Human Nutrition » Water and Dietary Fibre

What you'll learn this session

Study time: 30 minutes

The importance of water in the human body
Functions of water in nutrition and bodily processes
What dietary fibre is and its types
Health benefits of dietary fibre
Recommended intake of water and fibre
Conditions related to inadequate water and fibre intake

Water in Human Nutrition

Water is often overlooked as a nutrient, but it's actually the most essential component of our diet. Without water, we can survive only a few days, compared to weeks without food. Our bodies are made up of approximately 60% water, with some organs containing even higher percentages.

Key Definitions:

Hydration: The process of providing adequate water to body tissues.
Dehydration: A condition where the body loses more water than it takes in.
Electrolytes: Minerals in the body that carry an electric charge and are essential for many bodily functions.

💧 Functions of Water in the Body

Water plays numerous crucial roles in our bodies:

Acts as a transport medium for nutrients and waste products
Helps regulate body temperature through sweating
Serves as a lubricant for joints and internal organs
Forms part of blood plasma, helping transport oxygen
Aids digestion by forming part of digestive juices
Helps maintain blood pressure and volume

💦 Water Balance

The body carefully regulates water levels through:

Intake: Drinking water, consuming food with high water content
Output: Urine, sweat, breathing, faeces
Regulation: Hormones like ADH (antidiuretic hormone) control water retention by the kidneys
Thirst mechanism: Triggered when the body needs more water

Daily Water Requirements

The NHS recommends drinking 6-8 glasses of fluid per day, which is about 1.5-2 litres. However, requirements vary based on:

Body size and weight
Activity level and exercise intensity
Environmental temperature and humidity
Health status (some conditions require more or less water)

Did You Know? 💡

We get about 20% of our daily water intake from food. Foods like cucumber, lettuce, watermelon and strawberries contain over 90% water by weight!

Dehydration and Its Effects

Dehydration occurs when water output exceeds intake. Even mild dehydration (losing just 1-2% of body water) can have noticeable effects:

😕 Mild Dehydration

Symptoms include:

Thirst
Dry mouth
Headache
Darker urine
Tiredness

😧 Moderate Dehydration

Symptoms include:

Extreme thirst
Dry skin
Dizziness
Reduced urine output
Rapid heartbeat

😱 Severe Dehydration

Symptoms include:

Confusion
Lack of sweating
Low blood pressure
Rapid breathing
Can be life-threatening

Dietary Fibre

Dietary fibre, sometimes called roughage, is the indigestible part of plant foods. Unlike other nutrients, fibre passes through our digestive system relatively intact, providing numerous health benefits along the way.

Key Definitions:

Dietary fibre: Plant material that cannot be broken down by digestive enzymes in humans.
Soluble fibre: Type of fibre that dissolves in water to form a gel-like substance.
Insoluble fibre: Type of fibre that does not dissolve in water and adds bulk to stool.

🌽 Types of Dietary Fibre

Soluble Fibre:

Dissolves in water to form a gel-like substance
Slows digestion and nutrient absorption
Found in oats, barley, fruits, vegetables and legumes
Helps lower blood cholesterol and regulate blood sugar

Insoluble Fibre:

Does not dissolve in water
Adds bulk to stool and helps food pass more quickly through the digestive system
Found in whole grains, nuts, seeds and the skins of fruits and vegetables
Helps prevent constipation and promotes regular bowel movements

💪 Health Benefits of Dietary Fibre

Regular consumption of adequate fibre:

Promotes healthy bowel movements and prevents constipation
Helps maintain bowel health and may reduce risk of colorectal cancer
Lowers cholesterol levels, reducing risk of heart disease
Helps control blood sugar levels, important for managing diabetes
Aids in weight management by increasing feelings of fullness
Supports a healthy gut microbiome

Recommended Fibre Intake

The UK government recommends that adults consume 30g of fibre per day. However, most people in the UK only consume about 18g per day, well below the recommendation.

For children, the recommendations are:

2-5 years: 15g per day
5-11 years: 20g per day
11-16 years: 25g per day
17+ years: 30g per day

Case Study Focus: The Western Diet Problem

Modern Western diets often lack adequate fibre due to high consumption of processed foods. Studies show that populations with traditional high-fibre diets (like rural African communities) have significantly lower rates of digestive disorders like diverticulitis, irritable bowel syndrome and colorectal cancer compared to Western populations. This highlights how our shift away from whole foods has impacted digestive health.

Fibre Content in Common Foods

To help you understand how to reach your daily fibre target, here are some common foods and their fibre content:

🍞 Grains

Wholemeal bread (2 slices): 6.5g
Brown rice (1 cup cooked): 3.5g
Wholegrain pasta (1 cup cooked): 6g
Porridge oats (40g dry): 4g
Bran flakes (30g): 4g

🍇 Fruits & Vegetables

Apple (with skin): 4g
Banana: 3g
Pear: 5.5g
Broccoli (80g): 2.5g
Carrots (80g): 2g
Potato with skin (medium): 4g

🥜 Legumes & Nuts

Baked beans (200g): 7g
Chickpeas (200g): 8g
Lentils (200g cooked): 8g
Almonds (30g): 3.5g
Chia seeds (1 tbsp): 5g

Conditions Related to Inadequate Fibre Intake

Not consuming enough fibre can contribute to several health issues:

Constipation: Difficulty passing stools due to lack of bulk
Diverticular disease: Formation of small pouches in the colon that can become inflamed
Haemorrhoids: Swollen veins in the rectum often caused by straining during bowel movements
Increased risk of colorectal cancer: Studies show a link between low fibre intake and higher cancer risk
Weight gain: Fibre helps you feel full, so inadequate intake may lead to overeating

Tips for Increasing Water and Fibre Intake 💡

For water:

Carry a reusable water bottle with you
Set reminders to drink water throughout the day
Drink a glass of water before each meal
Add fruit slices or herbs to water for flavour

For fibre:

Switch to wholegrain versions of bread, pasta and rice
Leave the skin on fruits and vegetables when appropriate
Add beans or lentils to soups and salads
Snack on nuts, seeds and dried fruits
Increase fibre intake gradually to avoid digestive discomfort

Summary

Water and dietary fibre are essential components of a healthy diet, though they work in different ways. Water is vital for nearly all bodily functions, from regulating temperature to transporting nutrients. Fibre, while not digested by the body, plays crucial roles in digestive health, heart health and weight management.

Ensuring adequate intake of both water (6-8 glasses daily) and fibre (25-30g daily for teenagers) is important for maintaining overall health and preventing various conditions. Remember that both should be increased gradually to allow your body to adjust, particularly in the case of fibre.

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