read, so we make no claim.

Choosing, storing and food safety

• Pick produce that is not bruised or damaged, and cut away damaged or bruised areas. Choose pre-cut or packaged produce only if refrigerated or on ice. [18]
• Keep perishable produce in a refrigerator at 40°F or below; refrigerate all pre-cut produce. [18]
• Rinse under running water and scrub firm produce with a clean brush; soap, detergent or commercial produce wash is not recommended. [18]
• Keep produce eaten raw apart from raw meat, poultry and seafood. [18]

Related pages

• Food allergy basics and emergency signs
• Foods in kidney disease: potassium and oxalates
• Foods and medicine interactions: vitamin K, grapefruit and others
• Fresh, frozen and canned produce
• Toxic herbs and plant poisoning: what to know
• Food storage, leftovers and food safety basics