“Cooking destroys the nutrients” is one of those claims that sounds authoritative because it is partly true. Heat does degrade certain vitamins. But the sentence gets deployed as if it settles something — usually in favor of raw diets, expensive cold-pressed products, or a supplement meant to replace what cooking supposedly took away.
The full picture is more mixed and considerably more useful. Cooking does three different things at once: it degrades some nutrients, it leaches others into water, and it makes a third group substantially more absorbable. Which effect dominates depends on the nutrient, the food, and the method.
What heat actually damages
Vitamin C is the most fragile common nutrient. It is water-soluble, heat-sensitive, and oxidizes readily. Boiling broccoli can cost a large share of its vitamin C — some of it destroyed, much of it simply dissolved into water that goes down the drain. Prolonged high heat with a lot of water and a lot of cut surface area is the worst-case combination.
Folate behaves similarly: water-soluble and heat-labile, with meaningful losses in extended boiling.
Thiamine (B1) is moderately heat-sensitive. Other B vitamins are more variable — B6 and pantothenic acid take modest losses, riboflavin is fairly heat-stable but degrades in light.
Typical retention figures for these vitamins in normal home cooking land somewhere between 50% and 90%, depending heavily on method. That is a real loss. It is not annihilation, and it is not the same for every nutrient — which is where the slogan breaks down.
What heat does not touch
Minerals are not destroyed by cooking. Iron, zinc, calcium, magnesium, and potassium are elements. No temperature you can reach in a kitchen changes that. They can leach into cooking water, which is a retrieval problem, not a destruction problem — use the liquid in a soup, sauce, or grain and you keep them.
Fat-soluble vitamins — A, D, E, K — are considerably more heat-stable than the water-soluble ones, and being fat-soluble, they do not wash away in boiling water. See our water-soluble vs fat-soluble guide for why that distinction drives so much of this.
Fiber and protein survive cooking fine. Protein denatures, which is a structural change, not a nutritional loss — denatured protein is generally easier to digest, not harder.
What cooking makes better
This is the half of the story the myth leaves out entirely.
Carotenoids become far more available. Plant cells are enclosed in tough cellulose walls that human digestion handles poorly. Heat breaks those walls down and releases the carotenoids inside. Cooking tomatoes substantially increases absorbable lycopene — a well-replicated finding, and the reason tomato paste and cooked sauces rank higher in lycopene availability than raw tomatoes despite heat “damage.” The same principle applies to beta-carotene in carrots and lutein in leafy greens. Our lycopene research brief and carotenoids explained go deeper.
Add a little fat while you are at it — carotenoids are fat-soluble and absorption improves meaningfully when the meal contains some oil, avocado, or nuts.
Some binding compounds decrease. Boiling reduces oxalate in greens, which improves calcium availability from that meal. Soaking and cooking legumes reduces phytate, improving iron and zinc absorption, and proper boiling deactivates the lectin in dry kidney beans that causes acute illness when they are undercooked. That whole territory is mapped in antinutrients explained.
Digestibility improves broadly. Cooked starches and proteins are more accessible to digestive enzymes. Cooking is, in a real sense, external pre-digestion — one reason it appears in essentially every human food culture.
Some vegetables are safer cooked. Raw or lightly cooked kidney beans, raw cassava, and certain raw sprouts carry genuine risks that cooking addresses.
The trade-off nobody mentions: sulforaphane
Broccoli offers a nice illustration that the answer is not always “cook it.”
Cruciferous vegetables contain glucosinolates plus an enzyme, myrosinase, that converts them into isothiocyanates like sulforaphane. Myrosinase is heat-sensitive. Boil broccoli hard and you can inactivate the enzyme, reducing sulforaphane formation.
The practical workarounds are pleasingly specific: chop and let it sit for about 40 minutes before cooking so the conversion happens first, steam lightly rather than boil, or add a small amount of raw crucifer — mustard seed, arugula, or raw broccoli sprouts — to a cooked dish to supply myrosinase. Our sulforaphane research brief covers the compound in more detail.
So for this one class of vegetables, lighter cooking genuinely wins. For carotenoid-rich vegetables, heavier cooking wins. There is no single rule, which is exactly the point.
How to cook for retention
If you want to hold onto the heat- and water-sensitive vitamins without giving up the benefits of cooking:
Use less water. Most vitamin C loss in boiling is leaching, not destruction. Steaming, microwaving, roasting, and sautéing all limit water contact.
Microwaving is not the villain. It tends to retain water-soluble vitamins well, because the times are short and the water volume is small. The persistent belief that microwaves destroy nutrients does not hold up.
Cook shorter and hotter, not longer and gentler. Total heat exposure over time drives loss more than peak temperature.
Cut bigger. More surface area means more leaching. Cook whole or in large pieces where practical.
Keep the liquid. Steaming water, blanching water, and the liquid from braises hold minerals and water-soluble vitamins. Use it.
Eat some raw, some cooked. Variety in preparation captures the strengths of both. This is not a compromise position — it is the actual optimum given how differently nutrients respond.
Does this justify a supplement?
Generally, no — not on cooking-loss grounds alone. A varied diet with a mix of raw and cooked plants covers this easily. The situations where supplementation is worth discussing with a clinician have to do with intake patterns, life stage, absorption issues, or diagnosed deficiencies — not with whether you steamed or boiled your broccoli. Our food first vs supplements guide lays out how to make that call.
Two honest exceptions, neither caused by cooking:
- Vitamin B12 is not meaningfully present in plant foods regardless of preparation. People eating little or no animal food should be supplementing — typically 250-500 mcg daily of cyanocobalamin or methylcobalamin, or 1,000-2,000 mcg two to three times weekly. See vitamin B12 explained.
- Iron and zinc from plant sources are less absorbable, and raw-heavy diets make that harder rather than easier, since soaking and cooking are what reduce phytate. If you suspect an issue, test before supplementing — iron in particular should not be self-prescribed, as excess iron accumulates and is genuinely harmful, and iron supplements are a leading cause of poisoning in young children. Start with blood tests before supplementing.
Bottom line
Cooking reduces vitamin C, folate, and thiamine — mostly by leaching into water you can save — while leaving minerals and fat-soluble vitamins intact and substantially increasing absorbable carotenoids and overall digestibility. “Raw is more nutritious” is not a rule; it is true for a handful of compounds and false for many others. Steam or microwave more, boil less, keep the cooking liquid, add a little fat to carotenoid-rich vegetables, chop crucifers ahead of cooking, and eat both raw and cooked plants. That covers essentially everything this debate is actually about.
This article is educational and is not medical advice. Consult a healthcare provider before starting any supplement or making significant dietary changes — especially if you are pregnant, nursing, taking medication, or managing a health condition.