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A complete nutritional assessment of the patient is imperative before
specialized nutrition is initiated. Parameters to be considered are
nutrition and weight history, physical examination, anthropometric and
biochemical measurements, and malnutrition risk.
The nutritionalstatus of a patient can be assessed using the subjective
global assessment (SGA) technique, which has been found to be highly
predictive of outcome, because the SGA correlates strongly with other
subjective and objective measures of nutrition.
Patients who cannot meet their nutritional needs by consuming food
orally should be considered for specialized nutritionalsupport, which is
the provision of parenteral or enteral nutrients.
Protein and calorie goals are assessed on the basis of the disease status
and body weight of the patient.
Nutritionalsupport regimens should be tailored on the basis of the
requirements, response, and tolerance of the patient. Patients with
inflammatory bowel disease are particularly at risk for developing
vitamin and other micronutrient deficiencies, and therefore,
The fluid needs of a patient are determined by the following steps: (a)
need to correct fluid imbalances, (b) maintenance fluid requirements,
and (c) replacement of ongoing fluid losses.
Continued success of a nutritionalsupport regimen can be accomplished
by appropriate nutritional assessment after the initiation of therapy. The
parameters such as patient weight trends, nitrogen balance, and
prealbumin are considered when determining the need to adjust therapy.
Overfeeding should be avoided in patients, and a gradual and
conservative approach to instituting nutritionalsupport should be used to
prevent potential metabolic abnormalities.
Recognition of the importance of adequate and appropriate nutrition is paramount to
the maintenance of optimal health. When an imbalance exists between the supply and
the demand for the sources of nutrients and energy by the body, a nutritional disorder
can occur. Years of research and clinical experience have led to the creation of
various screening tools, assessment techniques, and guidelines to aid practitioners in
their quest to delay or prevent patients from developing dangerous sequelae
associated with deviations from optimal nutrition.
nutritional science, impaired nutritional status in developing nations continues to be a
main cause of morbidity and mortality, especially in young children.
Adequate levels of energy sources and essential nutrients are critical for retaining the
structural and biochemical integrity of the human body. Energy is provided in the diet
such as carbohydrates, protein, and lipid. Essential nutrients, none of which offer any
caloric value, are supplied to the body in the form of water, electrolytes, vitamins,
Humans need to consume food to sustain life. The unique structure and function of our
cellular architecture allow human beings to convert the chemical free energy
contained within the diet into high-energy, biologically active compounds. This
transformation of food energy into forms of viable free energy through cellular
respiration is an extremely inefficient process. Close examination of the distribution
of food energy within the human body reveals that approximately 50% is lost as heat,
45% is available to the body in the form of adenosine triphosphate, and the remaining
5% is thermodynamically required for the conversion to heat because the entropy of
the final products is greater than that of the initial substrates. Ultimately, all of the
energy derived from food is expended in the form of external work or heat.
In nutritional contexts, the energy available from food is expressed in terms of the
calorie. A calorie is technically defined by the amount of heat required to raise the
temperature of 1 g of water by 1°C. This unit, however, is too small from a dietary
perspective. A food calorie (sometimes written as Calorie with a large C, although
this convention is not strictly followed) is equivalent to 1,000 calories or 1
kilocalorie (kcal). One food calorie is also equal to 4.184 kilojoules.
uncommon for a single kilocalorie to be referred to as a calorie when communicating
the energy content of food. This ambiguity must be understood by practicing
clinicians to communicate properly not only with colleagues but also with patients
and the general public who may not have an appreciation for this subtlety and remain
confused when reading calories on nutrition labels yet and seeing kilocalories in
textbooks, scientific publications, patient records, and Internet.
Carbohydrates, also known as saccharides, are organic compounds that are
chemically the hydrates of carbon. There are four main types of carbohydrates:
monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Dieticians
frequently classify carbohydrates as either simple (monosaccharides and
disaccharides) or complex (oligosaccharides and polysaccharides); yet, the exact
delineation of these categories is often not clear. Although carbohydrates serve as a
common source of energy for living organisms, these compounds also function as
structural components and building blocks for complex genetic molecules.
Monosaccharides (e.g., glucose) are the simplest of carbohydrates and cannot be
hydrolyzed into smaller saccharide molecules. They are the major sources of fuel,
because glucose serves as a nearly universal and accessible reservoir of calories. In
the context of food science, monosaccharides, collectively along with disaccharides,
are commonly referred to as sugars and are found in foods such as candy and
desserts. Natural sources of monosaccharides include fruits and vegetables, but these
foods composed of a high proportion of fructose relative to glucose.
Oligosaccharides are short chains of monosaccharides typically composed of 3 to
10 molecules linked through glycosidic bonds. These molecules are typically found
connected to proteins or lipids functioning as chemical markers for cellular
recognition. Their important role in the classification of blood groups is an example.
Polymeric carbohydrate structures are referred to as polysaccharides and function
either as storage forms of energy, such as glycogen in animals or starch in plants, or
as a structural component, such as cellulose in plants. In humans, dietary
polysaccharides must be catabolized to their constituent monosaccharides before
Dietary carbohydrates are composed of approximately 60% polysaccharides,
mainly starch, and disaccharides such as sucrose and lactose, which represent 30%
and 10%, respectively. All carbohydrates provide 4 kcal of energy/gram. Although
the exact amount of dietary carbohydrates sufficient for good health is not known, a
mixed-fuel diet in which carbohydrates constitute 45% to 65% of the total energy
intake is considered an acceptable distribution range.
Polypeptides are linear chains of amino acids. These polypeptides can twist and fold
alone or together into three-dimensional globular or fibrous structures, generating a
biochemical compound known as the protein. Proteins are crucial to all living
organisms and participate in a wide spectrum of processes. Many proteins function
as enzymes, which serve as catalysts to biochemical reactions and are important for
metabolism. Additionally, proteins can play a role in structure and function, such as
actin and myosin in muscle—the largest source of protein in higher animals. Some
proteins stabilize blood by giving it the appropriate viscosity and osmolarity, and
yet, other proteins participate in cell signaling and immune responses.
Protein is the second largest store of energy in the body after adipose tissue.
Although protein differs from the other two primary dietary energy sources because
of its inclusion of nitrogen, the amino acid residues from proteins can be converted to
glucose via gluconeogenesis to supply a continuous source of glucose for the body
after the depletion of glycogen. Like carbohydrates, each gram of protein supplies 4
kcal of energy. The loss of more than 30% of body protein, however, can
compromise muscle strength, affect respiratory function, and negatively influence the
immune system, all of which ultimately lead to organ dysfunction and death. It should
be noted that protein and energy requirements of the body are intimately connected.
During the times of infection or injury, metabolic rates rise and body protein is
suddenly oxidized into amino acids and mobilized for fuel utilization. In most
instances, the injuries that patients experience are minimal and self-limiting;
however, patients with chronic illnesses or those with complicating factors that result
in a long-term hypermetabolic state can subsequently experience a dangerous loss of
Lipids comprise a broad spectrum of molecular species ranging from hydrophobic
triglycerides and sterol esters to hydrophilic phospholipids and cardiolipins, as well
as dietary cholesterol and phytosterols. Biologic lipids function as a form of energy
storage, serve as the structural components of cell membranes, and participate as
messengers in the vital process of cellular signaling.
In a nutritional context, fats that exist as liquids at room temperature are typically
called oils, whereas fats that remain solid at room temperature are labeled as fats.
Although the term lipid is frequently used synonymously for fat, fats are actually a
subgroup of lipids also known as triglycerides. Triglycerides are synthesized by
chemically combining glycerol with three fatty acid molecules. These fatty acids are
generally nonbranched hydrocarbons containing an even number of carbon atoms
ranging from 4 to 26 carbons. Adipose tissue is composed of fatty acids in varying
An unsaturated fat is a fatty acid that includes at least one double bond within the
fatty acid chain, and therefore, a saturated fat is one that contains no double bonds.
Unsaturated fatty acids result
in less energy after the oxidation process of cellular metabolism compared with an
equivalent amount of saturated fatty acids. Commercial manufacturers of processed
food favor saturated fats because they are less vulnerable to rancidity (lipid
peroxidation) and remain solid at room temperature. Foods containing unsaturated
fats include avocado, nuts, and vegetable oils such as canola and olive oils. Meat
products contain both saturated and unsaturated fats.
Importantly, each gram of fat yields 9 kcal of energy, twice that of either
carbohydrate or protein. Approximately 35% to 40% of the total daily calories
consumed by the average human being are lipids. Higher-fat diets can lead to more
rapid weight gain, a positive attribute if the individual is malnourished or
underweight, but a negative attribute if the individual is trying to achieve weight
6 Triglycerides make up by far the largest proportion of dietary lipids consumed
by humans. Although humans possess the biologic pathways to synthesize lipids,
there are two essential lipids that must originate from the diet to prevent essential
fatty acid deficiency—linoleic acid and α-linolenic acid.
Water plays a critical role in nearly every biologic function necessary for life. The
total body water in an adult male without fluid and electrolyte disorders is
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