Junk food! That's what the naysayers said about nibbling on nuts, but shelled or unshelled, they are back in the nutritionists' good graces apparently because of their high nutrient content. Some researchers even claim that 13g of nuts a day could cut the risk of heart attack thanks to the high omega-3 fatty acids, and say a good handful of nuts a day is the way to go.

However, before reaching for that can of nuts, there is a catch. How nuts are prepared makes a difference to their health benefits. Did you know, for example, that dry roasted nuts contain twice the salt of ordinary salted nuts? Or that hidden in an ounce of honey-roasted nuts is a teaspoon of sugar?

So what's the answer? Nuts which are unsalted, unroasted, and as fresh as possible. Certainly, Christmas is the perfect time to indulge in all the varieties of unshelled nuts that are about, and of course the nutcracker is good exercise for the hands. Before you get cracking, however, here's the nutritional low-down on the most popular nuts you are likely to reach for.

Brazils. Pros: High in calories, so particularly good for athletes and the very active. Rich in the anti-oxidant selenium, which supports the immune system and plays a role in prostate health. An excellent choice for men. Cons: At 190 calories per ounce eat in moderation. For dieters, that means no more than two or three a day. High concentration of saturated fat means they will go rancid. 1 oz = approx. 6-8 nuts.

Walnuts. Pros: Brain food. Packed with omega-3, 6 and 9 fatty acids, especially omega-3, which is vital for neuronal conduction (a firing of the nerves in the brain). Lower cholesterol because 75 percent of the fat is mono-unsaturated. Cons: Cooked walnuts lose health benefits. 1 oz. = approx. 14 nuts.

Almonds. Pros: Best source of protein. High in calcium. At 70 percent of fat content, is healthiest mono-unsaturated nut. High degree of oleic acid, the ingredient in olive oil thought to guard against heart disease. Cons: Hard to digest so could induce indigestion. Soaking overnight in milk or water activates enzymes, making them tastier and more digestible. 1 oz = approx. 20-24 nuts.

Cashews. Contain calcium, magnesium, iron, zinc, folic acid, vitamin E, and essential fats omega-3 and 6. Excellent source of minerals for healthy bones, good for healthy skin as nutrients assist with collagen formation. Cons: Too many can be fattening, particularly if eaten in a Chinese or Indian takeaway where cooking oil and sugar content outweigh health benefits. 1 oz = approx. 16-18 nuts.

Peanuts. Pros: Rich source of protein, niacin and vitamins E, B1, B6; high in copper, zinc and iron. Unshelled peanuts are best. Cons: Very high in saturated fat, so prone to going rancid. Also, shelled peanuts tend to harbour mould, which is believed to be the trigger for potentially fatal peanut allergy. 1 oz = approx. 28 nuts.

Macademias. Pros: Most nutrient-rich nut, containing a mix of omega-3, 6 and 9. Help to balance hormones, improve nerve function, memory and concentration, improve skin texture. Cons: At 200 calories per ounce, the highest calorie count of all the nuts. Very rich, so might upset digestion. 1 oz = approx. 10-12 nuts.

For a good healthy mix: 2 macademias, 8 almonds, 2 Brazil, 3 walnuts, 3 cashews.