Jamie Oliver’s nutritionist gives us an insight into the best and healthiest things to include in your diet this winter.

I crave comforting starchy root vegetables at this time of the year. I find my body gravitating away from salads - they just look too cold and uninviting in their bags - and instead either I dream of devouring a plate of roasted carrots, parsnips, swede and celeriac, with some roast chicken, or I find that at the end of the day a crispy-skinned jacket potato fluffed out with butter and grated cheese hits the spot. If you haven’t already tried it, check out a roasted Maris Piper - I think it makes the best jacket potato. The trick to making the skins crispy is to rub them with a little olive oil before popping them in to the oven. Ever since the arrival on the bookshelves of the nutritionally very worrying high-protein Atkins-style diets and the more recent and much more nutritionally sound glycaemic index (GI) charts (these, as you probably know, are concerned with how rapidly certain foods, because of their sugar and fibre content, cause glucose levels in our blood to rise and hence are converted into fat, listing baked and mashed potatoes as high-GI foods, quickly absorbed and more likely to turn into fat than low-GI), millions of people have been led to believe that root veggies are bad news. This just isn’t the case - like all foods when taken in balance, they can offer very positive nutritional as well as comforting stomach-satisfying benefits. Potatoes have become perhaps the most vilified vegetable of all, even though the GI scale tells us boiled potatoes have a medium GI rating so we should be able to eat them (and anyway, who said we have to always live the GI way?).

If you’re really worried that potatoes will whizz through your gut and be converted into sugar too quickly, you can partner them with some protein, such as eggs in a frittata or fish in a fishcake, as the protein slows down the sugar conversion. Interestingly, sweet potatoes despite their name are listed as medium-GI and are therefore healthier to eat - make a mixed mash of them and normal potatoes. I find sweet potatoes wonderfully satiating - both the white- and orange-fleshed varieties contain vitamins C and E and the orange one also contains beta-carotene. Potatoes are one of the cheapest sources of vitamin C, potassium and fibre. The skin contains the most fibre and the flesh just underneath hides all the vitamin C. New potatoes contain the most vitamins, so remember this for next summer, but for now, to maximise the amount of vitamin C gleaned from old potatoes, either cook them in their skins or peel them just before cooking - peeling potatoes and leaving them soaking in water means a lot of vitamin C is lost.

Carrots, potatoes, celeriac, parsnips, beetroots and the not-sure-what-todo- with-them Jerusalem artichokes can all contribute a great deal nutritionally. The last-named knobbly-looking root in particular is one of the richest sources of prebiotics, special types of starch (sugar), but unlike most sugars and starches, prebiotics cannot be digested and pass into the colon intact. Once there, they act as growth-enhancers for health-promoting lactobacillus and bifidus bacteria - the probiotics. As these good probiotic bacteria multiply,they secrete enzymes that break down prebiotics into acids such as acetic and butyric acid, which inhibit the growth of disease-causing bacteria. The whole prebiotic area of nutritional research is one of my passions, because I believe if we support a good bacterial presence in our gut, we not only help alleviate conditions such as irritable bowel syndrome but, as research shows, can improve our chances of not succumbing to some types of cancer and even reduce our risk of heart disease.

"Potatoes are one of the cheapest sources of vitamin C, potassium and fibre. The skin contains the most fibre, and the flesh just underneath hides all the vitamin C."

So artichokes are very good news, though not many people know what to do with them. I usually make them into a mixed vegetable mash with carrots, swede, sweet potatoes and parsnips: just peel the artichokes along with the other veg, chop everything into similarsized portions, then boil or steam them and mash with butter, natural yoghurt to give a slight tang, plenty of black pepper and a little sea salt. It’s even more delicious if you have other leftover roast vegetables such as tomatoes, aubergines, onions and garlic as well - just mash everything roughly together, pan-fry like bubble and squeak and serve with lean meat,oily fish or chicken.

Carrots, as you would expect from the name, are the richest source of betacarotene (more easily absorbed when carrots are cooked) which converts in the body to vitamin A. If you’re lacking this vitamin you can suffer from poor night vision - so carrots do literally help you see in the dark. Beta-carotene also helps fight cancer and heart disease. Parsnips have beta-carotene, vitamin B1, nicotinic acid, folate and vitamin C and are rich in potassium and iron.

Another very fashionable root vegetable is beetroot - usually purple, but you may also be lucky enough to find yellow beets. I tend not to boil it because I hate the smell while it’s cooking; just drizzle the halved beets with olive oil and roast them in a moderate oven, say gas mark 5, for about 50 minutes to turn this vegetable into a delicious roast potato substitute. Beetroot juice (as used raw in juice bars) is said to aid kidney function, but there is no scientific proof of this. The leafy tops make an excellent green vegetable, rich in calcium, beta-carotene and iron - steam them, then drizzle with olive oil, freshly ground black pepper and, if you need it, a little Maldon salt.

Finally, celeriac is a useful source of folate and vitamin C. I use it as a base for leek and potato soup - just sneak some celeriac (equal weight) in to replace some of the potato.

I hope I’ve persuaded you to look at carrots and other root vegetables in a different light - they’re not the prettiest foods (especially the organic ones) but looks are deceiving and they can be one of the best foods to eat at this time of the year when your body needs both nutrients and good old warm-feeling-in-the-stomach satisfaction.

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