Key Constituents of Nutrition

The goals of nutritional support and essential components of nutrition.

Goals of nutritional support

The goal of nutritional support is to supply the required amounts of energy and protein together with an adequate amount of water, minerals, vitamins, and trace minerals, in line with guidelines for nutritional requirements. In acute catabolism, tissue protein breakdown leads to increased nitrogen in the urine, which, together with obligatory losses, results in negative nitrogen balance.1


Carbohydrates, especially glucose, provide energy in parenteral nutrition (PN). An intake of too much carbohydrate can lead to hyperglycemia, which is unfavorable for the patient's status2 as it can lead to impaired immune function,3 increased production of inflammatory cytokines4 and increased muscle proteolysis.5


The European Society for Clinical Nutrition and Metabolism (ESPEN) guidelines for parenteral nutrition suggest that only minimal amounts of carbohydrates are essential.2 The minimal amount of carbohydrate required for nutritional support is ~2 g glucose/kg bodyweight/day.2


A major energy source in patients under stress is lipids.6 Besides energy provision, lipids fulfill a number of functions in the body, such as provision of essential fatty acids, regulation of gene expression and signal transduction pathways.7 Essential fatty acids are unsaturated fatty acids that cannot be manufactured in the body in humans and must be obtained from the diet. Both the omega-3 (ω-3) and omega-6 (ω-6) fatty acids are considered essential fatty acids as mammals are unable to produce alpha linolenic acid and linoleic acid. Symptoms of essential fatty acid deficiency include impaired growth and dermatitis, and, secondarily, steatosis, renal toxicity, pulmonary abnormalities, and increased metabolic rate.8


Currently in the United States, all of the intravenous lipid emulsions (IVLEs) are soybean oil-based. In Europe, physicians have alternative IVLEs available, including medium-chain triglycerides, olive oil and fish oil.9 These alternative IVLEs have different characteristics, especially on inflammatory responses. More research is needed to help determine which patient populations benefit most from alternative IVLEs (Table 1).

Table 1. Different lipids have different characteristics

  Soybean oil Olive oil Fish oil
Predominant fatty acids ω-69 ω-99 ω-39
Humoral immune effects Pro-inflammatory9 Neutral9 Anti-inflammatory9
Cellular immune effects Immuno-suppressive10 Neutral11 Immunosuppressive12,13

Soybean oil-based lipid emulsions are rich in omega-6 fatty acids, are proinflammatory,9 and have been associated with immunosuppressive effects, including increased number of infectious complications.10


Olive oil-based lipid emulsions, which are rich in the ω-9 fatty acid oleic acid,9 are regarded as being neutral with respect to effects on the immune system.11 Fish oil-based emulsions, rich in ω-3 fatty acids,9 are associated with anti-inflammatory properties,9 and fish oil admixtures may have beneficial actions on the immune system.12,13 Fish oil-based emulsions need to be given as part of a lipid regimen.

Essential components of a PN solution - the role of trace elements and vitamins in metabolism of macronutrients and the effects of deficiency

Vitamins and trace elements are essential nutrients that act as coenzymes and cofactors involved in metabolism, and should be provided on a daily basis with all nutritional support regimens.14 These micronutrients are critical to cellular metabolic processes, such as wound healing.15


Micronutrient deficiency is often subclinical initially. Screening is difficult, because the micronutrient reserves will be depleted at first before disorders become obvious;16 also, decreased serum levels may indicate redistribution rather than deficiency.17 Multiple factors potentially lead to increased micronutrient needs, including baseline vitamin deficiencies, malnutrition and metabolic changes due to acute and chronic illness.18


Many vitamins and trace elements are needed for healthy physiologic metabolic activity (Table 2).18 Vitamins are essential organic substances that cannot be synthesized in the human body.

Table 2. Clinical effects of vitamin and trace element deficiencies18

Vitamins Deficiency state
A Night blindness, follicular hyperkeratosis, xerosis or xerophthalmia, irreversible corneal lesions, anorexia, immunodepression, epithelial metaplasia
B1 (thiamine) Dry beriberi, hypothermia, wet beriberi, Wernicke-Korsakoff syndrome
B2 (riboflavin) Oral-buccal lesions, seborrheic dermatitis, genital skin changes, ocular disturbances, anemia
B3 (niacin) Pellagra
B5 (pantothenic acid) Growth retardation, infertility, abortion and neonatal death, listlessness and fatigue, skin and hair abnormalities, abdominal pain, vomiting, diarrhea, impaired mentation, insomnia, paresthesias, poor wound healing, increased risk of infection, adrenal cortical failure, sudden death
B6 (pyridoxine) Stomatitis, angular cheilosis, glossitis, irritability, depression, confusion, convulsions, dermatitis, anemia, neurologic symptoms and abdominal distress (infants)
B8 (biotin) Dry scaly dermatitis, anorexia, pallor, glossitis, nausea and vomiting, impaired mentation, hyperesthesias, muscle pain, hair loss, raised serum cholesterol and bile pigments
B9 (folic acid) Anemia, neonatal neural tube defects, glossitis, diarrhea, weight loss, impaired cell-mediated immunity, dementia
B12 (cyanocobalamin) Anemia, peripheral nerve and CNS damage, peripheral neuropathy, impaired vibration and position sense, unsteadiness, confusion, depression, impaired mentation and memory, delusion, psychosis, vision disturbances, leukopenia, thrombocytopenia
C (ascorbic acid) Anorexia, fatigue, muscle pain, increased risk of stress and infection, scurvy, weakening of collagenous structures, bleeding gums, petechiae and ecchymosis, perifollicular hemorrhage, impaired wound healing, anemia, joint effusions with arthralgia, fatigue, depression
D Rickets (infants), osteomalacia, osteopenia, hypocalcemia, bone pain/tenderness, hypophosphatemia
E Hemolytic anemia (infants), increased platelet aggregation, axonal neuropathy, retinal dysfunction, decreased serum creatinine, skeletal lesions
K Coagulopathy, fetal intracranial hemorrhage, easy bruising, mucosal bleeding, splinter hemorrhages, melena, hematuria, fetal chondrodysplasia
Trace elements
Chromium Hyperglycemia and glucosuria, peripheral neuropathy, encephalopathy, hyperlipidemia
Copper Anemia, neutropenia, osteopenia, skin and hair depigmentation, skeletal abnormalities, neurologic abnormalities
Fluoride Dental caries
Iodine Newborns: spontaneous abortions and stillbirths, congenital abnormalities, hypothyroidism, dwarfism, deafness, cretinism, increased perinatal and infant mortality; adults: thyroid goiter and hypothyroidism, impaired mentation
Iron Anemia, glossitis, impaired temperature regulation in the cold, decreased resistance to infection
Manganese Possible dermatitis and hypocholesterolemia
Molybdenum Possible amino acid intolerance, irritability, visual field defects, coma
Selenium Muscular discomfort or weakness, cardiomyopathy, anemia
Zinc Alopecia, skin rash, growth retardation, delayed sexual development, impaired wound healing and immune function, diarrhea, blunted taste and smell

References
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