Nutritional deficiencies can often worsen health outcomes (whether a disorder is present or not), and some disorders (eg, malabsorption) can cause nutritional deficiencies. Many medical centers have multidisciplinary nutrition support teams of physicians, nurses, dietitians, and pharmacists to help the clinician prevent, diagnose, and treat occult nutritional deficiencies.
Nutritional Disorders Sections (A-Z)
Mineral Deficiency and Toxicity
Nutrition: General Considerations
Nutrition is the science of food and its relationship to health. Nutrients are chemicals in foods that are used by the body for growth, maintenance, and energy. Nutrients that cannot be synthesized by the body and thus must be derived from the diet are considered essential. They include vitamins, minerals, some amino acids, and some fatty acids. Nutrients that the body can synthesize from other compounds, although they may also be derived from the diet, are considered nonessential. Macronutrients are required by the body in relatively large amounts; micronutrients are needed in minute amounts.
Obesity and the Metabolic Syndrome
Obesity is excess body weight, defined as a body mass index (BMI) of ≥ 30 kg/m2. Complications include cardiovascular disorders (particularly in people with excess abdominal fat), diabetes mellitus, certain cancers, cholelithiasis, fatty liver, cirrhosis, osteoarthritis, reproductive disorders in men and women, psychologic disorders, and, for people with BMI ≥ 35, premature death. Diagnosis is based on body mass index. Treatment includes lifestyle modification (eg, in diet, physical activity, and behavior) and, for certain patients, drugs or bariatric (weight-loss) surgery.
Undernutrition is a form of malnutrition. (Malnutrition also includes overnutrition—see Obesity and the Metabolic Syndrome). Undernutrition can result from inadequate ingestion of nutrients, malabsorption, impaired metabolism, loss of nutrients due to diarrhea, or increased nutritional requirements (as occurs in cancer or infection). Undernutrition progresses in stages; it may develop slowly when it is due to anorexia or very rapidly, as sometimes occurs when it is due to rapidly progressive cancer-related cachexia. First, nutrient levels in blood and tissues change, followed by intracellular changes in biochemical functions and structure. Ultimately, symptoms and signs appear. Diagnosis is by history, physical examination, body composition analysis (see page Obesity : Body composition analysis), and sometimes laboratory tests (eg, albumin).
Vitamin Deficiency, Dependency, and Toxicity
Vitamins may be fat soluble (vitamins A, D, E, and K) or water soluble (B vitamins and vitamin C). The B vitamins include biotin, folate, niacin , pantothenic acid, riboflavin (B2), thiamin (B1), B6 (eg, pyridoxine), and B12 (cobalamins). For dietary requirements, sources, functions, effects of deficiencies and toxicities, blood levels, and usual therapeutic dosages for vitamins, see Table: Recommended Daily Intakes for Vitamins and Sources, Functions, and Effects of Vitamins.