Heat-labile nutrients: what cooking measurably destroys

Below every raw-food argument sits a testable claim: that heat removes nutrition. Food science has been measuring exactly this for a century; and the numbers cut in both directions.

What does cooking destroy, measurably?

Start with the most fragile: vitamin C. Retention studies consistently show boiling vegetables destroys 30-50% of it, sometimes more; pressure cooking and long braising push losses higher. Steaming, stir-frying and microwaving fare better, because the two destructive agents, heat and water: are only ever both present at full strength in a boiling pot. Among the B vitamins, thiamine (B1), folate (B9), B6 and pantothenic acid are the casualties; in pork, a classic thiamine food, cooking losses of 30-50% are standard figures. Folate in leafy greens falls hardest with boiling. Official datasets, the USDA nutrient retention tables among them, quantify this per food and per method, which is why the "cooking destroys nutrients" claim, at its core, is not controversial. What is contested is the interpretation.

Heat, water, time: the three levers

The data decomposes neatly into three variables. Temperature sets the destruction rate of each compound. Water is the escape route: water-soluble vitamins and minerals leach into the cooking liquid and leave the meal when the liquid is poured away. Time multiplies both. A steamed carrot keeps most of its folate; the same carrot boiled forty minutes and drained loses most of it. This is why cooking method comparisons keep producing the same podium: steaming, sautéing and microwaving over boiling, boiling over long stewing, with the twist that stews which serve their liquid return much of what leached.

What the heat does not take

Fat-soluble vitamins. A, D, E, K, are substantially heat-stable; this is why butter and liver remain vitamin A and D foods after cooking. Minerals cannot be destroyed by any kitchen temperature; they only leave by dissolving. And the protein question runs against the raw intuition: heat denatures proteins, which sounds like damage but functionally pre-opens them to digestive enzymes, cooked protein is generally digested more efficiently, a point Wrangham's cooking hypothesis built a career on.

What cooking unlocks

The honest ledger includes the credit column. Lycopene in tomatoes becomes more bioavailable cooked: the basis of the Mediterranean cooked-sauce pattern. Beta-carotene in carrots and lutein in greens improve with moderate cooking. Starches gelatinize and become digestible at all. Legumes and tubers move from marginally edible to staple foods. Antinutrient compounds in both are reduced. None of this means cooking is superior; it means the raw-versus-cooked question has no single answer, only per-nutrient answers.

Where this leaves the raw claim

The primal diet's 40 °C ceiling, examined in its own folio, treats heat as the enemy of food value. The retention data supports the narrower version of that claim: for vitamin C and the fragile B vitamins, in water methods, with discarded liquid, losses are real and large. It does not support the broader version, in which cooking simply impoverishes food. The most defensible reading of a century of measurements is unglamorous: every cooking method is a trade, and the retention tables are the price list.

Cooking is not a tax on all nutrients. It is a renegotiation: and the tables tell you who pays.

Risk note: none needed for this folio's chemistry: but if it inspires raw consumption: raw animal foods carry pathogen risk (Salmonella, E, coli O157: H7, Listeria, Campylobacter) mitigated but not eliminated by source quality; at-risk groups are advised against them.