Much potassium in the blood can be dangerous, and damaged kidneys are often unable to regulate the amount of potassium in the blood. A low-calcium diet is used for patients with kidney stones and also for patients who have raised blood calcium levels as a result of, for example, hormonal imbalance. In all these diets the patient’s food intake is controlled in hospital. At home, a patient is provided with a list of foods relevant to the diet they should follow. The list usually ranks foods in terms of units, and the person must not exceed (or fall below) a certain numb% 1 of units each day.
Diets for metabolic diseases
In some diseases the body cannot handle a certain substance or nutrient and so the diet must be changed to avoid it. For example, coeliac disease is an allergy of the gut to gluten, the wheat protein. It progresses to malnutrition if ignored, but is cured by a gluten-
A nutritious and well-balanced diet is one of the main prerequisites of good health. Unfortunately people in most developed countries consume diets which are too high in fat, sugar and salt, and too low in fibre. Because of this we are likely to be overweight and suffer from conditions such as heart disease, constipation, diabetes, tooth decay and some forms of cancer, all of which are, in some part, related to nutrition. Besides the obvious advantages of a balanced diet, dietary adjustments are also helpful for those suffering from certain conditions or recovering from an illness. Such ‘therapeutic’ diets are used as a form of treatment for diabetes, obesity, hypercholestero-laemia (raised blood cholesterol level) and raised blood potassium level. Diagnostic diets are those in which the exclusion (or inclusion) of one specific foodstuff or component of the diet can help to pinpoint an illness.
Some examples of therapeutic diets
There are literally hundreds of special diets for the ill, young, old, convalescing and run-down. In some cases the diet is helping some other form of treatment and is not too critical; in others the prescribed diet is an integral part of the treatment and non-observance can result in illness, or even death. Dietary measures are always required for diabetes, whatever other forms of treatment are employed. The diet involves excluding concentrated sources of simple sugars but including, in controlled amounts, complex carbohydrate foods such as wholemeal bread and wholegrain cereals, and other starchy foods such as potatoes and rice. In this way, by dietary means, the level of sugar in the blood is kept roughly constant -something that the diabetic’s body, which lacks the hormone insulin, is otherwise unable to achieve. Diabetics should eat less animal fats; about 80 per cent of diabetics also need advice on how to lose weight. Every diabetic diet is devised to suit the individual patient.
Protein is the essential building material for body tissues, but sometimes its proportion in the diet needs to be altered. Low-protein diets can be prescribed for diseases of the liver and kidney; they involve reducing the consumption of both animal and vegetable high-protein foods. High-protein diets are advised for patients who need ‘building up’, such as cancer patients, the malnourished and those who have undergone surgery. In kidney diseases a restriction in salt intake may be required. A low-salt diet may also be used in cases of fluid retention (oedema), in some forms of heart disease and for patients suffering from high blood pressure (hypertension). The kidneys are especially sensitive to levels of minerals in the body, and several therapeutic diets involve cutting down on mineral intake to make their job easier. A controlled potassium diet helps some forms of kidney disease because both too little and too v free diet which excludes all products made from wheat, rye, oats and barley. This diet is also prescribed for patients suffering from the skin disorder dermatitis herpetiformis.
The inborn disease phenylketonuria (PKU) involves an inability of the sufferer’s body chemistry to metabolize the amino acid phenylalanine, which must, through dietary control, be kept at a low level.
High-fibre diets include foods such as wholemeal bread, flour and pastas, beans, pulses and lentils. Natural, unprocessed bran may also be included in such a diet, which is usually prescribed for constipation, irritable bowel syndrome, piles (haemorrhoids), controlled Crohn’s disease and ulcerative colitis.
For several conditions, notably allergies, dietary adjustments can help to diagnose a problem and hopefully lessen or cure it; hence the diagnostic diet becomes a therapeutic diet.
For example, the fat-balanced diet is used as a means of assessing the body’s ability to absorb fat. It involves following a constant-fat diet, usually 70 grammlz, for five days, with a two-day run-in period followed by three days when the faeces are collected for analysis. If the amount of fat excreted is more than six grammes per day then fat malabsorption is present and appropriate steps should be taken. This type of test must obviously be carried out under the supervision of a dietitian. There are, however, many examples of ad hoc ‘self-help’ exclusion-and-reintroduction diets to find out, for example, if you are allergic to strawberries or shellfish. With such relatively specific foodstuffs this is often fairly simple. But the galaxy of colourings, preservatives, flavourings and other chemicals added to modern processed foods, plus the often poor labelling of nutrients on packets, means that it may be difficult to track down a causative ingredient. In such circumstances the dietitian can help, but the best long-term course is to make manufacturers aware of an increased public concern about what we consume and whether it is healthy.