Potatoes and the Starchy Staples

TL;DR. The potato feeds more people than any crop except the three big cereals, and it is the most nutritionally maligned vegetable in the shop, mostly because of what is done to it. A boiled potato with its skin is a decent food: potassium, vitamin C, fibre, and the highest satiety score ever measured in a controlled test. A chip is a different product. Never refrigerate potatoes, because cold converts starch to sugar and that sugar becomes acrylamide when you fry or roast them. Cassava feeds around 800 million people and must be processed properly or it releases cyanide.

1. What they are

Don't be confused: a sweet potato is not a yam and not a potato. They belong to three different plant families. The confusion in North America dates to the twentieth century, when soft orange-fleshed sweet potatoes were marketed as "yams" to distinguish them from the firmer pale types. True yams are a different genus, are usually much larger, drier, and starchier, and are a staple across West Africa and the Caribbean.

2. Where they come from

Potato: the Andes, domesticated in the Lake Titicaca region of Peru and Bolivia around 8,000 to 10,000 years ago. Andean farmers still grow thousands of varieties, and the freeze-drying technique (chuño, alternately freezing potatoes at altitude overnight and treading out the water by day) is one of the oldest food preservation methods on Earth.

Spanish ships took potatoes to Europe in the sixteenth century, where they were treated with suspicion for two hundred years, partly because they were nightshades and partly because they were not mentioned in the Bible. Frederick the Great and the French agronomist Antoine Parmentier promoted them aggressively; Parmentier's tactic of posting guards on a potato field by day and withdrawing them at night, so that peasants would steal the crop, is probably embellished and captures the difficulty.

Once adopted, the potato transformed European demography: it produces more calories per hectare than grain, on poorer land, with less labour, and it is credited with a substantial share of Europe's population growth in the eighteenth and nineteenth centuries.

And then the famine. Ireland's potato crop was overwhelmingly a small number of clonal varieties, principally the Irish Lumper. When Phytophthora infestans, late blight, arrived from the Americas in 1845, there was no genetic resistance anywhere in the population. Roughly a million people died and a million emigrated, in a catastrophe made far worse by the fact that Ireland continued to export food throughout. It is the single clearest historical lesson about monoculture in a clonal crop, and it repeats in this book with bananas (Chapter 21) and citrus.

Cassava: Brazil, domesticated around 8,000 to 10,000 years ago, and taken to Africa by Portuguese traders in the sixteenth century, where it has become a dominant staple. Sweet potato: Central and South America, with the notable puzzle that it reached Polynesia in pre-Columbian times, which is one of the better pieces of evidence for early trans-Pacific contact.

Production: potatoes around 375 million tonnes (China, India, Ukraine, Russia, US); cassava around 315 million tonnes (Nigeria by far the largest, then DR Congo, Thailand, Ghana, Indonesia); sweet potatoes around 90 million tonnes (China, Malawi, Tanzania, Nigeria); yams around 75 million tonnes, overwhelmingly Nigeria, Ghana, and Côte d'Ivoire.

3. How they are grown

Potatoes are grown from seed potatoes, which are tubers, not seeds, so the crop is clonal. Certified seed potato production is a specialist industry concentrated in cool northern regions (Scotland, the Netherlands, Idaho, Prince Edward Island) because aphid pressure, and therefore virus transmission, is lower there.

Planting: tubers are placed 10 to 15 cm deep and earthed up as the plant grows, which serves two purposes: it gives more stem for tubers to form on, and it keeps developing tubers in the dark. Light exposure turns tubers green with chlorophyll and, more importantly, triggers glycoalkaloid synthesis.

Climate: a cool-season crop, optimum 15 to 20 °C. Tuber formation is inhibited above about 25 °C. It is frost-sensitive above ground and needs consistent water, particularly during tuber initiation and bulking; irregular water causes hollow heart, cracking, and knobbly secondary growth.

Late blight remains the defining threat, requiring forecast-driven fungicide programmes (often 10 to 15 sprays a season in wet climates) or resistant varieties. Blight-resistant GM and cisgenic potatoes have been developed and face the usual regulatory and consumer questions.

Curing is essential: after harvest, potatoes are held warm and humid for 1 to 2 weeks so wounds suberise and skins set. Cured potatoes store for months at 7 to 10 °C in the dark, with sprout suppressants used commercially.

Cassava is grown from stem cuttings, tolerates drought, poor acidic soil, and neglect, and can be left in the ground as a living store for up to two years. That resilience is why it is a famine-buffer crop across Africa. Its weakness is that once harvested it deteriorates within two to three days, which is a major post-harvest loss problem.

Sweet potato is grown from slips, rooted shoots taken from a mother tuber. It is heat-loving, drought-tolerant, and productive on poor soil. Orange-fleshed sweet potato has been the subject of a major biofortification effort by HarvestPlus and others across sub-Saharan Africa, replacing white-fleshed local varieties to combat vitamin A deficiency; it is one of the better-documented successes in applied nutrition, and it won the World Food Prize in 2016.

4. What is inside them

Per 100 g:

The chip and crisp columns are the point of this table. The potato does not change; the cooking method adds three to six times the calories, mostly as fat, plus a large sodium load. Almost every negative association between "potatoes" and health outcomes in epidemiology is driven by fried potatoes, and studies that separate them consistently find that boiled and baked potatoes behave differently from chips.

Vitamin C in potatoes surprises people. It is not high per 100 g, and portions are large and consumption is frequent, so potatoes have historically been a major vitamin C source in northern European diets. The Irish pre-famine diet, largely potatoes and milk, was nutritionally reasonable, which is part of why the population had grown so fast.

Orange sweet potato is one of the densest provitamin A foods available, at nearly four times the daily requirement per 100 g, and its beta-carotene is well absorbed when cooked with fat.

Potassium: potatoes are one of the best sources in an ordinary diet, well above bananas per serving.

5. What they do in your body

Satiety. In the 1995 Holt satiety index study, which fed people fixed-calorie portions of 38 foods and measured subsequent hunger and intake, boiled potato scored the highest of anything tested, at more than three times the satiety of white bread per calorie. This is a small, old, single study and it is repeatedly borne out in practice. Whatever else potatoes do, they fill people up.

Glycaemic response. Potatoes have a high glycaemic index (boiled around 78, baked and mashed higher, some varieties over 100), which is genuinely a mark against them for people managing blood glucose. Three things moderate it substantially:

• Variety matters: waxy, lower-amylopectin potatoes give lower responses than floury ones.
• Cooking and cooling converts a portion of the starch to resistant starch type 3, which reduces the glycaemic response by roughly 25 to 30 percent, and reheating does not fully undo it (Chapter 11). Cold potato salad is metabolically different from a hot baked potato.
• What you eat them with: fat, protein, acid, and vegetables all flatten the curve.

Glycoalkaloids. Potatoes contain solanine and chaconine, cholinesterase-inhibiting neurotoxins concentrated in the skin, the eyes, the sprouts, and any green tissue. Normal potatoes contain 10 to 100 mg/kg; the accepted commercial limit is 200 mg/kg; greened or sprouted potatoes can exceed 500 to 1,000 mg/kg in the affected parts. Symptoms start at roughly 1 to 3 mg per kg of body weight: nausea, vomiting, abdominal pain, then headache, confusion, and, rarely, death. They are heat-stable to about 170 °C, so cooking does not fix them. The 1979 incident in which 78 London schoolboys were hospitalised after eating stored potatoes is the best-documented outbreak (Chapter 18).

Practical rule: cut generously around any green or sprouting, and discard extensively green, bitter, or heavily sprouted potatoes. Bitterness is the warning sign and should be respected.

Acrylamide. When starchy food is cooked above about 120 °C in dry heat, the amino acid asparagine reacts with reducing sugars (glucose and fructose) in the Maillard reaction and forms acrylamide, which is classified by IARC as a probable human carcinogen based on animal studies. Fried and roasted potato products are among the largest dietary contributors.

The practical consequences are covered in Chapter 91, and one of them belongs here: refrigerating raw potatoes converts starch to reducing sugars, which directly increases acrylamide formation when they are subsequently fried or roasted. This is why food safety agencies advise storing potatoes in a cool dark place rather than the fridge, and why the standard advice is to cook them to golden rather than dark brown.

Cassava and cyanide. Bitter cassava contains linamarin, which releases hydrogen cyanide when the tissue is damaged. Traditional processing (peeling, grating, prolonged soaking or fermenting, pressing, and roasting or drying) removes 95 percent or more. Shortcutting it under famine conditions causes konzo, a sudden, permanent, symmetrical spastic paralysis of the legs, documented in outbreaks across Central Africa. This is the highest-stakes food processing requirement in the world (Chapter 18).

6. What the evidence actually shows

Established: boiled potato is highly satiating and a good source of potassium, vitamin C, and B6. Orange sweet potato corrects vitamin A deficiency in populations. Cooling cooked starch creates resistant starch. Glycoalkaloid and cyanide hazards are real and well characterised.

Strong: fried potato consumption is associated with worse cardiometabolic outcomes in cohort studies, and the association does not hold, or is much weaker, for boiled and baked potatoes. Higher potato intake overall is weakly associated with type 2 diabetes risk in some analyses, and the substitution matters: replacing potatoes with whole grains looks favourable, replacing them with white rice does not.

Mixed: whether potatoes per se, separate from preparation, are harmful. The most careful recent analyses suggest the preparation and what they displace explain most of it.

Thin: potato water for anything, raw potato juice as a remedy (it delivers glycoalkaloids), and purple potato antioxidant claims beyond the general anthocyanin story.

7. Who should eat more, who should be careful

Good for: most people, cooked simply. They are cheap, filling, storable, and locally grown almost everywhere.

Be careful if:

• You have diabetes or insulin resistance. High glycaemic index and large portions. Prefer waxy varieties, cook-and-cool, keep the skins, add fat and protein, and watch the portion.
• You have chronic kidney disease. Potatoes and sweet potatoes are high in potassium. The standard renal technique is leaching: peel, slice thinly, soak in a large volume of warm water for several hours, then boil in fresh water, which removes a substantial fraction.
• You form calcium oxalate kidney stones. Sweet potatoes are high in oxalate; ordinary potatoes are moderate.
• You are pregnant. No special restriction beyond avoiding green potatoes, which applies to everyone but matters more given the teratogenicity concerns raised (and never established) about glycoalkaloids.
• You are relying on cassava as a staple. Processing is not optional.

Ages. Potato and sweet potato are excellent first foods from 6 months: soft, bland, energy dense, no common allergens. Mash rather than serving chunks. Avoid salt.

8. When and how to eat them

• Boil, steam, or bake rather than fry, most of the time. That single choice accounts for most of the nutritional difference.
• Keep the skins. Half the fibre and a substantial share of the potassium and polyphenols are in and just under them. Scrub rather than peel.
• Boil whole and in their skins to reduce nutrient leaching, then peel afterwards if you must.
• Cook and cool for resistant starch: potato salad, cold new potatoes, or reheated leftovers all deliver less glucose than a freshly cooked hot potato.
• Cook to golden, not brown, when roasting or frying, to limit acrylamide. Soaking chipped potatoes in water for 30 minutes before frying removes surface sugars and reduces acrylamide measurably.
• Add fat to sweet potato for beta-carotene absorption.
• Salt is the real problem with chips and crisps, alongside the fat: a 100 g bag of crisps carries around 500 mg of sodium and 34 g of fat.
• Cassava must be peeled, soaked or fermented, and cooked thoroughly. Never eat it raw.
• Sweet potato leaves are edible and are a widely eaten green across Asia and Africa, higher in protein than the root.

9. Choosing and storing

Choosing. Firm, dry, smooth, with no green patches, sprouts, soft spots, wrinkles, or a musty smell. Avoid potatoes displayed under bright light, since light is what causes greening.

Storing. Two rules that matter more than anything else:

1. Cool, dark, dry, and ventilated. A paper or hessian sack in a cupboard or cellar at 7 to 10 °C. Light causes greening and glycoalkaloids; warmth causes sprouting; plastic bags cause rot.
2. Not the fridge. Below about 4 °C, starch converts to reducing sugars, which makes potatoes taste sweet, brown too fast, and, critically, form more acrylamide when fried or roasted. UK and EU food safety advice on this changed in recent years: the FSA now says home refrigeration of potatoes is acceptable and does not meaningfully raise cancer risk, while the cooking advice (golden, not brown) stands. The traditional advice remains the better default for quality reasons.

• Keep potatoes away from onions: potatoes emit moisture, onions emit ethylene, and each accelerates the other's decline.
• Sweet potatoes must never be refrigerated: they suffer chilling injury below about 13 °C, developing hard centres and off flavours. Store them at 13 to 15 °C.
• Properly cured and stored potatoes keep for months; sweet potatoes for a few weeks to months; cassava for two to three days once harvested, which is why it is usually sold waxed or frozen.

10. The varieties worth knowing

Potatoes divide by starch content, and using the wrong type is the commonest cooking failure:

New potatoes are simply immature potatoes with thin, unset skins; they are waxier and sweeter because the starch has not fully developed. Jersey Royals are a protected designation.

Sweet potatoes: orange-fleshed (Beauregard, Covington; moist, sweet, very high beta-carotene), white or cream-fleshed (drier, starchier, the traditional type across much of Asia and Africa), and purple-fleshed (Okinawan, Stokes; anthocyanins).

Cassava: sweet varieties (lower cyanide, can be boiled and eaten simply) and bitter varieties (higher yield, higher cyanide, require full processing). Tapioca is cassava starch; garri and fufu are processed cassava products.

11. Myths and confusions

• "Potatoes are fattening." Boiled potato is the most satiating food ever measured in a controlled test. What is fattening is what is done to it and what is put on it.
• "Potatoes have no nutrients." They are a major potassium, vitamin C, and B6 source in diets that include them regularly.
• "Sweet potatoes are much healthier than potatoes." Sweet potatoes are far higher in vitamin A and slightly lower in glycaemic index. Potatoes beat them on potassium and satiety. Both are fine.
• "Never eat a green potato at all." Cut generously around small green patches; discard extensively green or bitter ones.
• "Potato skins are toxic." Only when green or sprouted. Normal skins are the most nutrient-dense part.
• "Cooling potatoes removes the calories." It converts some starch to a form you do not absorb, which reduces the glycaemic response by 25 to 30 percent, not the calories to zero.
• "Raw potato juice cures ulcers." It delivers glycoalkaloids. Do not.

12. The bottom line

• The potato is one of the most important calorie crops in human history and the most nutritionally misrepresented vegetable in the shop. Boiled potato with the skin is a good food; a chip is a different product.
• Boiled potato is the most satiating food ever measured. It is also high glycaemic index, and cooking-and-cooling, waxy varieties, and eating it with fat and protein all moderate that.
• Never refrigerate raw potatoes and never refrigerate sweet potatoes. Cool, dark, dry, and away from onions.
• Green, sprouted, or bitter potatoes contain glycoalkaloids that cooking does not destroy. Discard them.
• Orange sweet potato is one of the densest provitamin A foods available and has been deployed successfully against vitamin A deficiency at national scale.
• Cassava feeds hundreds of millions and releases cyanide if processing is shortcut. That processing is not tradition; it is toxicology.

Sources and notes

Composition figures are from USDA FoodData Central; production figures are approximate FAOSTAT values for the early 2020s. Andean domestication and chuno follow Spooner et al.'s genetic work and ethnobotanical accounts. The Irish famine and clonal narrowness follow Woodham-Smith, The Great Hunger, 1962, and Ristaino's genetic work on the P. infestans lineage. Seed potato certification, earthing up, and curing follow extension publications and USDA Handbook 66. The satiety index placing boiled potato highest is Holt et al., European Journal of Clinical Nutrition, 1995. Resistant starch formation on cooling follows Englyst's classification and subsequent glycaemic comparisons. Glycoalkaloid levels, limits, and toxicity follow the EFSA 2020 opinion; the 1979 London school outbreak is McMillan and Thompson, Quarterly Journal of Medicine. Acrylamide formation from reducing sugars and asparagine follows Mottram et al. and Stadler et al., both Nature, 2002; the refrigeration guidance follows FSA advice, which was revised in 2023. Cassava linamarin processing and konzo follow Howard Bradbury's wetting-method work and WHO reporting. Orange-fleshed sweet potato biofortification follows the HarvestPlus programme and the 2016 World Food Prize citation. Fried potato and cardiometabolic associations follow Borgi et al. and subsequent cohort analyses.

Open questions. Whether potatoes as such are harmful, separate from how they are cooked and what they displace, is genuinely unresolved and cohort studies disagree. The FSA's revision of its potato refrigeration advice illustrates that the acrylamide guidance is still moving.

👉 Next: squashes, cucumbers, and aubergines.