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.