Asparagus Benefits: What the Evidence Actually Shows

Asparagus is a spring vegetable with an unusually long list of health claims attached to it, and the four deep dives below sort them by the quality of the evidence. One claim rests on some of the strongest results in nutrition: asparagus is one of the richest everyday sources of folate — 149 micrograms per 100 g cooked according to USDA, more than a third of the daily value — and folate is the vitamin that two landmark randomised trials showed prevents neural tube defects when taken around conception. One rests on solid but modest human data: the inulin-type fructans in asparagus are the best-studied prebiotic there is, and controlled trials show they feed bifidobacteria and soften stools, at the price of gas that people with irritable bowel cannot tolerate. One is a case where the evidence overturns the folklore: asparagus sits on old gout diet sheets as a “purine-rich vegetable”, and the largest cohort ever run found purine-rich vegetables do not raise gout risk at all. And one is mostly laboratory chemistry — the glutathione, rutin and saponins that make asparagus interesting in a test tube have not been shown to do anything measurable in a person eating it. Along the way: the genetics of the asparagus-urine smell, what boiling does to the folate, and why someone on warfarin should eat asparagus steadily rather than avoid it.

Deep-Dive Articles

Asparagus Folate, Vitamin K, and Pregnancy

How much folate a serving really carries (USDA figures by spear, half-cup and cup), the MRC and Hungarian trials that showed folic acid prevents neural tube defects, why the supplement is still advised even for people who eat well (food folate is about 80% as available as folic acid), what folate does for homocysteine and stroke risk, and what boiling versus steaming does to the vitamin. Then vitamin K: 51 micrograms per 100 g, green versus white, and the warfarin evidence — which says keep intake steady, not zero.

Asparagus Inulin, Prebiotic Fibre, and the Gut

What inulin-type fructans are and how much asparagus has, the human trials of inulin (more bifidobacteria, softer stools, large person-to-person variation, no disease outcomes), the one trial that fed people inulin-rich vegetables rather than powder, and the flip side: asparagus is a high-FODMAP food and the same fermentation is what hurts in irritable bowel syndrome. Plus the complete chemistry and genetics of the asparagus-urine smell, from the 1975 Science paper to the 6,909-person genome-wide study that found most people cannot smell it.

Asparagus, the Diuretic Tradition, Kidneys, and Purines

Two thousand years of asparagus as a kidney remedy, the discovery of asparagine in 1806, and what the diuretic evidence actually amounts to (potassium and water, a rat study, and no modern human trial). Then the gout question, answered by 47,150 men followed for twelve years: meat and seafood raise gout risk, dairy lowers it, and purine-rich vegetables including asparagus do nothing — confirmed by two further urate studies. Finally kidney stones: asparagus is a low-oxalate vegetable and does not belong on the avoidance lists it sometimes appears on.

Asparagus Glutathione, Saponins, and Antioxidants

Why asparagus is on every “top glutathione foods” list, and the human evidence on whether eaten glutathione gets in (a single dose does nothing; six months of supplement doses ten times a serving raised stores by a third). Rutin in the green tips, protodioscin in the white spears, anthocyanins in the purple, and where the concentrations were measured. The famous hangover study, read properly (liver cells in a dish, leaf extract), the blood-sugar rat study, and what chopping and boiling do to the flavonoids — which has been measured.

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Table of Contents

  1. Deep-Dive Articles
  2. What Is Actually In Asparagus
  3. Key Research Papers: Folate, Vitamin K and Pregnancy
  4. Key Research Papers: Inulin, the Gut and the Smell
  5. Key Research Papers: Kidneys, Gout and Blood Pressure
  6. Key Research Papers: Glutathione, Flavonoids and Saponins
  7. External Authoritative Resources
  8. Connections
  9. Featured Videos

What Is Actually In Asparagus

Before the claims, the raw material. Every figure below is from USDA FoodData Central for asparagus, cooked, boiled, drained, per 100 g — about six or seven medium spears. USDA's own household portions for this food are four spears (60 g) and half a cup (90 g), so a generous cup is about 180 g and you can double the numbers below for it.

Two things follow. First, asparagus is a folate-and-vitamin-K food; everything else it supplies is useful but unremarkable, and the antioxidant compounds that get the headlines have the least human evidence behind them. Second, form and cooking matter: folate, vitamin C and the fructans leach into boiling water, the flavonoids are lost to chopping and long cooking, and vitamin K and the carotenoids are absorbed far better with fat. The traditional ways of eating asparagus — briefly steamed or grilled, with butter, olive oil or a poached egg — turn out to be the nutritionally correct ones, and the four deep dives return to that from four directions.

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Key Research Papers: Folate, Vitamin K and Pregnancy

  1. MRC Vitamin Study Research Group (1991). Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. Lancet. — PubMed PMID: 1677062
  2. Czeizel AE, Dudás I (1992). Prevention of the first occurrence of neural-tube defects by periconceptional vitamin supplementation. The New England Journal of Medicine. — PubMed PMID: 1307234
  3. De-Regil LM, Peña-Rosas JP, Fernández-Gaxiola AC, Rayco-Solon P (2015). Effects and safety of periconceptional oral folate supplementation for preventing birth defects. The Cochrane Database of Systematic Reviews. — PubMed PMID: 26662928
  4. Winkels RM, Brouwer IA, Siebelink E, Katan MB, Verhoef P (2007). Bioavailability of food folates is 80% of that of folic acid. The American Journal of Clinical Nutrition. — PubMed PMID: 17284745
  5. McKillop DJ, Pentieva K, Daly D, et al. (2002). The effect of different cooking methods on folate retention in various foods that are amongst the major contributors to folate intake in the UK diet. The British Journal of Nutrition. — PubMed PMID: 12493090
  6. Li Y, Huang T, Zheng Y, Muka T, Troup J, Hu FB (2016). Folic Acid Supplementation and the Risk of Cardiovascular Diseases: A Meta-Analysis of Randomized Controlled Trials. Journal of the American Heart Association. — PubMed PMID: 27528407
  7. Franco V, Polanczyk CA, Clausell N, Rohde LE (2004). Role of dietary vitamin K intake in chronic oral anticoagulation: prospective evidence from observational and randomized protocols. The American Journal of Medicine. — PubMed PMID: 15121490
  8. Sconce E, Avery P, Wynne H, Kamali F (2007). Vitamin K supplementation can improve stability of anticoagulation for patients with unexplained variability in response to warfarin. Blood. — PubMed PMID: 17110451

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Key Research Papers: Inulin, the Gut and the Smell

  1. van Loo J, Coussement P, de Leenheer L, Hoebregs H, Smits G (1995). On the presence of inulin and oligofructose as natural ingredients in the western diet. Critical Reviews in Food Science and Nutrition. — PubMed PMID: 8777017
  2. Gibson GR, Roberfroid MB (1995). Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. The Journal of Nutrition. — PubMed PMID: 7782892
  3. Vandeputte D, Falony G, Vieira-Silva S, et al. (2017). Prebiotic inulin-type fructans induce specific changes in the human gut microbiota. Gut. — PubMed PMID: 28213610
  4. Hiel S, Bindels LB, Pachikian BD, et al. (2019). Effects of a diet based on inulin-rich vegetables on gut health and nutritional behavior in healthy humans. The American Journal of Clinical Nutrition. — PubMed PMID: 31108510
  5. Halmos EP, Power VA, Shepherd SJ, Gibson PR, Muir JG (2014). A diet low in FODMAPs reduces symptoms of irritable bowel syndrome. Gastroenterology. — PubMed PMID: 24076059
  6. White RH (1975). Occurrence of S-methyl thioesters in urines of humans after they have eaten asparagus. Science. — PubMed PMID: 1162354
  7. Pelchat ML, Bykowski C, Duke FF, Reed DR (2011). Excretion and perception of a characteristic odor in urine after asparagus ingestion: a psychophysical and genetic study. Chemical Senses. — PubMed PMID: 20876394
  8. Markt SC, Nuttall E, Turman C, et al. (2016). Sniffing out significant “Pee values”: genome wide association study of asparagus anosmia. BMJ. — PubMed PMID: 27965198

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Key Research Papers: Kidneys, Gout and Blood Pressure

  1. Choi HK, Atkinson K, Karlson EW, Willett W, Curhan G (2004). Purine-rich foods, dairy and protein intake, and the risk of gout in men. The New England Journal of Medicine. — PubMed PMID: 15014182
  2. Choi HK, Liu S, Curhan G (2005). Intake of purine-rich foods, protein, and dairy products and relationship to serum levels of uric acid: the Third National Health and Nutrition Examination Survey. Arthritis and Rheumatism. — PubMed PMID: 15641075
  3. Zgaga L, Theodoratou E, Kyle J, et al. (2012). The association of dietary intake of purine-rich vegetables, sugar-sweetened beverages and dairy with plasma urate, in a cross-sectional study. PLoS One. — PubMed PMID: 22701608
  4. Kaneko K, Aoyagi Y, Fukuuchi T, Inazawa K, Yamaoka N (2014). Total purine and purine base content of common foodstuffs for facilitating nutritional therapy for gout and hyperuricemia. Biological & Pharmaceutical Bulletin. — PubMed PMID: 24553148
  5. Taylor EN, Curhan GC (2007). Oxalate intake and the risk for nephrolithiasis. Journal of the American Society of Nephrology. — PubMed PMID: 17538185
  6. Aburto NJ, Hanson S, Gutierrez H, Hooper L, Elliott P, Cappuccio FP (2013). Effect of increased potassium intake on cardiovascular risk factors and disease: systematic review and meta-analyses. BMJ. — PubMed PMID: 23558164
  7. Sanae M, Yasuo A (2013). Green asparagus (Asparagus officinalis) prevented hypertension by an inhibitory effect on angiotensin-converting enzyme activity in the kidney of spontaneously hypertensive rats. Journal of Agricultural and Food Chemistry. — PubMed PMID: 23647085 (animal study)

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Key Research Papers: Glutathione, Flavonoids and Saponins

  1. Jones DP, Coates RJ, Flagg EW, et al. (1992). Glutathione in foods listed in the National Cancer Institute's Health Habits and History Food Frequency Questionnaire. Nutrition and Cancer. — PubMed PMID: 1574445
  2. Witschi A, Reddy S, Stofer B, Lauterburg BH (1992). The systemic availability of oral glutathione. European Journal of Clinical Pharmacology. — PubMed PMID: 1362956
  3. Richie JP Jr, Nichenametla S, Neidig W, et al. (2015). Randomized controlled trial of oral glutathione supplementation on body stores of glutathione. European Journal of Nutrition. — PubMed PMID: 24791752
  4. Lee EJ, Yoo KS, Patil BS (2010). Development of a rapid HPLC-UV method for simultaneous quantification of protodioscin and rutin in white and green asparagus spears. Journal of Food Science. — PubMed PMID: 21535581
  5. Fuentes-Alventosa JM, Jaramillo S, Rodríguez-Gutiérrez G, et al. (2008). Flavonoid profile of green asparagus genotypes. Journal of Agricultural and Food Chemistry. — PubMed PMID: 18656928
  6. Makris DP, Rossiter JT (2001). Domestic processing of onion bulbs (Allium cepa) and asparagus spears (Asparagus officinalis): effect on flavonol content and antioxidant status. Journal of Agricultural and Food Chemistry. — PubMed PMID: 11453754
  7. Kim BY, Cui ZG, Lee SR, et al. (2009). Effects of Asparagus officinalis extracts on liver cell toxicity and ethanol metabolism. Journal of Food Science. — PubMed PMID: 19895471 (cell study)
  8. Pegiou E, Mumm R, Acharya P, de Vos RCH, Hall RD (2019). Green and White Asparagus (Asparagus officinalis): A Source of Developmental, Chemical and Urinary Intrigue. Metabolites. — PubMed PMID: 31881716

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External Authoritative Resources

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Connections

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