Right 2 Flashcards
The average energy intake is
~2600 kcal/d for American
men and ~1800 kcal/d for American women, though these estimates
vary with body size and activity level.
Formulas for roughly estimating
REE are useful in assessing the energy needs of an individual whose
weight is stable. Thus,
for males, REE = 900 + 10m, and for females,
REE = 700 + 7m, where is m mass in kilograms
The calculated REE
is then adjusted for physical activity level by multiplying by
1.2 for
sedentary, 1.4 for moderately active, or 1.8 for very active individuals.
The nine essential
amino acids are
histidine, isoleucine, leucine, lysine, methionine/
cystine, phenylalanine/tyrosine, threonine, tryptophan, and valine
For adults, the recommended dietary allowance (RDA) for protein
is ~0.6 g/kg desirable body mass per day, assuming that energy needs
are met and that the protein is of relatively high biologic value. Current
recommendations for a healthy diet call for at least 10–14% of calories
from protein
Fats are a concentrated source of energy and
constitute, on average, 34% of calories in U.S. diets. However, for
optimal health, fat intake should total
no more than 30% of calories.
Saturated fat and trans fat should be limited to <10% of calories and
polyunsaturated fats to <10% of calories, with monounsaturated fats
accounting for the remainder of fat intake
least 45–55% of total
calories should be derived from carbohydrates. The brain requires
~100 g of glucose per day for fuel; other tissues use about 50 g/d. Some
tissues (e.g., brain and red blood cells) rely on glucose supplied either
exogenously or from muscle proteolysis. Over time, adaptations in
carbohydrate needs are possible during hypocaloric states. Like fat
(9 kcal/g), carbohydrate (4 kcal/g), and protein (4 kcal/g), alcohol
(ethanol) provides energy (7 kcal/g)
For adults, 1–1.5 mL of water per kilocalorie of energy expenditure
is sufficient under usual conditions to allow for normal variations
in physical activity, sweating, and solute load of the diet.
Water
losses include 50–100 mL/d in the feces; 500–1000 mL/d by evaporation
or exhalation; and, depending on the renal solute load, ≥1000
mL/d in the urine. I
Fever increases water losses by
~200 mL/d per °C; diarrheal losses vary but may be as great as
5 L/d
in severe diarrhea.
When renal function is normal and solute
intakes are adequate, the kidneys can adjust to increased water intake
by excreting up to
18 L of excess water per day
Increased water needs during pregnancy are ~30 mL/d.
During lactation, milk production increases daily water requirements
so that ~1000 mL of additional water is needed, or 1 mL for each milliliter
of milk produced
benchmark recommendations regarding
nutrient intakes have been developed to guide clinical practice.
These
quantitative estimates of nutrient intakes are collectively referred to
as the dietary reference intakes (DRIs
Thiamine deficiency is therefore
more common in cultures that rely heavily on a
rice-based diet.
Tea, coffee (regular and decaffeinated), raw fish, and shellfish contain
thiaminases, which can destroy the vitamin
drinking large
amounts of tea or coffee can theoretically lower thiamine body stores.
In Western countries, the primary causes of
thiamine deficiency are alcoholism and chronic illnesses such as cancer.
Alcohol interferes directly with the absorption of thiamine and
with the synthesis of thiamine pyrophosphate, and it increases urinary
excretion. Thiamine should always be replenished when a patient with
alcoholism is being refed, as carbohydrate repletion without adequate
thiamine can precipitate acute thiamine deficiency with lactic acidosis
Wet beriberi presents primarily
with cardiovascular symptoms that are due to impaired myocardial
energy metabolism and dysautonomia
; it can occur after 3 months
of a thiamine-deficient diet. Patients present with an enlarged heart,
tachycardia, high-output congestive heart failure, peripheral edema
dry beriberi present with a symmetric
peripheral neuropathy of the motor and sensory systems, with
diminished reflexes.
The neuropathy affects the legs most markedly,
and patients have difficulty rising from a squatting position
Alcoholic patients with chronic thiamine deficiency also may have
central nervous system (CNS) manifestations known as
Wernicke’s
encephalopathy, which consists of horizontal nystagmus, ophthalmoplegia
(due to weakness of one or more extraocular muscles),
cerebellar ataxia, and mental impairment (Chap. 467). When there
is an additional loss of memory and a confabulatory psychosis, the
syndrome is known as Wernicke-Korsakoff syndrome. Despite the
typical clinical picture and history, Wernicke-Korsakoff syndrome is
underdiagnosed.
The laboratory diagnosis of thiamine deficiency usually is made by
a functional enzymatic assay of transketolase activity measured before
and after the addition of thiamine pyrophosphate.
A >25% stimulation
in response to the addition of thiamine pyrophosphate (i.e., an activity
coefficient of 1.25) is interpreted as abnormal.
In acute thiamine deficiency with either cardiovascular or neurologic signs,
200 mg of thiamine three times daily should be given intravenously
until there is no further improvement in acute symptoms;
oral thiamine (10 mg/d) should subsequently be given until recovery
is complete.
niacin refers to nicotinic acid and nicotinamide and their
biologically active derivatives. Nicotinic acid and nicotinamide serve
as precursors of two coenzymes,
nicotinamide adenine dinucleotide
(NAD) and NAD phosphate (NADP), which are important in numerous
oxidation and reduction reactions in the body.
Niacin deficiency causes
pellagra, which is found
mostly among people eating corn-based diets in parts of China,
Africa, and India.
Pellagra in North America is found mainly
among alcoholics; among patients with congenital defects of intestinal
and kidney absorption of tryptophan (Hartnup disease
Bright red glossitis then ensues and is
followed by a characteristic skin rash that is pigmented and scaling,
particularly in skin areas exposed to sunlight. This rash is known as
Casal’s necklace because it forms a ring around the neck
The primary
manifestations of this syndrome are sometimes referred to as “the
four D’s”:
dermatitis, diarrhea, and dementia leading to death.
Treatment of pellagra consists of oral supplementation with
100– 200 mg of nicotinamide or nicotinic acid three times daily for 5 days.
High doses of nicotinic acid (2 g/d in a time-release form) are used
for the treatment of elevated cholesterol and triglyceride levels and/
or low high-density lipoprotein cholesterol levels
is also important for connective tissue
metabolism and cross-linking (proline hydroxylation), and it is a component
of many drug-metabolizing enzyme systems, particularly the
mixed-function oxidase systems.
Vitamin C
Administration of vitamin C (200 mg/d) improves the symptoms
of scurvy within several days.
High-dose vitamin C supplementation
(e.g., 1–2 g/d) may slightly decrease the symptoms and duration of
upper respiratory tract infections.
Vitamin C supplementation has also
been reported to be useful in
Chédiak-Higashi syndrome (Chap. 80)
and osteogenesis imperfecta
Taking g of vitamin C in a single dose may result in
abdominal pain, diarrhea, and nausea. Since vitamin C may be
metabolized to oxalate, it is feared that chronic high-dose vitamin C
supplementation could result in an increased prevalence of kidney
stones. However, except in patients with preexisting renal disease, this
association has not been borne out in several trials
> 2
is a water-soluble vitamin that plays a role in gene expression,
gluconeogenesis, and fatty acid synthesis and serves as a CO2 carrier on
the surface of both cytosolic and mitochondrial carboxylase enzymes.
Biotin
is believed to have caused
the “burning feet syndrome” seen in prisoners of war during World
War II.
Pantothenic acid deficiency
is a precursor for acetylcholine, phospholipids, and betaine.
Choline is necessary for the structural integrity of cell membranes, cholinergic neurotransmission, lipid and cholesterol metabolism, methyl-group metabolism, and transmembrane signaling
Choline
Retinaldehyde
(11-cis) is the essential form of vitamin A that is required for normal
vision, whereas
retinoic acid is necessary for normal morphogenesis,
growth, and cell differentiation.
is the most prevalent carotenoid
with provitamin A activity in the food supply
β-Carotene
VIt A deficiency
This condition
includes milder stages of night blindness and conjunctival xerosis (dryness)
with Bitot’s spots (white patches of keratinized epithelium
appearing on the sclera) as well as rare, potentially blinding corneal
ulceration and necrosis.
Keratomalacia (softening of the cornea) leads
to corneal scarring
Any stage of xerophthalmia should be treated with
60 mg (or RAE) of vitamin A in oily solution, usually contained in a soft-gel capsule.
The same dose is repeated 1 and 14 days later. Doses should be
reduced by half for patients 6–11 months of age. Mothers with night
blindness or Bitot’s spots should be given vitamin A orally–either 3
mg daily or 7.5 mg twice a week for 3 months
Infants 6–11 months of age should
receive 30 mg vitamin A;
children 12–59 months of age, 60 mg.
For reasons that are not clear, vitamin A supplementation has not
proven useful in high-risk settings for preventing morbidity or death
among infants 1–5 months of age.
vit a toxicity
Acute toxicity is manifested by increased intracranial pressure, vertigo, diplopia, bulging fontanels (in children), seizures, and exfoliative dermatitis
represents the classic disease of
vitamin D deficiency. Signs of deficiency are muscle soreness, weakness,
and bone pain. Some of these effects are independent of calcium
intake.
Rickets
There are two natural forms of vitamin K:
vitamin K1, also known as
phylloquinone, from vegetable and animal sources, and vitamin K2,
or menaquinone, which is synthesized by bacterial flora and found in
hepatic tissue. Phylloquinone can be converted to menaquinone in
some organs.