Biology 101: Chapter 5 - Carbohydrates

Carbohydrates

  • One of the main classes of nutrients.

  • Provide energy.

  • Often end in -ose.

  • Can be simple (sugars) or complex.

Simple Carbohydrates

  • Monosaccharides (one sugar unit):

    • Glucose (dextrose): main fuel for cells, found in fruits/veggies.

    • Fructose (fruit sugar or levulose): sweeter, found in fruit, honey; converted to glucose or fat.

    • Galactose: component of lactose.

  • Disaccharides:

    • Maltose (malt sugar): found in starchy grains, some fruit, honey.

    • Sucrose (table sugar): found in honey, maple syrup, carrots, pineapple; mostly consumed as refined sugar, which are empty calories.

    • Lactose (milk sugar): found in milk and some milk products.

Nutritive Sweeteners

  • Contain carbs that provide energy (4
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    Cal/g).

  • Added sugars: additives in processed foods.

  • Sugar alcohols (end in -ol): 2
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    Cal/g, not fully absorbed, don’t cause tooth decay, may cause diarrhea.

  • Scientific studies have not linked sugar to hyperactivity.

Nonnutritive Sweeteners (Artificial Sweeteners)

  • Add sweetness with minimal/no calories.

  • Listed as safe when consumed within acceptable daily intakes.

  • Many are high-intensity sweeteners.

Complex Carbohydrates

  • Made of many sugar units.

  • Starch: storage form of glucose in plants; found in grains, some veggies, tubers.

  • Glycogen: storage form of glucose in animals; stored in muscles/liver.

  • Fiber: not digestible by humans; may be fermented by gut microbiota.

Dietary Fiber

  • Soluble fiber: dissolves in water, may reduce blood cholesterol.

  • Insoluble fiber: doesn’t dissolve in water, helps with bowel movements.

  • Refinement lowers fiber content.

  • Adequate Intakes: 38
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    g/day 25
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    g/day for young females.

Fiber and Health

  • High-fiber diet may reduce the risk of: obesity, diabetes, cardiovascular disease, colorectal cancer, hemorrhoids, diverticulitis flare-ups.

  • Too much fiber: can interfere with mineral absorption and cause gas.

Carbohydrate Digestion

  • Salivary amylase: begins starch digestion in the mouth.

  • Pancreatic amylase: continues breaking starch to maltose in the small intestine.

  • Maltase: breaks maltose to glucose, which is absorbed.

  • Sucrase and lactase: break sucrose and lactose into monosaccharides, which are absorbed.

  • Fiber goes to the large intestine for fermentation.

Blood Glucose Maintenance

  • Insulin (from pancreas): lowers blood sugar by making glycogen from glucose.

  • Glucagon (from pancreas): raises blood sugar by breaking down glycogen; stimulates liver/kidney to make glucose from amino acids; stimulates fat breakdown.

  • Normal fasting blood glucose: between 70
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    mg/dl and 99
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    mg/dl.

Glucose as Fuel

  • Main fuel for cells.

  • Excess glucose is converted to fat and stored.

  • Nonalcoholic fatty liver disease can occur with insulin resistance, obesity, or high sugar intake.

Low-Carb Diets

  • Cells use fat as the main energy source, producing ketone bodies.

  • Ketosis occurs when ketone bodies accumulate.

  • Uncontrolled type I diabetes can cause ketoacidosis.

Carbohydrate Consumption

  • Dietary Guidelines recommend no more than 10% of calorie intake from added sugars.

Impact of Carbohydrates

  • Macronutrient content doesn’t overwhelmingly affect weight.

  • Ultra-processed foods and refined carbs are associated with weight gain.

  • High-carb diets mean dietary fats are stored instead of used as fuel.

Diabetes

  • Caused by hyperglycemia.

  • Types: type 1, type 2, gestational.

  • Normal blood glucose (fasting): 70 to 99
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    mg/dl, pre-diabetes: 100 to 125
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    mg/dl, diabetes: 126
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    mg/dl or more.

  • Signs and symptoms include:

  • Elevated blood glucose levels

  • Excessive thirst

  • Frequent urination

  • Blurry vision

Types of Diabetes

  • Type 1: autoimmune, immune system attacks pancreas cells, requires insulin.

  • Type 2: cells are insulin-resistant, rates have increased, risk factors include inactivity, excess fat, family history.

  • Gestational: develops during pregnancy.

Diabetes Control

  • Measure hemoglobin A1c to check blood glucose levels over time.

  • Losing weight and exercising helps.

  • May need insulin or meds.

  • Low glycemic index diet might be helpful.

Glycemic Index (GI) and Glycemic Load (GL)

  • GI: classifies foods by blood glucose rise compared to a standard.

  • GL: (grams of carbs in a food x food’s GI) / 100; indicates relative rise after eating a serving of food.

  • Helpful for diabetics to control blood glucose.

Hypoglycemia

  • Low blood sugar levels (<70
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    mg/dL$$).

  • Causes release of epinephrine, leading to shakiness, sweating, and irritability.

  • Can occur with too much insulin in diabetics.

Metabolic Syndrome

  • A set of signs/symptoms indicating a health problem; affects roughly 1/3 of Americans.

  • Risk factors: genetics, abdominal fat, lack of activity, insulin resistance.

Carbohydrate Intolerance

  • Inability to fully digest certain carbs.

  • Lactose intolerance: lack of lactase leads to gas, bloating, cramps, diarrhea.

  • Milk allergy = immune response.