Nutrition & Hydration

Dietary Energy (Calories Consumed)

Definition

Total caloric energy consumed from food and beverages, measured in kilocalories (kcal) or kilojoules (kJ).

Conversion: 1 kcal = 4.184 kJ

Why It Matters

Energy intake is fundamental to: - Weight management - Energy balance determines weight change - Nutritional status - Adequate energy for health - Athletic performance - Fueling training and recovery - Metabolic health - Chronic over/under-consumption affects health

How It's Tracked

HealthKit receives nutrition data from: - Food logging apps - MyFitnessPal, Cronometer, LoseIt, etc. - Barcode scanning - Quick food entry - Manual entry - User-entered meals - Recipe calculators - Home-cooked meal tracking

Important: Nutrition tracking is only as accurate as the input method.

Reference Guidance

Energy needs vary by: - Body size - Activity level - Age - Sex - Goals (weight loss, maintenance, gain)

General estimates (adults): - Sedentary women: 1,600-2,000 kcal/day - Sedentary men: 2,000-2,400 kcal/day - Active individuals: Higher based on activity

Energy Balance

Rule of thumb: ~3,500 kcal deficit = 1 lb fat loss (approximately)

Confounders & Limitations

• Logging accuracy - Portion sizes often underestimated
• Database errors - Food entries may be incorrect
• Preparation methods - Same food cooked differently varies
• Hidden calories - Oils, sauces, cooking fats
• Metabolic variation - Individual differences in absorption

Use Cases

• Weight management - Tracking intake for goals
• Dietary awareness - Understanding eating patterns
• Athletic performance - Adequate fueling
• Medical conditions - Specific caloric requirements

Practical Advice

• Focus on consistency over perfection
• Measure portions initially to calibrate estimates
• Track long enough to see patterns (7-14 days)
• Don't let tracking become obsessive

References

• USDA Dietary Guidelines

Macronutrients

Definition

The three main categories of nutrients that provide calories: - Protein - 4 kcal/gram - Carbohydrates - 4 kcal/gram - Fat - 9 kcal/gram

(Alcohol provides 7 kcal/gram but isn't considered a macronutrient)

Why It Matters

Macronutrient balance affects: - Body composition - Muscle vs fat - Energy levels - Sustained vs fluctuating - Satiety - Feeling full - Athletic performance - Fueling different activities - Metabolic health - Blood sugar, cholesterol, etc.

Protein

Functions

• Muscle building and repair
• Enzyme and hormone production
• Immune function
• Satiety

Recommended Intake

• General: 0.8 g/kg body weight/day minimum
• Active/athletes: 1.2-2.0 g/kg/day
• Older adults: 1.0-1.2 g/kg/day (prevent sarcopenia)

Sources

Complete: Meat, fish, eggs, dairy, soy Plant: Legumes, nuts, seeds, grains (combine for complete amino acids)

Carbohydrates

Functions

• Primary energy source
• Brain fuel
• Fiber for gut health
• Glycogen storage for exercise

Recommended Intake

• 45-65% of total calories
• Fiber: 25-38 g/day

Types

• Complex - Whole grains, vegetables (preferred)
• Simple - Sugars, refined grains (limit)
• Fiber - Non-digestible, supports gut health

Fat

Functions

• Energy storage
• Hormone production
• Vitamin absorption (A, D, E, K)
• Cell membrane structure
• Brain health

Recommended Intake

• 20-35% of total calories
• Limit saturated fat to <10% of calories
• Minimize trans fat

Types

• Saturated - Solid at room temp; limit intake
• Monounsaturated - Olive oil, nuts; beneficial
• Polyunsaturated - Omega-3, omega-6; essential
• Trans - Avoid; associated with heart disease

Typical Macro Targets

References

• USDA Dietary Guidelines
• NIH Office of Dietary Supplements

Minerals & Electrolytes

Definition

Essential inorganic nutrients required for various physiological functions. Electrolytes are minerals that carry electrical charges when dissolved in body fluids.

Why It Matters

Minerals and electrolytes are crucial for: - Fluid balance - Muscle contraction - Nerve signaling - Bone health - Enzyme function - Oxygen transport

Major Minerals

Sodium

• Functions: Fluid balance, nerve/muscle function
• Daily limit: <2,300 mg (ideally <1,500 mg for BP management)
• Sources: Salt, processed foods
• Note: Most people consume too much

Potassium

• Functions: Heart rhythm, muscle function, BP regulation
• Adequate intake: 2,600-3,400 mg/day
• Sources: Bananas, potatoes, beans, leafy greens
• Note: Counterbalances sodium

Calcium

• Functions: Bone health, muscle contraction, nerve signaling
• RDA: 1,000-1,200 mg/day
• Sources: Dairy, fortified foods, leafy greens
• Note: Vitamin D needed for absorption

Magnesium

• Functions: Energy production, muscle/nerve function, bone health
• RDA: 310-420 mg/day
• Sources: Nuts, seeds, whole grains, leafy greens
• Deficiency: Common; causes muscle cramps, fatigue

Phosphorus

• Functions: Bone structure, energy metabolism
• RDA: 700 mg/day
• Sources: Meat, dairy, nuts, legumes

Trace Minerals

Iron

• Functions: Oxygen transport (hemoglobin)
• RDA: 8-18 mg/day (higher for women of childbearing age)
• Sources: Meat, legumes, fortified cereals
• Deficiency: Anemia, fatigue

Zinc

• Functions: Immune function, wound healing, taste/smell
• RDA: 8-11 mg/day
• Sources: Meat, shellfish, legumes, nuts

Selenium

• Functions: Antioxidant, thyroid function
• RDA: 55 mcg/day
• Sources: Brazil nuts, seafood, meat

Iodine

• Functions: Thyroid hormone production
• RDA: 150 mcg/day
• Sources: Iodized salt, seafood, dairy

Electrolyte Balance

Important for: - Athletes (sweating losses) - Hot weather - Illness (vomiting, diarrhea) - Certain medications (diuretics)

Signs of imbalance: - Muscle cramps - Weakness - Irregular heartbeat - Confusion

References

• NIH Office of Dietary Supplements

Vitamins

Definition

Essential organic compounds required in small amounts for normal physiological function. HealthKit can track intake of various vitamins.

Why It Matters

Vitamins are crucial for: - Metabolism and energy production - Immune function - Cell growth and repair - Bone health - Nervous system function - Antioxidant protection

Fat-Soluble Vitamins

Stored in body fat; can accumulate to toxic levels.

Vitamin A

• Functions: Vision, immune function, skin health
• RDA: 700-900 mcg RAE/day
• Sources: Liver, dairy, orange/yellow vegetables
• Deficiency: Night blindness, immune dysfunction

Vitamin D

• Functions: Calcium absorption, bone health, immune function
• RDA: 600-800 IU/day (higher for deficiency)
• Sources: Sunlight, fatty fish, fortified foods
• Deficiency: Bone weakness, muscle weakness

Vitamin E

• Functions: Antioxidant, immune function
• RDA: 15 mg/day
• Sources: Nuts, seeds, vegetable oils
• Deficiency: Nerve damage (rare)

Vitamin K

• Functions: Blood clotting, bone metabolism
• RDA: 90-120 mcg/day
• Sources: Green leafy vegetables
• Note: Interacts with blood thinners

Water-Soluble Vitamins

Not stored; need regular intake. Excess excreted in urine.

B-Complex Vitamins

Vitamin C

• Functions: Antioxidant, collagen synthesis, immune support
• RDA: 75-90 mg/day
• Sources: Citrus, berries, peppers, broccoli
• Deficiency: Scurvy (rare)

Tracking Considerations

• Food logging apps estimate vitamin intake from foods
• Supplements should be logged separately
• Accuracy depends on food database quality
• Bioavailability varies by source and individual

References

• NIH Office of Dietary Supplements

Water Intake

Definition

The volume of water and other fluids consumed, typically measured in milliliters (mL) or ounces (oz).

Why It Matters

Adequate hydration is essential for: - Thermoregulation - Body temperature control - Cognitive function - Concentration and mental clarity - Physical performance - Endurance and strength - Kidney function - Waste elimination - Cardiovascular health - Blood volume and circulation - Digestion - Nutrient absorption and waste transport

How It's Tracked

• Manual logging - Record glasses/bottles consumed
• Smart water bottles - Automatically track intake
• Food logging apps - Include water tracking
• Health apps - Dedicated hydration trackers

Reference Guidance

Water needs vary significantly by: - Body size - Activity level - Climate/temperature - Health conditions

General recommendations: - Women: ~2.7 L (91 oz) total water/day - Men: ~3.7 L (125 oz) total water/day

Includes water from all sources (beverages + food)

Simpler rule: Drink enough that urine is pale yellow.

Signs of Dehydration

• Dark urine
• Thirst (late sign)
• Dry mouth
• Fatigue
• Headache
• Dizziness
• Decreased urine output

Confounders & Limitations

• Food water content - Fruits, vegetables, soups contribute
• Caffeine/alcohol - Mild diuretic effects
• Exercise - Increases needs significantly
• Climate - Heat and humidity increase needs
• Illness - Fever, vomiting, diarrhea increase needs

Use Cases

• Daily habit tracking - Meeting hydration goals
• Athletic performance - Pre/during/post workout hydration
• Weight management - Sometimes thirst mimics hunger
• Health conditions - Kidney stones, UTI prevention

Practical Advice

• Keep water accessible throughout the day
• Drink with meals
• Increase intake during exercise and hot weather
• Pale urine is a good indicator of adequate hydration
• Don't wait until thirsty

References

• National Academies - Dietary Reference Intakes for Water