Nutrition: Carbohydrates, Lipids, and Proteins Review

Vocabulary practice cards reviewing carbohydrates, lipids, and proteins based on lecture concepts and annotated notes from Chapters 4, 5, and 6.

Primary Dietary Source of Carbohydrates

Plants, which synthesize and supply the vast majority of dietary carbohydrates.

Energy Density of Carbohydrates

Provides $4\,\text{kcal/g}$ of metabolizable energy.

AMDR for Carbohydrates

Acceptable Macronutrient Distribution Range recommending that $45\% - 65\%$ of total daily caloric intake comes from carbohydrates.

Primary Functions of Carbohydrates

Supplying cellular energy, facilitating the breakdown of fat, exerting a protein-sparing effect, and regulating blood glucose levels.

Simple Sugars

Monosaccharides and disaccharides; the Dietary Guidelines specifically recommend limiting added sugars.

Glucose

A primary monosaccharide circulating in the bloodstream, commonly referred to as blood sugar.

Fructose

A naturally occurring monosaccharide recognized as the sweetest sugar.

Galactose

A monosaccharide that is rarely consumed alone in the diet and typically occurs bonded to glucose.

Lactose

A disaccharide formed by the chemical combination of glucose and galactose.

Maltose

A disaccharide composed of two glucose molecules ($\text{glucose} + \text{glucose}$).

Polysaccharide

A complex carbohydrate consisting of long chains of more than two monosaccharides.

Glycogen

The storage form of glucose in animals and humans, stored primarily in the liver and skeletal muscle tissue.

Dietary Fiber

A nondigestible polysaccharide; individuals increasing their fiber intake require higher fluid (water) consumption.

Soluble, Viscous Fiber

Fiber that dissolves in water and forms a thick gel; mostly fermentable, found in oats, barley, psyllium, legumes, and certain fruits. It helps lower LDL cholesterol, slows glucose absorption, and may improve stool consistency.

Soluble, Nonviscous Fiber

Fiber that dissolves in water but does not form a gel; frequently fermented by gut bacteria, found in onions, garlic, bananas, and legumes. It supports beneficial gut bacteria and yields short-chain fatty acids.

Insoluble, Poorly Fermented Fiber

Fiber that remains mostly intact throughout digestion; found in wheat bran, whole grains, vegetables, nuts, and seeds. It promotes bowel regularity and adds bulk to stool.

Resistant Starch

Starch that resists digestion in the small intestine and undergoes fermentation in the colon; found in legumes, green bananas, intact grains, and cooked-and-cooled potatoes or rice. It supports gut bacteria, produces short-chain fatty acids, and moderates blood glucose.

Adequate Intake (AI) for Fiber

The established daily target of $25 - 38\,\text{g/day}$, or approximately $14\,\text{g} / 1000\,\text{kcal}$.

Excess Fiber Intake Complications

Consuming $50 - 60\,\text{g/day}$ of fiber, which can cause constipation, especially when accompanied by inadequate water intake.

Whole Grain

A grain product that retains all three original components of the kernel: the bran, germ, and endosperm.

Refined Grain

A grain that has undergone processing to remove essential components, such as the bran and germ.

Hyperglycemia

An abnormally high concentration of glucose circulating in the blood, serving as a primary diagnostic indicator for diabetes.

Diagnostic Thresholds for Diabetes

A fasting plasma glucose concentration of $\ge 126\,\text{mg/dL}$ ($7.0\,\text{mmol/L}$) or a glycated hemoglobin ($\text{HbA1c}$) measurement of $\ge 6.5\%$.

Prediabetes Diagnostic Criteria

An intermediate metabolic stage marked by impaired fasting glucose of $100 - 125\,\text{mg/dL}$ or an $\text{HbA1c}$ level of $5.7\% - 6.4\%$.

Diabetes Prevention Program (DPP)

A landmark clinical study demonstrating that intensive lifestyle changes targeting weight reduction and exercise reduced type 2 diabetes risk by $58\%$, outperforming metformin.

Carbohydrate Digestion Pathway

Mechanical digestion and salivary amylase in the mouth, pause in the stomach, luminal hydrolysis by pancreatic amylase in the small intestine, and final cleavage by brush-border enzymes into absorbable monosaccharides.

Metabolic Fate of Absorbed Monosaccharides

Monosaccharides enter the hepatic portal vein to reach the liver, where fructose and galactose are converted to glucose, which is then released into the blood, stored as glycogen, or converted into triglycerides if caloric surplus exists.

Food Sources of Fructose

Abundant naturally in fruits, honey, and root vegetables, and commercially supplied through high-fructose corn syrup.

Food Sources of Lactose

Primarily found in mammalian dairy products, including milk, yogurt, and ice cream.

Food Sources of Sucrose

Found naturally in sugar cane, sugar beets, maple syrup, and fruits, as well as refined table sugar.

Food Sources of Starch

Abundantly concentrated in cereal grains (wheat, rice, oats, corn), starchy tubers (potatoes, yams), and legumes (beans, peas, lentils).

Food Sources of Dietary Fiber

Supplied by intact whole grains, legumes, vegetables, fruits, nuts, and seeds.

Primary Tissues Dependent on Carbohydrate Fuel

The brain, central nervous system, and erythrocytes (red blood cells), which rely almost exclusively on circulating glucose for cellular energy.

Insulin

A pancreatic hormone released in response to elevated blood glucose that promotes cellular uptake and glycogen synthesis, lowering circulating sugar.

Glucagon

A pancreatic hormone secreted in response to declining blood sugar that stimulates hepatic glycogenolysis and gluconeogenesis, elevating circulating sugar.

Recommended Upper Limit for Added Sugars

Less than $10\%$ of total daily caloric intake, as established by the Dietary Guidelines for Americans.

Lactose Maldigestion

A digestive condition resulting from insufficient lactase production, causing gas, bloating, and diarrhea, though small amounts of dairy are often still tolerated.

Type 1 Diabetes Mellitus

An autoimmune condition characterized by the destruction of pancreatic beta cells, causing absolute insulin deficiency and lifelong dependence on exogenous insulin.

Type 2 Diabetes Mellitus

A metabolic disorder characterized by peripheral insulin resistance and progressive secretory defect, strongly associated with excess adiposity and physical inactivity.

Vascular Complications of Chronic Hyperglycemia

Macrovascular conditions such as coronary artery disease and stroke, accompanied by microvascular pathology such as retinopathy, nephropathy, and neuropathy.

Energy Density of Lipids

Provides $9\,\text{kcal/g}$ of metabolizable energy, making it the most energy-dense macronutrient.

Primary Classes of Lipids

Triglycerides (triacylglycerols), phospholipids, and sterols (such as cholesterol).

Biological Functions of Lipids

Long-term cellular energy reserve, thermal insulation, structural lipid bilayer formation, visceral organ protection, steroid hormone synthesis, and carrier for fat-soluble vitamins (A, D, E, K).

Fatty Acid Structure and Significance

A hydrocarbon chain capped by a methyl ($-\text{CH}_3$) group and a carboxyl ($-\text{COOH}$) group that serves as the core building block of triglycerides and phospholipids.

Saturated Fatty Acid

A fatty acid chain containing no carbon-carbon double bonds, fully saturated with hydrogen atoms, typically solid at room temperature.

Monounsaturated Fatty Acid

A hydrocarbon chain featuring exactly one carbon-carbon double bond, commonly found in olive and canola oils and typically liquid at room temperature.

Polyunsaturated Fatty Acid (PUFA)

A hydrocarbon chain containing two or more carbon-carbon double bonds, abundant in vegetable oils (corn, soybean) and cold-water fish, remaining liquid at room temperature.

Essential Fatty Acids

Dietary fats that cannot be synthesized by human cells, specifically alpha-linolenic acid (omega-$3$) and linoleic acid (omega-$6$).

Nonessential Dietary Lipids

Cholesterol, saturated fatty acids, and monounsaturated fatty acids, which human cells can synthesize endogenously in the liver.

Energy Content of Reduced-Fat vs. Full-Fat Foods

Often comparable in total calories because manufacturers add refined starches and sugars to replace extracted fat and preserve palatability.

Lipase

The digestive enzyme responsible for hydrolyzing lipid molecules into free fatty acids and monoglycerides.

Enzymatic Lipid Digestion and Absorption Pathway

Bile salts emulsify fat droplets in the small intestine, pancreatic lipase cleaves triglycerides into free fatty acids and monoglycerides, mixed micelles transport lipids across microvilli, and enterocytes package them into chylomicrons.

Lipoproteins

Lipid-protein transport particles in the bloodstream that move fats through circulation; variations in density (e.g., LDL vs. HDL) influence atherosclerosis and cardiovascular disease risk.

Chylomicrons

Lipoproteins assembled in the intestinal mucosa that transport exogenous dietary triglycerides and fat-soluble vitamins through the lymphatic system into systemic circulation.

Very-Low-Density Lipoproteins (VLDL)

Lipoproteins synthesized by the liver to transport endogenous triglycerides to peripheral tissues, transforming into LDL as triglycerides are unloaded.

Low-Density Lipoproteins (LDL)

Cholesterol-rich lipoproteins that deliver cholesterol to peripheral tissues; elevated levels promote subendothelial oxidation and atheroma formation.

High-Density Lipoproteins (HDL)

Protein-dense lipoproteins that pick up excess cholesterol from peripheral tissues and return it to the liver for excretion (reverse cholesterol transport), reducing cardiovascular disease risk.

Dietary Recommendations for Lipid Consumption

Restrict saturated fatty acids to less than $10\%$ of daily calories, eliminate artificial trans fats, and replace them with monounsaturated and polyunsaturated fats.

Atherosclerosis

A cardiovascular condition marked by arterial plaque accumulation, narrowing blood vessels and restricting blood flow.

Stages of Atherosclerotic Plaque Formation

Arterial endothelial injury, subendothelial infiltration and oxidation of LDL, uptake by macrophages to produce foam cells, fatty streak formation, fibrous plaque development, and fibrous cap rupture causing thrombosis.

Critical Progression Step in Atherosclerosis

The oxidation of subendothelial LDL particles, which initiates vascular inflammation and triggers foam cell accumulation.

Major Cardiovascular Disease (CVD) Risk Factors

Hypertension, elevated serum LDL, low HDL, cigarette smoking, diabetes mellitus, obesity, sedentary lifestyle, advanced age, and family history.

Unique Elemental Feature of Proteins

The incorporation of nitrogen within the amine structure, which is absent in standard carbohydrates and lipids.

Biological Functions of Proteins

Enzyme catalysis, peptide hormone signaling, structural support (collagen, keratin), immune defense (antibodies), intravascular oncotic pressure maintenance (albumin), fluid balance, and transport.

Fundamental Chemical Structure of Amino Acids

A central alpha-carbon bonded to an amino group ($-\text{NH}_2$), a carboxyl group ($-\text{COOH}$), a hydrogen atom ($-\text{H}$), and a distinct variable side chain (R-group).

Peptide Bond

The specialized covalent chemical linkage formed between the amino group of one amino acid and the carboxyl group of another.

Essential Amino Acids

A set of nine amino acids that the body cannot manufacture in sufficient quantities, requiring regular dietary intake.

Nonessential Amino Acids

A group of eleven amino acids that the human body can synthesize internally in sufficient amounts via transamination pathways.

Conditionally Essential Amino Acids

Amino acids normally synthesized by the body that must be supplied by the diet during periods of severe physiological stress, illness, or enzyme deficiency.

Genetic Direction of Protein Synthesis

Nuclear DNA genes are transcribed into messenger RNA (mRNA), which travels to ribosomes where transfer RNA (tRNA) delivers amino acids in sequence.

Protein Denaturation

The disruption and unfolding of a protein's three-dimensional structure caused by heat, acid, or physical agitation, without breaking the primary peptide bonds.

Metabolic Fate of Nitrogen During Protein Catabolism

During deamination, the removed amino group is converted into toxic ammonia ($\text{NH}_3$), synthesized into urea by the liver, and excreted by the kidneys.

Plant Milk Closest in Protein to Cow's Milk

Soy milk, providing approximately $7 - 8\,\text{g}$ of complete protein per cup.

High-Quality (Complete) Protein

A dietary protein containing all nine essential amino acids in proportions fitting human needs; examples include meat, fish, poultry, eggs, dairy, soy, and quinoa.

Low-Quality (Incomplete) Protein

A dietary protein source deficient in one or more essential amino acids, characteristic of plant foods such as grains, legumes, nuts, and seeds.

Limiting Amino Acid

The specific essential amino acid present in the lowest concentration relative to physiological need within an incomplete food source.

Complementary Proteins

Two or more incomplete dietary protein sources that, when consumed together, compensate for each other's limiting amino acids to provide all essential amino acids.

Key Nutrients Provided by Plant Protein Sources

Dietary fiber, phytochemicals, unsaturated fats, potassium, magnesium, and folate, while lacking vitamin $\text{B}_{12}$ and containing less bioavailable non-heme iron and zinc.

Health Risks of Excessive Animal Protein Intake

Higher intake of saturated fat and cholesterol, elevated risk of coronary heart disease, higher risk of colorectal cancer from red/processed meat, and potential progression of pre-existing kidney disease.

Adverse Effects of Purified Amino Acid Supplements

Competitive inhibition at shared intestinal amino acid transport proteins causing absorption imbalances, risk of cellular toxicity, and the absence of whole-food micronutrients.

Chronic Diseases Reduced by Vegetarian Diets

Ischemic heart disease, hypertension, type 2 diabetes mellitus, obesity, and specific malignancies such as colorectal cancer.

Primary Types of Vegetarian Diets

Vegan (strictly plant-derived), lacto-vegetarian (plants plus dairy), ovo-vegetarian (plants plus eggs), lacto-ovo vegetarian (plants plus dairy and eggs), and pescatarian (plants plus fish).

Reasons for Adopting a Vegetarian Diet

Health benefits, ecological and environmental preservation, ethical treatment of animals, and cultural or religious observances.

Micronutrient Considerations in Vegetarian Diets

Vitamin $\text{B}_{12}$, vitamin D, iron, zinc, calcium, and long-chain omega-$3$ fatty acids; managed using fortified plant milks, nutritional yeast, enriched cereals, and supplements.

Vegan Iron Sources and Enhancers

Non-heme iron provided by lentils, beans, tofu, spinach, and fortified grains; absorption is substantially boosted by concurrent vitamin C (ascorbic acid) intake.

Protein Turnover

The ongoing cellular cycle of degrading existing endogenous proteins and synthesizing new functional proteins in the body.

AMDR for Protein

Acceptable Macronutrient Distribution Range recommending that $10\% - 35\%$ of daily caloric intake originates from dietary protein.

Protein-Calorie Malnutrition (PCM)

Severe undernutrition resulting from inadequate energy or protein intake, presenting in forms such as kwashiorkor and marasmus.

Kwashiorkor

A severe form of protein-calorie malnutrition characterized by peripheral edema, abdominal distension, and fatty liver despite marginal energy intake.

Marasmus

A severe form of chronic undernutrition characterized by profound wasting of body fat and skeletal muscle, producing an emaciated appearance.

Sucrose

A disaccharide composed of glucose and fructose ($\text{glucose} + \text{fructose}$), commonly known as table sugar.

Total Energy Calculation Formula

$$\text{Total kcal} = (\text{g CHO} \times 4\,\text{kcal/g}) + (\text{g PRO} \times 4\,\text{kcal/g}) + (\text{g Fat} \times 9\,\text{kcal/g}) + (\text{g Alcohol} \times 7\,\text{kcal/g})$$

Macronutrient Energy Percentage Formula

$$\text{Macronutrient Percentage} = \left( \frac{\text{Macronutrient kcal}}{\text{Total kcal}} \right) \times 100\%$$

Gram Calculation from Caloric Percentage Formula

$$\text{Grams} = \frac{\text{Total kcal} \times \text{Target Percentage}}{\text{Nutrient kcal/g}}$$