nutri Flashcards
Triglyceride (TG) present in adipose tissue is the body’s major fuel reserve and is critical for survival during periods of starvation
The high energy density and hydrophobic nature of
TGs make them a five-fold better fuel per unit mass than glycogen.
TGs liberate 9.3 kcal/g when oxidized and are stored compactly as oil inside the fat cell
comparison, glycogen produces only 4.1 kcal/g on oxidation and is stored intracellularly as a gel
During endurance exercise, glycogen and TGs in muscle tissue provide an important source of fuel for working muscles
Daily total energy expenditure (TEE) has three components:
resting energy expenditure (REE) (≈70% of TEE);
the energy expenditure of physical activity (≈20% of TEE)
the thermic effect of feeding (≈10% of TEE), which is thetemporary increase in energy expenditure that accompanies enteral ingestion or parenteral administration of nutrients
REE represents energy expenditure while a person lies quietly awake in an interprandial state; under these conditions, about 1 kcal/kg body weight is consumed per hour in healthy adults.
The liver, intestine, brain, kidneys, and heart constitute roughly 10% of total body weight but account for about 75% of REE.
In contrast, skeletal muscle at rest consumes some 20% of REE, but represents approximately 40% of body weight
Adipose tissue consumes less than 5% of REE but usually accounts for greater than 20% of body weight.
accurate assessment of REE is best obtained by indirect calorimetry, in which in vivo energy expenditure is estimated by measuring carbon dioxide production and oxygen consumption
while the subject is at rest.
Although indirect calorimetry is considered a gold standard for determining REE, obtaining such a measurement is not always practical
Harris-Benedict and Mifflin equations are designed for use in adults, whereas the WHO formulas includes equations for both children and adults.
Protein energy malnutrition (PEM) and hypocaloric feeding without superimposed illness each decrease REE to values 10% to 15% below those expected for actual body size, whereas acute illness or trauma predictably increases energy expenditure
Highly trained athletes can increase their TEE 10- to 20-fold during athletic events
The energy expended during a particular physical activity is equal to (REE per hour) × (activity factor) × (duration of activity in hours).
TEE represents the summation of energy expended during all daily activities, including rest periods
Eating or infusing nutrients increases metabolic rate.
Dietary protein causes the greatest stimulation of metabolic rate, followed by carbohydrate
and then fat.
A meal containing all these nutrients usually increases metabolic rate by 5% to 10% of ingested or infused calories
In arriving at a nutritional plan for hospitalized patients, it is usually not necessary to obtain actual measurements of energy expenditure with a bedside indirect calorimeter
The increase in energy expenditure is roughly proportional to the magnitude of the stress
Thus, the total daily energy requirement of an acutely ill patient can be estimated by multiplying the predicted REE (as determined by the Harris-Benedict or WHO equations) by a stress factor:
In acutely ill hospitalized patients, it is not usually necessary to include an activity factor
An alternative and simple formula for adult inpatients,
although accompanied by some further loss in accuracy, is
20 to 25 kcal/kg of actual body weight (ABW)/day for unstressed or mildly stressed patients
25 to 30 kcal/ABW/day for moderately stressed patients
30 to 35 kcal/ABW/day for severely stressed patients
In using this formula, adjustments are necessary when the ABW is a misleading reflection of lean body mass.
An adjusted ideal body weight (IBW) should be substituted for ABW in obese individuals who are more than 30% heavier than their IBW (desirable body weights
Using an adjusted IBW helps prevent an overestimation of energy requirements and is calculated as:
Adjusted IBW = IBW + 0.5 (ABW − IBW)
Relative Thermic Effect of Various Levels of Physical Activity
Resting 1.0
Very light Standing, driving, typing 1.1-2.0
Light Walking 2-3 miles/hr, shopping, light housekeeping 2.1-4.0
Moderate Walking 3-4 miles/hr, biking, gardening, scrubbing floors
4.1-6.0
Heavy Running, swimming, climbing, basketball
6.1-10.0
In patients with large artifactual increases in weight due to extracellular fluid retention (e.g., ascites), the IBW should be used to estimate energy requirements rather than the ABW
The most accurate and extensively validated equation for predicting daily energy expenditure in ill patients is one that does not incorporate a stress factor; it does, however, require knowledge of the minute ventilation, so its use is restricted to patients on mechanical ventilation.
This formula (often referred to as the “Penn State Equation”)
Injury or Illness Relative Stress Factor*
Second- or third-degree burns, >40% BSA
1.6-2.0
Multiple trauma 1.5-1.7
Second- or third-degree burns, 20%-40% BSA
1.4-1.5
Severe infections 1.3-1.4
Acute pancreatitis 1.1-1.2
Second- or third-degree burns, 10%-20% BSA
1.2-1.4
Long bone fracture 1.2
Peritonitis 1.2
Uncomplicated postoperative state 1.1
*A stress factor of 1.0 is assumed for healthy controls.
significantly reduced in those randomized to intensive insulin therapy who maintained serum glucose levels below 111 mg/dL, compared with those whose glucose values were maintained below 215 mg/dL.
popular nutritional approach to such patients is
so-called hypocaloric feeding, in which only 60% to 70% of the estimated energy requirement (or 11 to 14 kcal/kg of ABW) is delivered in conjunction with 2 to 2.5 grams of protein/kg of IBW per day,
the latter minimizing the risk of producing net protein catabolism and loss of lean body mass purported advantages of hypocaloric feeding include improved glycemic control and prevention of metabolic complications like hypercapnia and hypertriglyceridemia.
Estimated Energy Requirements for Hospitalized Patients Based on Body Mass Index
Energy Requirements (kcal/kg/ day)*
<15 =35-40
15-19 =30-35
20-29 =20-25
≥30 =15-20
These values are recommended for critically ill patients and all obese patients; add 20% of the total calories when estimating energy requirements in non–critically ill patients.
Twenty different amino acids (AAs) are commonly found in human proteins.
Some AAs (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine, and possibly arginine) are considered essential because their carbon skeletons cannot be synthesized by the body
The body of an average 75-kg man contains about 12 kg of protein. In contrast to fat and carbohydrate, there is no storage depot for protein, so excess intake is catabolized and the nitrogen component is excreted
The U.S. Recommended Daily Allowance (RDA) of protein has been established at 0.8 g/kg/day, which reflects a mean calculated requirement of 0.6 g/kg/day plus an added factor to take into account the biological
variance in requirement observed in a healthy population
Clinical Condition Daily Protein Requirement (g/kg IBW)
Normal 0.80
Metabolic stress 1.0-1.6
Hemodialysis 1.2-1.4
Peritoneal dialysis 1.3-1.5
As metabolic stress (and with it, metabolic rate) increases, nitrogen excretion increases proportionately; quantitatively, the relationship is approximately 2 mg nitrogen (N)/kcal of REE.
in metabolic stress, a larger proportion of the total substrate oxidized for energy is from protein.
The first is that illness, by increasing catabolism and metabolic rate, increases the absolute requirement
for protein and does so in a manner that is
roughly proportional to the degree of stress.
Second, because a greater proportion of energy substrate in acute illness comes from protein, nitrogen balance is more readily achieved if a larger proportion
of the total calories are from protein
Most patients with hepatic encephalopathy respond
to simple pharmacologic measures and, therefore, do not require protein restriction; those who do not respond may benefit from a modest protein restriction (≈0.6 g/kg/day)
Nitrogen (N) balance is commonly used as a proxy measure of protein balance
Every 6.25 g of administered protein (or AAs) contains approximately 1 g of N.
The additional 4 g of N loss incorporated into
the equation is intended to account for the insensible losses from the other sources listed and because urinary urea N only accounts for approximately 80% of total urinary nitrogen.
N balance is a suitable surrogate for protein balance, because roughly 98% of total body N is in protein, regardless of one’s health.
A positive N balance (i.e., intake > loss) represents anabolism and a net increase in total body protein, whereas a negative N balance represents net protein catabolism.
For example, a negative N balance of 1 g/day represents a 6.25 g/day loss of body protein, which is equivalent to a 30 g/day loss of hydrated lean tissue
Complete digestion of the principal dietary digestible carbohydrates— starch, sucrose, and lactose—generate monosaccharides (glucose, fructose, and galactose).
In addition, 5 to 20 g of indigestible carbohydrates (soluble and insoluble fibers) are typically
consumed daily.
glucose is the required or preferred fuel for red and white blood cells, the renal medulla, eye tissues, peripheral nerves, and the brain.
However, once glucose requirements for these tissues are met (≈150 g/day), the protein-sparing effects of carbohydrate and fat are similar
Dietary lipids are composed mainly of TGs,
which contain saturated and unsaturated long-chain fatty acids (FAs) of 16 to 18 carbons.
Use of fat as a fuel requires hydrolysis
of endogenous or exogenous TGs and cellular uptake of released FAs (see Chapter 102).
Long-chain FAs are delivered across the outer and inner mitochondrial membranes by a carnitine- dependent transport system.
Humans lack the desaturase enzyme needed to produce the n-3 (double bond between carbons 3 and 4) and n-6 (double bond between carbons 6 and 7) FA series.
Linoleic acid (C18:2, n-6) and linolenic acid (C18:3, n-3) are essential FAs and, therefore, should constitute at least 2% and 0.5%,
Adults who have moderate-to-severe fat malabsorption
(fractional fat excretion >20%) from other causes and
who are not TPN-dependent also frequently display a biochemical profile of EFAD
The biochemical diagnosis of EFAD is defined as an absolute and relative deficiency in the 2 EFAs in the plasma FA profile.
The full clinical EFAD syndrome includes alopecia, scaly dermatitis, capillary fragility, poor wound healing, increased susceptibility to infection, fatty liver, and growth retardation in infants and children