The Hay diet was developed by an American doctor, William Hay in the 1920s. 
Dr. Hay believed that proteins and carbohydrates should not be eaten together.
This he believed was because they require different conditions for indigestion.
- an acidic habitat for proteins
- an alkaline habitat for carbohydrates
Dr Hay classified foods into three main types according to their chemical needs for efficient digestion and absorbtion.
- Alkali-forming foods-fruits and vegetables.
- Concentrated proteins-meat, game,fish,eggs and cheese.
- Concentrated carbohydrates or starch foods-grains, bread, and all foods containing flour, and all sugars and foods containing sugar. He did not include here naturally occurring sugars found in fruit.
Dr Hay listed food in the following order of importance.
- Raw salad foods and leafy greens
- Root vegetables
Following are The Hay Rules for health;
- Carbohydrates should not be eaten with proteins and acidic fruits.
- Vegetables, salads and fruits should form the major part of the diet
- Proteins, starches and fats should be eaten only in small amounts.
- Refined and processed foods such as sausages should be avoided. As should white flour and sugar and highly processed fats such as margarine and drinks such as cola´s.
- At least four hours must be left between meals of different types of food.
Following rule one allows food to digest in the most efficient way.
Rules two and three relate to the balance of the diet.
Rule Four is the most important.
It is these highly refined foods and drinks that are believed to be responsible for so many of our Western degenerative diseases such as coronary heart disease, diabetes, obesity, various cancers and dental cavities.
Below is a typical meal plan for the Hay diet.
- Breakfast (Alkaline)
- Plenty of fresh fruit, small carton of natural yoghurt sprinkled with wheatgerm or mixed nuts, herb tea and freshly squeezed fruit juice.
- Lunch (Protein)
- Portion of eggs or cheese; fresh raw salad, or cooked vegetables (not potatoes). This can be followed by any of the fresh acid fruits such as apples, pears or oranges.
- Dinner (Starch).
- Jacket potato with butter or wholemeal bread and butter, cooked vegetables or salad, followed by a fresh fruit such as a banana.
Dr Hay maintained that provided fruit was properly combined with the meal i.e. sweet fruit with starches and acid fruit with proteins, no fermentation would occur.
Dr Hay believed that many diseases and ailments such as arthritis, indigestion, allergy and skin disorders were due to the wrong chemical conditions in the body, which in turn were caused by eating too much meat and refined carbohydrate, as well as by poor digestion and constipation.
Many advocates of the Hay diet believe that is a good method of losing weight.