Vegetables and mushrooms: seasonality, freshness, storage, safety, nutrition and cooking.
Cooking tomato does not create lycopene, but it can make the pigment more bioavailable by disrupting cell walls and changing its physical form. Vitamin C and other heat-sensitive compounds can decline at the same time. Eating tomato with some fat, such as olive oil, also supports absorption of fat-soluble carotenoids.
Cooked carrots do not lose their main nutritional advantage. Beta-carotene remains and can become easier to absorb because heat softens the plant matrix. Fiber largely remains; some heat-sensitive vitamins can decline. Cooking may speed carbohydrate digestion, but a normal carrot serving still contains relatively little available carbohydrate.
Frozen vegetables are not nutritionally second-rate. Blanching before freezing can reduce vitamin C and folate, but freezing then slows further loss. Fresh vegetables also lose sensitive vitamins during transport and refrigerator storage. Fiber, minerals and carotenoids are generally well retained in both forms.
Spinach does contain meaningful iron, but the reputation needs context. Raw spinach has about 2.7 mg/100 g, while cooked spinach can look higher per 100 g because water and volume are lost. The iron is nonheme, so absorption is more variable and depends on the food matrix and the rest of the meal.
Yes, vegetables contain protein, but even the standouts usually provide only about 3–4 grams per 100 grams. The useful question is not whether broccoli can imitate chicken, but how much protein it actually adds to a plate.