There’s a lot of debate around how to cook veges to maximise their nutrient levels. In general, the longer vitamins are exposed to heat, the more their levels will fall. Water-soluble vitamins, like vitamin C; and B vitamins like thiamine, riboflavin and folic acid, will often be reduced during cooking, especially when veges are boiled. In broccoli and spinach, up to half of the vitamin C can be lost. In leafy greens, the levels of B vitamins also fall by up to 40 per cent. But some of the vitamins will remain in the cooking liquid, so boiling is a good choice if you’re making stock or soup. While cooking may reduce vitamin content, the levels of other nutrients may rise. A 2002 study found although the amount of vitamin C is reduced in cooked tomatoes, cooking boosts levels of other antioxidants, like lycopene, that can be absorbed by the body. Senior research dietitian Helen Rasmussen of Tufts University says this is because the heat breaks down the cell matrix of the plant, allowing carotenoids to be released from the cell walls. As for the best method, sautéing and stir-frying veg will retain more nutrients than boiling, and can improve the absorption of fat-soluble vitamins like vitamins A, D and K. Steaming or microwaving are also good options. Microwaving can reduce the vitamin C in green veg by 30 per cent – less than most cooking methods.