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Carbohydrate and protein each yield about 4 kcal per gram, while fat yields about 9 kcal per gram and alcohol about 7 kcal per gram. These Atwater factors are used to estimate the energy content of foods and diets.
Vitamins A, D, E, and K are fat-soluble and are absorbed with dietary fat and stored in body tissues. The B-complex vitamins and vitamin C are water-soluble.
Vitamin C is required for collagen synthesis, and deficiency causes scurvy with bleeding gums, poor wound healing, and petechiae. Rickets results from vitamin D deficiency, pellagra from niacin deficiency, and beriberi from thiamin deficiency.
Soluble fibers such as pectin form gels and bind bile acids, increasing their excretion and lowering LDL cholesterol. Insoluble fibers such as cellulose and lignin mainly add bulk and promote laxation.
Bacteria multiply most rapidly between 41°F and 135°F, so perishable foods should be kept out of this range. Below 41°F growth slows, and above 135°F most pathogens are inhibited or killed during cooking.
Celiac disease is an autoimmune enteropathy triggered by gluten proteins from wheat, barley, and rye. Casein, albumin, and collagen are not the trigger.
In adults, BMI 18.5–24.9 is normal, 25–29.9 is overweight, and 30 or greater is obesity. Values below 18.5 indicate underweight.
Nectar-thick liquids are mildly thickened so they pour slowly and are easier to control orally than thin liquids. Thin liquids are regular consistency, spoon-thick liquids are much thicker, and solid foods are not liquids.
Vitamin C reduces ferric iron to ferrous iron and forms a soluble chelate, enhancing nonheme iron absorption. Calcium, tannins, and phytates inhibit absorption.
Oxalic acid binds calcium to form insoluble calcium oxalate, reducing absorption; spinach and rhubarb are high in oxalate. Vitamin D, lactose, and adequate protein do not reduce calcium absorption.
The glycemic index compares the blood glucose response to a fixed amount of available carbohydrate, so the type of carbohydrate and its rate of digestion are key. Fat, protein, and fiber can modify the response but are not the basis of the index.
Cereals such as rice are low in lysine, while legumes are rich in lysine but low in methionine; eaten together they provide a more complete amino acid pattern. The combination does not depend on fat or fiber content.
HACCP begins with hazard analysis to identify biological, chemical, and physical hazards, followed by determining critical control points, limits, monitoring, corrective actions, verification, and record keeping.
One carbohydrate exchange contains about 15 g of carbohydrate, 3 g of protein, and 80 kcal. This value is used for carbohydrate counting and meal planning.
A food providing 20% or more of the Daily Value per reference amount is considered high in that nutrient; 10–19% is a good source. Low means 5% or less.
Antidiuretic hormone increases water permeability in the renal collecting ducts, reducing urine output. Aldosterone promotes sodium reabsorption, atrial natriuretic peptide promotes sodium and water excretion, and insulin regulates glucose.
Lean body mass is metabolically active and raises basal metabolic rate, so muscular individuals have higher rates. Aging, fasting, and female sex are associated with lower basal metabolic rate.
DASH emphasizes fruits, vegetables, low-fat dairy, and reduced sodium to lower blood pressure. It is not designed to treat kidney stones or increase iron absorption, and it limits saturated fat.
Waist circumference above 35 inches in women and 40 inches in men indicates increased cardiometabolic risk. These cutoffs reflect abdominal adiposity independent of BMI.
Vitamin B12 requires intrinsic factor secreted by gastric parietal cells for absorption in the terminal ileum. Bile salts and pancreatic lipase aid fat digestion, and vitamin C aids iron absorption.
PKU is a deficiency of phenylalanine hydroxylase, so phenylalanine must be restricted while tyrosine, the product of that enzyme, becomes conditionally essential and must be supplied. Unrestricted protein would worsen phenylalanine accumulation.
Refeeding syndrome causes intracellular shifts of phosphate, potassium, and magnesium after carbohydrate reintroduction, with hypophosphatemia being characteristic. It can cause cardiac and respiratory failure if not monitored.
Catabolic stress such as burns increases protein breakdown and nitrogen excretion, producing negative nitrogen balance. Positive balance occurs in growth and recovery, and equilibrium occurs in healthy adults on adequate intake.
Rapid bolus feeding can overwhelm digestive capacity and cause dumping syndrome with cramping, diarrhea, and hypotension. Slower drip or pump feeding reduces this risk.
Linoleic acid (omega-6) and alpha-linolenic acid (omega-3) are essential because humans lack the desaturases to synthesize them. Oleic, stearic, and short-chain fatty acids can be synthesized or are not essential.
Carbohydrate and protein each provide about 4 kcal per gram, while fat provides 9 kcal per gram. Alcohol provides 7 kcal per gram but is not a nutrient. These factors are used in food energy calculations.
Vitamins A, D, E, and K are fat-soluble and require bile and micelles for absorption. Vitamin C and the B-complex vitamins, including B12 and folate, are water-soluble.
Protein supplies amino acids that are used to synthesize body proteins, enzymes, and other nitrogen-containing compounds. Energy production is a secondary role when carbohydrate and fat are insufficient. Fat, not protein, is the main storage form of energy.
Total body water is about 60% of body weight in adult men and about 50% to 55% in adult women. Lean tissue contains more water than adipose tissue, so body composition affects the percentage. Values outside this range suggest severe dehydration or overhydration.
Iodine is incorporated into thyroxine (T4) and triiodothyronine (T3) in the thyroid gland. Deficiency leads to goiter and impaired growth and development. Iron, calcium, and zinc have other primary functions.
The Institute of Medicine recommends 25 to 35 lb total gain for women with a normal prepregnancy BMI. Underweight women are advised to gain 28 to 40 lb, and obese women 11 to 20 lb. Inadequate or excessive gain increases maternal and fetal risks.
Bacteria multiply most rapidly between 40°F and 140°F, so perishable foods should be kept outside this range. Refrigeration below 40°F slows growth, and holding hot foods above 140°F limits it. The range applies to food safety practice.
Folic acid is added to enriched flour and other grain products to reduce the risk of neural tube defects. Fortification programs increased folate intake in the population. Vitamin B12, vitamin E, and calcium are not added for this purpose.
Soluble fiber binds bile acids in the intestine and increases their excretion. The liver then uses cholesterol to synthesize replacement bile acids, lowering serum LDL cholesterol. This is why oats, barley, and psyllium are recommended for cholesterol management.
Vitamin C is required for collagen synthesis, and deficiency causes scurvy with bleeding gums, poor wound healing, and petechiae. Beriberi is caused by thiamin deficiency, pellagra by niacin deficiency, and rickets by vitamin D deficiency.
Legumes are typically low in methionine and cysteine but rich in lysine. Cereal grains are the opposite, which is why combining legumes with grains improves protein quality. The limiting amino acid is the one present in the shortest supply relative to needs.
Serum ferritin reflects the amount of iron stored in the body and falls early in iron depletion. Hemoglobin and hematocrit indicate anemia but not the size of iron stores. Mean corpuscular volume changes later as iron deficiency progresses.
The liver breaks down glycogen to release glucose into the blood, helping maintain blood glucose during fasting. Muscle glycogen is used locally for muscle contraction and does not directly raise blood glucose. Fat is stored in adipose tissue, and essential amino acids must come from the diet.
Bile salts emulsify fat, breaking large fat globules into smaller droplets and increasing the surface area for pancreatic lipase. Lipase hydrolyzes triglycerides, and absorbed fatty acids are packaged into chylomicrons inside enterocytes. Bile itself does not hydrolyze fat.
Kwashiorkor is a protein-deficient form of malnutrition characterized by edema, fatty liver, and skin changes. Marasmus results from severe overall energy and protein deficiency and causes wasting without edema. Stunting is chronic linear growth failure.
The Mediterranean pattern emphasizes olive oil, fruits, vegetables, legumes, whole grains, fish, and nuts. It limits red meat, butter, and processed foods. This pattern is associated with lower cardiovascular risk.
The term 'reduced' means at least 25% less of the specified nutrient than the reference food. 'Low fat' means 3 g or less per reference amount, and 'fat free' means less than 0.5 g per reference amount. The 25% rule applies to other 'reduced' claims as well.
Gut bacteria synthesize vitamin K, which contributes to the body's vitamin K status along with dietary leafy greens. Vitamin C and B12 must come from the diet, and vitamin D is made in the skin or obtained from food. Colonic synthesis alone is not sufficient to meet all needs.
Lactase, located in the brush border of the small intestine, hydrolyzes lactose into glucose and galactose. When lactase activity is low, undigested lactose is fermented by colonic bacteria, causing gas, bloating, and diarrhea. Amylase, maltase, and sucrase digest other carbohydrates.
Hyperglycemia in TPN often reflects a dextrose infusion rate that exceeds the patient's tolerance. Reducing the dextrose concentration or adding insulin to the bag or via a separate infusion is appropriate. Lipids do not directly treat hyperglycemia, and stopping nutrition abruptly can cause rebound hypoglycemia.
Maple syrup urine disease is a defect in branched-chain alpha-keto acid dehydrogenase, causing accumulation of leucine, isoleucine, and valine. Treatment restricts these amino acids while meeting other protein needs. Phenylalanine restriction is used for phenylketonuria, not MSUD.
Carnitine shuttles long-chain fatty acids across the inner mitochondrial membrane for beta-oxidation. Without carnitine, long-chain fatty acid oxidation is impaired. Ketone body synthesis, glycogenesis, and fat-soluble vitamin absorption do not require carnitine as a primary cofactor.
Vitamin B6 is a coenzyme for kynureninase in the tryptophan-to-niacin pathway. Beta-carotene conversion requires vitamin A enzymes, vitamin D synthesis requires UV light, and homocysteine remethylation requires vitamin B12 and folate. B6 also participates in transamination and heme synthesis.
Thiamin deficiency, often seen in chronic alcohol use, causes Wernicke encephalopathy and Korsakoff psychosis. Thiamin is a coenzyme for glucose metabolism, and deficiency impairs brain energy use. Niacin, riboflavin, and vitamin B6 deficiencies cause different syndromes.
Warfarin inhibits vitamin K epoxide reductase, reducing synthesis of vitamin K-dependent clotting factors. A consistent dietary intake of vitamin K prevents large swings in the international normalized ratio. Patients should not eliminate vitamin K but keep intake stable.