General Thoughts on Nutrition
In order to maintain optimal nutrition, an individual must consume a diet that contains a variety of foods. You might respond to this first sentence with, “Of course! I know that.” But let me emphasize that the critical word in the first sentence is the last one, “foods.” Human biochemistry is still attuned to a diet made up of wild meats and large amounts of fresh, whole vegetables. Those are the foods it expects. Snack chips, sweet rolls, pies, cakes, pickled this and that, highballs, martinis, and fast food burgers deliver unfortunate biochemical slams to the jaw of good nutrition.
Even when food selections are correct, the amounts eaten are important, for an excess, deficiency or an imbalance of nutrients can result in malnutrition – defined here to mean that nutrient intake does not support balanced, optimal metabolism. For example, an excess intake of energy in the form of calories can lead to obesity. High intakes of vitamin A could be toxic, leading to bone fractures. Deficiency of protein results in kwashiorkor, and infants who may survive through this deficiency never reach their full physical and mental potential. Inadequate food intake can lead to vitamin and mineral deficiencies resulting in some of the classic deficiency diseases we all read about in school: scurvy, beriberi, pellagra, rickets, night blindness and anemia.
In the United States, although severe nutritional deficiency diseases are seldom found, many individuals suffer from marginal intakes of micronutrients, that is, vitamins, minerals and bioactive food substances. Data supporting this last statement is easily found at the US Department of Agriculture (USDA) website. Epidemiological studies of the US population demonstrate that almost every key vitamin and mineral is undersupplied to most age groups, both male and female. Yet these deficiencies are not severe enough to cause the obvious disease states mentioned at the end of the paragraph above. Instead, the marginal intakes result in no well-defined clinical symptoms, yet nevertheless prevent the individual from achieving his or her best state of health.
In the United States, a more obvious nutritional problem is excess intake of macronutrients, fat, protein and carbohydrate with the latter being the primary culprit. Obesity is increasing even though the general population knows it predisposes an person to various illnesses (diabetes, arthritis, cardiovascular disease, etc.) and shortens lifespan. And it may not be that only excessive intake of calories leads to obesity when we see that some individuals find it impossible to reduce their girth by decreasing caloric intake and increasing physical activity. Man-made chemicals in processed foods, referred to as obesogens, can alter gene expression in such a way as to inhibit conversion of fatty acids stored in adipose tissue into energy.
Every individual is uniquely different with different nutrient requirements that cannot be precisely determined by any nutritional status survey taken of a large group of people. As a result, allowances have been established that factor in a margin of safety to account for individual variation. Federally sanctioned scientific panels struggled to set the recommended daily intakes (RDI), adequate intakes (AI), and recommended daily allowances (RDA) that we currently use to evaluate any single diet. We expect that optimal health will be achieved if we can take in nutrients at levels that will meet the AI, RDI or RDA, but it is not always the case. Some individuals may simply need more of certain nutrients in order to meet their needs, and achieve their own personal, genetically and environmentally determined state of optimal health.
Disease states obliterate the safety margin and balance of nutrients set forth in RDA, RDI and AI calculations. When the diet must be modified because of illness, the objective is to maintain the patient in optimal nutrition. The patient’s food habits must be considered in diet planning, but poor dietary practices the patient may have been following must be eliminated if recovery is to proceed apace. In order to avoid rejection by the patient, it is essential that the rationale for the diet be carefully and tactfully explained to the patient.
Nutritional Requirements Of Disease
Illness may have several different effects on nutrition. Nutrient requirements may either decrease or increase because of changes in metabolism. Nutrient absorption is often diminished because of anorexia, vomiting, pain, or a simple lack of physical activity during the recovery period that reduces appetite. Malabsorption, which may result from malabsorptive syndromes such as celiac disease, sprue, chronic inflammation, diarrhea, cystic fibrosis, or after surgery on the gastrointestinal tract, will lead to a reduced intake of nutrients, nutrients that will ultimately be essential in healing and restoring health. Fever, post surgical recovery and burns call for greatly increased uptake of both macro and micro nutrients. Burn patients in particular have such excessive requirements that it is impossible to provide enough food and nutrition orally. Parenteral nutrition is almost always employed as a supplement.
In certain metabolic disorders, there is an inability to use nutrients once they are absorbed. In phenylketonuria for example, the essential amino acid, phenylalanine, cannot be metabolized. In galactosemia, galactose cannot be utilized. In diabetes mellitus, glucose tolerance is impaired. In order to effect treatment, the offending nutrient in each case must either be excluded from the diet or, in cases where it is an essential nutrient, must be provided in small quantities only. Protein must be restricted in liver disease since ammonia cannot be converted to urea and urea cannot be removed from the circulation. Sodium may also need to be restricted in liver and renal disease.
Many illnesses result in a catabolic state, where body tissue is broken down and removed faster than it can be replaced. Inactivity after surgery or other serious ailment can contribute to catabolism. After surgery, negative nitrogen balance occurs (indicating a loss of lean muscle tissue) and negative calcium balance occurs (indicating a loss of skeletal tissue) even when adequate nutrients are provided primarily because the patient is at rest in bed, immobilized, unable to exercise his muscles or skeleton. A catabolic state can also occur without illness as witnessed in both the sophisticated atmosphere of weightless astronauts confined to space capsules and the unsophisticated atmosphere of earthbound humans couched in front of a television or video gaming terminal for hours on end.
Ironically, therapy instituted for the management of illness may sometimes contribute to a nutritional deficiency state. Cancer patients subject to radiation or chemotherapy have historically become anorexic and unable to eat, although newer anti-nausea medications and others have somewhat reversed this trend Drug-induced nutritional deficiencies occur and are more severe in the patient whose nutritional intake is inadequate. Drugs such as phenolphthalein, colchicine, methotrexate, para aminosalicylic acid, cholestyramine and neomycin interfere with absorption of nutrients from the small intestine. Other drugs compound with vitamins and minerals, rendering them unabsorbable. Vitamin B6 deficiency can develop when isonicotinic acid hydrazide, hydralazine, penicillamine, and L-dopa are administered. Methotrexate, pyrimethamine and aminopterin act as vitamin antagonists, binding to them to inhibit absorption or blocking their absorption altogether. Multiple vitamin deficiencies may result from taking anticonvulsants or oral contraceptives. Staten drugs, for the control of cholesterol, are known to reduce coenzyme Q 10 levels, putting heart function, energy production and immunity at risk. We can see, therefore, that the nutritional status of a patient on drug therapy must be evaluated, and compensatory dietary modification and supplementation prescribed. This can best be managed by joint consultation of the patient’s physician, pharmacist and clinical nutritionist.
© Mark Timon, MS Clinical Nutrition