T a time -- usually in middle-age -- when your doctor will look at you over her half-moon glasses and inform you solemnly that your cholesterol is too high. There are several different kinds of cholesterol. But she is most likely to be worried about the , or low-density lipoprotein, sort. That is the stuff that can build up in your arteries, restricting blood flow and raising the risk of a heart attack or a stroke.

Next, she will probably tell you that drugs are not required -- at least not yet. Changing your diet can be as effective as cholesterol-lowering pills. But what exactly should you eat?

To understand which foods to aim for, consider cholesterol's life cycle. Not all cholesterol is bad: cells need it for their membranes, and it serves as the chemical base from which all sorts of vital hormones, including testosterone and estrogen, are synthesised. Some cholesterol comes from the diet. But most is built up from chemical precursors in the liver. Cholesterol does not travel well through the blood by itself. Instead, the liver packages it inside carrier molecules such as .

One reason for high blood cholesterol is having too few receptors in the liver. These work as docking stations at which depleted , having done its job, can be recycled, with any remaining cholesterol sent to the gut to be cleared from the body. A diet high in saturated fats, which are abundant in things like butter, cheese, coconut oil and fatty meats, can lower the number of receptors, which slows the rate of clearance. Conversely, clinical studies suggest that eating less saturated fat boosts receptor numbers and lowers circulating levels of cholesterol.

The problem with the liver's strategy of dumping excess cholesterol into the gut is that some of it ends up re-absorbed back into the body. Some foods can slow that process down, particularly those rich in viscous fibre (think apples, barley and oats, among others) and a class of chemicals called phytosterols. These are similar enough to cholesterol that they can clog up the chemical pathways by which it is usually taken up in the gut. Seeds and nuts are rich sources, and manufacturers sometimes add them to things like yoghurts and spreads.

Combining several types of cholesterol-lowering foods can have a big effect. That is the idea behind the Portfolio Diet, which was developed by David Jenkins, a nutritionist at the University of Toronto, in 2002. Fad diets are a dime a dozen, but this is a diet that seems to work. In a randomised-controlled trial, the clinical gold standard, Dr Jenkins and his colleagues added four groups of foods to the diets of people with high cholesterol: 50g of soy protein (such as tofu and soy milk), 30g of almonds, 20g of viscous fibre from foods rich in the stuff and 2g of plant phytosterols from enriched margarine (about the same as ten handfuls of mixed nuts). After four weeks, the participants' cholesterol fell by nearly 30%, similar to what can be achieved by cholesterol-busting drugs such as statins.

The Portfolio Diet's name comes from the idea that, rather than sticking rigorously to a meal plan, followers can choose food that suits their tastes: different sorts of nuts, say, or other kinds of plant protein. Some seeds and spices can be used to jazz up meals. Turmeric, flaxseeds, sumac and garlic powder, for instance, have all been shown to lower cholesterol. After all, as your doctor will also tell you, if a diet is not enjoyable, you are unlikely to stick to it.■