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With the background as to the metabolic changes we can better define the appropriate mix of macronutrients, namely carbohydrates, fat and protein. Because of the hormonal imbalance favoring excess glucose production, there is a well defined limit as to the quantity of carbohydrates which can be effectively metabolized. That value appears to be 7 to 8 grams/kg/day or 55-60% of Kcals provided, preferably in the form of complex carbohydrates, using the enteral route. Because of intense anti insulin activity, insulin is often required. If severe hyperglycemia persists, glucose intake needs to be decreased.

Fat or fatty acids are utilized to a limited degree especially when compared to starvation. In addition certain fatty acids are immunosuppressive. No more than 25% of Kcals should be provided as lipids.

Protein should makeup 20-25% of Kcals because amino acids are used at an excessive rate for fuel and also required for increased protein synthesis. Obviously not all the protein provided will be used for energy but 25% of total Kcals assures sufficient amino acid availability for both energy and synthesis. Micronutrients must be provided as well.

Glutamine is the most abundant amino acid in the body composing two thirds of the amino acid pool. Under normal conditions glutamine is a non-essential amino acid and requirements can be met by endogenous production. Synthesis occurs mainly in skeletal muscle from any of the other amino acids in muscle protein via the generation of alpha ketoglutatrate which then can be converted to glutamate and then glutamine. However, in stress states such as trauma and burns, glutamine is considered a conditionally essential amino acid and exogenous glutamine is essential, as endogenous production is totally inadequate to meet the increased needs. A glutamine deficiency state is well recognized immediately after burns and trauma or critical illness. They key intra and extra-cellular functions of glutamine are therefore impaired.

The Macronutrients include protein carbohydrates and fat.

Protein intake correlates best with healing and preservation of lean mass. All proteins are not alike and one should select proteins with the best biologic value.  This term refers to the quality of the amino acids, i.e. those most commonly used for protein synthesis.  Milk proteins and egg albumin re the best.  Components of proteins include peptides which can either be produced by standard protein breakdown in the GI tract or components of a nutrient supplement, where protein is provided as a hydrolysis.  Peptides, besides not requiring energy for absorption, also have biological activities such as anabolic and wound healing properties.

Carbohydrates are the primary source of energy. Carbohydrates are provided as simple sugars and as complex carbohydrates. Sugars are absorbed rapidly and can lead to hyperglycemia especially after a burn. Complex carbohydrates are broken down and
absorbed more slowly, thereby used snore efficiently.  Foods and supplements should be chosen which have less sugar and more
complex carbohydrates.

Fat can be provided in a number of forms. Fat in foods is absorbed primarily as long chain triglycerides which are carried to the liver in the form of chylomicrons Polyunsaturated fats are preferred over saturated fatty acids over the long term but Stake little difference
in the delivery of calories during the stress response.

Medium chain triglycerides (MCT) are all excellent source of calories and are burned like carbohydrates, therefore do not require lipoprotein transport. Hypertriglycendemia, i.e. over 250mg/dl reflects excess fat intake. MCT's do riot raise triglyceride levels. They
are provided independent of regular foods in man made supplements rich in MCT's or manufactured in the forth of structured lipids which contain a high MCT content. Omega-3 fatty acids are preferred over the more standard Omega-6 because the latter leads to
increased prostaglandins which are immunosuppressive and vasoactive.

 

MACRONUTRIENT CHOICES

PROTEIN AND PEPTIDES

PROTEINS WHOLE PROTEIN High biologic value - milk, egg albumin best Lactalbumin, casein, whey proteins

 

PEPTIDES Small peptides - hydrolyzed proteins with a molecular weight less than 1000 daltons, typically dipeptides and tripeptides Passively absorbed across the brush border of the intestinal mucosa by non-energy-dependent diffusion, whereas free amino acids are absorbed by active transport In cases of a compromised intestinal tract, peptides may be better absorbed than free amino acids Stimulate better nitrogen retention than do either intact proteins or free amino acid

 

CARBOHYDRATES

COMPLEX CARBOHYDRATES

Gut breakdown and absorption is gradual, minimizing increases in blood glucose and insulin surges Optimum way of delivering carbohydrates

SIMPLE SUGARS

Rapidly absorbed for immediate energy use Increased glucose and insulin producing fat

 

POLYUNSATURATED FATTY ACIDS (PUFA)

PUFAs contain two of more double bonds on the carbon chain Essential fatty acids required for membrane integrity, eicosanoid synthesis fat soluble vitamin transport, cell-cell interaction Can be classified into two major families, w-3 and w-6 (w refers to the location of the first double bond from the terminal methyl end of the carbon chain) Both omega-3 and omega-6 fatty acids produce eiconsanoids, prostaglandins, and leukotrienes Most current enteral products contain and elevated rationof omega-3 and omega-6 fatty acids

 

MEDIUM CHAIN TRIGLYCERIDES (MCTs)

MCT's typically contain eight to 12 carbon chains Excellent immediate source of energy More readily available as energy source compared to long chain (LCT) Do not require chylomicron formation for absorption, rapidly transported tot eh liver for B oxidation Do not require carnitine for oxidation