Asparagus contains asparagusic acid, a sulfur compound that may be behind the odd smell some people notice in their urine after eating it. Many people never notice. In a Harvard study of 6,909 US adults, 58% of men and 61.5% of women did not report a strong asparagus odor, and variants in a cluster of olfactory receptor genes were linked to it. A smaller lab study of 38 adults found that about 8% did not make enough of the odor to detect, so people differ in both making it and smelling it.
The amino acid asparagine is named after the vegetable. French chemists isolated crystals of it from asparagus juice in 1806, and it is usually credited as the first amino acid ever isolated. Asparagus plants are usually either male or female, and the female plants make thicker spears and red berries that are toxic to people. Its genome has been used to study how a young Y chromosome arose, and extension services now recommend all-male hybrids, which are more productive and bear no berries. A bed lives 12 to 15 years or longer.
Green and white asparagus are the same plant. White spears are grown under mounded soil, so they never see light and never turn green. Asparagus was once filed in the lily family with onions and garlic, and genetic work now puts it in its own family, Asparagaceae. A cup (134 g) of raw spears has 27 calories, 2.8 g of fiber and 46% of the daily value of vitamin K.
Health benefits of asparagus
The top findings from 17 studies, strongest evidence first
What the stars mean
- Strong. Several randomized trials, pooled in a meta-analysis, point the same way, or regulators (FDA or EFSA) have approved the claim.
- Moderate. Good randomized trials support it, but there are fewer of them, or their results vary.
- Limited. Small, short or single trials, or mixed results. Promising, but it needs confirmation.
Population and lab studies get no stars: they show a link or a mechanism, not proof.
How we rate evidence →- ★Better sleep quality with asparagus productsAcross 18 studies of asparagus-based products taken by mouth, sleep quality improved consistently. In 33 nurses with no control group, a sleep score improved from 7.41 to 6.03 (lower is better).
- ★Lower blood sugar and blood fatsAsparagus powder for 12 weeks lowered fasting blood glucose and triglycerides compared with placebo in 44 overweight or obese adults. Triglycerides rose in the placebo group, which explains part of the gap.
- ★Lower blood pressure from stem powder6 g a day of powdered asparagus bottom stems for 10 weeks lowered blood pressure, fasting glucose and total cholesterol in 28 healthy volunteers. It was not blinded and did not test the spears people eat.
- ★Less fatigue and stress hormone in small trialsAn asparagus stem extract, 150 mg a day for 28 days, improved self-rated fatigue and mood in healthy volunteers. In a separate trial in healthy men, cortisol, a stress hormone, rose on placebo but not on the extract.
- ★Many do not notice the asparagus urine smellIn 6,909 US adults, 58% of men and 61.5% of women did not strongly agree that they noticed a strong asparagus odor in their urine. In a smaller test, about 8% of 38 adults did not make enough odor to be detected.
All 17 studies, strongest evidence first
Across 18 studies of asparagus products, sleep quality improved consistently, with only modest gains in thinking, mood and stress
Systematic review of 18 studies, including 13 randomized trials and 3 before-and-after studies, with 503 adults who took asparagus-based products by mouth. Reaction time, anxiety, depression and cortisol also moved in a helpful direction, but results varied with dose, group and study length. Studies were small and varied, and two authors work for the Japanese company Amino Up.
Asparagus powder for 12 weeks lowered fasting blood glucose and triglycerides compared with placebo in overweight adults
Exploratory randomized trial in 44 overweight or obese adults aged 18 to 59, who took asparagus powder (40 mg per kg of body weight a day) or a placebo. A blood marker of oxidative stress (MDA) was also lower than on placebo, while insulin, insulin resistance and LDL cholesterol did not differ between groups. Triglycerides and insulin resistance rose in the placebo group, which explains part of the gap. The abstract does not say which part of the plant the powder came from.
6 g a day of powdered asparagus bottom stems for 10 weeks lowered blood pressure, fasting glucose and total cholesterol
Open clinical trial in 28 healthy volunteers who took powder from either the needle-like branches (cladophylls) or the bottom stems, parts usually thrown away at harvest. The branch powder also lowered diastolic pressure, fasting glucose and total cholesterol. It was not blinded and did not test the spears people eat.
An asparagus stem extract, 150 mg a day for 28 days, improved self-rated fatigue and mood in healthy volunteers
Randomized, double-blind, placebo-controlled crossover trial of enzyme-treated asparagus extract (ETAS). Salivary immunoglobulin A rose and volunteers gave more correct answers in a timed stress test, while cortisol and catecholamines did not change. The first author works for Amino Up Chemical, the maker of the extract.
The same extract kept blood and saliva cortisol from rising in healthy men, while it rose on placebo, but total sleep time did not change
Two randomized, double-blind, placebo-controlled studies in healthy men; the cortisol result comes from the crossover trial. Sleep changed only in men with low sleep efficiency or very long sleep, in a subgroup split. The first author works for Amino Up Chemical, the maker of the extract.
A standardized asparagus stem extract for 12 weeks eased agitation and depression scores in people with dementia, in a small pilot
Double-blind crossover pilot in 27 people with mild-to-moderate dementia, who took the extract (ETAS®50) for 12 weeks and a placebo for 12 weeks. Overall symptom severity differed between the periods (p=0.045), with agitation (p=0.015) and depression (p=0.045) improving and apathy only trending (p=0.058). The abstract reports symptom scores, not a memory result.
Nurses taking a product with asparagus extract improved their sleep score from 7.41 to 6.03 (lower is better)
Before-and-after study in 33 hospital nurses on two-shift work (34 started), who took a “Foods with Function Claims” product with asparagus extract for at least 2 weeks. Fatigue and work engagement also improved, but impaired work functioning did not. There was no control group, so a placebo effect cannot be ruled out.
Asparagus products added to chemotherapy raised the tumor response rate (risk ratio 1.88), but the evidence was low certainty
Systematic review of 10 studies (7 randomized trials) with 8,898 participants, using asparagus granules, syrup or oral liquid, not the vegetable. Survival-based and quality-of-life “effective rates” also improved with granules (risk ratios 1.55 and 1.76). The authors ask for better trials, especially in lung cancer.
After eating asparagus spears, the urine odor faded with a half-life of about 4.7 hours
Crowdsourced experiment: 87 attendees of two clinical pharmacology meetings were assigned a number of spears to eat and reported what they smelled. More spears meant a stronger effect, and age explained part of the difference between people. It relied on self-report from a small, self-selected group.
About 8% of 38 adults did not make enough asparagus odor in their urine to be detected, and 2 could not smell it
Lab experiment in which adults ate asparagus, gave urine samples and then picked the asparagus sample from pairs. Being unable to smell the odor was linked to one DNA change (rs4481887) inside a cluster of about 50 olfactory receptor genes. The reason some people do not produce the odor is unknown.
In 6,909 US adults, 58% of men and 61.5% of women did not notice a strong asparagus odor in their urine
Genome-wide study in two Harvard cohorts of European-American adults. Anyone who did not strongly agree that they noticed a strong odor after eating asparagus counted as unable to smell it. All 871 DNA variants linked to this sat in one region of chromosome 1 that holds olfactory receptor genes, and the authors ask for replication. The odor was self-reported.
Among 27 people with asparagus allergy, 3 had anaphylaxis after eating it and 8 had occupational asthma from handling it
Retrospective series from a Spanish allergy clinic over 5 years: 8 patients had contact dermatitis, 17 had IgE-mediated allergy and 2 had both. Two lipid transfer proteins seem to be the main allergens. These are patients who came to a clinic, so it says nothing about how common the allergy is.
Rats fed a diet with 5% green asparagus for 10 weeks had a systolic blood pressure of 159 against 192 mm Hg in rats on a normal diet
Study in rats bred to develop high blood pressure, not people. Kidney ACE activity was lower and creatinine clearance higher on the asparagus diet. The researchers isolated a compound, 2″-hydroxynicotianamine, that blocks ACE in a boiling-water extract.
Mice fed a diet with 2% cooked asparagus survived chemical-induced colitis better and had milder disease
Study in mice, not people. Mice ate cooked asparagus or the flavonoid rutin for 2 weeks before and during colitis. Both improved survival and a disease activity score, and purified rutin did best at limiting colon damage and gut bacteria imbalance.
Rutin was the main polyphenol in asparagus spears, and boiling raised it in spears harvested in April
Lab study of two Italian cultivars, raw, boiled and after simulated digestion. Raw edible parts held 1,770.72 and 995.20 mg/kg of rutin, and after simulated digestion 146.95 to 454.58 mg/kg of polyphenols stayed available for absorption. This is lab chemistry, not a study in people.
Boiling asparagus for 60 minutes cut its flavonols by 43.9%
Lab test of home processing of asparagus spears and onions. Chopping alone lowered rutin in asparagus by 18.5% over 60 minutes. An hour is far longer than normal cooking, so this shows the direction of the effect, not the loss from a short boil.
Extracts of asparagus shoots and leaves raised the activity of two alcohol-processing enzymes more than 2-fold in liver cells
Lab study in human liver cancer cells (HepG2), not people. The extracts also eased cell damage from hydrogen peroxide, ethanol and carbon tetrachloride. Asparagus as a hangover remedy was not tested in people.
Who should be careful with asparagus
Most people can eat asparagus freely. Take a little care if one of these applies:
- Warfarin. Asparagus contains vitamin K (41.6 µg per 100 g, 35% of the daily value), which can change how this blood thinner works, and a UK hospital trust lists it among foods with vitamin K. You do not need to avoid it; keep the amount steady from week to week and check with your clinic before big changes.
- Irritable bowel syndrome. Monash University lists asparagus among its high-FODMAP vegetables, a group of carbohydrates that can trigger symptoms. Check the Monash FODMAP app for the current serving size.
- Allergy. It is rare, but a Spanish clinic series of 27 people included 3 with anaphylaxis after eating asparagus, and most other reactions followed handling it. Stop eating it and see a doctor if you get hives, swelling or breathing trouble.
How to choose, store and eat asparagus
- Green or white: they are the same plant, but white spears are grown under soil and their lower ends must be peeled.
- Cooked briefly: in lab tests boiling for 60 minutes cut flavonols by 43.9%, while boiling did not lower the main polyphenol, rutin, in spears harvested in April. Clemson Extension says boiling takes 2 to 5 minutes and steaming 5 to 8, until a fork pierces the stalk.
- Powders and extracts: the sleep and blood sugar trials used powders or stem extracts, and none tested a plate of spears.
Choose firm green spears with tightly closed, dry tips, and skip limp or wilted ones. Keep them unwashed with the cut ends wrapped in a wet paper towel inside a bag in the fridge, and use them within one to four days. Residues are no reason to skip asparagus: in USDA tests of 298 samples in 2019, 94.6% had no pesticide detected and none was above an established limit.
Sources
- Dietary advice for patients taking warfarin. Cambridge University Hospitals NHS Foundation Trust.
- High and low FODMAP foods. Monash University FODMAP Diet.
- Tabar AI, Alvarez-Puebla MJ, Gomez B, et al. Diversity of asparagus allergy: clinical and immunological features. Clin Exp Allergy. 2004.
- Makris DP, Rossiter JT. Domestic processing of onion bulbs (Allium cepa) and asparagus spears (Asparagus officinalis): effect on flavonol content and antioxidant status. J Agric Food Chem. 2001.
- Di Matteo A, Paolillo A, Ciriaco L, et al. Effect of cooking and in vitro digestion on the polyphenols and antioxidant properties of Asparagus officinalis L. cultivars. Foods. 2025.
- Using & storing asparagus. Clemson Cooperative Extension, Home and Garden Information Center.
- Asparagus. University of Nebraska–Lincoln Extension.
- Asparagus. Wikipedia.
- Pesticide Data Program annual summary, calendar year 2019. USDA Agricultural Marketing Service.
History of asparagus
Wild asparagus grows across much of Europe and western temperate Asia, and sources differ on exactly where it began. Roman farmers grew it. Cato the Elder’s farm manual De agri cultura, written around 160 BC and the oldest surviving work of Latin prose, has a section on planting asparagus. He says to plant the beds after the spring equinox, cover them thickly with manure, pull the first spears in the third or fourth year, and dig up and replant the roots after eight or nine years.
Asparagus was also a food in Rome. A recipe for it appears in the 1st-century collection attributed to Apicius, and in the 2nd century AD the Greek physician Galen called it a beneficial herb. As Roman power faded, mentions of it faded too, but it stayed popular in the Byzantine Empire. In legend, Emperor Augustus used the saying “faster than cooking asparagus” for quick action.
The word comes from Greek aspáragos, whose own origin is uncertain. In English it was once sperage, and folk speech bent it into “sparrow grass”. In 1791 John Walker wrote that the folk name was so common that “asparagus” sounded stiff and pedantic.
European settlers brought asparagus to North America by at least 1655. Adriaen van der Donck, a Dutch immigrant to New Netherland, mentions it in his account of Dutch farming there, and in 1685 one of William Penn’s advertisements for Pennsylvania listed it among the crops that grew well. In France the tips were served to Madame de Pompadour (1721 to 1764) as points d’amour, or love tips.
Today asparagus is a worldwide crop. World production reached 8.9 million tonnes in 2024, and China grew 87% of it. In Germany the white asparagus season, Spargelzeit, traditionally ends on June 24, and roadside stands and open-air markets sell about half of the country’s white asparagus. In the UK the season traditionally runs from April 23 to Midsummer Day.
Sources
- Asparagus. Wikipedia.
- Cato the Elder. On Agriculture (De agri cultura), sections 158 to 162. Translated by W. D. Hooper and H. B. Ash. Loeb Classical Library, 1934. LacusCurtius.
- Cato the Elder. Wikipedia.
- Asparagine. Wikipedia.
- Pierre Jean Robiquet. Wikipedia.
- Harkess A, Zhou J, Xu C, et al. The asparagus genome sheds light on the origin and evolution of a young Y chromosome. Nat Commun. 2017.
- Pegiou E, Mumm R, Acharya P, de Vos RCH, Hall RD. Green and white asparagus (Asparagus officinalis): a source of developmental, chemical and urinary intrigue. Metabolites. 2019.
- Mitchell SC. Asparagus, urinary odor, and 1,2-dithiolane-4-carboxylic acid. Perspect Biol Med. 2013.
- Markt SC, Nuttall E, Turman C, et al. Sniffing out significant “Pee values”: genome wide association study of asparagus anosmia. BMJ. 2016.
- Pelchat ML, Bykowski C, Duke FF, Reed DR. Excretion and perception of a characteristic odor in urine after asparagus ingestion: a psychophysical and genetic study. Chem Senses. 2011.
- Growing asparagus in the home garden. University of Maryland Extension.
Frequently asked questions about asparagus
Is asparagus good for you?
For most people, yes. A cup (134 g) of raw spears has 27 calories and 2.8 g of fiber, and covers 46% of the daily value of vitamin K and 17% of folate. The health trials are few and small, and most tested powders or extracts, so no asparagus finding here reaches moderate or strong evidence. The most consistent result, from a review of 18 studies of asparagus products with 503 adults, was better sleep quality.
Why does asparagus make your pee smell?
Asparagus contains asparagusic acid, a sulfur compound that a review suggests is behind the distinctive urine odor. In a crowdsourced experiment with 87 people, the effect faded with a half-life of about 4.7 hours. The same review calls asparagusic acid apparently harmless toxicologically.
Why can some people not smell asparagus pee?
Genes play a part. In 6,909 US adults, 58% of men and 61.5% of women did not report a strong asparagus odor, and variants near a cluster of olfactory receptor genes were linked to it. A smaller lab study of 38 adults found that about 8% did not make enough of the odor to detect, so both making it and smelling it differ between people.
Can you eat asparagus raw?
Yes, young spears can be eaten raw, but no study here compares raw and cooked asparagus in people. Wash the spears well, because the base often holds sand and soil. In lab tests, boiling for 60 minutes cut flavonols by 43.9%, while boiled spears kept their main polyphenol, rutin, so a short cook looks fine too.
How much asparagus can you eat a day?
No study here sets an ideal amount. The trials used 6 g a day of powdered asparagus parts for 10 weeks, 40 mg per kg of body weight of asparagus powder for 12 weeks, and 150 mg a day of a stem extract. A cup of raw spears (134 g) has 27 calories. If you take warfarin, keep the amount steady from week to week and ask your clinic.
Is asparagus good for weight loss?
No study here tested weight loss. Raw asparagus has 20 calories and 2.1 g of fiber per 100 g and is 93% water, so it fills a plate cheaply. That is a swap effect for higher-calorie foods, not a proven effect of asparagus itself.
Is asparagus high in protein?
Fairly high for a vegetable, though not a main source. Raw asparagus has 2.2 g of protein per 100 g, or 2.9 g in a cup (134 g), which is about 4 in 10 of its calories. Its protein quality score on this site is 93 out of 100, limited by lysine.
Does asparagus cause gas?
It can in some people, and no trial here measured gas directly. Monash University lists asparagus among its high-FODMAP vegetables, a group of carbohydrates that can trigger symptoms in people with irritable bowel syndrome. If it bothers you, try a smaller portion and check the Monash FODMAP app for serving sizes.