Dr. William Howard Hay introduced food combining in 1911. After 16 yrs medical practice his own health began to deteriorate, and he developed high blood pressure, Brights disease (now more commonly known as acute or chronic nephritis, a kidney disease) and a dilated heart. There being no treatment available for dilated heart at the time, Dr. Hay was inspired to treat his own symptoms. His basic premise is that there is one underlying cause for health problems and that is the wrong chemical condition in the body.

He did this by eating 'fundamentally' as he called it; taking foods in a natural form and not mixing proteins and starches at the same meal. The wrong chemical condition is acidity which is caused by the manufacture and accumulation of acid from the products of digestion and metabolism in amounts greater than the body can eliminate. 

Along with dietary changes, Dr. Hay also advised fresh air, exercise and general lifestyle changes. The basic rules of this diet are: starches and sugar should not be eaten with proteins and acid fruits at the same meal; vegetables, salads and fruits should play a major part in the diet; proteins, starches and fats should be eaten in small quantities and only wholegrain unprocessed starches should be used; and finally at least 4 hours should elapse between meals of different food groups. It is also known as the "food combining" diet. Acid foods are protein rich, meat, fish, dairy, etc., and alkaline the carbohydrate-rich starch foods like rice, grains and potatoes.

Following the simple rules of the Hay Diet can reverse chronic and degenerative conditions such as constipation, indigestion and arthritis.  It can be beneficial to asthma and allergy sufferers.  It can also stimulate natural weight loss, thus reducing the health risks linked to obesity, such as diabetes, gallstones and coronary heart disease.