To cook or not to cook

To cook or not to cook?

My clients often ask me whether it’s better to eat their food – particularly vegetables – cooked or raw. It’s not one or the other, it’s both, really. Raw vegetables, especially if eaten or frozen very soon after harvest, contain more vitamins than cooked. Scientists think that the discovery of cooking might even be what gave humans the edge over other primates: It allowed us to consume a lot more food – and thus calories – which then enabled us to grow a bigger (and very hungry) brain. Moreover, cooking of course reduces the risk of infection as it kills most microbes.


Yes, vitamins tend to degrade through cooking (and storage), minerals are indestructible, but they, too, may be lost if you throw out the water you cooked your veg in. However, all the vitamins in your vegetables will do you no good if you cannot absorb them. You are, after all, not so much what you eat, but what you absorb. Some foods even contain ‘anti-nutrients’, compounds that can be harmful if overconsumed, and cooking or soaking can render those harmless or reduce the amounts present in the food.

Carrots, for example, are not easy to digest. They are a good source of beta-carotene, a phytonutrient (plant nutrient) that is converted into vitamin A in the body. But you must first be able to absorb it, and that is easier when the carrots are steamed or roasted. Add a little olive oil, because beta-carotene is fat soluble and needs fat for proper absorption.

Tomatoes contain a phytonutrient called lycopene. It is responsible for the tomato’s red colour. Lycopene is thought to protect the arteries from oxidative damage and is anti-inflammatory, and cooking significantly increases the absorbability of lycopene, so don’t eat all of your tomatoes raw, make sure to have some cooked, whether that’s as tomato sauce, soup or in a casserole or on a homemade pizza.

Cruciferous vegetables (cabbage, cauliflower, broccoli, kale etc.) contain nutrients called sulforaphane and indole-3-carbinol, which are said to have cancer protective properties. These are made available when you simply chop the veg … but are destroyed by heat. So, to make the best use of those nutrients, you would want to eat your cruciferous veg raw. The downside of that is that they also contain goitrogenic compounds, which can affect the thyroid. Cooking renders those harmless. So, it’s a bit of a toss-up, depending on what you need and how healthy you are. If you have thyroid issues, it is best to limit raw brassica, but if you are healthy, you’d have to eat an awful lot for the goitrogens to affect your thyroid. The best of both worlds may be to lightly steam and soften the veg, which will still preserve some of the sulforaphane and I3C.

Green leafy vegetables, such as spinach, watercress, rocket, and kale, are a great source of vitamins and minerals, especially vitamin C, B vitamins (incl. folic acid), vitamin K, magnesium and calcium and of course fibre. Vitamin C is very sensitive and quickly diminishes once a vegetable is harvested. Heat reduces vitamin C even more and folic acid is lost as well when the leaves are cooked, so salads and raw green smoothies sound like a good idea. But green leaves are also a source of oxalic acid. Oxalic acid interferes with the absorption of minerals, such as calcium, magnesium and iron – the very nutrients that are so abundant in green veg. Oxalic acid also contributes to the formation of kidney stones, so if you have had problems with those in the past, you’ll want to be more careful. Cooking the leaves destroys the oxalic acid, while – remember – leaving the minerals intact and then ready to absorb. Now, don’t let me scare you: A couple of handfuls of green leaves per day are not going to kill you. Rotate your leaves (i.e. don’t eat the same every day) as different plants contain different types of oxalates. Make sure to cook some of your leaves, too, for the improved absorption of minerals.

Mushrooms, too, are not easy to digest. Their cell walls don’t break down easily, so it’s really quite difficult for us to get to the nutrients they contain. Again, cooking helps us out, breaking down the cell walls for us. And a rather peculiar thing happens with mushrooms: While normally vitamin C decreases with cooking, in mushrooms it increases – at least in shiitake mushrooms.

Whole grains, beans, lentils and nuts contain a substance called phytic acid. If it binds to minerals in the gut, it takes prevents them from being absorbed and they will be excreted in the waste. This could, for example, affect your iron levels. Cooking, soaking, sprouting and fermenting reduces the amount of phytic acid in foods.

Does cooking decrease fibre? No! Like minerals, fibre is virtually indestructible until it reaches the large intestine, where our good bacteria get to work on it. Processing (chopping, blending, cooking) and chewing breaks fibre down mechanically, making it easier to digest, but it is not going to disappear and will still work its magic in the digestive tract.

How to cook?

Steaming is one of the gentler ways of cooking. Either use a steamer, where your food doesn’t touch the water at all, or cook it in very little water with the lid on. Most veg soften in just a few minutes.

Slow-cooking is a great way to gently cook your veg. The temperature is kept low (that’s why it takes hours) to preserve as many nutrients as possible. As slow-cooked meals are usually soups, sauces, or stews, you won’t be throwing out the water and therefore get to eat the minerals.