Root Vegetables

TL;DR. Carrots, beetroot, parsnips, turnips, swedes, radishes, and celeriac: cheap, storable, and the vegetables most improved by cooking. Carrot beta-carotene is two to six times more available from cooked carrots than raw, and requires fat in the same meal to be absorbed at all. Beetroot is the highest-nitrate common vegetable and the basis of the beetroot juice used in blood pressure and sports performance research. Carrots really do help your vision, in the narrow sense that vitamin A deficiency causes night blindness, and the wartime story that popularised the claim was deliberate misinformation.

1. What they are

Storage organs, mostly true roots, holding the plant's energy reserves for a second year of growth. Most are biennials: they build the root in year one and flower in year two, and we harvest at the end of year one.

2. Where they come from

Carrots were originally purple and yellow, domesticated in Afghanistan and Persia around the tenth century, and reached Europe in the medieval period. The orange carrot is a later Dutch selection from the sixteenth and seventeenth centuries. The popular story that Dutch growers bred orange carrots to honour the House of Orange is charming and unsupported; the orange types appear to have been selected for sweetness and size, with the colour following.

Beetroot was originally grown for its leaves; the swollen root was selected in the Roman era and later. Sugar beet, the same species, was developed in Prussia in the late eighteenth century after Andreas Marggraf identified sucrose in beet, and it became strategically vital during the Napoleonic blockade of cane sugar. Sugar beet now supplies roughly a fifth of world sugar.

Parsnips and turnips were staple European carbohydrate crops before the potato arrived, and were largely displaced by it.

Production: carrots and turnips together around 42 million tonnes, led by China, Uzbekistan, the US, and Russia. Beetroot production is harder to separate from sugar beet, which is a different industry entirely at around 270 million tonnes.

3. How they are grown

Cool-season crops tolerant of frost, most of which sweeten in cold weather: below about 5 °C the plant converts stored starch to sugars as antifreeze, so carrots, parsnips, and swedes harvested after frost are genuinely sweeter. Parsnip growers deliberately leave the crop in the ground through winter for this.

Soil is the whole game for root crops. They need deep, stone-free, loose soil. Any obstruction causes forking or stunting, which is why heavy or stony ground produces the misshapen carrots that get rejected at grading and become a large share of on-farm waste. Commercial carrot growing concentrates on deep sandy and peaty soils for precisely this reason.

Do not over-fertilise with nitrogen or add fresh manure: excess nitrogen produces leafy tops and forked, hairy roots.

Pests. Carrot root fly is the defining problem: the adult locates carrots by smell, flies low, and lays eggs at the base; the larvae tunnel through the root. Control is by fine mesh barriers (they fly below about 60 cm, so a low barrier works), by resistant varieties, and by avoiding thinning, which releases the scent that attracts them.

Storage is where root vegetables earn their historical importance. Properly stored, they last months: this is what fed northern Europe through winter before refrigeration and imports. The traditional method is a clamp, a heap of roots covered in straw and earth, or storage in damp sand in a cellar.

Beetroot for juice is now a distinct market, grown for high nitrate content.

4. What is inside them

Per 100 g raw:

The headline numbers:

• Carrots are the outstanding beta-carotene source in the ordinary diet: 100 g supplies more than three times the daily vitamin A requirement in provitamin form, with the important caveat about conversion efficiency and fat requirement below.
• Beetroot is the highest-nitrate common vegetable and one of the better folate sources.
• Parsnips are the highest in fibre and calories, being the starchiest of the group.
• Radish and turnip are brassicas and carry glucosinolates, which is why radish is peppery. Raw radish and horseradish are useful sources of myrosinase for adding to cooked brassicas (Chapter 39).

Betalains in beetroot are the deep red-purple pigments (betacyanins) and yellow ones (betaxanthins), chemically unrelated to anthocyanins. They are what make golden beetroot yellow and Chioggia beetroot striped.

5. What they do in your body

Carotenoids, cooking, and fat

Carrot beta-carotene is bound within tough cellulose cell walls and in crystalline form, which makes raw carrot a poor delivery system. Cooking ruptures the cell walls and disperses the crystals, and measured bioavailability increases roughly two- to sixfold with cooking. Pureeing increases it further. Adding fat is not optional: beta-carotene is fat-soluble and absorption in a fat-free meal is close to zero.

The practical version: cooked carrots with some oil or butter deliver several times more usable beta-carotene than a raw carrot stick. Both are worth eating, for different reasons; raw carrots retain vitamin C and are a good crunchy snack.

Conversion is regulated: the body converts beta-carotene to retinol according to need, which is why plant carotenoids cannot cause vitamin A toxicity, unlike preformed retinol (Chapter 15). Conversion efficiency varies substantially between individuals, with common genetic variants in the BCMO1 gene reducing conversion by 30 to 60 percent in a substantial minority of people.

Carotenoderma: very high carotene intake turns the skin, particularly palms and soles, yellow-orange. It is harmless, reversible, and distinguishable from jaundice because it does not affect the whites of the eyes.

The night vision story. Vitamin A deficiency genuinely causes night blindness, because retinal (a vitamin A derivative) is the light-sensitive molecule in rod cells. So carrots help vision in exactly one circumstance: if you are deficient. Eating more when you are already replete does nothing.

The popular belief comes from a Second World War British propaganda campaign. The RAF's success at night interception was due to airborne radar, which was secret. The Ministry of Food publicised the story that pilots such as John "Cat's Eyes" Cunningham owed their night vision to eating carrots. It served two purposes: it obscured radar from the Germans and it encouraged the public to eat a vegetable that was plentiful and unrationed. It is one of the most successful pieces of nutrition misinformation ever created, and it was deliberate.

Beetroot and nitrate

The mechanism is set out in Chapter 38: dietary nitrate is concentrated in saliva, reduced to nitrite by tongue bacteria, and converted to nitric oxide, which dilates blood vessels.

Beetroot juice is the most-studied vehicle, and the effects are consistent:

• Blood pressure: meta-analyses find reductions of roughly 4 to 5 mmHg systolic with beetroot juice supplementation.
• Exercise: improved exercise economy (lower oxygen cost at a given workload), improved time-to-exhaustion, and small time-trial improvements, most reliably in recreational rather than elite athletes. Typical protocols use around 400 to 800 mg of nitrate (roughly 140 to 500 mL of concentrated beetroot juice) 2 to 3 hours before exercise.
• Blocked by antibacterial mouthwash, which removes the tongue bacteria that do step one.

Beeturia: roughly 10 to 15 percent of people excrete pink or red urine after eating beetroot, because they absorb and excrete betalains intact rather than degrading them. It is harmless, depends on stomach acidity and iron status, and can be alarming if unexpected. It also produces reddish stools.

6. What the evidence actually shows

Established: carrots are the leading provitamin A source in most diets, and cooking with fat substantially increases absorption. Beetroot nitrate lowers blood pressure and improves exercise economy.

Strong: root vegetable and carotenoid intake is associated with lower cardiovascular and cancer risk in cohort studies.

Mixed: beetroot for cognitive performance and for endurance in elite athletes, where results are inconsistent.

Thin: any claim about carrots improving vision beyond correcting deficiency; beetroot for liver detoxification; radish or horseradish for sinus conditions beyond the immediate physical effect of pungency clearing the nose.

7. Who should eat more, who should be careful

Good for: almost everyone. These are among the cheapest, most storable, and most versatile vegetables available, and they are strongly under-eaten relative to their value.

Be careful if:

• You form calcium oxalate kidney stones. Beetroot is high in oxalate; beetroot juice concentrates it, and cases of oxalate nephropathy after aggressive beetroot juicing have been reported.
• You have IBS. Beetroot and Jerusalem artichoke are high-FODMAP. Jerusalem artichokes are extreme: they store energy as inulin rather than starch, which is entirely fermented in the colon, producing a legendary quantity of gas. The seventeenth-century English writer John Goodyer described them as fit "more for swine than men" for this reason. Carrots, parsnips, swede, and radish are low-FODMAP.
• You have advanced kidney disease. All root vegetables are moderate to high in potassium.
• You take blood pressure medication. Beetroot juice adds to the effect. This is usually desirable and worth knowing.
• You have a birch pollen allergy. Carrot and celeriac are among the most common cross-reactive foods, and celeriac in particular can cause severe systemic reactions, including anaphylaxis, more often than most plant foods. It is a named allergen requiring declaration in the EU.
• You handle parsnips and celery in sunlight. These contain furanocoumarins, and skin contact with the sap followed by UV exposure causes phytophotodermatitis: blistering burns in the pattern of contact. It is a genuine occupational hazard for harvesters and gardeners. Wild parsnip and giant hogweed, in the same family, cause severe versions.

Ages. Excellent weaning foods: cooked carrot and parsnip purée are sweet and well accepted. Raw carrot is a leading choking hazard for under-4s because of its hardness and cylindrical shape. Grate it or cook it. Whole raw carrot sticks are fine for older children.

8. When and how to eat them

• Cook them with fat for carotenoid absorption, and eat some raw for vitamin C and texture.
• Roast them. Roasting caramelises the sugars and produces far better flavour than boiling. Parsnips, carrots, beetroot, and celeriac are all transformed by it.
• Do not peel unless you need to. Most of the fibre and a disproportionate share of the polyphenols sit in and just under the skin. Scrub instead. The bitter compounds in carrot skin that older cookbooks worried about are largely absent in modern varieties.
• Eat the tops. Beetroot greens are excellent (and are effectively chard, being the same species). Carrot tops make a decent pesto. Radish and turnip tops are edible. They are removed before sale because they draw water from the root.
• Roast beetroot whole in foil rather than boiling: less colour and nutrient loss into water, and the skin slips off afterwards.
• Grate raw beetroot, carrot, and celeriac into salads. Céleri rémoulade is the classic celeriac preparation.
• Radish and daikon work as a raw myrosinase source alongside cooked brassicas, and daikon is the base of much Korean and Japanese pickling.
• Save the peelings and ends for stock.

9. Choosing and storing

Choosing. Firm, heavy, smooth, with no soft spots, splits, or whiskery secondary roots. Smaller is usually sweeter and more tender; very large carrots, parsnips, and radishes develop a woody core. Fresh green tops are a good freshness sign and should be removed before storing.

Storing. Root vegetables are the best keepers in the vegetable kingdom.

• Remove the tops immediately, or they will draw moisture out of the root within days.
• Fridge, in a perforated bag or wrapped in damp paper, in the crisper: carrots and parsnips keep 3 to 4 weeks, beetroot 2 to 3 weeks, swede and celeriac a month or more.
• Cool cellar or garage in damp sand replicates traditional storage and keeps them for months.
• Do not store with apples or bananas. Ethylene makes carrots bitter, through the production of isocoumarins, which is a specific and well-documented effect.
• Limp roots revive in cold water for 30 minutes, because what was lost was water.
• Freeze blanched and diced; texture suffers but flavour and nutrition hold.

10. The varieties worth knowing

Carrots: Nantes (cylindrical, sweet, tender), Chantenay (short, conical, stores well), Imperator (long, the US supermarket standard), Danvers, plus purple, black, yellow, and white heritage types, which carry anthocyanins in the purple ones and are worth buying for that. Baby carrots sold in bags are usually not young carrots; they are mature carrots machine-cut and tumbled to shape, a process invented in the 1980s to use misshapen crop, which is a genuine food-waste success story.

Beetroot: standard red (Detroit, Boltardy), golden (milder, no staining, lower betacyanin), Chioggia (pink and white concentric rings that fade on cooking).

Radish: small red globe types, French breakfast, daikon/mooli (large, mild, Asian cooking), watermelon radish, and black winter radish (very pungent).

Turnip and swede are frequently confused, and it varies by country. In most of the UK, "turnip" is the small white-and-purple B. rapa and "swede" is the larger yellow-fleshed B. napus; in Scotland the swede is called a turnip or neep. In the US the swede is a rutabaga.

Jerusalem artichoke and yacón store inulin rather than starch and are marketed as low-GI vegetables, which is true and comes with the gastrointestinal consequences described above.

11. Myths and confusions

Don't be confused: sugar beet and beetroot are the same species. Sugar beet is a white, low-flavour, high-sucrose selection grown for refining; beetroot is the red culinary selection. The sugar from beet is chemically identical to sugar from cane.

• "Carrots improve your eyesight." Only if you are vitamin A deficient. The belief was manufactured as wartime propaganda to conceal radar.
• "Raw is best for carrots." Cooking multiplies beta-carotene availability several-fold.
• "Baby carrots are young carrots." Machine-cut mature carrots, in most cases.
• "Beetroot juice is a detox." It lowers blood pressure through a well-characterised nitric oxide pathway and does not detoxify anything.
• "Red urine after beetroot means something is wrong." Beeturia affects 10 to 15 percent of people and is harmless. Red urine without a beetroot explanation does need investigating.
• "You must peel root vegetables." Scrubbing is usually enough and keeps more fibre and polyphenols.

12. The bottom line

• Root vegetables are cheap, store for weeks to months, sweeten after frost, and are among the most under-eaten vegetables relative to their value.
• Cook carrots and add fat. Beta-carotene availability rises several-fold with cooking and absorption is near zero without dietary fat.
• Beetroot is the highest-nitrate common vegetable, lowering blood pressure by 4 to 5 mmHg and improving exercise economy. Antibacterial mouthwash abolishes the effect.
• Carrots help night vision only by correcting deficiency. The rest of the story was deliberate wartime propaganda.
• Remove the tops before storing, keep them away from apples and bananas, and eat the greens.
• Celeriac is a notable severe allergen in birch-pollen-allergic people, and parsnip sap plus sunlight causes blistering burns.

Sources and notes

Composition figures are from USDA FoodData Central; production figures are approximate FAOSTAT values for the early 2020s. Carrot domestication and the origin of orange types follow Iorizzo et al.'s carrot genome work and Banga's historical account. Sugar beet history follows Marggraf's isolation of sucrose and the Napoleonic blockade record. Carrot root fly behaviour and barrier control follow horticultural extension guidance. Beta-carotene bioavailability increases with cooking and pureeing follow Hedren et al. and Rock et al.'s measurements; BCMO1 conversion variation follows Lietz and Hickenbottom's work. The wartime carrot and night vision propaganda campaign is documented by the Imperial War Museum and Smith's history of Ministry of Food publicity. Dietary nitrate in beetroot and its blood pressure and exercise effects follow Webb et al., Hypertension, 2008, Larsen et al., and Jones' reviews of beetroot juice in sport. Beeturia prevalence and its dependence on iron status follow Watts et al. Isocoumarin bitterness in carrots stored with ethylene follows post-harvest literature. Celeriac and carrot allergy follows Ballmer- Weber's work on birch-related food allergy; furanocoumarin phytophotodermatitis follows dermatology case series. Jerusalem artichoke inulin and its gastrointestinal effects follow Goodyer's seventeenth-century description and modern FODMAP data.

Open questions. How much beetroot juice helps trained athletes as opposed to recreational ones is inconsistent across trials. Whether the blood pressure effect persists over months of daily intake has not been well studied.

👉 Next: potatoes and the starchy staples.