Nutritional Aspects of Malabsorption and Clinical Illness

Importance of Maintaining Body Protein

amino acids are constantly synthesized, degraded, and recycled

gluconeogenesis*, skin, hair, excretions are the major sources of negative protein balance

Þ 0.6 - 0.8 g/kg/day are needed to maintain a zero protein balance in healthy adults (more in kids, pregnancy)

starvation: body conserves protein by decreasing gluconeogenesis and using keto acids

severe stress (trauma, burns, sepsis): gluconeogenesis persists; basal energy use increases in proportion to the injury

Þ loss of lean body mass is accelerated in proportion to the severity of the injury (energy expended)

protein breakdown amounts to 14 - 20% of energy spent; 4 kcal/g Þ 35 - 50 g of protein per 1000 cal of energy

Þ protein and energy balance is a very important consideration in the critically ill

Nutrition Measurements

Measuring Energy Expenditure – or determining basal energy requirements

first done by Harris and Benedict in a giant human calorimeter

seal the subject off, measure O₂ use, CO₂ production, heat production, etc Þ Basal Energy Expenditure (also called basal metabolic rate)

BEE_men = 66.47 + 13.75(kg wt.) + 5.00(cm Ht.) - 6.75(yrs age)

BEE_women = 655.10 + 9.56(kg wt.) + 1.85(cm Ht.) - 4.68(yrs age)

BEE is energy of existing - no activity; energy increases with increasing activity (~20-30% increase over basal in a hospital patient)

energy expenditure can be measured at the bedside with O₂ consumption data

BEE falls during starvation, but increases with severe injury

Measuring Protein Use

measure protein nitrogen intake and compare to nitrogen lost in feces, shed skin, and urine

skin loss is negligible; fecal loss is about 1g/day Þ 24hr urea excretion in the urine is usually enough

Meeting Nutritional Requirements (parenteral/enteral feedings)

energy requirements to maintain a zero or positive balance must be met

injury factor: minor operation = 1.2; skeletal trauma = 1.35; sepsis = 1.60; severe burns = 2.10

enteral route is often ineffective, so total nutrition must be supplied IV

main source of energy is glucose
based on 15% of energy expenditure being from protein, the amount of protein required is calculated

protein is often increased to aid recovery from injury
if liver disease, must determine if there is hepatic encephalopathy - if so, need to decrease protein

safflower oil can provide essential fatty acids linoleic and arachadonic acid as IV emulsions (also provide 9 kcal/ml in energy!)
other nutrients and minerals are added as needed
hypertonic solutions can cause thrombosis of small veins and must be administered directly to the vena cava

chemically defined diets: administered via feeding tube - can be monomeric (elemental) or more complex

monomeric: crystalline amino acids, glucose/oligosaccharides, safflower oil, required vit, min, etc

requires no digestion Þ good for patients with limited enzyme, pancreas, liver function

more complex: peptides, corn starch, corn syrup or dextrins, safflower or corn oil, vit, min, etc

neither contain fiber so are good for people with severe colonic disease

hypertonic solutions administered via feeding tube can cause osmotic diarrhea

Medium Chain Triglycerides (C₈,C₁₀)

found in coconut oil

more water soluble than the usual plant and animal triglycerides (C₁₈)

normal triglyceride metabolism: TG Þ FA, monoglycerides via lipase Þ micelles via bile salts Þ TG resynthesis

medium chain triglycerides are absorbed directly and are able to bypass defects in these steps

advantages of medium-chain triglycerides

more rapidly hydrolyzed by lipase; micelle formation, not essential for medium chain trigclyceride absorption
more rapidly absorbed
absorbed intact (no lipase or bile needed)
transported via the portal vein as albuminbound FA (can bypass blocked lymphatics; no chylomicrons needed)
rapidly oxidized