How Physical Activity Impacts Metabolism, Nutrient, and Fluid Needs: A Women's Health Perspective

Written by Georgia Spence, ANutr, BSc and Founder of Georgia Spence Nutrition

Women's bodies, due to hormonal fluctuations and physiological differences, have unique nutrition and hydration needs, especially when engaging in regular physical activity. This blog will explore how physical activity affects metabolism, nutrient, and fluid needs, how these changes influence energy and nutrition requirements, and why individual needs may differ from population-level dietary reference values (DRVs).

The Impact of Physical Activity on Metabolism

Physical activity has a profound effect on metabolism. Simply put, metabolism refers to the chemical processes that occur within the body to maintain life, including energy production, muscle repair, and cellular function. When we engage in physical activity—whether it's a brisk walk, weight lifting, yoga, rock or high-intensity interval training (HIIT) to name a few—our bodies require more energy to fuel these activities.

For women, metabolic responses to physical activity can be influenced by factors such as age, hormonal status (e.g., premenstrual, pregnancy, menopause), and body composition

1. Resting Metabolic Rate (RMR): Physical activity can increase lean muscle mass, which in turn raises the resting metabolic rate (RMR). This means that even at rest, individuals with higher muscle mass burn more calories than those with less. Women engaging in resistance training or weight-bearing exercises may notice an increase in RMR as they build muscle.

2. Hormonal Influence: Hormones, particularly oestrogen, play a significant role in how women's bodies utilise and store energy. During different phases of the menstrual cycle, energy expenditure and nutrient utilization can vary. For example, metabolism tends to be slightly higher in the luteal phase (after ovulation), which can impact a woman’s nutrient and caloric needs.

   
   

Nutrient and Fluid Needs During Physical Activity

Physical activity not only increases energy needs but also raises the demand for specific nutrients and fluids to support recovery, prevent injury, and maintain overall health.

1. Macronutrient Needs:

   • Carbohydrates: Carbohydrates are the primary energy source for moderate to intense physical activity. Women who are physically active need to ensure adequate carbohydrate intake to replenish glycogen stores in muscles. Without enough carbohydrates, energy levels can plummet.

   • Protein: Protein is crucial for muscle repair and recovery, especially after strength training or endurance activities. Women engaging in regular exercise may require more protein than the average sedentary individual.

   • Fats: Fats are essential for hormone production and long-term energy needs, particularly for endurance activities. Women should focus on consuming omega-3 fatty acids and other unsaturated fats to support both energy needs and hormonal balance.

     
     

2. Micronutrient Needs:

   • Iron: Women are at higher risk of iron deficiency, particularly if they are menstruating. Regular physical activity can further deplete iron stores through sweat and increased blood production. Iron-rich foods like spinach, lentils, and lean meats, along with vitamin C for absorption, are crucial to prevent deficiency.

   • Calcium and Vitamin D: Weight-bearing activities like running, walking, or resistance training can increase bone density, but adequate calcium and vitamin D are essential to support bone health, particularly for women who may be at risk of osteoporosis.

   • Magnesium: Magnesium is vital for muscle function and recovery, as well as energy production. Women who engage in regular exercise may have increased magnesium needs, especially if they experience muscle cramps or fatigue.

     
     

3. Fluid Needs: Physical activity increases sweat production, leading to greater fluid loss. Women need to stay adequately hydrated before, during, and after exercise. On average, women need about 1.5-2 litres of water per day, but this can increase significantly with exercise, particularly in hot or humid environments.

   
   

Individualized Needs vs. Population-Level Dietary Reference Values (DRVs)

Dietary Reference Values (DRVs) provide general guidelines for nutrient and energy intake for the population. However, these guidelines may not always reflect the specific needs of individual women, particularly those who are physically active or have unique metabolic demands.

1. Energy Requirements: DRVs provide general calorie recommendations based on average energy expenditure, but women engaging in regular exercise will often have higher caloric needs to support both activity and recovery. For example, a woman who is training for a marathon will require more calories than a sedentary woman of the same age and weight.

2. Macronutrient Ratios: While DRVs suggest standard macronutrient ratios (carbs, protein, fats), physically active women may need to adjust these ratios based on their activity type. Endurance athletes may need more carbohydrates, while those focusing on strength training may require higher protein intake for muscle recovery and growth.

3. Special Considerations: Life stages such as pregnancy, breastfeeding, or menopause further impact nutrient needs. For example, pregnant women may need more protein and iron to support fetal development, while postmenopausal women may need more calcium and vitamin D to maintain bone health. These unique requirements often exceed the general DRVs.

4. Nutrient Absorption: Individual factors such as digestive health, stress levels, and hormonal fluctuations can influence nutrient absorption. Women with conditions like celiac disease, irritable bowel syndrome (IBS), or those under high stress may require adjustments to their diet to ensure adequate nutrient intake.

   
   

Conclusion

Physical activity significantly influences metabolism, nutrient, and fluid needs, making it essential for women to adapt their diets to meet their unique requirements. While DRVs provide a helpful baseline, individual factors such as exercise frequency, intensity, life stage, and hormonal fluctuations mean that women’s nutritional needs may vary greatly from population-level recommendations.

For women aiming to optimize their health, it’s important to work with a registered nutritional professional who can provide personalised advice, ensuring that nutrient and energy intake aligns with their physical activity levels and individual health goals. Whether you’re training for a race, balancing work and family life, or navigating the challenges of menopause, your body’s needs are as dynamic as your life itself.

By understanding the relationship between physical activity, metabolism, and nutrient needs, women can empower themselves to make informed decisions that enhance their overall health and well-being.

A note from Georgia: Whilst in this blog post I discuss exercise's such as endurance races, weight lifting and HIT workouts I want to highlight that exercise is personal to YOU. So please do not feel pressured to do exercise which you do not enjoy. For me my regular exercise looks like a dog walk and a yoga class- but for you it may look like cycling and a rock climbing session or a paddleboarding class. All movement is good movement. Love G x