Like a lot of people, I have seen fad diets come and go over the years. One I encountered early on in my nutritional career was the food-combining diet. Also known as the Hay diet, this advocated keeping certain foods separate at meal times, which, it was claimed, could bring benefits for the body in terms of enhanced weight loss and well-being. For a time, books on the subject topped the bestseller lists.

However, the diet was not without its detractors. Many doctors and dieticians were quick to assert that the gut is designed to cope with the simultaneous breakdown of different types of foods. The Hay diet eventually faded in popularity, but was recently brought to my attention again by a reader's letter inquiring about its merits.

The core principle is to avoid the eating of protein-based foods (such as meat, fish, eggs and cheese) with starch-dense foods (such as bread, potatoes, rice and pasta). Prior to absorption into the body, proteins and starches are digested using fairly distinct mechanisms. For instance, while proteins are initially digested best in the harsh acidic environment of the stomach, starches are broken down most efficiently in the more alkali milieu of the small intestine. Also, the enzymes used to digest protein are quite different from those used to digest starch.

While conventional wisdom dictates that the gut should be able to digest a mishmash of food perfectly well, gut physiology dictates that mixing protein and starch at meals tends to make digestion harder than having just one of these foods at a time.

The central theme of the food-combining diet is therefore based around lightening the digestive load by eating meals comprised of either protein or starch, combined with 'neutral' foods such as green vegetables and tomatoes. According to this principle, meals consisting of meat or fish with salad or vegetables (other than potatoes) are permissible, as are vegetable curry and rice, or pasta with a red sauce and salad.

In theory at least, such meals should be more easily, quickly and completely digested than protein-starch combinations. Better digestion helps the body extract more nutritional value from our food. It is also believed that swifter digestion means that food is less likely to cause excesses of internal effluent, or 'toxicity'. This may help to explain why many individuals find food combining can indeed help them shed weight and boost their overall health.

There are circumstances when it can be useful, particularly in the evening, when digestive capacity is believed to be at a low point. My experience is that food combining almost always offers significant relief to individuals suffering from indigestion and/or heartburn. I also believe that, in certain circumstances, keeping protein and starch apart at meals can be a winning combination.