Diets can be designed to restrict (or eliminate) virtually any nutrient or food component. The most commonly used restricted diets are those that limit sodium, fat, carbohydrate, and protein. Other restrictive diets include gluten restriction in gluten enteropathy, potassium and phosphate reduction in chronic kidney disease, and various elimination diets for food allergies.
Low-sodium diets can be useful in the management of hypertension and in conditions in which sodium retention and edema are prominent features, particularly heart failure, chronic liver disease, and chronic kidney disease. Sodium restriction may be beneficial with or without diuretic therapy. When used in conjunction with diuretics, sodium restriction allows lower dosage of the diuretic medication and may prevent side effects. Potassium excretion, in particular, is directly related to distal renal tubule sodium delivery, and sodium restriction will decrease diuretic-related potassium losses.
Typical American diets contain 4–6 g (175–260 mEq) of sodium per day. A no-added-salt diet contains approximately 3 g (132 mEq) of sodium per day. Further restriction can be achieved with diets of 2 or 1 g of sodium per day. Diets with more severe restriction are poorly accepted by patients and are rarely used. Current Institute of Medicine guidelines recommend 2.3 g of sodium per day, which is approximately 1 teaspoon of salt.
Dietary sodium includes sodium naturally occurring in foods, sodium added during food processing, and sodium added by the consumer during cooking and at the table. About 80% of the current US dietary intake is from processed and pre-prepared foods. Diets designed for 2.3 g of sodium per day require elimination of most processed foods, added salt, and foods with particularly high sodium content. Many patients with mild hypertension will achieve significant reductions in blood pressure (approximately 5 mm Hg diastolic) with this degree of sodium restriction.
Diets allowing 1 g of sodium require further restriction of commonly eaten foods. Special “low-sodium” products are available to facilitate such diets. These diets are difficult for most people to follow and are generally reserved for hospitalized patients, most commonly those with heart failure, chronic kidney disease, or severe liver disease and ascites.
FAT-RESTRICTED DIETS & LOW-SATURATED-FAT DIETS
Traditional fat-restricted diets are useful in the treatment of fat malabsorption syndromes. Such diets will improve the symptoms of diarrhea with steatorrhea independent of the primary physiologic abnormality by limiting the quantity of fatty acids that reach the colon. The degree of fat restriction necessary to control symptoms must be individualized. Patients with severe malabsorption can be limited to 40–60 g of fat per day. Diets containing 60–80 g of fat per day can be designed for patients with less severe abnormalities.
Fat-restricted diets that specifically restrict saturated fats are the mainstay of dietary treatment of hyperlipidemia with elevated low-density lipoprotein cholesterol (see Chapter 28). Similar diets are often recommended for the prevention ...