Nutrition Basics & Macronutrients
Know the three macronutrients, how many calories each provides, and why protein matters so much for healing.
Nutrients are divided into macronutrients (carbohydrates, proteins, fats — they provide energy) and micronutrients (vitamins and minerals — no calories, but essential for body processes). Energy is measured in calories (kcal).
- Carbohydrates4 kcal/g
- Body's main energy source; spares protein. Sources: grains, fruit, starchy vegetables, sugar.
- Protein4 kcal/g
- Tissue building & repair, wound healing, immune function, fluid balance. Sources: meat, fish, eggs, dairy, beans, soy.
- Fat9 kcal/g
- Concentrated energy, insulation, absorbs fat-soluble vitamins. Sources: oils, butter, nuts, fatty meats.
- Alcohol7 kcal/g
- (Not a nutrient — "empty" calories.) Beer, wine, liquor.
Protein & Healing
- Protein needs increase with wounds, burns, surgery, infection, and pressure injuries — the body needs the building blocks to rebuild tissue.
- Complete proteins (animal sources, soy) contain all essential amino acids; incomplete proteins (most plants) must be combined (e.g., rice + beans).
- Albumin and prealbumin are lab markers of protein/nutrition status. Low albumin = poor nutrition and poor wound healing.
Nitrogen Balance & BMI
- Positive nitrogen balance = building tissue (growth, pregnancy, healing). Negative nitrogen balance = breaking down tissue (starvation, severe illness, burns).
- BMI: <18.5 underweight · 18.5–24.9 normal · 25–29.9 overweight · ≥30 obese.
Carbs and protein both give 4 calories per gram. Fat gives more than double — 9 calories per gram. Alcohol is in between at 7. So when a question asks which nutrient is most calorie-dense, the answer is fat.
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Therapeutic Diet Progression
After surgery or a GI rest, diets advance from nothing → clear liquids → full liquids → soft → regular, as tolerated.
- NPOnothing by mouth
- No food or fluids. Before surgery/procedures, acute GI bleed/obstruction, before certain tests, aspiration risk.
- Clear liquid
- See-through liquids: water, clear broth, apple/cranberry/grape juice (no pulp), plain gelatin, popsicles, clear soda, tea, black coffee. No milk, no orange juice. First diet after surgery, bowel prep, acute GI upset. Not nutritionally complete — short term only.
- Full liquid
- Anything liquid at room temperature: clear liquids PLUS milk, ice cream, pudding, custard, strained creamed soups, vegetable juice, refined cooked cereals (cream of wheat). Step between clear liquid and soft/regular.
- Pureed
- Blended to a smooth, no-chew consistency. For dysphagia, swallowing problems, after oral/jaw surgery.
- Mechanical soft
- Chopped, ground, mashed, soft-cooked foods; no tough meats, nuts, or raw crunchy foods. For chewing difficulty, poor dentition, missing teeth.
- Regular
- No restrictions.
Advancing the Diet After Surgery
The typical post-op progression is clear liquids → full liquids → soft → regular, advanced as the patient tolerates and once bowel sounds return / the patient passes flatus. If the patient becomes nauseated or distended, hold and return to the previous step.
A clear liquid diet provides fluid and some energy but lacks protein, fat, and most vitamins. It should only be used short term. If a patient is stuck on clear liquids for more than a few days, expect the team to add supplements or advance the diet.
The simplest test: can you see through it? If yes (broth, apple juice, gelatin) → clear liquid. If it's opaque (milk, ice cream, cream soup) → full liquid. Milk and orange juice are the classic "trap" foods that are NOT clear liquids.
Condition-Specific Diets
Match the disease to the diet — these pairings show up constantly on the exit exam.
- Heart failure / hypertension
- Low sodium (2–3 g/day), low fat (DASH). Avoid canned soups, processed/deli/cured meats, pickles, salty snacks, table salt. Read labels.
- Diabetes
- Carbohydrate-controlled / consistent carb. Spread carbs evenly, choose complex carbs & fiber, limit simple sugars. Consistency keeps blood glucose stable.
- CKD (pre-dialysis)
- Low protein, low sodium, low potassium, low phosphorus, fluid restriction. "Limit the P's." Avoid salt substitutes (high in potassium). On dialysis = MORE protein needed.
- Liver failure / hepatic encephalopathy
- Low protein, high carbohydrate. Less protein → less ammonia for a failing liver to clear → less confusion.
- Gout
- Low purine. Avoid organ meats, anchovies, sardines, shellfish, red meat, gravy, and beer. Increase fluids.
- Celiac disease
- Gluten-free. Avoid wheat, barley, and rye. Rice, corn, and potato are safe.
- Acute diverticulitis / IBD flare
- Low-residue (low fiber). Rests the bowel during a flare.
- Diverticulosis / constipation prevention
- High-fiber, increased fluids. Note: high fiber PREVENTS, but is avoided during an acute flare.
- Dumping syndrome (post-gastrectomy)
- High protein, high fat, low carb; small frequent meals. Drink fluids BETWEEN meals, not with them. Lie down after eating.
Both restrict protein but for opposite reasons. Renal (CKD, pre-dialysis): limit protein, potassium, phosphorus, sodium, and fluid. Liver (hepatic encephalopathy): low protein specifically to lower ammonia. And remember the twist — a kidney patient who is ON dialysis needs more protein, not less.
High-purine foods to avoid spell out a "surf and turf" theme: organ meats, anchovies, sardines, shellfish, red meat, and beer. Purines break down into uric acid, which triggers gout attacks. Push fluids to flush uric acid.
Vitamins, Minerals & Deficiencies
Fat-soluble vitamins are stored (toxicity risk); water-soluble vitamins wash out (need them daily).
Fat-Soluble vs Water-Soluble
- Fat-soluble = A, D, E, K. Stored in liver and fat, need dietary fat to absorb, and can build up to toxic levels.
- Water-soluble = B-complex and C. Not stored well (B12 is the main exception), excreted in urine, must be replaced daily → deficiencies appear faster.
- Vitamin Afat-soluble
- Vision, skin, immunity. Deficiency: night blindness, dry eyes.
- Vitamin Dfat-soluble
- Calcium absorption, bone health. Deficiency: rickets (children), osteomalacia (adults).
- Vitamin Kfat-soluble
- Blood clotting. Deficiency: bleeding/bruising. Newborns get an IM vitamin K injection at birth.
- Vitamin Cwater-soluble
- Collagen, wound healing, iron absorption. Deficiency: scurvy — bleeding gums, poor wound healing.
- B1 thiamine
- Nerve & energy metabolism. Deficiency: beriberi; Wernicke-Korsakoff (alcoholism).
- B3 niacin
- Energy metabolism, skin. Deficiency: pellagra — the "3 D's": dermatitis, diarrhea, dementia.
- B9 folate / folic acid
- DNA & red cell formation. Deficiency: neural tube defects in pregnancy; megaloblastic anemia.
- B12 cobalamin
- Nerve function, red cell formation. Deficiency: pernicious anemia + neuro symptoms (needs intrinsic factor to absorb).
Key Minerals
- Iron: needed for hemoglobin; deficiency causes anemia. Take on an empty stomach with vitamin C to boost absorption; give liquid iron through a straw (stains teeth); expect dark/black stools and possible constipation.
- Calcium: bone and muscle; absorbed with vitamin D.
- Potassium & sodium: see the Fluid & Electrolytes guide for imbalance details.
The four fat-soluble vitamins spell ADEK. They're the ones that can reach toxic levels because the body stores them. Everything else (B-complex and C) is water-soluble — the body flushes the extra out in urine, so you need a steady daily supply.
Folic acid (vitamin B9) taken before and during early pregnancy prevents neural tube defects such as spina bifida. This is why women of childbearing age are advised to get adequate folate (about 400–800 mcg/day). A common teaching/priority question.
Food-Drug Interactions
A handful of these are tested almost every exam — especially warfarin and MAOIs.
- Warfarin (Coumadin)
- Vitamin K — green leafy vegetables (spinach, kale, broccoli, Brussels sprouts). Vitamin K opposes warfarin. Teach consistent intake, not avoidance — keep greens steady week to week.
- MAOIs
- Tyramine — aged cheese, cured/smoked meats, draft beer, red wine, fermented soy, overripe avocado. Can trigger a hypertensive crisis. Strictly avoid tyramine-rich foods.
- Tetracyclines & fluoroquinolones
- Dairy, calcium, antacids, iron. Bind the drug → decreased absorption. Separate doses by ~2 hours.
- Statins, some calcium channel blockers
- Grapefruit juice raises drug levels → toxicity. Avoid grapefruit.
- Levodopa (Parkinson's)
- High-protein meals, vitamin B6 → decreased absorption/effect. Avoid taking with high-protein meals.
- Lithium
- Low sodium raises lithium → toxicity. Keep sodium and fluid intake consistent.
- Potassium-sparing diuretics (spironolactone)
- Salt substitutes, high-potassium foods → risk of hyperkalemia. Avoid salt substitutes (they're potassium chloride).
This is the most dangerous food-drug interaction tested. A patient on an MAOI who eats aged cheese, cured meats, or drinks draft beer/red wine can have a sudden, severe rise in blood pressure with a pounding headache. Teach strict avoidance of tyramine-containing foods.
Students often think the answer is "stop eating green vegetables." It isn't. The correct teaching is to keep vitamin K intake steady — the same general amount each week — so the warfarin dose stays balanced. Big swings up or down are what cause problems.
? What is the correct warfarin teaching about green leafy vegetables — avoid them, or eat them consistently?
Dysphagia & Aspiration Precautions
Difficulty swallowing is common after stroke and in the elderly — and aspiration is the danger.
Dysphagia is difficulty swallowing. Common causes include stroke, Parkinson's disease, head/neck cancer, and advanced age. The major risk is aspiration — food or fluid entering the airway — which can cause pneumonia.
Warning Signs of Dysphagia
- Coughing or choking while eating or drinking
- A wet or "gurgly" voice after swallowing
- Pocketing food in the cheeks; drooling
- Long meal times, food refusal, unexplained weight loss
Aspiration Precautions
- Sit fully upright (90° / high Fowler's) for meals and stay up for 30–60 minutes after.
- Chin-tuck position — slightly flex the head forward when swallowing (helps close the airway).
- Thicken thin liquids (to nectar or honey consistency) — thin liquids are the hardest to control.
- Small bites, slow pace, one texture at a time; minimize distractions.
- Place food on the unaffected (stronger) side of the mouth after a stroke.
- Keep suction available; have a speech-language pathologist (SLP) evaluate swallowing.
It seems backwards, but water and juice are more dangerous than pudding for a patient with dysphagia — thin liquids move fast and are easily aspirated. That's why they get thickened. Always stay with a dysphagia patient during meals and watch for coughing.
High Fowler's (upright 90°) + chin tuck + thickened liquids + food on the strong side + remain sitting up 30–60 min after eating. If a question asks the priority intervention to prevent aspiration, sitting the patient fully upright is almost always the answer.
Enteral Nutrition (Tube Feedings)
For a patient who can't eat by mouth but has a working gut — and aspiration is still the top risk.
Enteral nutrition delivers formula directly into a working GI tract through a tube. It's used when a patient can't take food orally (dysphagia, intubation, decreased level of consciousness, severe anorexia) but the gut still digests and absorbs.
- NG / OG tube: nose or mouth to stomach — short term (under 4–6 weeks).
- PEG / gastrostomy (G-tube) / jejunostomy (J-tube): surgically placed — long term.
Safe Tube-Feeding Practice
- Verify placement: X-ray confirms position after insertion (gold standard). Before each feeding, check the external tube length/marking and aspirate gastric contents to check pH (gastric pH is usually ≤ 5). Auscultating an air bolus is NOT a reliable check.
- Head of bed up 30–45° during the feeding and for at least 30–60 minutes after — the single most important step to prevent aspiration.
- Check gastric residual volume (GRV) before intermittent feedings; hold and notify the provider if it's high (often > 250–500 mL per facility policy). Return the aspirate to avoid losing electrolytes.
- Flush with about 30 mL of water before and after feedings and medications, and between medications.
- Give medications in liquid form when possible; do not crush enteric-coated or sustained-release tablets.
- Use formula at room temperature (cold formula causes cramping).
Always confirm tube placement and raise the head of the bed to at least 30° before feeding. If the patient vomits, becomes distended, or has a high residual — hold the feeding and notify the provider. Aspiration pneumonia is the complication you're guarding against.
Diarrhea is common with enteral feeding. Don't automatically stop it — consider slowing the rate, checking formula concentration/temperature, and reviewing medications (many liquid meds contain sorbitol). A fiber-containing formula may help.
Parenteral Nutrition (TPN)
IV nutrition that bypasses the gut — high glucose, central line, and never stopped abruptly.
Total parenteral nutrition (TPN) delivers complete nutrition (dextrose, amino acids, lipids, electrolytes, vitamins) directly into the bloodstream when the GI tract can't be used (bowel obstruction, severe malabsorption, prolonged NPO). Because it's very hypertonic and high in dextrose, TPN is given through a central line. (Lower-concentration PPN can go peripherally, short term.)
Key Nursing Responsibilities
- Monitor blood glucose (often every 4–6 hours) — hyperglycemia is common because of the high dextrose load.
- Never stop TPN abruptly → rebound hypoglycemia. Taper it down. If the next bag isn't ready, hang D10W and notify the provider.
- Strict aseptic technique — a central line bathed in dextrose is a prime site for infection/sepsis. Change tubing and bag every 24 hours.
- Run at the ordered rate via pump — don't speed it up to "catch up" or slow it down to make up for being behind.
- Monitor daily weights, strict I&O, and electrolytes. Watch for refeeding syndrome (falling phosphorus, potassium, magnesium) in malnourished patients — start slow.
- Don't add medications to the TPN bag.
The body ramps up insulin to handle TPN's heavy glucose load. Stop it suddenly and that insulin causes rebound hypoglycemia. If the next bag is delayed or unavailable, hang D10W at the same rate and call the provider — do not just turn it off.
Think of the trio: Glucose (hyperglycemia from the dextrose), Infection (central line sepsis — aseptic technique), and don't stop it Suddenly (rebound hypoglycemia). If you remember Glucose, Infection, and "no Sudden stops," you've got most TPN questions covered.
Frequently Asked Questions
Common student questions on this topic.
What is the difference between a clear liquid and a full liquid diet?
What diet is ordered for a patient with chronic kidney disease (CKD)?
What foods should a patient on warfarin (Coumadin) watch out for?
How do I prevent aspiration during tube feedings?
What is refeeding syndrome and who is at risk?
What is the difference between fat-soluble and water-soluble vitamins?
Quick-Reference Cheatsheet
Every key point from this guide on a single printable page.
Nutrition & Diet Therapy Cheatsheet
One-page PDF — free download.