Protein

Muscle accounts for 45% of body weight in young adults. This drops to 27% in the very old, who chronically show a marked decrease in the size and strength of all skeletal muscle.1 Muscle changes are conspicuous in the small muscles of the hands and face and in the muscles of mastication. The facial muscles sag and become imbalanced. Chronic dietary protein inadequacy may be involved in depressed immune function, decreasing muscle strength, and poor wound healing in older adults.2

Until recently, it was thought that adults should ingest 0.8 g of protein per kilogram of weight daily,3 but recent guidelines have suggested an increase to 1 to 1.25 g of high-quality protein.4,5 The best sources of protein are meat and fish. These foods should be boiled (poached or braised), not fried; boiling prepares meats and fish for the gastrointestinal tract by breaking down the complex proteins into the more easily digested proteoses, whereas frying denatures and coagulates the proteins and makes them difficult to digest.1

Fat

The United States Food and Drug Administration (FDA) guidelines recommend a diet with 25 to 35% of its daily caloric intake in the form of fat. In addition, it advises that saturated fat intake be reduced to less than 10% of daily calories, and that cholesterol be limited to less than 300 mg daily.6,7 These recommendations are for all adults, with no differentiation for the elderly.

Carbohydrates

Current dietary guidelines from the United States Department of Agriculture (USDA)6 suggest that carbohydrates should compose from 45 to 65% of daily calories, and the complex carbohydrates (starches) are preferred over simple carbohydrates (sugars). More recently, carbohydrate intake of 130 g/day has been suggested for adults over 70 years of age, with a recommendation that “added sugars” (soft drinks, candy, desserts, etc.) make up no more than 25% of total energy intake.8

Water

Water, the most important nutrient in the diet, is essential to all body functions. Water loss from perspiration, elimination, and the lungs must be balanced every day by an adequate intake from drinking water, beverages, soups, and other foods, especially vegetables. If this balance is not maintained, and if water loss exceeds intake, chronic dehydration can result. Bariatric patients are particularly susceptible to negative water balance, often caused by excessive water loss through insufficient or damaged kidneys.

Mucosal surfaces become dry and easily irritated in the dehydrated patient. Insufficient fluid consumption in general (and water consumption in particular) can have a deleterious effect on salivary gland function and on overall health. The average sedentary male adult must consume at least 2900 mL of fluid daily, and the average sedentary female adult at least 2200 mL per day, in the form of noncaffeinated, nonalcoholic beverages, soups, and foods. Solid foods contribute approximately 1000 mL of water, with an additional 250 mL derived from the water of oxidation.9

Fiber

There is no definite requirement for dietary fiber in the daily diet of bariatric patients. Different kinds of dietary fiber contribute to the motility of the gastrointestinal tract. In studies of different populations, a diet rich in fiber seems to be correlated with decreased rates of cancer and cardiac disease. An increase in dietary fiber is prescribed in the treatment of several common diseases, namely constipation, hemorrhoids, diverticulosis, hiatal hernia, varicose veins, diabetes mellitus, hyperlipidemia, and obesity.10,11 The current recommendation is 14 g of fiber for every 1000 calories consumed per day,12 and the U.S. FDA requires that dietary fiber be listed on the nutrition facts panel on food labels.13

Calcium

Bone serves as the skeletal structure to which the muscles are attached and acts as a storehouse for calcium. Calcium is an essential mineral that is necessary for many functions in the body, including transmission of nerve impulses (lack of calcium leads to convulsions), cell membrane integrity, and blood coagulation. Bone serves as the internal source of calcium when the exogenous sources (dietary) become deficient.1,14

Adequate calcium intake is essential for bariatric patients of all ages. Milk and milk products are the best sources of calcium. Almost all of the approximately 2 to 3 pounds of calcium present in the body is concentrated in the bones and teeth. The calcium needs of bariatric patients are approximately 1000 mg per day.

The Process of Wound Healing

Several mechanisms are involved in wound healing, including inflammation, epithelialization, collagen synthesis, angiogenesis, collagen remodeling, and fibronectin-mediated wound contraction. This complex process occurs optimally when there is a sufficient supply of the raw materials—protein, carbohydrate, fat, vitamins, and minerals—that are needed to rebuild the damaged tissues. The lack of any of these important building blocks adversely affects healing.

Protein

Protein deficiency is a major factor in poor wound healing, primarily as a result of depression of fibroblast proliferation and thus of the syntheses of connective tissue ground substance (proteoglycans), collagen, new blood vessels, and remodeling of the healing site.16 For surgical patients, the recommended daily intake for protein rises to 2 to 4 g of protein per kilogram of body weight per day.17 The essential amino acids are those that cannot be synthesized via transamination; they must be ingested in food. One of these, methionine, has been shown to accelerate the rate of fibroplasia by its conversion to cystine. The mechanism is unclear, but formation of protein-strengthening disulfide bonds in collagen protein synthesis and self-assembly are critical to the stability of this complex molecule, which is essential in scar formation and healing.15 Another essential amino acid, histidine, influences the tensile strength of wounds. Deficiency of histidine in experimental animals reduced the strength of wounds; addition of histidine to the diet restored wound strength to normal levels.18

In protein deficiency, there is a protraction of the inflammatory phase of wound healing,19 in which proteolytic enzymes are secreted by macrophages and granulocytes, with a resulting 30 to 50% increase in proteolysis of the tissues around the wound site.20 Protein malnutrition is characterized by dry, flaking skin and by peripheral edema,21 which can mask malnutrition by concealing the amount of muscle wasting that has occurred in the patient.22 In addition, the tissue edema can impair nutrient diffusion to the wound.23 Hair appears dull, lacking normal color, and demonstrates increased pluckability. Muscle cramping and wasting also can be seen.24

Carbohydrates and Fat

The precise role of carbohydrates and fat in wound healing is less well known than that of proteins. Glucose is utilized as an energy source for cellular metabolism, including metabolism by those cells involved in wound healing. Leukocytes participate in phagocytosis and inflammatory activities, influencing growth factor release that stimulates the proliferation of fibroblasts needed for initial healing activities. Fats are essential components of cell membranes and are needed for synthesis of new cells. However, no known impairment of wound healing has been associated with a deficiency of essential fatty acids.25

Iron and Trace Minerals

Minerals play critical and interrelated roles in wound healing, especially in the processes involved in the synthesis of collagen. The enzymes essential to the synthetic process require cofactors to be present to catalyze the steps in the synthesis. These cofactors include magnesium,25 iron, manganese, copper, and calcium.17 Studies to date have not implicated nutritional deficiencies of manganese or copper in impairment of wound healing in patients with good oral intake, primarily because these elements are present in enough different foods that deficiency usually does not occur. A significant exception has been documented, however, in patients who received long-term TPN without additional supplementation of these minerals.26 Copper is important in erythropoiesis and in collagen stability.16

Severe iron-deficiency anemia, which is more common in bariatric patients, may reduce the bactericidal competence of leukocytes; this may be offset by a concomitant reduction in the rate of bacterial growth.16 Iron is essential for the restoration of normal red blood cell numbers following blood loss from surgery. The serum level of transferrin, a protein used to transport iron, is higher than normal in the iron-deficient patient, and its level of saturation with iron is low. Iron is also used as a cofactor in the hydroxylation of proline in the collagen synthetic pathway. A deficiency of iron decreases the structural integrity of collagen and hence decreases wound strength.

Zinc

In contrast to the trace minerals, a deficiency of zinc has markedly adverse effects on wound healing by decreasing the rate of epithelialization, reducing the rate of increase in wound strength, and reducing collagen strength. Zinc has been found to be a cofactor of enzymes responsible for cellular proliferation and protein synthesis (DNA polymerase, RNA polymerase, reverse transcriptase, and ribosomes). A deficiency would interfere with the cellular proliferation required in the wound-healing process, including that of inflammatory cells, epithelial cells, and fibroblasts. In addition, zinc acts to stabilize cell membranes by inhibiting lipid peroxidases and may play a role in the storage of vitamin A in the liver.16 Zinc deficiency also has a negative effect on the immune system by decreasing cellular and humoral immune function; the patient can become more susceptible to infections that may interfere with healing.

Experiments with high levels of zinc supplementation have been tried, in the unsuccessful attempt to accelerate the healing process. It is known that insufficient zinc impairs wound healing and that a return to normal blood levels results in a return to the normal rate of healing.28,29 Excessive zinc interferes with copper metabolism and with wound healing by affecting lysyl oxidase, the enzyme crucial to collagen cross-linking.16 The recommended daily allowance (RDA) for zinc is 15 mg for healthy adults.

Topical zinc oxide as a wound dressing has been found to enhance the re-epithelialization of partial-thickness wounds30 and to decrease inflammation.31

Vitamins

Vitamins are essential cofactors in many functions of the body, including wound healing. Vitamin C (ascorbic acid) is essential in the synthesis of collagen. Vitamin C deficiency produces a marked alteration in the healing process: without it, the primary sequence of amino acids in the collagen protein is improperly elaborated, the procollagen protein cannot be secreted from the fibroblast, and self-assembly of the collagen polymer cannot occur, as vitamin C is required for the hydroxylation of proline residues.

Consequences of vitamin C deficiency are incomplete wound healing and an increased risk for wound dehiscence.32 Scurvy is the clinical disease resulting from vitamin C deficiency, manifested as decreased integrity of bone, soft tissue, and small blood vessels. Because vitamin C is water-soluble, it is excreted renally and must be replenished frequently. The RDA for vitamin C is 60 mg per day. It has been suggested that adequate supplementation of vitamin C be given both pre- and postoperatively, in view of the possibility that surgical patients require more ascorbic acid than healthy persons.33

Vitamin A can influence the course of patients who receive systemic steroids by reversing the impaired healing effect that steroids have on lysosomal membranes34–36 and may be a cofactor in collagen synthesis and cross-linking.37 Vitamin A plays a role in cellular differentiation of epithelial cells; deficiency can lead to hyperkeratosis. Like zinc, it has been used as a topical agent to mitigate delayed epithelialization and closure of wounds. Deficiency of vitamin A also plays a role in the increase in the incidence of infections.38 Vitamin A appears to improve host defenses by enhancing cell-mediated immune function.39–43 It increases the number of antibody-producing cells, thus fostering antibody production, and can increase the phagocytic and tumoricidal ability of macrophages.44–47 In a well-nourished patient, vitamin A is stored in the liver in adequate amounts, as it is a fat-soluble vitamin.

Vitamin D is essential in the diet. Calcium therapy plus vitamin D have been used successfully in treating osteoporosis. Small amounts of fluoride may increase the effectiveness of calcium–vitamin D therapy. An adequate well-balanced diet, sunshine, and exercise are also recommended.

An excess of vitamin E delays wound healing and interferes with the beneficial effects of vitamin A. It is similar to steroids in the inhibition of collagen synthesis and wound healing.48,49 It has been tried as a topical agent for reduction of hypertrophic scar and keloid formation, but it has not been found to be particularly effective.

Vitamin K is used in the synthesis of prothrombin and clotting factors and plays a role in bone healing, where it is required for the synthesis of calcium-binding protein.50 Vitamin K deficiency results in excessive bleeding into the wound area during healing and can predispose the area to the development of infection.16 Other vitamins that contribute on a minor scale by aiding cross-linking of collagen are riboflavin, pyridoxine, and thiamine.51

It should be stressed that vitamin therapy alone is not a substitute for a well-balanced diet.

Alteration of Taste, Food Aversions, and Dumping Syndrome

One symptom reported by patients who have had gastric bypass surgery has been an aversion to certain foods, particularly to sweet food and to meat.60–63 It has been found that patients with Roux-en-Y gastric bypass (RYGBP) surgery reported significantly less intake of milk, ice cream, and sweet foods than those who had horizontal gastroplasty.64 The RYGBP patients also reported dizziness and nausea after consuming sweets that has been attributed to “dumping syndrome.” The syndrome is a physiologic response caused by rapid emptying of the sugary stomach contents into the small intestine, which leads to an osmotic imbalance, drawing water into the intestine and causing intestinal swelling, cramping, pain, nausea, diarrhea, and diaphoresis.

Patients undergoing RYGBP were found to have a lowering of their taste threshold to sweet (i.e., increased sensitivity to sweet) that led to the perception of sweet foods as unpalatable with resultant aversion. Half of the patients tested reported aversions to eating meat that may have resulted more from nausea than from the size of the bolus entering the reduced stomach pouch or from chewing fatigue than from actual changes in the way the meat tasted. Although decreased levels of zinc are known to alter taste sensation, there was no relationship found between alterations in plasma zinc concentration and changes in taste in this study. The authors concluded that in patients undergoing RYGBP surgery who experience changes in taste acuity for sweet foods or for meat, dietary modifications are necessary to prevent specific nutritional deficiencies.65