Chapter 4: “Food and digestion”
Your body is made up of chemicals. You get these chemicals from the food you eat. Your body needs this for:
• For energy
You need food to work your muscles and other organs. Your food is the fuel that keeps you going. Your body won’t work without food.
• For growth and repair
As you grow you make new cells. You also need to replace old or damaged cells. You make new cells from chemicals in your food.
• To stay healthy
Lots of reactions take place in the cells of your body. Chemicals in your food are needed for these reactions.
So nutrition means getting food to provide energy and substances needed for growth and repair.
In our food are the nutrition’s:
If we want to stay healthy our body must have:
• Enough food
• A variety of food – so that our body gets all the different things it needs.
• Enough water
We need a healthy balanced diet.
Your body is made up of billions of cells. These cells are made mainly from proteins.
When you grow your body needs protein to make new cells. Your body may need to replaced damaged or old cells. For this you also need protein.
Proteins are made up of amino acids. There are 20 different types of amino acids.
Haemoglobin, enzymes, antibodies and some hormones are soluble proteins. Keratin is a fibrous protein found in the skin and hair.
Sugars are carbohydrates.
Sugar for in your tea is called sucrose
Sugar in you milk is called lactose
Sugar that our body uses the most is glucose
Starch is also a carbohydrate. This is a large molecule. It is made up of lots of smaller glucose molecules joined together.
Glycogen is a large carbohydrate just like starch. This is also made up of glucose molecules joined together. We store glycogen in our liver and muscles. Our bodies change glycogen to glucose when we need it.
Different types of fats. Fats are made up of three different fatty acids joined together. There are different kind of fatty acids.
Fats give us energy. It contains more energy than carbohydrates. Our body uses fats as an energy store. We store fat under the skin and around the heart and kidneys. When we are short of energy our body uses this.
Fats are good insulators. They cut down heat loss.
Fats also give buoyancy. Be able to float on water.
We need: Proteins for growth and repair of cells.
Carbohydrates for energy
Fats as a store of energy and for warmth.
There are two types of main fat:
• Saturated fat (from animals)
• Unsaturated fat (from plants)
Saturated fats increase the level of cholesterol in our blood.
Cholesterol is a chemical made in liver and found in the blood. The amount of cholesterol that we produce depends on your diet, but also inherited factors. High levels of cholesterol are linked to an increased risk of heart disease and an increase in blood pressure due to a narrowing of the blood vessels.
Food gives us energy. We need this for all the activities that we do (even lying down!!!!). Carbohydrates and fats are high- energy foods.
Energy in food is measured in kilojoules (kJ). 1 kilojoule= 1000 joules.
We can measure the amount of energy in some foods by burning it. As the food burns it gives out energy. We can use this energy to heat up some water. The hotter the water gets the more energy is in the food.
Most foods have their energy content on the label. The amount of energy is given in kilojoules per 100g of food.
The amount of food that you need depends on how much energy you use up every day.
The amount of energy you need depends on:
• Your body size
• How active you are in a day
• How fast you grow
The food you eat in a day should provide you with enough energy to get through the day.
When you’re lying on your bed you still use a lot of energy to keep:
• Your heart beating
• Your lungs breathing
• Your body temperature constant
• Keeping all the chemical reactions in your body going.
This “ticking over” speed at which our bodies works is the basal metabolic rate (BMR).
When you eat more food than you need, your body stores the extra as fat.
Your energy intake is the amount of energy you get in your food in a day.
Your energy output if our energy intake is greater than our energy output, we put on weight.
In countries like Britain and the USA more people suffer from overeating than from eating too little. But when people eat too much they become obese. Being too fat
Major causes of obesity include:
• High intake of fatty foods and refined foods containing a lot of added sugar. Junk food
• Too little exercise
• Social and emotional stress, leading to “comfort eating” eating because you’re feeling sad for example.
There are 2 ways in which people can identify being obese:
• Being 20% above the recommended weight for his/ her height
• Having a body mass index (BMI) greater than 30.
Body mass index=
A person with a BMI of <20 is underweight, between 25 and 30 is overweight, and >30 is obese. Between 20 and 24 is perfect.
Waistband measurements are easier to calculate than BMI.
Overweight people are much more likely than thinner people to have the following health problems:
• Heart disease
• High blood pressure
• Diabetes (high blood sugar)
• Arthritis (worn joints)
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