Carbohydrates: Sugars, Starches, Fibers, and Metabolism

A comprehensive vocabulary review set covering carbohydrates, dietary fibers, digestion, endocrine blood glucose regulation, and diabetes mellitus classification and complications.

Ketosis

A metabolic process that occurs when the body lacks sufficient glucose for energy and burns stored fats instead, resulting in an accumulation of acids called ketones.

Monosaccharide

A simple carbohydrate consisting of a single sugar unit; includes glucose, fructose, and galactose.

Disaccharide

A simple carbohydrate formed by two monosaccharide units bonded together; includes sucrose, maltose, and lactose.

Sucrose

A disaccharide composed of glucose bonded to fructose, commonly referred to as table sugar and derived from sugar cane, beets, and honey.

Maltose

A disaccharide composed of two glucose molecules bonded together; found in malt beverages and malt beer.

Lactose

A disaccharide composed of galactose bonded to glucose, commonly known as milk sugar and found in milk and dairy products.

Aspartame

A nutritive artificial sweetener composed of two amino acids plus methanol that yields $4\,\text{kcal/g}$, is $200\times$ sweeter than sucrose, is destroyed by heat, and carries a warning for people with phenylketonuria (PKU).

Phenylketonuria (PKU)

A genetic disorder tested at birth in which the body cannot metabolize the amino acid phenylalanine; consumption by a woman with PKU during pregnancy causes infant mental retardation.

Sucralose

A $0\,\text{kcal}$ artificial sweetener manufactured from sucrose that is $600\times$ sweeter than table sugar, lacks a bitter aftertaste, and is heat stable (brand name Splenda).

Stevia

A $0\,\text{kcal}$, non-nutritive sweetener derived from sunflowers grown in Central America (sold under the brand name Truvia).

Sugar Alcohols

Sweetening agents with a structure of sugar and alcohol groups (e.g., sorbitol, mannitol, xylitol) that provide fewer kilocalories than sugar, do not readily promote tooth decay, but can cause diarrhea when consumed in excess.

Amylose

A linear, unbranched chain of glucose molecules bonded together through $\alpha\text{-1,4}$ glycosidic bonds found in plant starch.

Amylopectin

A highly branched plant starch arrangement of glucose molecules connected by linear $\alpha\text{-1,4}$ glycosidic bonds and branch points connected by $\alpha\text{-1,6}$ glycosidic bonds.

Glycogen

The storage form of glucose in animals and humans stored predominantly in the liver and muscle, containing $\alpha\text{-1,4}$ and $\alpha\text{-1,6}$ glycosidic bonds in a highly branched arrangement for rapid glucose mobilization.

Dietary Fiber

A non-digestible complex carbohydrate consisting of linear chains of glucose joined by $\beta\text{-1,4}$ glycosidic bonds that human enzymes cannot break down.

Soluble Fiber

Dietary fiber that forms a gel-like substance in the gastrointestinal tract, binds bile, glucose, and minerals, promotes beneficial intestinal bacteria, and lowers blood cholesterol, blood pressure, and blood glucose.

Insoluble Fiber

Dietary fiber that passes through the gastrointestinal tract unchanged, aids digestive motility, prevents constipation, hemorrhoids, and diverticular disease, and reduces colon cancer risk.

Diverticulosis

A condition characterized by the formation of small, protruding pouches called diverticula along the wall of the large intestine.

Cellulose

An insoluble fiber consisting of glucose molecules with $\beta$-glycosidic bonds that serves as the main structural component of plant cell walls, increasing stool weight and potentially decreasing transit time.

Pectin

A soluble fiber found in the skin of ripe fruits composed of various monosaccharides and used commercially to make jams and jellies; lowers cholesterol through bile acid excretion and reduces glycemic response.

Salivary $\alpha$-Amylase

An enzyme released by the salivary glands in the mouth that hydrolyzes $\alpha\text{-1,4}$ glycosidic bonds in amylose and amylopectin, forming dextrins until it is destroyed by gastric juice acidity.

Pancreatic $\alpha$-Amylase

An enzyme secreted by the pancreas into the small intestine that hydrolyzes $\alpha\text{-1,4}$ glycosidic bonds of dextrins to form maltose and limit dextrins.

$\alpha$-Dextrinase

A brush border enzyme in the small intestine that hydrolyzes the $\alpha\text{-1,6}$ glycosidic bonds in limit dextrins to release free glucose.

Enterocyte Monosaccharide Transporters

Membrane proteins facilitating carbohydrate absorption; glucose and galactose are absorbed via carrier-mediated active transport requiring ATP, whereas fructose is absorbed via facilitated diffusion.

Glycemic Index (GI)

A relative scale from $0$ to $100$ (pure glucose = $100$) that reflects the rise in blood glucose levels following ingestion of a food containing a standard carbohydrate amount.

Glycemic Load (GL)

A parameter defined as the Glycemic Index divided by $100$ and multiplied by the grams of carbohydrate in a serving: $\text{GL} = \frac{\text{GI}}{100} \times \text{carbohydrate (g)}$.

Insulin

A hormone produced by pancreatic $\beta$-cells of the islets of Langerhans in response to elevated blood glucose; it stimulates glucose uptake into muscle and adipose cells and promotes glycogenesis, protein synthesis, and lipogenesis.

Glucagon

A hormone produced by pancreatic $\alpha$-cells in response to declining blood glucose; it stimulates liver glycogenolysis, adipose lipolysis, hepatic ketogenesis, and gluconeogenesis.

Glycogenesis

The biochemical conversion of glucose into stored glycogen in the liver and skeletal muscle cells, promoted by insulin.

Glycogenolysis

The biochemical breakdown of stored glycogen into glucose within the liver, stimulated by glucagon to elevate blood glucose.

Gluconeogenesis

The metabolic pathway promoted by glucagon that utilizes noncarbohydrate sources in the liver to produce glucose.

Type 1 Diabetes Mellitus

An autoimmune disorder destroying the pancreatic $\beta$-cells, causing an absolute lack of insulin, severe hyperglycemia, rapid weight loss, and ketoacidosis, requiring daily insulin therapy.

Type 2 Diabetes Mellitus

A metabolic disease characterized by insulin resistance in skeletal muscle and adipose tissue and relative insulin deficiency, strongly associated with obesity, physical inactivity, and family history.

Gestational Diabetes

A temporary form of insulin resistance developing in $4\text{ to }7\%$ of pregnant women due to hormonal changes; linked to macrosomia and higher risk of future maternal type 2 diabetes.

Secondary Diabetes

A category of diabetes brought on secondarily by other underlying diseases, medical conditions, or medications.

Impaired Wound Healing

A short-term complication of diabetes mellitus characterized by delayed tissue repair and elevated susceptibility to infection.