Energy and Metabolism

• Energy is the capacity to do work, with the sun as the ultimate energy source for all life.
• Plants convert sunlight into chemical energy stored in sugars through photosynthesis.
• Energy manifests as heat, mechanical, electrical, or chemical energy in the body.
• Heat energy maintains body temperature, mechanical energy moves muscles, and electrical energy transmits nerve impulses.
• Chemical energy is stored in food and in the body.

Chemical Reactions in the Body

• Energy metabolism involves the body obtaining and spending energy from food.
• Enzymes and coenzymes facilitate metabolic reactions.

Adenosine Triphosphate (ATP)

• ATP is a high-energy compound composed of a purine, a sugar, and three phosphate groups.
• Hydrolysis breaks the bonds between phosphate groups in ATP, releasing energy.
• ATP transfers energy from catabolic to anabolic reactions.
• The body converts about 50% of food energy into ATP, which powers various bodily functions.

Glucose Metabolism - Glycolysis

• Glycolysis is the breakdown of one glucose molecule (6-carbon) into two pyruvate molecules (3-carbon).
• Glycolysis is an anaerobic pathway.
• The process can be reversed to create glucose from pyruvate.

Pyruvate Pathways - Aerobic

• Pyruvate enters the mitochondria and is converted to acetyl CoA (2-carbon compound).
• Acetyl CoA proceeds through the TCA cycle and electron transport chain if energy is needed, converting to 2 CO2 molecules.
• If energy is not needed, acetyl CoA is used to synthesize fatty acids.

Pyruvate Pathways - Anaerobic

• Pyruvate is converted to lactic acid (3-carbon compound) during anaerobic metabolism.
• This occurs mainly during high-intensity exercise.
• The liver converts lactic acid to glucose in the Cori cycle.

Glycerol and Fatty Acid Metabolism

• Glycerol can be converted to glucose or pyruvate, and then to acetyl CoA and carbon dioxide.
• Fatty acids undergo fatty acid oxidation to form acetyl CoA, releasing energy.
• Acetyl CoA molecules combine to form body fat if the cell does not need energy.
• Fatty acids cannot be used to make glucose.

Amino Acid Metabolism

• If needed for energy, amino acids are deaminated (lose their amino group).
• Deaminated amino acids are converted to pyruvate, acetyl CoA, or enter the TCA cycle.
• Amino acids converted to pyruvate can provide glucose.
• Amino acids converted to acetyl CoA can provide energy or make body fat.
• Amino acids entering the TCA cycle generate energy or glucose.

Key Points

• Excess carbohydrates, proteins, and lipids are converted to body fat.
• The body will break down protein to make glucose if you only consume fat.
• The body will convert protein to glucose if you only consume protein.

Fasting

• The body prioritizes meeting cells' energy needs, usually through eating regularly.
• During fasting, the body uses its tissues for fuel.
• Glycogen from the liver and fatty acids from adipose tissue are broken down to fuel cells.
• After a few hours of fasting, liver glycogen is depleted and blood glucose decreases.
• Fat breakdown is stimulated, and cells rely on fatty acids for fuel.
• Red blood cells and nervous system cells require glucose, even when other fuels are available.
• Body protein from lean tissues (liver & muscle) is broken down.
• In the first few days of fasting, body protein provides 90% of glucose and 10% of glycerol.
• Fat breakdown doubles, providing energy and glycerol for glucose production.
• Ketone production increases to fuel the brain and nervous system.
• Excess ketone acids disturb the body's acid-base balance.
• Continued fasting sacrifices protein for the brain.
• Metabolism slows down to conserve body tissue.
• Energy output decreases, and fat and lean tissue are conserved.
• Lean organ tissues waste and shrink, reducing their capacity to work, while the loss of fat reduces insulation and hormone production.
• Physical symptoms of energy deprivation include low heart rate, respiration, metabolism, low body temperature, impaired vision, organ failure, and reduced resistance to disease.
• Psychological symptoms of energy deprivation include depression, anxiety, and food-related dreams.

High-Protein Low-Carbohydrate Diets

• Short-term weight loss results from a low kcal intake (800-1200 kcals/day).
• High in fat, saturated fat, and cholesterol leading to increased disease risk.
• Too little variety which can be boring and unsustainable long term.
• Metabolism is similar to fasting.
• The body uses protein from tissues, leading to water loss.
• Weight loss includes water and protein, not just fat.

Alcohol in the Body

• Alcohol does not require digestion.
• 20% of alcohol is absorbed directly through the stomach wall.
• Absorption is slowed with a full stomach.
• Alcohol is rapidly absorbed in the small intestine.
• Alcohol is absorbed and metabolized before most nutrients.
• Liver cells prefer fatty acids as fuel.
• In the presence of alcohol, fatty acids accumulate.
• Alcohol impairs the liver’s ability to metabolize fats, leading to deterioration.

Alcohol Nutrition

• No more than 1 drink per hour.
• The liver needs time to metabolize alcohol.
• Alcohol alters both amino acid and protein metabolism.
• Alcohol affects brain cells causing damage by impairing ability of brain cells to regenerate.
• Alcohol provides empty calories.

Long Term Effects

• 1-2 drinks per day initiate destructive processes that can be reversed with abstinence.
• Allow 24 hours for the body to clear alcohol completely.
• Avoid alcohol consumption during pregnancy.