Bodies need fuel to function, grow and repair themselves. The digestive system is like a long, muscular assembly line about 10 metres long that breaks down the food that is eaten into its simplest parts (carbs, fats, proteins) for the body to absorb as fuel. Anything not used is eliminated through waste.

It is made up of the following organs:

• Digestive tract (mouth - oesophagus, stomach, small and large intestines, rectum and anus)
• Liver
• Pancreas
• Gall bladder

Enzymes

The body produces digestive enzymes in various glands and organs along the digestive tract, including the mouth, stomach, pancreas and small intestine. These enzymes break down complex food molecules into simpler components like sugars and amino acids, making them easier for absorption into the bloodstream (they help digest food). If an individual has a digestive enzyme deficiency, they may need to supplement their diet with enzymes to aid digestion.

Important digestive enzymes include:

• Amylase 
• Maltase
• Lactase
• Lipase
• Proteases
• Sucrase

Source: https://www.verywellhealth.com/

pH

pH = the potential of Hydrogen. It measures the amount of hydrogen ions in a substance. The pH scale is arranged with acidic solutions at number 1 and alkaline solutions at number 14. Water is neutral and is in the middle at number 7. See below for where stomach acid is on the pH scale. It has a really low pH level and helps the breakdown of food in the digestive process.

Source: https://www.australianenvironmentaleducation.com.au/

The digestive system is packed with specialised structures designed to maximise nutrient breakdown and absorption. These include:

Teeth: These hard structures in the mouth mechanically break down food into smaller pieces, increasing surface area for enzyme action and easier swallowing.

Tongue: This muscular organ manipulates food, mixing it with saliva and aiding in the formation of a food bolus for swallowing.

Stomach Muscles: The muscular walls of the stomach churn and mix food with digestive juices, ensuring thorough breakdown.

Small Intestine Villi: These tiny finger-like projections in the small intestine dramatically increase the surface area, allowing for optimal absorption of nutrients into the bloodstream.

Microvilli: Present on the surface of the villi, these microscopic brush-like projections further increase the surface area for nutrient absorption.

The Liver and Gallbladder: The liver produces bile, which helps break down fats in the small intestine. The gallbladder acts as a storage unit, concentrating bile for release when needed.

Source: https://www.niddk.nih.gov/

Stress and the Digestive System

Stress can have a significant impact on the digestive system, leading to a variety of symptoms and conditions which can indirectly affect movement and physical activity.

Stress can cause:

• Ulcers
• Nausea
• Diarrhoea
• Constipation
• Changes in gut microbiota
• Irritable bowel syndrome (IBS)
• Increased production of stomach acid
• Reduced blood flow to the digestive organs

Stress can impair the digestive system's ability to absorb nutrients, affecting energy levels and overall performance.

Chronic stress can lead to increased muscle fatigue and reduced endurance. Stress-related digestive issues can cause pain and discomfort, affecting physical activity levels.

Stress can negatively impact motivation and focus, making it difficult to engage in physical activity. Chronic stress can weaken the immune system, increasing the risk of injuries.

Stress can significantly impact movement and physical activity.

Managing stress is crucial for optimising performance and preventing injuries. A balanced diet and healthy lifestyle can help mitigate the negative effects of stress on the body.

Sources:

American Psychological Association. (2023). Stress and Health.

National Institutes of Health. (2023). Digestive System.

Cleveland Clinic Health Essentials. (2023). Stress and the Digestive System.

Macronutrients provide the body with energy and building blocks for cells and tissues. They are essential for digestive health and overall wellbeing.

Carbohydrates: Provide the primary source of energy for the body. They are broken down into glucose, which fuels cells.

Proteins: Essential for building and repairing tissues, including those of the digestive system. They also play a role in hormone production.

Fats: Provide essential fatty acids, which are important for cell membranes, hormone production and nutrient absorption. They also help to absorb fat-soluble vitamins.

Key Roles of Macronutrients in Digestive Health

Energy: Provide fuel for digestive processes.

Tissue Repair: Help repair the lining of the digestive tract.

Nutrient Absorption: Facilitate the absorption of other nutrients.

Hormone Production: Contribute to the production of hormones that regulate digestion.

Micronutrients including vitamins and minerals, are essential for various bodily functions 

including digestive health.

• Vitamins:

Vitamin B12: Essential for the absorption of nutrients from the digestive system.

Vitamin C: Helps maintain the integrity of the digestive tract lining.

Vitamin D: Plays a role in calcium absorption which is important for digestive health.

• Minerals:

Zinc: Involved in various digestive processes, including the production of digestive enzymes.

Magnesium: Helps regulate bowel movements and can aid in digestion.

Potassium: Essential for electrolyte balance, which is important for proper digestive function.

Key Roles of Micronutrients in Digestive Health

Nutrient Absorption: Facilitate the absorption of other nutrients.

Digestive Enzyme Production: Support the production of enzymes needed for digestion.

Electrolyte Balance: Help maintain proper electrolyte balance which is essential for digestive function.

The Thermic Effect of Food

The thermic effect of food (TEF), also known as diet-induced thermogenesis (DIT) or specific dynamic action (SDA) refers to the energy the body expends to digest, absorb, store and dispose of food eaten.

The following highlights the complex relationship between food, nutrition and energy balance in the human body. It represents about 10% of an individual’s daily calorie expenditure for healthy adults on a mixed diet and can vary depending on several factors. TEF helps regulate the body weight by contributing to overall calorie expenditure and plays a role in nutrient breakdown, absorption and storage.

Key Points

Diet plays a crucial role in maintaining energy balance, which is the equilibrium between calories consumed and calories burned.

Macronutrients (protein, carbs, fats) have different impacts on energy expenditure. Protein has a higher thermic effect of food (TEF) compared to carbs and fats. TEF is the energy the body uses to process food.

Micronutrients (vitamins, minerals) are essential for various bodily functions that influence energy metabolism.

Dietary patterns that emphasise whole foods, fruits, vegetables and lean protein can promote healthy energy balance.

Processed foods, sugary drinks and excessive saturated/trans fats can negatively impact energy balance and contribute to weight gain.

Factors affecting TEF

• Macronutrient composition:
• Protein has the highest TEF (around 20-30% of its calorie content is burned during processing).
• Carbs have a moderate TEF (around 5-10% burned).
• Fats have the lowest TEF (around 0-5% burned).
• Meal size: Larger meals generally have a higher TEF compared to smaller, more frequent meals.
• Individual factors: Age, genetics and activity level can also influence TEF.

Source: https://pubmed.ncbi.nlm.nih.gov/32331288/ 

Nutritional Considerations

Nutritional considerations include pre, during and post performance needs. Nutrition is vital to bodily functions and should always be in balance. Athletes should always eat enough vegetables, fruit, dairy, protein, fats and grains. As athletes place more stress on their bodies and use their bodies more than others, they require greater amounts of these nutrients than non-athletes. 

The Australian Guide to Healthy Eating indicates the amount of each food group that is recommended for all Australians. An athlete will require roughly the same percentage of each food group, but will consume greater amounts of them. In addition to this, an athlete may benefit from other nutritional considerations before, during and after a performance.

These include carbohydrate loading before endurance events, the consumption of glucose and electrolytes during events lasting longer than 60 minutes and replacing glycogen and fluid lost after performance.

Pre-Performance

Before competition an athlete should ensure they are well hydrated. Hydration is vital to performance and an athlete needs to ensure they drink a minimum 2-3L the day before competition, then drink 500mL in the morning of the competition and a further 250mL 30min before competition provided hydration has been maintained throughout the day.

Before competition an athlete should not try to eat anything new. If an athlete tries new food and they have a reaction to it their performance will be negatively affected. Instead an athlete should eat complex carbohydrates in a familiar form, consuming around 100g 3-4 hrs before competition. An example of this might be a bowl of porridge, a dark wholemeal bread or muesli. As competition approaches food size should get smaller, moving from a full meal to a small snack such as a muesli bar or banana 1-2 hrs before competition and only liquids after this time.

Carbohydrate loading is the process used by athletes to ensure glycogen stores in muscle and the liver are at their maximum. They do this by tapering training levels and consuming large amounts of complex carbohydrates in the week before competition. Carbohydrate loading benefits performance that would normally deplete glycogen stores and delays the onset of fatigue caused by a greater reliance on fat to produce ATP in the aerobic energy system. Thus carbohydrate loading will allow for higher aerobic intensities being maintained for longer, and can help ensure glycogen stores remain for a late burst of speed in the lactic acid energy system. Carbohydrate loading will only benefit sports that go longer than 60 min, such as soccer, rugby league or Australian Rules Football.

During Performance

Nutritional requirements during performance include the need to maintain hydration and for extended periods of exercise, taking the opportunity to replenish blood glucose levels.

During performance an athlete needs to maintain hydration. Hydration aids performance and dehydration hinders performance, decreasing concentration and reducing the body’s ability to function. All athletes sweat at different rates during performance, but it is recommended that they drink around 1L spread throughout every hour of activity. The more frequent this consumption the better, so a marathon runner might drink some water every 5 min, while a rugby player may drink every 10 minutes depending on the events on the field and stoppages.

There is mixed information about sports drinks and their use during sports performance as many Australian and global nutritional agencies are supported by sports drink companies. Athletes need to seek professional advice from their sports nutritionist about appropriate beverages to consume in addition to water. The salts in sports drinks help the body to hold fluid and replace the salt lost through sweat production. Salts lost through sweat include sodium and potassium. Salt in blood helps to retain fluid, particularly preventing fluid loss through excrement, requiring water to remain in the blood and not be filtered out by the kidney to the bladder. So an athlete in an AFL game might consume a beverage to replace fluid and salt lost through sweat and in order to gain glucose to aid performance by delaying fatigue caused by glycogen depletion, but there is some debate about the effectiveness of sports drinks and even the natural form of electrolytes in coconut. Much of the literature discusses the extreme benefits of water as the preferred and only source required for optimal performance. 

Sources:

https://www.sportsdietitians.com.au/factsheets/fuelling-recovery/sports-drinks/

https://www.ais.gov.au/__data/assets/pdf_file/0009/1001106/Sports-Drinks-Infographic-2pg.pdf

 The goal of nutrition post-performance is to restore the body's fuel stores and provide the nutrients required for muscular repair and recovery. The nutrients needed are water, carbohydrates and protein. Athletes sweat at varying rates, but it is important for an athlete to know their sweat rate and to replace any fluid lost during competition. Athletes can calculate their sweat rate by weighing themselves before and post-performance and keeping track of the fluid they consume. They can then subtract their end weight from their pre-performance weight minus the fluid consumed to find how much sweat they lost during the competition. Athletes should then consume all the fluid lost over the first hour post-event and then continue to maintain hydration.

Carbohydrates are consumed in order to restore glycogen stores that have been lost in both muscle and liver. Initially high GI foods can be eaten, but a large meal of complex carbohydrates 1-2 hrs post-performance is recommended. This will help replace glycogen stores. Further carbohydrates will need to be consumed over 24 - 48hrs in order to restore and possibly increase glycogen stores.

Protein should be consumed 1-2 hrs post-performance to help repair damaged tissue. This is particularly important for power and strength based activities and contact sports, where body tissue is frequently damaged. The protein consumed is used by the body to repair the damaged tissue and may help strengthen the tissue to avoid damage next time.

In addition to this, sleep and rest is vital for recovery. The body repairs itself and recovers during sleep. Sleep is still THE BEST recovery strategy available.

Sources: 

https://www.sportsdietitians.com.au/section/food-for-your-sport/  https://www.betterhealth.vic.gov.au/health/healthyliving/sporting-performance-and-food#using-nutritional-supplements-to-improve-sporting-performance 

Function

The endocrine system is a network of glands that produce chemical messengers called hormones. These hormones travel through the bloodstream, acting like signals to influence various bodily functions in target cells or tissues. It works in close collaboration with the nervous and immune systems to maintain internal balance (homeostasis) and manage the body's response to stress.

Structure

The main endocrine glands/organs include:

Pituitary Gland: "Master gland" controlling other glands and hormone levels.

Thyroid Gland: Regulates metabolism and growth.

Parathyroid Glands: Maintain calcium and phosphate balance.

Adrenal Glands: Produce various hormones, including stress hormone (adrenaline) and cortisol (blood sugar regulation).

Pancreas: Functions as both an endocrine and exocrine gland. As an endocrine gland, it releases insulin and glucagon for blood sugar control.

Ovaries (females): Produce sex hormones like oestrogen and progesterone.

Testes (males): Produce testosterone, the primary male sex hormone.

Other: Adipose tissue, kidneys, and gut also play a role in hormone production.

Interaction with Other Systems:

Muscular System: The endocrine system acts as a chemical conductor for the muscular system. Hormones influence muscle growth, fuel availability, strength, and endurance.

Nervous System: The nervous system can directly influence hormone release from some glands.

Immune System: The endocrine system affects the immune system's response to inflammation and infection.

Hormone Action:

Hormones bind to specific receptors on target cells, triggering a cascade of signals within the cell to produce a desired effect. The endocrine system is tightly regulated through feedback loops. The release of a hormone can be influenced by other hormones, proteins, or nerve signals, ensuring hormone levels stay within the optimal range.

Source: https://www.betterhealth.vic.gov.au/

Factors that impact on the efficiency of the endocrine systems

Stress and the Endocrine System

Stress, whether physical or emotional, can significantly impact the endocrine system, a network of glands that secrete hormones.

Adrenal Glands: Under stress, the adrenal glands release stress hormones like cortisol and adrenaline. These hormones can:

• Increase blood sugar levels
• Raise blood pressure
• Suppress the immune system
• Impact digestion
• Impact muscle function and performance 

Hypothalamus-Pituitary-Adrenal (HPA) Axis: Chronic stress can disrupt the HPA axis, leading to imbalances in hormone production and affecting various bodily functions, including movement and physical activity.

Macronutrients can influence hormone production and levels, affecting the endocrine system's function.

Carbohydrates: Excess carbohydrate intake can lead to fluctuations in blood sugar levels, impacting hormone production.

Proteins: Adequate protein intake is essential for the production of hormones, including those involved in metabolism and growth.

Fats: Certain fatty acids are precursors to hormones, and a balanced intake of fats is important for endocrine health.

Micronutrients play a crucial role in hormone production and regulation.

Please refer to the tables below.

Please refer to the diagram below.