Carbohydrates

The Food Pyramid and most nutritionists say we should eat plenty of carbohydrates like potatoes and the cereals food group, which includes rice, pasta and bread. But some cereals are much more refined than others. When they are refined they can lose some of their food value, and can also be combined with trans fats (as in commercial baking).

There's not much debate about this in itself, but there is a big disagreement about its significance.

The prevailing view is that it doesn't matter too much. Wholegrain cereals are best, but if your diet (or your kids' diet) gets its bulk from breakfast cereal or toast, sandwiches, and pasta/rice/spuds for dinner, you'll probably have a good basis on which to work. Of course, that's provided you don't use cereal just as an opportunity to eat sugar, and sandwiches just as an opportunity to eat butter!

Willett says this is wrong. The Harvard view is that wholegrain foods should be eaten "at most meals", but that refined carbos, in which they include white rice, white bread, pasta and potatoes, should be eaten "sparingly".

Willett says a diet high in refined carbohydrates is fuelling the rapid increase in diabetes, heart disease and obesity now taking place throughout the Western world.

Most nutritionists agree that it's wrong to eat lots of simple and refined carbohydrates. Instant noodles, most biscuits, cakes and muffins, some sugar-coated breakfast cereals and the like may be carbo-based, but they're not healthy choices.

But white bread is not high in sugar and fat (although many toppings are), and nor is white rice or pasta.

Nutritionists criticise the Harvard researchers for praising the traditional Asian diet, while seemingly ignoring the fact that it is based on white rice. Similarly, they note that many - but not all - Mediterranean diets are based on pasta and white bread.

In our view, it makes sense to switch to wholegrain carbos if you can. One of its key values is that it's very filling, so you eat less overall.

But if you don't like wholegrain foods (or your kids won't even eat them), you probably shouldn't fret. For one thing, there's no point in trying to eat a diet of food you don't like. You'll just give up.

For another, it's obvious there is a difference between refined carbos that are low in sugar and fat, and those that are not. Don't give up on bread, rice and pasta.

The humble spud

What about potatoes? They're a good source of vitamins, minerals and fibre - but, as the Harvard team says, a boiled potato will raise your blood sugar levels more than the same amount of energy in table sugar.

This is because potatoes are mostly starch, which is quickly broken down to glucose. Table sugar is made up of glucose and fructose, and the fructose takes longer to convert to glucose. This leads to a slower rise in blood glucose levels.

But does it follow that potatoes should be eaten "sparingly", as Willett suggests? We doubt it. Potatoes are normally eaten as part of a meal, together with protein, fat and fibre. These all slow the rise in blood glucose - plus you get the value of the potato's other nutrients.

Sugar, however, often comes by itself in sweets and chocolate, so the rise in blood glucose will be quicker.

Potatoes have a useful role in a healthy diet. But go easy on the butter, and avoid chips fried in animal fats or palm oil!