Nutrition and Fitness

Introduction

This chapter explores the relationship between nutrition and physical fitness, focusing on the components of fitness, the role of macronutrients and micronutrients in exercise, hydration, and ergogenic aids. Understanding these concepts is essential for optimizing health and athletic performance.

Components of Physical Fitness

Five Basic Components

• Cardiorespiratory Endurance: The ability to sustain cardiorespiratory exercise for extended periods. This depends on the efficiency of the cardiovascular and respiratory systems to deliver oxygen and energy to muscles. Examples: Running, biking.

• Muscle Strength: The ability to produce force for brief periods. Essential for activities requiring power and lifting.

• Muscle Endurance: The ability to exert force over a long period without fatigue. Best developed through strength training with higher repetitions and lighter weights.

• Flexibility: The range of motion around a joint. Improved with regular stretching exercises.

• Body Composition: The proportion of muscle, fat, water, and other tissues that make up body weight.

Benefits of Physical Fitness

• Helps achieve and maintain a healthy body weight.

• Reduces risk of cardiovascular disease, type 2 diabetes, and some cancers.

• Improves body composition, bone health, and immune system function.

• Enhances overall health, including better sleep and stress reduction.

• Note: Over half of adults in the United States do not meet recommended physical activity levels.

Designing a Physical Fitness Program

Types of Exercise

• Cardiorespiratory Exercise: Improves endurance and body composition. Involves continuous activities using large muscle groups (e.g., aerobics, stair climbing, brisk walking).

• Strength Training: Enhances muscle strength, endurance, and body composition. Low repetitions with heavy weights build strength; high repetitions with lighter weights build endurance.

• Flexibility Training: Stretching exercises improve range of motion and prevent injury.

The FITT Principle

• Frequency: How often activity is performed.

• Intensity: How hard the activity is (measured by heart rate, RPE, or RM).

• Time: Duration of each session.

• Type: The kind of activity (aerobic, strength, flexibility).

Example: For substantial health benefits, adults should aim for at least 150 minutes of moderate-intensity activity per week.

Progressive Overload Principle

• Gradually increasing the intensity, duration, or frequency of exercise to improve fitness and avoid plateaus.

Target Heart Rate Calculation

• Estimated maximum heart rate:

• Exercise intensity is often prescribed as a percentage of this value.

Energy Sources During Exercise

ATP and Creatine Phosphate

• Initial energy for activity comes from anaerobic breakdown of ATP and creatine phosphate stored in muscles.

Carbohydrates

• Primary energy source during high-intensity exercise.

• Stored as glycogen in muscles and liver; well-trained muscles store more glycogen.

• Liver glycogen helps maintain blood glucose levels.

• Lactic acid is produced at high intensities and can be used as energy by other tissues.

• Carbohydrate needs depend on exercise duration and intensity.

Fats

• Main energy source during low- to moderate-intensity exercise.

• Fatty acids are derived from adipose tissue and muscle triglycerides.

• Fat oxidation is slower and requires more oxygen than carbohydrate metabolism.

• Well-trained muscles use more fat and spare glycogen, increasing endurance.

• Recommended intake: 25-30% of total calories, mostly from unsaturated fats; limit saturated fat to <10%.

Proteins

• Primarily used for muscle repair and growth, not as a main energy source.

• Amino acids can be converted to glucose in the liver if needed.

• Endurance athletes: 1.2-1.4 g/kg body weight/day; strength athletes: 1.2-1.7 g/kg body weight/day.

Meal Timing and Food Choices for Exercise

Before Exercise

• Allow time for digestion: large meal (3-4 hours), small meal (2-3 hours), snack (1 hour).

• Consume 1-4.5 g carbohydrate/kg body weight 1-4 hours before exercise.

• Protein before exercise can enhance muscle glycogen synthesis.

• Avoid high-fat foods before exercise to prevent discomfort.

During Exercise

• For activities >1 hour, consume 30-60 g carbohydrate/hour, starting soon after exercise begins.

• Best sources: glucose, sucrose, maltodextrin (quick absorption).

• Avoid fructose (may cause GI distress).

• Combining carbohydrate and protein supports muscle maintenance.

After Exercise

• Consume a meal or snack with a 3:1 carbohydrate to protein ratio soon after exercise for optimal recovery.

• Whey protein is preferred for rapid absorption and complete amino acid profile.

• Eat a high-carbohydrate, moderate-protein, low-fat meal within 2 hours post-exercise.

Vitamins and Minerals in Fitness

Roles and Importance

• Essential for energy metabolism and as antioxidants to protect against exercise-induced oxidative stress.

• Supplements of vitamins E and C have not been shown to improve performance; best to meet needs through food.

Key Minerals

• Iron: Needed for oxygen transport; deficiency can cause fatigue. Female athletes and endurance athletes are at higher risk.

• Calcium: Important for bone health; lost in sweat. Exercise increases bone mineral content.

• Magnesium: Needs may be higher with activity, but supplements are not usually necessary if diet is adequate.

Fluid and Electrolyte Balance

Hydration and Exercise

• Water is lost through sweat and breathing; sodium, chloride, and potassium are lost in sweat.

• Electrolyte imbalance can cause cramps, nausea, and other symptoms.

• Evaporation of sweat cools the body; hot, humid weather increases risk of heat exhaustion and heat stroke.

Hydration Recommendations (ACSM)

• Sports drinks are beneficial for endurance events (>60 min) due to carbohydrate and electrolyte content.

• Water is sufficient for shorter activities; avoid high-sugar, carbonated, alcoholic, or caffeinated beverages during exercise.

• Thirst is not a reliable indicator of hydration status for athletes.

• Hyponatremia (low blood sodium) can result from excessive water intake without electrolytes.

Ergogenic Aids and Supplements

Overview

• Dietary supplements are not strictly regulated; safety and efficacy are not guaranteed.

• Some ergogenic aids may improve performance but can have side effects.

• Sports bars, shakes, and meal replacers are convenient but often unnecessary if diet is adequate.

• Excess protein intake does not necessarily increase muscle mass and may have negative effects.

Special Topics

Relative Energy Deficiency in Sport (RED-S)

• Characterized by low energy availability, menstrual dysfunction, and low bone mineral density.

Vegan Diets for Athletes

• Can be healthful and provide adequate nutrients if well planned.

• Challenges include obtaining enough protein and micronutrients; requires careful planning, especially for traveling athletes.