Clinical Skills · Nutrition Assessment
Nutritional Concepts
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Nutrition How the body takes in, digests, absorbs, and uses food Full entry → is the process by which the body takes in food, breaks it down, absorbs it, and uses the resulting nutrients for energy, growth, and repair. Nutrients are organized into a few big classes: macronutrients (carbohydrates, proteins, and fats — needed in large amounts and providing energy), micronutrients (vitamins and minerals — needed in small amounts to regulate body processes), and water, which is essential to every one of those processes. Energy from food is measured in kilocalories, and nutrients the body cannot make in sufficient amounts — essential nutrients — must come from the diet.
Nurses are not dietitians, but they must understand these basics because almost every clinical problem has a nutritional dimension: wounds need protein to heal, anemia is linked to iron status, bone health depends on calcium and vitamin D, and immune function relies on adequate intake. This topic builds the vocabulary and framework the rest of the chapter — factors affecting nutrition, specialized diets, and nutritional assessment — depends on.
Why this matters
- Nutrition underpins healing and recovery. Surgical incisions, pressure injuries, fractures, and infections all require nutrients — especially protein and energy — to repair tissue.
- Malnutrition changes outcomes. People who are undernourished have weaker immunity, slower wound healing, more complications, and longer hospital stays.
- Medications and food interact. Some drugs must be taken with food, others on an empty stomach, and some change appetite or nutrient absorption — nurses help patients manage these.
- Nurses screen, teach, and refer. Recognizing poor intake, monitoring weight, and flagging concerns for the provider and registered dietitian are everyday nursing tasks.
- It is the foundation of this chapter. Understanding what nutrients do makes the later topics — why intake fails, what diets change, and what assessment measures — make sense.
The college version
Core Concepts
Macronutrients: fuel and building blocks
- Carbohydrates are the body's preferred fuel. Simple carbohydrates (sugars) are absorbed quickly; complex carbohydrates (starches and fiber) provide longer-lasting energy. Fiber, a carbohydrate the body cannot digest, supports bowel function. Glucose, the breakdown product, is the main fuel for the brain and muscles.
- Proteins are made of amino acids. Some amino acids are essential — the body cannot make enough of them, so food must supply them. Proteins with all essential amino acids (found in animal foods and soy) are called complete proteins; most plant proteins are incomplete and are often combined with other foods. Protein builds and repairs muscle and skin, forms enzymes and immune cells, and transports substances in the blood. Needs increase during illness, healing, and growth.
- Fats (lipids) are the most energy-dense nutrient, provide essential fatty acids, form cell membranes, and carry the fat-soluble vitamins. Fats differ in structure — saturated, unsaturated, and trans fats — which is why dietary guidance distinguishes among them. Because fats store energy efficiently, they are also the body's reserve fuel.
Micronutrients: vitamins and minerals
- Water-soluble vitamins (the B-complex vitamins and vitamin C) are not stored in large amounts; excess is excreted in urine, so they are generally needed regularly in the diet.
- Fat-soluble vitamins (A, D, E, and K) dissolve in fat and are stored in body tissues, so they do not need to be consumed as often — but very large amounts can accumulate.
- Minerals include macrominerals needed in larger amounts (such as calcium and phosphorus) and trace minerals needed in tiny amounts (such as iron, zinc, and iodine). They build bone, transport oxygen, and support enzyme and hormone function.
Specific vitamin and mineral targets come from published dietary guidelines (for example, the Dietary Reference Intakes, or DRIs) and vary by age, sex, and life stage. Do not memorize invented numbers — learn the concepts here and look up current values when needed.
Water: the essential nutrient people forget
Water is the largest single component of the body. It transports nutrients, regulates temperature, removes waste, and lubricates joints. Intake comes from fluids and from water in foods; output occurs through urine, sweat, breath, and stool. Fluid balance is delicate at the extremes of age: infants and older adults become dehydrated quickly, and illness (fever, vomiting, diarrhea) increases losses.
Energy balance
Energy in food is measured in kilocalories — the "Calories" on food labels. The body uses energy for basic life functions at rest (the Basal metabolic rate Energy the body uses at complete rest Full entry →, or BMR), plus everything added by activity, digestion, and stress. When intake exceeds expenditure, the body stores the surplus and weight rises; when expenditure exceeds intake, the body draws on stores and weight falls. Illness raises energy needs — fever, infection, surgery, and wound healing all increase metabolic demand — at exactly the time intake often drops.
Digestion and absorption: the journey of food
- Mouth: chewing and salivary enzymes begin breaking down carbohydrates.
- Stomach: acid and enzymes start protein digestion.
- Small intestine: most digestion and absorption happen here.
- Large intestine: water is reabsorbed and waste is formed.
Enzymes break macronutrients into absorbable pieces, which enter the blood or lymph. A practical nursing takeaway: you are what you absorb. A person can eat an adequate diet yet still become malnourished if disease of the gut (or surgery on it) blocks digestion or absorption.
Dietary guidance frameworks
Published guidance gives the public and clinicians a picture of a balanced diet. Common frameworks include the Dietary Reference Intakes (DRIs) — a family of values including recommended intake levels and upper limits — and MyPlate, a visual guide dividing a plate into fruits, vegetables, grains, and protein with dairy alongside. These are frameworks, not fixed laws: they are updated periodically and individualized by the care team for people with medical conditions.
Common Confusions
| Do not confuse | With | Difference |
|---|---|---|
| Carbohydrates being "bad" | Carbs being the preferred fuel | Quality and amount matter; the body runs on glucose |
| Fat-free foods | Calorie-free foods | Fat-free items can still be high in sugar and kilocalories |
| Vitamins providing energy | Vitamins supporting energy release | Only carbs, proteins, and fats supply usable energy |
| Protein being only for athletes | Protein being needed by everyone | Illness and healing increase protein needs for every body |
| A "Calorie" | A scientific calorie | One food Calorie = one kilocalorie (1,000 small calories) |
| Eating enough food | Absorbing enough nutrients | GI disease or surgery can block absorption |
Eli explains
The same idea, in plain words
Explain it like I’m 10
Food is fuel and building blocks for your body. Carbohydrates are like the fast fuel, proteins are the bricks used to build and fix things, and fats are the reserve fuel tank. Vitamins and minerals are tiny workers that keep everything running, and water is the oil that keeps the whole machine moving. Eating a variety of foods makes sure the body has all of them.
Worked example
Mr. Osei, age 52, had gallbladder surgery and is now on a light diet after a period of nothing by mouth. His body's energy needs are higher than usual because fever and tissue repair raise his metabolic rate. The nurse notices he has eaten less than half of his tray and tells a student: "His intake is down while his needs are up — that puts him in negative energy balance, which means weight loss and slower healing if it lasts." The plan follows: small, frequent meals; an antiemetic per order to control nausea; protein-rich choices as tolerated; and the nurse tracks his intake, tolerance, and weight. This walkthrough shows how the abstract idea of energy balance becomes a concrete nursing observation and response.
Key takeaways
- Macronutrients (carbs, proteins, fats) provide energy and structure; micronutrients (vitamins, minerals) regulate processes; water is essential to all of them.
- The kilocalorie is the unit of food energy — one food-label "Calorie" equals one kilocalorie.
- Essential nutrients cannot be made in sufficient amounts and must come from food.
- Fat-soluble vitamins (A, D, E, K) are stored; water-soluble vitamins (B, C) are not — an exam favorite.
- Complete proteins contain all essential amino acids (animal foods, soy); most plant proteins are incomplete.
- Energy balance — intake versus expenditure — determines weight gain, loss, or stability.
- Illness raises metabolic demand, often while appetite falls — a double risk for malnutrition.
- Fiber is a complex carbohydrate the body cannot digest; it supports bowel health.
Check yourself
5 review questions from the chapter. Try each one, then open the answer.
Name the three macronutrients and the two classes of micronutrients.
Show answer
Macronutrients: carbohydrates, proteins, and fats. Micronutrients: vitamins and minerals.
What is the difference between water-soluble and fat-soluble vitamins?
Show answer
Water-soluble vitamins (B-complex, C) are not stored in large amounts and are generally needed regularly; fat-soluble vitamins (A, D, E, K) are stored in fat tissue and can accumulate.
Define Energy balance Food intake versus energy expenditure Full entry → and state what happens in each direction.
Show answer
Energy balance is food intake versus energy expenditure. Intake greater than expenditure produces weight gain; expenditure greater than intake produces weight loss.
Why does illness raise the risk of malnutrition even when a person is eating?
Show answer
Illness raises metabolic demand (fever, healing, infection) at the same time it often reduces appetite and intake — a double hit that can quickly produce a deficit.
What is an Essential nutrient A nutrient the body cannot make in enough quantity Full entry →, and why does that matter for the diet?
Show answer
An essential nutrient cannot be made in sufficient amounts by the body, so it must come from food; without it, deficiency diseases or impaired function develop.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- Nutrition
- How the body takes in, digests, absorbs, and uses food
- Macronutrient
- Nutrient needed in large amounts: carbohydrate, protein, fat
- Micronutrient
- Nutrient needed in small amounts: vitamin or mineral
- Kilocalorie
- The energy unit used for food ("Calorie" on labels)
- Essential nutrient
- A nutrient the body cannot make in enough quantity
- Complete protein
- A protein containing all essential amino acids
- Water-soluble vitamin
- Vitamin not stored in large amounts (B-complex, C)
- Fat-soluble vitamin
- Vitamin stored in fat tissue (A, D, E, K)
- Basal metabolic rate
- Energy the body uses at complete rest
- Energy balance
- Food intake versus energy expenditure
- Digestion / absorption
- Breaking food down / taking nutrients into the body
Sources & references
This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.
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