21.1: Nutritional Concepts

Learning Objectives

By the end of this section, you will be able to:

• Explain how nutrition supports energy production
• Recognize nutrients used for energy in the body
• Recall nutrients used for regulation in the body
• Describe optimal nutritional status for proper bodily functioning

The science of nutrition has impacted clinical care in significant ways. As scientists learn more about the roles and uses of nutrients in health and medicine, new and improved nutritional guidelines and recommendations are developed. The dietary reference intake (DRI) are scientifically developed reference values that set baseline standards and guide recommendations for daily nutritional intake. The U.S. Department of Agriculture (USDA) uses recommended dietary allowances (RDAs), which provide general guidelines for consuming the nutrients that make up a healthy diet each day. RDAs help guide mealtime planning and food choices and aid in the development of food labels. They are based on DRIs to guide nutrition policy in the United States. reference daily intake (RDI) is the average daily intake of a population. It is important for nurses to develop a sound understanding of nutrition science and clinical judgment skills regarding the implementation of healthy dietary practices. This section provides an overview of nutrient metabolism and regulation.

Energy Production

Human life cannot exist without energy. Energy fuels all the physiological demands of the human body. It is required for cellular growth, development, and regulation. It powers musculoskeletal movement, cognitive function, and neuromuscular reflexes. All living cells in the human body depend on energy derived from adenosine triphosphate (ATP). ATP is a molecule that releases energy when converted to adenosine diphosphate (ADP). This stepwise process is known as cellular respiration. Energy-rich nutrients (carbohydrates, fats, and proteins) are chemically broken down to provide ATP. ATP is then oxidized and converted to ADP, carbon dioxide, and water. Energy release in the form of ADP fuels all cellular functions within the body. To meet the body’s metabolic demands, carbohydrates, proteins, and fats must be consumed and either digested or stored to meet the ongoing energy demands of the body.

Metabolic Requirements

The process by which substances are chemically broken down to meet the body’s nutrient and energy needs is metabolism. The energy needs of the body require the consumption and metabolism of carbohydrates, proteins, and fats in significant quantities. These three energy-rich nutrients provide a consistent amount of energy per gram of nutrient. The calorie is a unit of measure for energy. Both carbohydrates and proteins provide four calories of energy per gram of nutrient, while fats provide nine calories per gram. The rate at which calories burn is called the basal metabolic rate (BMR). A high metabolic rate burns calories faster than a slow metabolic rate. Many factors influence metabolic rates, including age, sex, activity level, genetics, and overall fitness. Underlying medical conditions also significantly affect both metabolic rates and needs. Nutritional wellness occurs when cells burn calories efficiently and excess energy is stored effectively, thus achieving metabolic homeostasis.

The goal of metabolic homeostasis is to balance caloric intake with caloric need. Metabolic imbalance negatively impacts overall wellness and can occur when either too many or too few calories are consumed to meet the body’s immediate needs. When calories consumed exceed caloric need, excess energy is stored as fat, which can lead to weight gain and the development of obesity, metabolic syndrome, and other chronic medical conditions. Caloric deficits can be just as detrimental. When caloric need outweighs caloric intake, a caloric deficit occurs, and the body turns to energy stores to meet energy needs. Carbohydrates, stored as glycogen in the liver, are metabolized first, followed by energy stored in fat cells. If a caloric deficit is prolonged and starvation ensues, the body will metabolize proteins, which can lead to life-threatening medical conditions and death. Metabolic homeostasis is essential to healthy living.

Body Weight Standards

Across a person’s life span, body weight is greatly affected by caloric imbalances. Overconsumption and underconsumption of calories can result in body weight alterations that negatively impact overall health. Thus, it is important for individuals to achieve and maintain an ideal body weight. The measure of ideal body weight (IBW) correlates with positive health benefits. An individual’s IBW is influenced by individual characteristics such as height, weight, body frame, age, and sex. General guidelines have been developed using these characteristics to identify IBW standards. IBW can be a helpful tool when analyzing nutritional health based on generalized standards.

The measure of body mass index (BMI) is a commonly used tool that analyzes height and weight to provide a measurement relative to generalized standards. The Centers for Disease Control and Prevention (CDC) classifies BMI into the following categories: underweight, healthy weight, overweight, and obese (Table 21.1). A calculated BMI is based on an individual’s height, weight, age, and sex and can be a helpful tool in determining an individual’s relative fitness and overall wellness. Since body fat distribution can naturally differ by ethnicity, and other factors (such as exercise) can impact BMI, it should not be used as the only determination of nutritional and related health. There are many BMI calculators available on the web.

BMI	Weight Status
Below 18.5	Underweight
18.5–24.9	Healthy weight
25.0–29.9	Overweight
30.0 and above	Obese

Table 21.1 BMI Interpretation for Weight Status (Centers for Disease Control and Prevention, 2022.)

Link to Learning

BMI is a tool commonly used to provide a measurement relative to the IBW standard. The CDC provides a BMI calculator to make calculating BMI easy.

Waist circumference is another commonly used measure. Waist circumference is a relative indicator of excess fat storage deposited in the midsection; it is often used as a relative measure to gauge overall caloric balance. Growth charts are used to analyze body height and weight standards across the continuum of growth and development in children through adulthood. The CDC and the World Health Organization (WHO) have developed growth charts for use in clinical settings to track physical growth trends.

Link to Learning

The CDC has developed growth charts to track physical growth trends in infants and children. These charts are used to promote pediatric health.

Growth charts for infants include measurements of length, weight, and head circumference; charts for children and adolescents include measures of weight and height. Growth charts trend measurements according to percentiles, which compare a measure to an average. Thus, for a child in the fiftieth percentile for weight, 50 percent of children will be above and 50 percent of children will be below that child’s measure. Growth and BMI charts are useful tools for studying trends involving growth, development, and general nutrition.

Caloric Requirements

Energy is measured in calories. The energy-rich nutrients (carbohydrates, fats, and proteins) provide a substantial number of calories per unit of weight: Carbohydrates provide 4 cal/g, proteins provide 4 cal/g, and fats provide 9 cal/g. The USDA provides guidance on daily dietary recommendations including energy requirements. According to the USDA, human energy requirements range between 1,000 and 3,200 calories per day depending on the individual. Individual estimates of energy needs vary based on a variety of characteristics including age, sex, height, weight, health status, and level of physical activity.

Life-Stage Context

Caloric Needs of Older Adults

People age 65 years and older are considered older adults. Older adults are more likely to experience chronic illness and disease. They have lower caloric needs than younger people, though they still need a diet full of nutrient-dense foods because their nutrient needs increase. The caloric needs of older adults decrease due to decreases in activity, metabolic rates, and muscle mass. Chronic disease and medication can contribute to decreased nutrient absorption.

Protein and vitamin B12 are commonly underconsumed in older adults. Protein is necessary to prevent loss of muscle mass. Vitamin B12 deficiency can be a problem for older adults because absorption of vitamin B12 decreases with age and with certain medications. Adequate hydration is also a concern for older adults because feelings of thirst decrease with age, which can lead to poor fluid intake. Additionally, older adults may be concerned with bladder dysfunction so they may consciously choose to limit fluid intake. Loneliness, diminished ability to chew and swallow, and poverty can also decrease dietary intake in older adults. Organizations such as Meals on Wheels, local senior centers, and other community programs can provide socialization and well-balanced meals to older adults.

Nutrients for Energy

Carbohydrates, proteins, and fats are energy-rich nutrients consumed on a daily basis to meet the body’s caloric needs. Each of these three nutrients is considered a macronutrient because large quantities of each are consumed daily to meet the body’s energy needs. Each of these energy-rich nutrients is metabolized at the cellular level to release energy used to fuel cellular functions. Carbohydrates break down into sugars for quick release of energy to meet immediate caloric needs. Excess sugars are converted to glycogen and stored in the liver; they can be converted back to glucose for release in the bloodstream as glucose when needed. When blood glucose levels drop, fat cells, also known as lipids, break down to meet immediate caloric needs. Fat cells are complex molecules that provide a slow but very efficient release of energy. Proteins are larger molecules made up of amino acids that also provide a slow release of energy. When carbohydrate and fat energy stores are depleted, proteins are metabolized to provide needed energy. These three energy-rich macronutrients are essential to life and work in concert to meet the body’s need for fuel.

Carbohydrates

A macronutrient used to fuel the immediate energy needs of the body is a carbohydrate. Carbohydrates are classified as simple (monosaccharides and disaccharides) or complex (oligosaccharides and polysaccharides). Simple carbohydrates are also known as sugars. Glucose, a monosaccharide, is the body’s primary energy source; it is used to meet immediate energy needs. When glucose is transported into a cell, it undergoes cellular metabolism, which releases ATP and energy. Larger, complex carbohydrates are broken down by enzymes into monosaccharides to be metabolized for energy. Every gram of carbohydrate provides 4 calories of energy. Carbohydrates should make up 45 to 65 percent of a healthy diet.

Simple and complex carbohydrates differ in significant ways, though all are made up of carbon, hydrogen, and oxygen. Sugars typically taste sweet and are found in foods like honey and fruits. Complex carbohydrates are longer sugar chains that are digested in the intestines and broken down into monosaccharides that can then be used by the cells. They release energy more slowly than simple sugars. Starches, fiber, and glycogen are complex carbohydrates. Starches are polysaccharides that are digested by enzymes in the intestinal tract. Rice and potatoes are examples of starches. Dietary fiber is broken down in the large intestine by bacteria rather than metabolized by enzymes. Soluble fiber is found in fruits, vegetables, whole grains, and legumes; it helps control blood sugar by reducing absorption of postprandial blood sugar in the gut. Insoluble fiber, such as cellulose, is a bulking agent for stool.

Proteins

A macronutrient made up of amino acids is a protein; they are much larger molecules than carbohydrates. There are twenty different amino acids used by the human body. Nine of these amino acids must be consumed within the diet. These are referred to as essential amino acids. The other amino acids can be synthesized within the body. All proteins are made of strings of amino acids called polypeptides. During digestion, proteins are broken down into smaller units that can then be used to make new proteins. Proteins are essential to human life. They are the main building blocks for muscle, skin, and connective tissue and are involved in the growth, maintenance, and repair of body tissues. Enzymes, hormones, and hemoglobin are proteins. While proteins are not a primary source of energy, they can be broken down for glucose metabolism if cells are starved for energy. Proteins yield 4 calories of energy for every gram of nutrient.

Dietary proteins should make up 10 to 15 percent of an individual’s daily caloric intake. There are situations where protein needs are higher, such as in growing children or when a person is pregnant, lactating, or experiencing a critical illness. However, excessive dietary protein can be harmful to individuals with underlying kidney impairment. Thus, it is important to maintain a protein intake that is healthy and also balanced for individual nutritional needs. Meat, poultry, eggs, and seafood are all good sources of animal protein. Unfortunately, some of these protein sources are associated with high levels of saturated fat, which can negatively impact health and should be limited in a healthy diet. Protein from plants, such as soy products, nuts, seeds, and legumes, can supply adequate amounts of protein as well, though these sources are not metabolized as efficiently as animal protein. The USDA recommends a balanced intake of animal and plant protein. Table 21.2 compares the protein content of animal- and plant-based foods, information that is useful for developing a balanced diet while reducing saturated fat content.

Type	Source	Measure	Protein Content
Animal based	Whey powder	3 scoops	50 g
	Beef	3 oz	29 g
	Turkey	3 oz	26 g
	Lamb	3 oz	25 g
	Pork	3 oz	25 g
	Salmon	3 oz	23 g
	Chicken	3 oz	20 g
	Cod	3 oz	19 g
	Milk	8 oz	9 g
	Yogurt	4 oz	9 g
	Egg	1 whole	6 g
Plant based	Black beans	1 cup	42 g
	Peanuts	1 cup	36 g
	Pumpkin seeds	1 cup	35 g
	Almonds	1 cup	29 g
	Tofu	0.5 cup	22 g
	Edamame	1 cup	13 g
	Kidney beans	1 cup	8 g
	Peas	1 cup	8 g
	Broccoli	1 cup	6 g
	Spinach	1 cup	5 g

Table 21.2 Protein Content (Source: U.S. Department of Agriculture, Agricultural Research Service, Beltsville Human Nutrition Research Center, 2024.)

Fats

A large, complex molecule made up of fatty acids and glycerol is a fat. Fats, also known as lipids, are a highly efficient source of stored energy, releasing energy when needed at a very slow, measured rate. Each gram of fat releases 9 calories of energy.

Cholesterol and triglycerides are important lipids within the body. They are associated with essential functions including brain function, hormone regulation, and energy production. Adipose tissue, commonly found in subcutaneous fat, is composed of fat cells that help regulate energy supply within the body. Energy, in the form of excess blood sugar, is converted to lipids and stored as adipose tissue for future use. When glucose stores are depleted, the body turns to these fat stores for energy by breaking down the triglycerides in adipose tissue into simple sugars, which then release energy for immediate use within the body. Cholesterol is a key component of cell membranes; it is transported, along with triglycerides, throughout the body by protein-based compounds called lipoproteins. Lipoproteins, which are classified according to the ratio of lipid to protein, bind to cholesterol and triglycerides for transport through the body. Low-density lipoproteins (LDLs) are essential for healthy cellular function but in excess are associated with increased cardiovascular risk. LDL is often referred to as “bad cholesterol” and can be found in high-fat diets that contain fried foods, red meat, high-fat dairy products, and processed baked goods. High-density lipoproteins are considered “good cholesterol” and are beneficial to cell function. Examples of good cholesterol include nuts, seeds, fish, and legumes.

Lipids are either saturated or unsaturated; unsaturated fats may be monounsaturated or polyunsaturated. Saturated fats are associated with increased cardiovascular risk, leading to atherosclerosis, coronary artery disease, and stroke; they should be limited in a healthy diet. Animal products contain saturated fat, while fat derived from plants typically contains unsaturated fat. Trans fats are human-made fats derived from partially hydrogenated oil. Eliminating trans fats from the diet is recommended because these fats are associated with development of atherosclerosis and adversely affect cholesterol levels. The USDA recommends limiting the consumption of dietary fat to 28 percent or less of daily caloric intake. Saturated fat should be limited to 8 percent or less.

Nutrients for Regulation

Energy-dense macronutrients are not the only nutrients needed to regulate body function. Other nutrients, such as electrolytes, vitamins, minerals, and water, are required for growth, development, and maintenance of regulatory processes in the human body. Electrolytes, such as sodium, potassium, and calcium, are considered macronutrients because they are needed in relatively large quantities. Water is also a macronutrient. A micronutrient is a nutrient found in small quantities within the body but which is still necessary for physiological functions. Vitamins and minerals are examples of micronutrients. Table 21.3 lists the RDA of vitamins and minerals for children, and Table 21.4 lists the RDA of vitamins and minerals for adults.

Age	6–11 Months	1–2 Years	2–3 Years	4–8 Years	9–13 Years	14–18 Years
Calories (kCal)		800	1,000	1,200–1,400	1,600–1,800	1,800–2,200
Protein (g)	11	13	13	19	34	46–52
Carbohydrates (g)	95	130	130	130	130	130
Vitamin A (µg)	500	300	300	400	600	700–900
Vitamin D (IU)	400	600	600	600	600	600
Vitamin E (mg)	5	6	6	7	11	15
Vitamin K (µg)	2.5	30	30	55	60	75
Vitamin C (mg)	50	15	15	25	45	65–75
Thiamine (mg)	0.3	0.5	0.5	0.6	0.9	1.0–1.2
Riboflavin (mg)	0.4	0.5	0.5	0.6	0.9	1.0–1.3
Niacin (mg)	4	6	6	8	12	14–16
Vitamin B6 (µg)	0.3	0.5	0.5	0.6	1.0	1.2–1.3
Folate (µg)	80	150	150	200	300	400
Vitamin B12 (µg)	0.5	0.9	0.9	1.2	1.8	2.4
Calcium (mg)	260	700	700	1,000	1,300	1,300
Phosphorous (mg)	275	460	460	500	1,250	1,250
Magnesium (mg)	75	80	80	130	240	360–410
Iron (mg)	11	7	7	10	8	11–15
Zinc (mg)	3	3	3	5	8	9–11
Sodium (mg)	370	1,200	1,200	1,500	1,800	2,300
Potassium (mg)	860	2,000	2,000	2,300	2,300–2,500	2,300–2,600

Table 21.3 Daily Nutritional Goals for Children (Source: U.S. Department of Agriculture & U.S. Department of Health and Human Services, 2020.)

Age	19–30 Years	31–50 Years	51+ Years
Calories (kCal)	2,000–2,400	1,800–2,200	1,600–2,000
Protein (g)	46–56	46–56	46–56
Carbohydrates (g)	130	130	130
Vitamin A (µg)	700–900	700–900	700–900
Vitamin D (IU)	600	600	600
Vitamin E (mg)	15	15	15
Vitamin K (µg)	90–120	90–120	90–120
Vitamin C (mg)	75–90	75–90	75–90
Thiamine (mg)	1.1–1.2	1.1–1.2	1.1–1.2
Riboflavin (mg)	1.1–1.3	1.1–1.3	1.1–1.3
Niacin (mg)	14–16	14–16	14–16
Vitamin B6 (µg)	1.3	1.3	1.5–1.7
Folate (µg)	400	400	400
Vitamin B12 (µg)	2.4	2.4	2.4
Calcium (mg)	1,000	1,000	1,000–1,200
Phosphorous (mg)	700	700	700
Magnesium (mg)	310–400	320–420	320–420
Iron (mg)	8–18	8–18	8
Zinc (mg)	8–11	8–11	8–11
Sodium (mg)	2,300	2,300	2,300
Potassium (mg)	2,600–3,400	2,600–3,400	2,600–3,400

Table 21.4 Daily Nutritional Goals for Adults (Source: U.S. Department of Agriculture & U.S. Department of Health and Human Services, 2020.)

Vitamins

A vitamin is an essential micronutrient, vital to biochemical regulation within the human body. Vitamins are exogenous (not made by the body) and must be ingested as part of a healthy diet. They are classified by solubility. Vitamins are either absorbed and transported in water (water soluble), or they are absorbed and transported in fat (fat soluble). The body’s ability to absorb both fat- and water-soluble vitamins can be affected by various medical conditions. Many drugs can interfere with absorption and metabolism of vitamins. Vitamins can be toxic if taken in excess, but vitamin deficiencies can also have detrimental effects. Therefore, scientists have determined RDA for many vitamins to help reduce associated risks.

Vitamin C and the complex of B vitamins are examples of water-soluble vitamins: that is, they dissolve in water. Water-soluble vitamins are eliminated in the urine fairly quickly, so toxicities are rare. Deficiencies are often due to lack of access to quality food. Vitamin C is found in citrus fruits, vegetables, and potatoes. It helps regulate collagen, hormone, and amino acid production and assists with iron absorption and wound healing. The complex of B vitamins helps regulate a variety of physiological and neurological processes. Common B vitamins include B1 (thiamine), B2 (riboflavin), B3 (niacin), and B12 (cyanocobalamin). Foods rich in B-complex vitamins include meat, fish, eggs, and legumes.

Fat-soluble vitamins dissolve in lipids. Common fat-soluble vitamins include vitamin A, vitamin D, and vitamin K. Vitamin A is essential to maintain vision and healthy skin and is found in fish liver oils, egg yolks, and vegetables. Vitamin D helps build and maintain healthy bones and is not found naturally in food. Instead, vitamin D is absorbed through direct sunlight, though many fortified foods now contain vitamin D. Vitamin K promotes blood clotting and reduces bleeding risk and is found in dark green, leafy vegetables. Vitamin E is a fat-soluble vitamin with antioxidant properties, protecting cells against the effects of free radicals. Foods rich in vitamin E include vegetable oils, peanuts, and leafy greens. Many fat-soluble vitamins are stored in the liver and can have toxic effects on the body if taken in excess.

Minerals

Another essential component of physiological processing is the mineral. Some minerals are macronutrients, and some are micronutrients. Electrolytes are macronutrient minerals that are essential to cardiac, musculoskeletal, and neurological functions. They help maintain water balance and acid-base balance. Important electrolytes include sodium, potassium, calcium, phosphorous, and magnesium. Each of these electrolytes must be balanced within a tight therapeutic range to maintain homeostasis and avoid harmful effects.

Some minerals are micronutrients and are found in minute quantities within the body. These minerals, also known as trace minerals, have RDA to avoid toxicities. Important trace minerals include iodine, iron, and zinc. Iodine is essential to thyroid hormone production and is mainly found in sea salt. Iron is an important component of blood, specifically hemoglobin. It is found in animal products. Zinc is essential to immune and metabolic processes and can be found in many meat products.

Water

Water is an essential macronutrient that must be maintained in homeostatic balance to avoid the detrimental effects of both over- and underhydration. Two-thirds of the volume of total body water (TBW) are found inside body cells (intracellular). The other third is extracellular and found in the vascular system and interstitial fluids (Figure 21.2a). TBW is roughly 50 to 60 percent of overall body weight, but the amount is age dependent (Figure 21.2b). Water is ingested and absorbed in the digestive tract and regulated by various mechanisms: the thirst mechanism, kidney function, pituitary function, and osmosis. The body loses about a liter of fluid a day through urine, sweat, and so on. Thus, the average recommended daily intake of water is 2.5 L to maintain adequate kidney function and vital capacity.

Figure 21.2 (a) Total body water is a critical component of a person’s health. Many structures of the human body are mostly water. (b) As people age, the percentage of their bodies that consists of water decreases. (credit a: modification of work from Anatomy and Physiology. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license; credit b: data source: Lu, H., Ayers, E., Patel, P., & Mattoo, T. K. (2023). Body water percentage from childhood to old age. Kidney Research and Clinical Practice, 42(3), 340–348. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Optimal Nutritional Status

The human body performs best under conditions of optimal nutrition. Nutrient deficiencies can compromise the body and affect both physical and mental functioning. Likewise, excessive nutrient intake can result in toxicity. Homeostatic balance is the goal for both macro- and micronutrients. The USDA provides recommendations for daily nutrient intake and guidance on how to support daily patterns of healthy eating to promote optimal health across the life span.

Optimal nutrition begins before birth. During pregnancy, higher levels of macronutrients are needed to support the growth and development of the fetus. Following birth, good nutrition is vital to maintaining the rapid growth and development of the infant. Throughout each life stage, (infancy, toddlerhood, childhood, adolescence, adulthood, pregnancy/lactation, and older adulthood), optimal nutrition is foundational to healthy living and human flourishing. When optimal nutrition is not achieved, over time malnutrition occurs, which can lead to various negative outcomes depending on the nutritional deficit.

Patient Conversations

What If Your Patient Is on a Fad Diet?

Scenario: Nurse is completing an admissions assessment on a patient being admitted with anemia, beginning with height and weight measurement. The patient sees that she weighs 140 pounds and smiles at the nurse.

Nurse: Ms. Erving, I see you’re happy with your weight, huh?

Patient: Yes, I am! I’ve been on a diet for two months now, and I’ve lost over 30 pounds!

Nurse: Really? That’s a lot of weight very quickly. What diet are you currently on?

Patient: I’m only eating fruits. It’s called a fruitarian diet. I can eat all the fruit I want.

Nurse: So, you just eat fruit? Nothing else? No protein, dairy, grains, or vegetables?

Patient: Yes, that’s right.

Nurse: Did you know that your body requires optimal nutrition to remain healthy? That includes a healthy balance of macronutrients and micronutrients. When your body doesn’t get these important things in your diet, you can develop nutritional deficits.

Patient: I didn’t know that. I thought my weight was the most important thing to be healthy, and being overweight was unhealthy.

Nurse: Sure, being overweight can be unhealthy, but you can be an average weight for your height and still be unhealthy. I saw in your initial lab tests that your calcium, iron, vitamin B12, and vitamin D are all low. Have you been feeling tired since you started your diet?

Patient: Actually, I have, but I didn’t think it was related to what I was eating because fruit is healthy, and I was losing weight.

Nurse: Restricting your diet to only one food group is not a healthy way to lose weight. Your body needs a variety of vitamins and minerals to stay healthy. If it’s OK with you, I’d like to have the nutritionist come and talk to you about how you can incorporate healthy foods into your diet for optimal nutrition and maintain a healthy weight.

Patient: Thank you, that would be great.

Malnutrition

An imbalance between the nutrients consumed and nutrients needed leads to malnutrition. These nutritional imbalances can result in both undernutrition and overnutrition and can involve both macronutrients and micronutrients. The RDA are a helpful tool to identify individuals at risk (see Table 21.3 and Table 21.4). However, malnutrition is multifactorial, and careful clinical follow-up is necessary to minimize long-term negative impacts of poor nutrition.

Undernutrition

Undernutrition is a state of malnutrition in which there is inadequate intake or impaired absorption of nutrients in the body. Undernutrition can be experienced across a person’s life span. It often refers to calorie or protein deficits (macronutrient undernutrition), but it also includes deficiencies in vitamins and minerals (micronutrient undernutrition). Low calorie intake is a common cause of undernutrition and is commonly associated with poverty, homelessness, mental disorders, and cognitive disorders. Caloric intake can also be affected by medical conditions that restrict ingestion of food, such as dysphagia, or conditions that interfere with absorption in the gastrointestinal tract.

Caloric deficits result in the breakdown of fats to meet the body’s energy needs. Prolonged caloric deficits will deplete fat stores and stimulate the metabolism of proteins, thus causing the breakdown of muscle and tissues. Prolonged caloric deficits can lead to starvation and the visible wasting of muscle and fat. In the same manner, poor caloric intake will lead to deficiencies in essential vitamins and nutrients. The negative impact of these deficits on the body depends on the cause and severity of the deficiency. Populations most at risk include individuals with low income and those living in poverty, those who are chronically ill, children, and older adults.

Overnutrition

The WHO now includes overnutrition as a form of malnutrition. Overnutrition results from an excessive intake of nutrients, far beyond the body’s need. Overnutrition results in excessive weight gain and obesity. Obesity is associated with a BMI of thirty or higher; severe obesity is associated with a BMI of forty or higher. Increasingly, children are experiencing obesity, causing the CDC to develop growth charts for children that extend the BMI-for-age (see Link to Learning: Pediatric Growth Charts). Obesity affects many aspects of health. It is associated with low socioeconomic conditions and discrimination, as well as mental stress resulting in depression and anxiety. It is a lead indicator for the development of cardiovascular disease, metabolic syndrome, diabetes, and various respiratory and musculoskeletal disorders. The population most at risk includes individuals with low incomes and those living in poverty due to the scarcity of nutritious whole, unprocessed foods. Individuals with sedentary lifestyles are at risk as well.

Hydration

As shown in Figure 21.3, the human body maintains water homeostasis through a balance of ingestion and elimination. Most water is ingested by drinking fluids, such as plain water, juices, and caffeinated beverages. Ingested water also comes from food, especially fruits and vegetables. Water that is visible and measurable as it is lost is called sensible fluid loss. Urination is an example of sensible fluid loss. Insensible fluid loss cannot be measured. An example of insensible loss is water vapor lost through breathing. Adequate hydration will balance the water that enters and exits the human body. An imbalance in hydration can lead to either a fluid volume deficit or fluid volume overload. Both of these conditions present problems, but for very different reasons.

Figure 21.3 The human body maintains water homeostasis by ingesting and producing water and eliminating it through a number of processes. Water loss can be increased in dry climates or when a patient has diarrhea. (CC BY 4.0; Rice University & OpenStax)

Dehydration

A fluid volume deficit is called dehydration; this occurs with inadequate water intake or excessive water loss or both. Conditions associated with dehydration include vomiting, diarrhea, prolonged fevers, and excessive sweat due to heat stroke. Some neurological conditions can impair the thirst mechanism or impair the ability to swallow, which can lead to poor fluid intake. In some cases, sodium levels are altered. Volume depletion can lead to kidney and cardiac impairment, and severe shock can result. Populations most at risk include infants and children, the chronically ill, and older adults.

Overhydration

Fluid volume overload, or overhydration, occurs with excess water intake or poor water elimination. These can lead to volume expansion affecting cardiac, respiratory, and kidney function. Impaired elimination of water in the body is a common consequence of chronic disease and is often associated with an alteration in sodium levels. The three chronic conditions that most commonly lead to overhydration are heart failure, kidney failure, and liver failure; pregnancy is another common cause of overhydration. Symptoms of fluid overload include pitting edema, ascites, and dyspnea and crackles from fluid in the lungs. Edema is swelling in dependent tissues due to fluid accumulation in the interstitial spaces. Ascites is fluid retained in the abdomen. Treatment depends on the cause of the fluid retention. Sodium and fluids are typically restricted, and diuretics are often prescribed to eliminate the excess fluid.

Clinical Safety and Procedures (QSEN)

QSEN Competency: Safety

Competent nurses will employ assessment skills to identify patients in fluid overload and to detect when they are improving or deteriorating. Take the example of Nurse Rita who works at an outpatient wound care clinic. Rita is taking care of 42-year-old Mr. Mahoney who has weekly wound care dressings scheduled for the next six weeks with labs. She has been his nurse for over five years at this same clinic.

Week 1: Blood pressure 110/65, heart rate 72, lungs clear bilaterally, Respirations 12, nonpitting edema on right lower extremity. Sodium 139, Potassium 4.2, Calcium 9.

Patient is calm, cooperative, and considers himself “a funny guy. Rita you are the best nurse here.”

Week 4: Blood pressure 130/75, heart rate 80, fine crackles in bilateral lower lung bases, Respirations 16, 2 + edema on lower extremities. Pt is calm, cooperative and stated “I love your new haircut Rita.”

Week 6: Blood pressure 160/85, heart rate 80, crackles heard in lower and upper lung fields bilaterally, Respirations 32, 3+ edema on lower extremities, clear drainage from right lower leg. Sodium 120, Potassium 3.1, Calcium 9.

Reports not sleeping well at night and using three pillows or sleeping in the recliner. Out of breath all the time. Produces little urine. When Rita asks about how he is sleeping, patient states “Who are you again?”

This patient has had several changes in his assessment. The competent nurse will recognize when a patient’s assessment changes and report these findings to the healthcare team. This patient needed further assessment and interventions at each assessment to prevent further deterioration.