Nutrition and Metabolic Stress

http://evolve.elsevier.com/Grodner/foundations/ Nutrition Concepts Online

One of the first body functions affected by impaired nutritional status is the immune system.

Role in Wellness

In its never-ending quest to maintain homeostasis, the human body responds to stress, physiologic or psychologic, with a chain reaction that involves the central nervous system and hormones that affect the entire body. Magnitude and duration of the stress determine just how the body will react. It is important for nurses to understand metabolic changes that take place in reaction to stress, both in uncomplicated stress that is present when patients are at nutritional risk and in more multifarious variations that result from severe stress brought about by trauma or disease.

Immune System

One of the first body functions affected by impaired nutritional status is the immune system. When metabolic stress develops, hormonal and metabolic changes subdue the immune system’s ability to protect the body. This activity is further depressed if impaired nutritional status accompanies the metabolic stress. A deadly cycle often develops: impaired immunity leads to increased risk of disease, disease impairs nutritional status, and compromised nutritional status further impairs immunity. Recovery requires that this cycle be broken.

Role of Nutrition

For the immune system to function optimally, adequate nutrients must be available. A well-nourished body will not be ravaged by infections the way a poorly nourished body will be. (See the Cultural Considerations box, The Process of Balance, for a multicultural perspective on balanced eating for good health.) To prove this point, think of the leading causes of death in industrialized countries such as the United States. The majority are chronic diseases associated with lifestyle. In developing countries, however, infections lead to high morbidity and mortality rates, especially in children, largely because of the high rate of protein-energy malnutrition (PEM). The majority of people in the United States who have serious problems with malnutrition and infections are (1) those with severe medical problems, (2) those who suffer from major metabolic stress, (3) those who suffer from a diseased state that causes metabolic stress and/or decreased nutrient intake and/or nutrient malabsorption, and (4) those who have poor nutritional intakes as a result of socioeconomic conditions (e.g., poverty, homelessness).

Cultural Considerations

The Process of Balance

What is a balanced way of eating for good health? To most Americans, the response is to eat foods from each of the food groups, with particular emphasis on fruits and vegetables. Among other cultures, foods consumed to achieve balance and good health do not follow the American food categories. The Chinese system of yin-yang sorts foods into yin (bean curd or tofu, bean sprouts, bland and boiled foods, broccoli, carrots, duck, milk, potatoes, spinach, and water) and yang (bamboo, beef, broiled meat, chicken, eggs, fried foods, garlic, gingerroot, green peppers, and tomatoes). Foods should be selected from each group to achieve balance. Which foods belong in each group may vary by region, but some foods such as rice and noodles are considered neutral. The overall goal is to maintain the harmony of the body with adjustments for climate variations and physiologic factors.

Balance is also the focus of the hot-cold classification of foods practiced in the Middle East, Latin American, India, and the Philippines. This concept is derived from the Greek humoral medicine based on the four natural world characteristics of air-cold, fire-hot, water-moist, and earth-dry related to the body humors of hot and moist (blood), cold and moist (phlegm), hot and dry (yellow/green bile), and cold and dry (black bile). Although this concept is related to the development of disease and their remedies, it also applies to foods. The hot and cold aspects of specific foods are emphasized. This does not relate to the actual temperature of the foods but to their innate characteristics. To achieve balance, eating cold foods offsets hot foods. The list of foods in each category varies among subgroups within each culture. Often, younger generations follow this concept but without knowing that it is based on the hot-cold theory of balance.

Application to nursing: Each of the cultures, subscribing to the yin-yang concept and the hot-cold theory, has sizable populations in the United States. When treating Americans of Chinese, Indian, Latino, Middle Eastern, and Filipino descent, these concepts of food selection to achieve health and harmony may affect client food choices. Although healthy selections are often selected, subtle effects may occur. For example, within the hot-cold theory, pregnancy may be considered “hot” as are vitamins. Consequently, vitamins are not taken during pregnancy because to do so would not restore balance. If a client seems unwilling to follow dietary and supplement recommendations, discussion of these classifications and ways to remedy the situation can be created.

Data from Kittler PG, Sucher KP: Food and culture in America: A nutrition handbook, ed 5, Belmont, Calif, 2007, Wardsworth.

Compromised nutritional status creates a vulnerable immune system by making it difficult to mount both a stress response and an immune response when confronted with a metabolic stress. A number of nutrients are known to affect immune system functioning. It is difficult to determine which specific nutrient factor results in symptoms when a patient is malnourished because of overlapping nutrient deficiencies combined with illness and accompanied by weakness, anorexia, and infection.¹

Immune system components affected by malnutrition include mucous membrane, skin, gastrointestinal tract, T-lymphocytes, macrophages, granulocytes, and antibodies. The effects on the mucous membrane are that the microvilli become flat, which reduces nutrient absorption and decreases antibody secretions. Integrity of the skin may be compromised as it loses density, and wound healing is slowed. Injury to the gastrointestinal tract because of malnutrition may increase risk of infection-causing bacteria spreading from inside the tract to outside the intestinal system. T-lymphocytes are affected as the distribution of T cells is depressed. The effect on macrophages and granulocytes requires that more time is needed for phagocytosis kill time and lymphocyte activation to occur. Antibodies may be less available because of damage to the antibody response ¹. Table 15-1 outlines how specific nutrient deficiencies affect immune system functions; note that fat and water-soluble vitamins, fatty acids, minerals, and protein are important for adequate functioning of most immune system components.

TABLE 15-1

ROLE OF NUTRIENTS AND NUTRITIONAL STATUS ON IMMUNE SYSTEM COMPONENTS

IMMUNE SYSTEM COMPONENT	EFFECTS OF MALNUTRITION	VITAL NUTRIENTS
Mucus	Decreased antibody secretions	Vitamin B₁₂, biotin, vitamins B₆ and C
Gastrointestinal tract	Flat microvilli, increased risk of bacterial spread to outside GI tract	Arginine, omega-3 fatty acids
Skin	Integrity compromised, density reduced, wound healing slowed	Protein, vitamins A and C, niacin, zinc, copper, linoleic acid, vitamin B₁₂
T-lymphocytes	Depressed T-cell distribution	Protein, arginine, omega-3 fatty acids, vitamins A, B₁₂, B₆, folic acid, thiamine, riboflavin, niacin, pantothenic acid, zinc, iron
Macrophages and granulocytes	Longer time for phagocytosis kill time and lymphocyte activation	Protein, vitamins A, C, B₁₂, B₆, folic acid, thiamine, riboflavin, niacin, zinc, iron
Antibodies	Reduced antibody response	Protein, vitamins A, C, B₁₂, B₆, folic acid, thiamine, biotin, riboflavin, niacin

The Stress Response

The body’s response to metabolic stress depends on the magnitude and duration of the stress. Stress sets up a chain reaction that involves hormones and the central nervous system that affects the entire body. Whether stress is uncomplicated (altered food intake or activity level) or multifarious (trauma or disease), metabolic changes take place throughout the body.

According to Gould,² the body’s constant response to minor changes brought about by needs or environment was first noted in 1946 by Hans Selye when he described the “fight or flight” response, or general adaptation syndrome (GAS). The body constantly responds to minor changes to maintain homeostasis. Research following Selye’s work has identified that the stress response involves an integrated series of actions that include the hypothalamus and hypophysis, sympathetic nervous system, adrenal medulla, and adrenal cortex.² Significant effects of this response to stress are outlined in Table 15-2. These responses to stress produce multiple changes in metabolic processes throughout the body. The effect of different levels of stress on metabolic rate is illustrated in Figure 15-1.

TABLE 15-2

EFFECTS OF THE STRESS RESPONSE *

TARGET ORGAN	HORMONAL RESPONSE	PHYSIOLOGIC RESPONSE	SIGNS/SYMPTOMS
Sympathetic nervous system and adrenal medulla	Norepinephrine	Vasoconstriction	Pallor, decreased glomerular filtration rate, nausea, elevated blood pressure
Adrenal medulla	Epinephrine	Vasoconstriction	See above
		Increased heart rate	Elevated blood pressure
		Vasodilation	Increased skeletal muscle function
		Central nervous system (CNS) stimulation	More alert, increased muscle tone
		Bronchodilation	Increased O₂
		Glycogenolysis, lipolysis, gluconeogenesis	Increased blood glucose
Adrenal pituitary and cortex	Cortisol (glucocorticoids)	CNS stimulation	Increased blood glucose, increased serum amino acids, delayed wound healing
		Protein catabolism, gluconeogenesis
		Stabilize cardiovascular system	Enhance catecholamine action
		Gastric secretion	Ulcers
		Inflammatory response decreased	Decreased white blood cells (WBCs)
		Allergic response decreased
		Immune response decreased
	Aldosterone (mineralocorticoid)		Retain sodium and water, increased blood volume, increased blood pressure
Posterior pituitary	Antidiuretic hormone	Water reabsorbed, increased blood volume, increased blood pressure
Other feedback mechanisms	Aldosterone and antidiuretic hormone	See above	See above

^*Possible complications include hypertension, tension headaches, insomnia, diabetes mellitus, infection, heart failure, peptic ulcer, and fatigue.

Data from Gould BE: Pathophysiology for the health-related professions, ed 3, Philadelphia, 2006, Saunders.

Starvation

If someone must involuntarily go without food, that can be defined as starvation. If we withhold food from ourselves, such as when we try to lose weight, that act can be defined as dieting or fasting. Whatever the cause of inadequate food intake and nourishment, results are the same. After a brief period of going without food (fasting) or an interval of nutrient intake below metabolic needs, the body is able to extract stored carbohydrate, fat, and protein (from muscles and organs) to meet energy demands.

Liver glycogen is used to maintain normal blood glucose levels to provide energy for cells. Although readily available, this source of energy is limited, and glycogen stores are usually depleted after 8 to 12 hours of fasting. Unlike glycogen stores, lipid (triglyceride) stores may be substantial, and the body also begins to mobilize this energy source. As the amount of liver glycogen decreases, mobilization of free fatty acids from adipose tissue increases to provide energy needed by the nervous system. After approximately 24 hours without energy intake (especially carbohydrates), the prime source of glucose is from gluconeogenesis.³

Some body cells, brain cells in particular, use mainly glucose for energy. During early starvation (about 2 to 3 days of starvation), the brain uses glucose produced from muscle protein. As muscle protein is broken down for energy, the level of branched-chain amino acids (BCAA) consisting of leucine, isoleucine, and valine increases in circulation, although they are primarily metabolized directly inside muscle.³ The body does not store any amino acids as it does glucose and triglycerides; therefore, the only sources of amino acids are lean body mass (muscle tissue), vital organs including heart muscle, or other protein-based body constituents such as enzymes, hormones, immune system components, or blood proteins. By the second or third day of starvation, approximately 75 g of muscle protein can be catabolized daily, a level inadequate to supply full energy needs of the brain.³ At this point, other sources of energy become more available. Fatty acids are hydrolyzed from the glycerol backbone, and both free fatty acids and glycerol are released into the bloodstream. Free fatty acids are used as indicated earlier, and glycerol can be used by the liver to generate glucose via the process of gluconeogenesis.

As starvation is prolonged, the body preserves proteins by mobilizing more and more fat for energy (Figure 15-2). Ketone body production from fatty acids is accelerated, and the body’s requirement for glucose decreases. Although some glucose is still vital for brain cells and red blood corpuscles, these and other body tissues obtain the major proportion of their energy from ketone bodies. Muscle protein is still being catabolized but at a much lower rate, which prolongs survival.

Fig 15-2 Metabolic changes in starvation. *FFA,* Free fatty acids; *RBC,* red blood cells; *WBC,* white blood cells. (From Simmons RL, Steed DL: *Basic science review for surgeons,* Philadelphia, 1992, Saunders.)

An additional defense mechanism of the body to conserve energy is to slow its metabolic rate, thereby decreasing energy needs. As a result of declining metabolic rate, body temperature drops; activity level decreases, and sleep periods increase—all to allow the body to preserve energy sources. If starvation continues, intercostal muscles necessary for respiration are lost, which may lead to pneumonia and respiratory failure. Starvation will continue until adipose stores are exhausted.

Severe Stress

Whether stress is accidental (e.g., from broken bones or burns) or necessary (e.g., from surgery), the body reacts to these stresses much as it does to the stress of starvation—with a major difference. During starvation, the body’s metabolic rate slows, becoming hypometabolic. During severe stress, the body’s metabolic rate rises profoundly, thus becoming hypermetabolic.

The body’s response to stress can be summarized by two phases: ebb phase and flow phase (Figure 15-3). The ebb phase, or early phase (Table 15-3), begins immediately after the injury and is identified by decreased oxygen consumption, hypothermia (lowered body temperature), and lethargy. The major medical concern during this time is to maintain cardiovascular effectiveness and tissue perfusion. As the body responds to injury, the ebb phase evolves into the flow phase, usually about 36 to 48 hours after injury.⁴ The flow phase is characterized by increased oxygen consumption, hyperthermia (increased body temperature), and increased nitrogen excretion, as well as expedited catabolism of carbohydrate, protein, and triglycerides to meet the increased metabolic demands.⁴ The flow stage will last for days, weeks, or months until the injury is healed.

TABLE 15-3

METABOLIC RESPONSES TO SEVERE STRESS

EBB PHASE	FLOW PHASE
↓ Oxygen consumption	↑ Oxygen consumption
↓ Cardiac output	↑ Cardiac output
↓ Plasma volume	↑ Plasma volume
Hypothermia	Hyperthermia
	↑ Nitrogen excretion
↓ Insulin levels	Normal or elevated insulin levels
Hyperglycemia	Hyperglycemia
Hypovolemia
Hypotension
↑ Lactate	Normal lactate
↑ Free fatty acids	↑ Free fatty acids
↑Catecholamines, glucagon, cortisol	↑ Catecholamines, glucagon, cortisol
Insulin resistance	↑ Insulin resistance

Multiple stresses result in increased catabolism and even greater loss of body proteins. Unfortunately, some stresses that patients are obliged to endure are iatrogenic. Think, for example, of the series of stresses a patient admitted for elective surgery might experience. Preoperatively, most surgical patients receive only clear liquids or nothing by mouth (NPO). After surgery, they may remain NPO until the return of bowel sounds, and then progress through clear liquid and full-liquid diets until they can tolerate food.

If the patient is in poor nutritional status before the stress of surgery, he or she is at greater risk for developing pneumonia or a wound infection accompanied by fever as a result of decreased protein synthesis. As in starvation, energy requirements will be met from endogenous sources (within the body) if exogenous sources (outside the body) are not available or adequate. Thus intercostal muscles may be depleted, leading to pneumonia, or inadequate amino acids may be available to synthesize antibodies, leading to impaired immune response to infection. Either complication has a negative impact on metabolic demands.

Nutrients affected by hypermetabolic stress include protein, vitamins, and minerals, as well as related nutritional concerns for total energy and fluid intake. During moderate metabolic stress, protein requirements have been reported to increase from 0.8 g/kg body weight (amount recommended for an average healthy adult) to 1 to 1.5 g/kg body weight and for severe stress (e.g., thermal injuries exceeding 20% total body surface area) can rise to 1.5 to 2 g/kg body weight.¹ These levels are based on sufficient energy consumption to allow for protein synthesis. Requirements of vitamins and minerals all increase during stress. Tissue repair especially depends on adequate intakes of vitamin C, zinc, calcium, magnesium, manganese, and copper. At the least, Dietary Reference Intake (DRI) levels of nutrients should be consumed, preferably from foods rather than from vitamin or mineral supplements. Achieving requirements through food intake also supports provision of sufficient kcal to meet increased energy demands during critical illness.

Several formulas have been used to determine the energy needs of patients experiencing hypermetabolic stress. The Mifflin-St. Jeor equation best predicts resting metabolic rate (RMR)⁵. Total energy expenditure can be determined by multiplying RMR by activity level and an injury factor.⁶ Activity level considers energy required if the patient is confined to bed or is ambulatory. Severity of injury is a factor based on whether the injury is caused by major or minor surgery, mild to severe infection, skeletal or blunt trauma, or burns (based on percentage of body surface area affected) (Box 15-1).

BOX 15-1

Medical Nutrition Therapy for Metabolically Stressed Patients

Energy requirements are highly individual and may vary widely from person to person. Total kcal requirements are dependent on the basal energy expenditure (BEE) plus the presence of trauma, surgery, infection, sepsis, and other factors. The most accurate method to determine energy needs is indirect calorimetry. When indirect calorimetry cannot be performed, use of predictive formulas is necessary.

Predictive Formulas

Formulas with the best prediction accuracy for critically ill patients are Penn State (2003a version), Swinamer, and Ireton-Jones (1992), while inaccuracy of predicted and actual energy needs result in under- or overfeeding.

Penn State