The Science of a Balanced Diet

Few subjects generate as much confusing advice as what we ought to eat. Every year brings a new fashion, a food to fear or a food to celebrate, and the result is that many people feel they no longer know what a healthy meal looks like. In my view this confusion is largely unnecessary. The core principles of a balanced diet are well established and surprisingly simple, and I believe most of us would be far better served by returning to them than by chasing the latest trend. A balanced diet is one that supplies the body with the right types and amounts of nutrients to maintain health, and its foundations have changed remarkably little despite the noise that surrounds them.

The body needs several kinds of nutrient, and each plays a distinct part. Carbohydrates are the body's main source of everyday energy. Proteins supply the raw materials for building and repairing tissues. Fats provide a concentrated store of energy and help the body carry out a range of essential functions. Alongside these come vitamins and minerals, needed in far smaller quantities but vital nonetheless, and water, without which the body cannot function at all. No single one of these can be neglected, and a diet that leaves out an entire category is, I would argue, always a mistake, however popular such diets sometimes become.

Balance, though, is not only about including every group; it is also about proportion. It is quite possible to eat food from every category and still eat badly, if the quantities are wrong. Most nutrition authorities agree that carbohydrates, ideally from whole grains, vegetables and fruit, should make up the largest part of the diet, with generous amounts of vegetables and fruit, moderate portions of protein, and only small amounts of fat and sugar. I find this general shape convincing, and I think the endless argument over the precise percentages distracts from a picture that is, in its broad outline, clear enough to act on.

Not all fats, and not all carbohydrates, are the same, and here the details do matter. The fats found in fish, nuts and certain plant oils are, on the whole, beneficial, while large amounts of the saturated fat in fatty meat and many processed foods are best limited. In the same way, the carbohydrates in whole grains and vegetables are released slowly and come packaged with other useful substances, whereas the sugar in sweets and sugary drinks delivers a rapid surge of energy and little else. I would strongly encourage anyone to favour the first kind over the second; this, to me, is one of the most useful distinctions in all of nutrition.

One ingredient deserves particular caution, and that is added sugar. Sugar occurs naturally in fruit and milk, where it comes wrapped in fibre, vitamins and other goodness, and I have no quarrel with it there. My concern is with the large quantities of sugar added to processed foods and drinks, which contribute energy while crowding out more nourishing choices. I am convinced that reducing added sugar is one of the single most valuable changes most people could make to their diet, and I make no apology for saying so plainly.

The way food is processed also matters a great deal. Heavily processed foods are often engineered to be intensely palatable, high in sugar, fat and salt, and easy to eat in large amounts, and they tend to be low in the fibre and nutrients that whole foods provide. I am wary of these products, and I think the steady drift towards them is one of the least helpful developments in modern eating. Wherever possible, I would rather see people prepare meals from fresh ingredients, not because home cooking is a virtue in itself, but because it gives the eater far more control over what actually goes into the food.

None of this, I should stress, requires perfection or rigid rules. A balanced diet is best understood as a pattern maintained over weeks and months, not the content of any single meal, and there is room within it for the occasional treat. Indeed, I think an approach so strict that it becomes a source of anxiety is unlikely to last, and a diet that cannot be sustained is of little use. The aim is a sensible, flexible habit rather than a short-lived act of willpower.

If there is one message I would leave, it is that eating well is neither as complicated nor as miserable as it is often made to sound. A diet built mainly on vegetables, fruit, whole grains and modest portions of good-quality protein and fat, with sugary and heavily processed foods kept to the margins, will serve most people well for a lifetime. The science behind this advice is not new, and in my judgement it does not need to be reinvented with every passing season.