While some vegetables are best served raw, in others the vitamins, minerals and beneficial plant compounds are more effectively absorbed into our system when we cook them. To cook, or not to cook? — that is the question.
Carrots - best eaten Cooked
Eating a raw carrot stick might seem virtuous, but you’d be better off cooking them, according to a study published in the Journal of Agricultural and Food Chemistry by food scientists at the University of Arkansas. They found that cooked then pureed carrots had up to 34.3 per cent higher levels of beta carotene.
Beetroot - best eaten Raw
Beetroot contains vitamin C, folate and betalains - pigment compounds that give the root vegetable its purple hue and have powerful antioxidant properties. Boiling or roasting beetroot for lengthy periods can cause a drop in all of these. It is nitrates, however, that are beetroot’s USP. These compounds are converted by the body to nitrite, which not only relaxes and widens blood vessels but influences how efficiently our cells use oxygen. .
Green beans - best eaten cooked
They are sometimes added raw to salads but cooking green beans can increase the availability of nutrients in the vegetable. Indeed, food technologists at the University of Murcia and the University of Complutense in Spain who studied the effects of six cooking methods - boiling, pressure cooking, baking, microwaving, griddling and frying - on nutrient levels of different vegetables found green beans to be one of the few to have increased antioxidants after being cooked by any of these methods except boiling.
Kale - best eaten raw
Kale is labelled a super-veg with reason. It provides fibre and vitamins A, K, B6 and C, plus calcium, potassium, copper and manganese for an all-round health boost. What makes it a star, though, is the presence of glucosinolates, which are converted into metabolites with anti-inflammatory and antioxidant properties when it is chopped or chewed. While it might be tough to swallow, cooking kale can destroy an enzyme called myrosinase.
Celery -best eaten cooked
It’s not the most inspiring vegetable, but crunchy celery stalks do contain fibre, antioxidants that may have anti-inflammatory properties, potassium and vitamin K, which is important for healthy bones. Before you think of tossing it into a salad, bear in mind that the Spanish food technologists found that pressure cooking, baking, griddling or frying celery increased its antioxidant levels.
Tomatoes - best eaten cooked
All tomatoes and tomato-based products contain the powerful antioxidant lycopene, consumption of which has been linked to reduced risk of some cancers, cardiovascular disease and neurodegeneration. Plenty of research has shown that lycopene bioavailability is higher when tomatoes have been heated or cooked, and especially if prepared with a dash of oil.
Potatoes - Best eaten cooked, but cooled
The humble spud is an important supplier of vitamin C, vitamin B6, folate and iron, potassium and even fibre in the diet. It’s unthinkable to serve them raw, not just because they taste appalling but because uncooked potatoes contain resistant starch, which is difficult to digest and can cause gastrointestinal issues. Cooking will reduce levels of some watersoluble nutrients, such as vitamin C, and a little fibre but potatoes retain enough to remain beneficial.
Mushrooms - best eaten cooked
Mushrooms contain fibre and most varieties have an array of B vitamins and are a source of potassium, chloride and copper, as well as being high in selenium - nutrients that are lacking in many UK diets. But they also have tough cell walls and some find raw mushrooms difficult to digest. Even common edible mushrooms can contain potentially hazardous toxins. You are better off cooking them, but how? The best way to preserve nutrients is cook under the grill or in a microwave.
Spinach-best eaten cooked
An excellent source of vitamin C, vitamin B6, magnesium, calcium and iron, spinach is also packed with oxalate, a substance that blocks the absorption of iron and calcium by the body. Boiling and steaming for even a minute or so have been shown to reduce oxalate by up to 87 per cent, meaning there is more calcium available for the body to absorb - although cooking in water will result in the loss of some vitamin C.
Garlic/onions - best eaten raw
The benefits of garlic and onions are most potent in their uncooked form, which is bad for your breath but good for your body. Both contain allicin an active compound responsible for the strong odour that is released when they are chopped, sliced or smashed. Allicin acts like an antioxidant and has been implicated in healthy cardiovascular function, immune function and protection against disease, but is deactivated when cooked.
Asparagus- best eaten cooked
Thinly sliced or marinated raw asparagus spears are a superfood salad staple. But you’d be better off cooking it to boost its nutrient value. Researchers have shown that lightly cooking asparagus increases its total antioxidant activity by 16-25 per cent with levels of two super-antioxidants.
Peppers - best eaten raw
Peppers provide vitamin C, carotenoids and beneficial polyphenols, but lose up to 75 per cent of their nutrients when cooked according to the Spanish scientists. If you do cook them, stick to dry-heat methods such as stir-frying or roasting.
Broccoli- Best eaten raw
With its high levels of the beneficial glucosinolates - natural substances that break down during chopping and digestion into biologically active compounds - broccoli is a star of the vegetable world. However, researchers have shown that heat, particularly boiling and microwaving, damages the beneficial enzyme myrosinase.
Cauliflower- best eaten raw
In the Spanish study, the highest antioxidant losses of all vegetables were observed in cauliflower after boiling and microwaving. Griddling - described as cooking on a flat metal surface with no oil or stir-frying were the best options if cooking. Avoid boiling, which destroys the beneficial compounds of cruciferous veg.