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Alcohol, Energy Metabolism, and Vitamins: Study Guide (Chapters 7-10)

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Alcohol

Forms, Energy Content, and Standard Drinks

Alcohol, specifically ethanol, is the type of alcohol found in beverages. It provides energy and is measured in standard drink sizes.

  • Ethanol is the consumable form of alcohol.

  • Energy content: 7 kcal/gram.

  • Standard drink equivalents:

    • 12 oz beer

    • 5 oz wine

    • 1.5 oz hard liquor

  • Alcohol content is measured by "proof" (half the proof equals the percent alcohol).

  • Moderate drinking may reduce heart disease risk in older adults.

Digestion, Absorption, and Metabolism

Alcohol is absorbed and metabolized through specific pathways, primarily in the liver.

  • Absorption begins in the stomach, but most occurs in the small intestine.

  • Alcohol dehydrogenase (ADH) metabolizes alcohol to acetaldehyde, which is further metabolized for energy or stored as fat.

  • After absorption, alcohol enters the bloodstream, watery tissues, and the brain.

  • The liver is the main site of alcohol metabolism.

  • Metabolic pathways:

    • ADH pathway: Used first for moderate intake.

    • MEOS (Microsomal Ethanol Oxidizing System): Used with excessive intake.

  • Women are more affected due to less ADH, less muscle mass, and more body fat.

Nutritional Problems Associated with Alcohol

  • Decreased nutrient absorption and transport in the small intestine and stomach.

  • Reduction in digestive enzymes.

  • Increased risk of gastritis and pancreatitis.

Liver Disease Progression

  • Fatty liver: Fat deposits after a few days of excessive drinking; reversible with abstinence.

  • Alcoholic hepatitis: Inflammation of the liver; may not be reversible.

  • Cirrhosis: Irreversible scarring of the liver.

  • Early onset of drinking increases risk of alcoholism later in life.

Energy Metabolism

Overview of Metabolism

Metabolism encompasses all chemical reactions in cells, primarily catalyzed by enzymes, to convert food into usable energy.

  • Food is digested and metabolized to produce adenosine triphosphate (ATP).

  • ATP stores energy in its phosphate bonds:

    • Adenosine~Phosphate~Phosphate~Phosphate (~ indicates high-energy bonds)

Major Metabolic Pathways

  • Glycolysis:

    • Occurs in the cytosol (cytoplasm) of cells.

    • Anaerobic (does not require oxygen).

    • Breaks down glucose into pyruvate, producing a small amount of ATP.

  • TCA Cycle (Krebs Cycle):

    • Occurs in the mitochondria.

    • Aerobic (requires oxygen).

    • Metabolizes Acetyl CoA (gateway molecule) to produce more ATP.

    • Fatty acids, some amino acids, and pyruvate are converted to Acetyl CoA for energy production or fat storage.

  • Electron Transport System:

    • Hydrogens generated by the TCA cycle are used to produce ATP.

Equation for ATP hydrolysis:

Vitamins

General Properties of Vitamins

  • Organic compounds: Can be destroyed by light, heat, air, or chemicals.

  • Bioavailability varies; plant sources may be less absorbed due to fiber content.

  • Vitamins provide no calories.

  • Essential for life and required in small amounts.

  • Regulate metabolism.

  • Supplements do not prevent cancer if the diet is already healthy.

  • Fortification: Addition of vitamins to foods.

  • Rinsing foods can cause loss of water-soluble vitamins.

Classification of Vitamins

Class

Examples

Storage

Absorption

Toxicity

Fat-Soluble

A, D, E, K

Stored in fat

Require fat for absorption

Possible in large amounts

Water-Soluble

B-complex, C

Not stored (excess excreted)

Dissolve in fluids

Rare

Fat-Soluble Vitamins

  • Preformed vitamins: Active form in food (e.g., vitamin A from animal sources).

  • Provitamins (precursors): Converted to active form in the body (e.g., beta-carotene to vitamin A).

  • Vitamin A:

    • Preformed: Animal fats, liver; can be toxic in excess.

    • Provitamin A (beta-carotene): Yellow-orange and dark green plant foods (e.g., pumpkin, carrots).

  • Vitamin D (Cholecalciferol):

    • Many people have inadequate intake; supplementation may be necessary.

    • Deficiency linked to rickets in children (soft bones), and possibly some cancers and diabetes.

  • Vitamin E:

    • Functions as an antioxidant, stabilizing free radicals.

    • Sources: Vegetable oils, nuts.

    • Other antioxidants: Vitamin C, selenium, phytochemicals (flavonoids, lycopene, beta-carotene).

    • Antioxidants may help reduce risk of neurodegenerative diseases.

  • Vitamin K:

    • May help prevent bone fractures.

    • Sources: Dark green vegetables (e.g., kale).

Water-Soluble Vitamins

  • Dissolve in fluids; excess is excreted in urine.

  • Toxicity is rare due to lack of storage.

  • Destroyed by high temperatures, light, and air.

  • B-complex vitamins:

    • Function as coenzymes, assisting enzymes in metabolic reactions.

    • Several B vitamins are involved in energy generation.

    • Riboflavin (B2): Found in milk; sensitive to light (hence, milk is packaged in opaque containers).

    • Niacin (B3): Can be synthesized from tryptophan; high doses (under medical supervision) can lower cholesterol but may cause skin flushing.

    • Pantothenic Acid: Needed to produce Acetyl CoA, the gateway to the TCA cycle.

    • Folic Acid (Folate): Essential for pregnant women to prevent neural tube defects (e.g., spina bifida).

    • Vitamin B12: Found only in animal products; deficiency (or folate deficiency) can cause macrocytic anemia.

  • Vitamin C (Ascorbic Acid):

    • Functions as an antioxidant, aids in wound healing, collagen synthesis, and infection resistance.

    • Must be obtained from diet or supplements; the body cannot synthesize it.

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