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Normal nutrition
Dietary nutrients required for good health include water, protein, fat, carbohydrates, vitamins, and minerals. Energy is required for normal body function, growth, and repair.
Protein is necessary for growth and development and to maintain body structures and function. Protein is the source of essential amino acids and nitrogen needed for the synthesis of nonessential amino acids. Dietary protein replaces the essential amino acids and nitrogen that are lost through protein turnover and normal body functions. Nitrogen balance is essential for good health and requires intake of protein and energy. At higher energy intakes, less protein is needed to achieve nitrogen balance. During illness, protein requirements increase.
Fat is the food substance with the highest concentration of calories. Fatty acids and cholesterol make up most of the fat in our diets. Linoleic acid is the only essential fatty acid required in the diet. It is necessary for the synthesis of arachidonic acid, which is a major precursor of prostaglandin. Linoleic acid comes mainly from polyunsaturated vegetable oils. A deficiency of essential fatty acids results in poor wound healing, hair loss, and dermatitis.
Carbohydrates include sugar, starch, and fiber. When carbohydrates are not included in the diet, ketosis begins to occur and there is excessive breakdown of protein into amino acids which are then used for gluconeogenesis.
Water-soluble and fat-soluble vitamins cannot be synthesized in adequate amounts by the body. Fat-soluble vitamins are required for absorption, transport, metabolism, and storage of energy. They are not excreted in the urine like the water-soluble vitamins, and excess accumulation can lead to well-known toxic conditions. Major minerals, as well as trace elements, are also important in human nutrition.
Malnutrition and malignancy
The malnutrition seen in cancer patients is commonly referred to as cancer cachexia. The Delphi consensus definition and classification of cancer cachexia was published in 2011, which defined it as greater than 5% weight loss in the previous 6 months or 2% to 5% weight loss with either a body mass index of less than 20 kg/m 2 or reduced muscle mass. The extent of malnutrition depends on the type and site of the cancer. Cancers such as ovarian cancer, with its potential effect on the gastrointestinal (GI) tract, appear to contribute to malnutrition to a greater degree than does cervical cancer, for example. As expected, malnutrition becomes worse as the cancer progresses and can lead to fatigue, functional impairment, increased treatment-related toxicity, poor quality of life, and reduced survival. The mechanism of cancer-related malnutrition is likely multifactorial. Decreased food intake because of anorexia, early satiety, nausea, vomiting, diarrhea, generalized weakness, lack of appetite due to loss of taste or smell, and food aversion in patients undergoing chemotherapy or radiation can all play a role. Poor absorption of nutrients due to the location of the tumor (e.g., a mass causing a partial bowel obstruction) can also be a contributing factor.
The extent of malnutrition in patients, however, may be greater than what can be explained by decreased intake. There may be an increased nutritional requirement because of the increased demands of the patient and the tumor. Resting metabolic rates can vary greatly but may be elevated in as many as 60% of patients. Cytokines produced by the patient in response to a growing neoplasm may result in metabolic derangements including insulin resistance, increased gluconeogenesis (which can result in decreased protein synthesis), and abnormalities in protein and fat metabolism. Some patients with cancer show a 10% to 20% increase in protein turnover when compared to similar patients without cancer.
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