The science behind a balanced diet

by Zoë Gamble

If you eat too much, you’ll get fat. Too little, and you’ll get thin.

Simple!    …or is it?

Having a healthy diet doesn’t just depend on the amount of food you eat. Our bodies require a mix of different types of foods to stay healthy, and we also need to exercise to keep our bodies in good condition.

Food Groups

Food groups required in a balanced diet

Proteins, carbohydrates, fats. CC-BY-NC science made simple

 

 

 

 

 

 

 

A mix of all of the food groups is essential for maintaining a healthy diet. The three main food groups and their uses are outlined in the table:

foodgroupchart

These food groups all provide the body with energy. They are used by the body to provide fuel for respiration:

respirationequation

Image: science made simple (CC-BY-NC)

 

 

 

 

 

 

 

As well as protein, carbohydrate and fat, the body also requires:

  • Water – the human body is made up of about 60% water. If we don’t drink enough fluids, our bodies become dehydrated. The recommended amount is about 8 glasses for women and 10 for men, but an individual’s needs will vary depending on activity level, and temperature.
  • Vitamins  – Our bodies need a variety of vitamins to keep working properly. Vitamin C, found in oranges, is essential to prevent scurvy, and also important in the immune system. Vitamin B, found in vegetables and fruit, has many functions.
  • Minerals – iron and calcium are essential minerals, found in a variety of foods, needed for turning the food you eat into energy, and building healthy teeth and bones
  • Fibre – found in food that comes from plants. Many benefits to our bodies, including aiding digestion.

A balanced diet can be very different for different people. That’s why if you’re trying to eat healthily, there is no secret formula that will work for everybody. The exact requirements of your body depends on your age, gender, how active you are, and whether you have any special dietary requirements (e.g. you choose not to eat certain food types, or have a food allergy).

BMI

The Body Mass Index is a guide to whether a person is a healthy weight for their height. It gives an indication of where a person is on a scale from underweight to obese. However, it is not a perfect tool. As muscle weighs more than fat, a professional body builder or rugby player for example, could have a high BMI indicating they are obese, when in fact they are very fit and healthy.

What the BMI number means

BMI indicator

How to calculate your BMI

Mass in kilograms ÷ (height in meters)²

For example, I am 57kg and 163cm.

57 ÷ (1.63)² = 21.4

This means I am within the normal weight range for my height. If you want to check your answer, try this online BMI calculator.

Want to find out how you compare to others? Find out here:

Where are you on the Global Fat Scale? 

What happens when we eat too much?

As well as the mobility difficulties which arise from becoming obese, there are also many health problems being overweight can cause. Obese people are more likely to suffer from arthritis, diabetes, high blood pressure and heart disease than people with a lower BMI.

What happens when we eat too little?

Being underweight is also associated with many health problems. People with a very low BMI may suffer from a lack of energy, be less able to resist infection from diseases, and develop deficiency diseases. These are when the body does not have enough of a certain thing it needs to work properly. For example, in developing countries, a disease called kwashiorkor is common. It results from not having enough protein in the diet and causes a swollen abdomen.

Calories and calorimetry

You might have heard of ‘calorie controlled diets’, but what is a calorie?

Calories are the energy within food. A calorie is the amount of energy it takes to heat up one gram of water one ºCelsius . We can find out how many calories are within different foods using a process called calorimetry. This involves burning the food, and seeing which one releases the most heat.

Calorimetry experiment

Image: sciencemadesimple (CC-BY-NC)

Top up your ‘good bacteria’

File:Yakult Light in Hong Kong 100ml.JPG

Yakult Light: Photo: Dezzawong (CC-BY-SA)

We’ve all seen the adverts for yoghurt drinks which claim to top up your ‘good bacteria’, but is there any truth behind their claims? And why would we want to top up on probiotics?

Actually, we humans benefit from something called our ‘gut flora’. This is what we call the microorganisms that live inside our intestines. While it is possible to live without them, they do a range of beneficial things inside our bodies. They can ferment unused carbohydrates, releasing energy, limit the growth of harmful (pathogenic) bacteria, play a role in cell growth, and even defend against certain diseases!

A healthy individual will already have a good balance of bacteria present inside their gut: there is then not much benefit to drinking probiotic drinks. It’s all about the balance – it is actually beneficial not to eliminate all of the ‘bad’ bacteria. If a person’s balance gets skewed, it can then be beneficial to take medical probiotics. Whether drinking probiotic yoghurt drinks has any benefit, well the scientific jury is still out on that one!

Now you know your BMI, the essential food groups, why they are needed in the body, and how to work out the amount of calories in foods.

Finally, test your knowledge with this healthy eating quiz from NHS choices

Curriculum Links

Wales

Interdependence of organisms

  • how food is used by the body as fuel during respiration and why the components of a balanced diet are needed for good health

England

Nutrition and digestion

  • the content of a healthy human diet: carbohydrates, lipids (fats and oils), proteins, vitamins, minerals, dietary fibre and water, and why each is needed

  • the consequences of imbalances in the diet, including obesity, starvation and deficiency diseases

  • the importance of bacteria in the human digestive system

Atoms, elements and compounds

  • conservation of mass changes of state and chemical reactions

Northern Ireland

Organisms and health

  • Healthy body and mind

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Posted in Activity, Biology