Cooking breaks down plant cell walls and releases nutrients
Raw plant cells are enclosed in cellulose and pectin walls that resist digestion. Heat softens and ruptures these walls, releasing nutrients like lycopene, beta-carotene, and minerals that your body can absorb more easily. Tomatoes cooked into sauce deliver several times more absorbable lycopene than fresh tomatoes because the heat ruptures cell walls.
Carrots and spinach show similar patterns: steaming or roasting makes their carotenoids and iron more available, while raw versions lock these nutrients behind indigestible fiber. The tradeoff is that some heat-sensitive vitamins, especially water-soluble B and C vitamins, leach into cooking water or break down from the heat itself.
Foods that lose when cooked
Cabbage, kale, and cruciferous vegetables contain glucosinolates, compounds with potential anti-cancer activity, that break down partially when cooked. Raw versions preserve these compounds intact, though cooking also inactivates compounds that interfere with mineral absorption. The net benefit depends on the specific nutrient and cooking method.
Garlic's sulfur compounds, which have antimicrobial properties, form only when raw cells are crushed and mixed. Once heated, these compounds degrade within minutes. This is why raw garlic has a distinct nutritional and health profile from cooked, and why letting crushed garlic rest before cooking preserves more of its bioactive compounds.