Nutrition Science: Water, Metabolism, and Alcohol
Water Functions and Hydration Essentials
Water constitutes approximately 60% of body weight, though this varies by age, sex, and body fat percentage.
It regulates body temperature through the process of sweating.
It provides essential cushioning for joints and organs.
It facilitates the transport of nutrients, oxygen, and waste throughout the body.
It is critical for maintaining blood volume and blood pressure.
Electrolytes and Fluid Balance
Electrolytes are charged ions that dissolve in water and are vital for physiological function.
They are required for:
Maintaining a steady heartbeat
Facilitating muscle contraction
Supporting nerve transmission
Sodium (Na⁺) Functions and Risks
Sodium is the primary extracellular electrolyte found outside the cell.
It maintains fluid volume outside cells.
It is required for glucose absorption via sodium-dependent glucose uptake.
Low sodium levels lead to hyponatremia, which can occur during water intoxication.
Excessive sodium levels lead to hypernatremia.
Potassium (K⁺) and Intracellular Balance
Potassium is the primary intracellular electrolyte found inside the cell.
It maintains fluid balance inside cells.
Many individuals do not consume adequate amounts of potassium in their daily diet.
The Process of Osmosis
Osmosis is the movement of water across a semi-permeable cell membrane.
Water moves from areas of low solute concentration (low salt) to high solute concentration (high salt).
The goal of this process is to equalize concentrations on both sides of the membrane.
Water Intake and Output
Intake (Input): Sources include drinking liquids, eating foods, and metabolic water produced during chemical reactions.
Loss (Output): Water is excreted through urine (kidneys), sweat (skin), breath (lungs), and feces.
Effects of Dehydration
An increase in antidiuretic hormone (ADH) occurs to help the body conserve water.
It leads to increased blood salt concentration.
It results in decreased blood volume and blood pressure.
These changes trigger the thirst mechanism.
Hormonal Control of Thirst
The hypothalamus detects the physiological need for fluids.
The pituitary gland releases ADH in response.
ADH signals the kidneys to retain water rather than excreting it.
Comparing Bottled and Tap Water
Bottled water is often less strictly regulated than tap water.
The FDA only requires fluoride levels to be listed on the label.
Bottled water may originate from municipal sources rather than natural springs.
Hard vs. Soft Water Differences
Soft water contains higher sodium levels, which may worsen hypertension.
Hard water is high in calcium and magnesium, which can be protective for heart health.
Common Water Sources
Sources include surface water, groundwater, artesian water (from confined aquifers), and reservoirs used for municipal water.
Energy and Metabolism Fundamentals
Understanding Cellular Metabolism
Cells do not utilize food directly for energy.
Food must be broken down to release energy from chemical bonds.
An example of this is the breakdown of glucose (C₆H₁₂O₆).
Role of Oxygen and ATP
Hemoglobin transports oxygen to the cells.
Oxygen is essential for aerobic respiration.
Carbon dioxide (CO₂) is removed from the body via the lungs.
ATP serves as the energy currency of the cell; energy is released when a phosphate bond is broken.
Components of Energy Expenditure
Basal Metabolic Rate (BMR)
Physical activity
Thermic Effect of Food (TEF)
Basal Metabolic Rate (BMR) Factors
BMR is the energy used at rest for involuntary processes such as breathing, circulation, and temperature regulation.
It excludes the energy used for digestion and exercise.
Factors that increase BMR: Youth, a tall and lean body, pregnancy, fever, stress hormones, and high thyroxine levels.
Factors that decrease BMR: Starvation, fasting, and aging. Note that muscle tissue burns more energy than fat, and BMR is lowest during sleep.
Energy Storage in the Body
Glucose is stored as glycogen in the liver and muscles, though storage capacity is limited.
Fat is stored in adipose tissue, which has a very large storage capacity.
Importance of Glucose as Fuel
Glucose is the primary fuel source for the brain, nerves, and red blood cells.
Physiology of Fasting and Starvation
Fasting leads to low insulin levels and the production of ketones for energy.
Gluconeogenesis occurs to synthesize new glucose, and protein breakdown begins.
A loss of more than 50% of body protein leads to death. It is important to note that fat cannot be converted into glucose.
Estimated Energy Requirement (EER)
EER depends on several factors, including body size, weight, age, gender, and physical activity levels.
Impact of High-Protein Diets
These diets increase nitrogen excretion and urea production, which can stress the kidneys.
They are not recommended for dialysis patients.
Alcohol Metabolism and Health Effects
Alcohol Basics and Caloric Value
Alcohol is a toxin, not a nutrient, and provides 7 kcal per gram.
It offers empty calories and is metabolized first as a priority nutrient.
Alcohol Metabolism Pathways
Metabolism primarily occurs in the liver.
ADH Pathway (80%): Alcohol is converted to toxic acetaldehyde, then to acetate, and finally to acetyl-CoA. This pathway produces calories and inhibits the citric acid cycle, leading to fat formation.
MEOS Pathway (~10%): This is used when alcohol intake is high; it produces reactive oxygen species and interferes with drug metabolism.
Excretion and Physiological Effects
Approximately 10% of alcohol is excreted via breath, sweat, and urine.
Alcohol increases fat synthesis, weakens immunity, causes hypoglycemia, interferes with vitamin absorption, and suppresses ADH, leading to dehydration.
Chronic Use and Treatment
Chronic use leads to fatty liver (reversible) and cirrhosis (irreversible).
Antabuse inhibits ADH, causing sickness when drinking; it is used alongside therapy for alcoholism.
Nutrition Calculations and Formulas
Standard Caloric Values
Carbohydrates: 4 kcal/g
Protein: 4 kcal/g
Fat: 9 kcal/g
Alcohol: 7 kcal/g
Essential Formulas
Total Calories: (Carbs × 4) + (Protein × 4) + (Fat × 9) + (Alcohol × 7)
Percentage of Calories: (Nutrient kcal ÷ Total kcal) × 100
Grams to Calories: Multiply grams by the kcal/g value.
Calories to Grams: Divide calories by the kcal/g value.
Total Package Calories: Total servings × calories per serving
Daily Value (DV): (Amount consumed ÷ Recommended intake) × 100
Predominant Carbohydrate: Total carbs – fiber – sugar = starch. The largest value is the predominant type.
Protein Requirements: 0.8 g of protein per kg of body weight. Convert pounds to kilograms by dividing by 2.2.