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A Healthy Diet
Summary
Title of the Chapter: A healthy diet
A healthy diet đđĨĻ
In this chapter, you will learn:
That a balanced diet is made up of proteins, carbohydrates, fats and oils, water, minerals, and vitamins in the correct amounts.
About the different amounts of nutrients that animals need.
That carbohydrates and fats can be used to store energy in animals.
About the importance of fibre (Science extra).
How to think and work like a scientist to discover a vitamin (Science in context).
About treating iodine deficiency (Science extra).
About the job of dietitians (Science in context).
About cholesterol and the circulatory system (Science in context).
How your health, growth, and development can be affected by how you live.
In this chapter, you'll also learn about habits such as smoking.
Do you remember? đ¤
What is a diet?
Why do you need to think about your diet?
Name the parts of the digestive system and describe what happens in them.
You are reminded about treating malnutrition and famine (not having enough food).
Diet 1
No breakfast đŗâ
Eat sweets on the way to school.
Eat a chocolate bar and have a fizzy drink at morning break.
Have fried food such as potato chips or fries with lunch.
Eat some more sweets or candies in the afternoon.
Have a snack of crisps (potato chips), sweets, or candies and fizzy drinks during the evening.
Diet 2
Have breakfast of cereal and milk, toast, and fruit juice.
Eat an apple at morning break.
Have many different foods for lunch during the week, including different vegetables, pasta, and rice.
Eat an orange in the afternoon.
Eat a small snack with green vegetables.
Have a milky drink at bedtime.
Nutrients needed by the body đĒ
A chemical that is needed by the body to keep it healthy is called a nutrient.
The human body needs a large number of different nutrients to keep it healthy.
They can be divided up into these groups:
Proteins
Fats and oils
Carbohydrates
Vitamins
Minerals
In addition to these nutrients, the body also needs water.
Water is needed to help control your body temperature.
Fibre is also needed by the body.
Water carries dissolved materials (things that are mixed in water) around the body and helps control your body temperature.
Did You Know?
The word 'carbohydrate' comes from the names of the chemicals that make it up: carbon (carbo) and hydrogen and oxygen (hydrate).
Glucose is a chemical form of energy that moves easily in blood (used in foods) and is a source of energy in the cells of the body.
Starch (found in things like potatoes) stores energy in plants but is one of the most widely known kinds of carbohydrate that we eat.
Sucrose (in table sugar) is another type of carbohydrate that we eat.
There are many types of carbohydrate, and animals and humans eat food to get them.
Plants also make another carbohydrate, called cellulose, which they use to make cell walls. It forms the part of our diet called fibre.
The crunchy stalks of celery are made from cellulose.
Chocolate contains a substance called theobromine, which slightly breaks down the tooth enamel (the strong outer layer).
However, if a dog eats chocolate, the theobromine can make the dog sick and possibly die.
Proteins
Proteins are found in both plants and animals.
They are the materials that form most of the parts in our bodies, such as muscle and bone.
Proteins are also needed for the body to grow and for fixing any damage from being sick or having an accident.
Did You Know?
Hair is made of protein that grows out from your skin.
Proteins are made from the tiny parts called the elements carbon, hydrogen, oxygen, and nitrogen.
Some proteins also contain sulfur (S).
Fats
Fats can be used as a way to store energy in animals and plants.
Mammals (like us) increase their body fat in the autumn so that they can use the energy stores in plants.
Fats are used as a store of energy in animals and are used for insulation (a warm layer) beneath the skin to keep the bodies of mammals warm.
Oils (like sunflower oil) are produced by plants.
Fats are the solid fats we eat, and oils are the liquid fats or oils produced by plants, such as sunflower oil, that we eat to get our food.
The solid fats we eat are called lipids.
The body cannot release the energy in fats as quickly as the energy in carbohydrates.
Did You Know?
Fats are made from the elements carbon, hydrogen, and oxygen.
Food that has fat can leave a translucent (letting light pass through) mark on paper, but it scatters the light, so you can see water.
However, water dries up (evaporates) from paper, but the fat in food does not.
This information can be used to create a fat test.
Science extra: Is it fat or water? đ§
Work safely: Hands should be washed well after this experiment.
Do not use the Sun as part of your test, as it can permanently hurt your eyes.
You will need:
A piece of paper that soaks things up, like newspaper.
A small piece of butter.
A container.
A plastic knife.
A small container of water.
A pipette or dropper (for water).
Plan and investigation:
1. Make a fair test to compare the size of marks of fat and water on the paper.
2. Design a plan that includes the following things:
3. A test to see if the marks are translucent (see-through).
4. Allowing a time and a place for the water to dry up (evaporation).
5. Show your teacher your plan. If approved, try it.
The nutrients in food đ
The amounts of different nutrients in foods have been found out by doing experiments.
The next section shows the nutrients in a small amount of food (100g) for a few different foods.
Table 4.2 The nutrients in some common foods (the symbol mu g stands for 'microgram', which is a millionth of a gram).
Table 4.2 The Nutrients in Some Common Foods (per 100g)
(Note: mu g is a microgramâa tiny amount!)
Carrot
Energy: 134 kJ
Protein: 0.7 g
Carbohydrates: 5.4 g
Fat: 0 g
Calcium: 48 mg
Iron: 0.7 mg
Vitamin C: 6 mg
Vitamin D: 0 mu g
Potato
Energy: 358 kJ
Protein: 2.1 g
Carbohydrates: 18.0 g
Fat: 0 g
Calcium: 8 mg
Iron: 0.7 mg
Vitamin C: 8-30 mg
Vitamin D: 0 $\mu$g
Bread (Wholemeal)
Energy: 1025 kJ
Protein: 9.3 g
Carbohydrates: 46.7 g
Fat: 1.0 g
Calcium: 28 mg
Iron: 3.0 mg
Vitamin C: 0 mg
Vitamin D: 0 $\mu$g
Rice
Energy: 1549 kJ
Protein: 6.2 g
Carbohydrates: 84.0 g
Fat: 0.4 g
Calcium: 4 mg
Iron: 0.4 mg
Vitamin C: 0 mg
Vitamin D: 0 $\mu$g
Spaghetti
Energy: 1531 kJ
Protein: 9.9 g
Carbohydrates: 7.9 g
Fat: 1.0 g
Calcium: 4 mg
Iron: 0.4 mg
Vitamin C: 0 mg
Vitamin D: 0 $\mu$g
Lentil
Energy: 1256 kJ
Protein: 23.8 g
Carbohydrates: 53.2 g
Fat: 0.5 g
Calcium: 39 mg
Iron: 7.6 mg
Vitamin C: 0 mg
Vitamin D: 0 $\mu$g
Pea
Energy: 273 kJ
Protein: 5.8 g
Carbohydrates: 10.6 g
Fat: 0.5 g
Calcium: 18 mg
Iron: 1.9 mg
Vitamin C: 25 mg
Vitamin D: 0 $\mu$g
Jam
Energy: 1075 kJ
Protein: 0.5 g
Carbohydrates: 69.2 g
Fat: 0 g
Calcium: 18 mg
Iron: 1.2 mg
Vitamin C: 10 mg
Vitamin D: 0 $\mu$g
Lamb
Energy: 1388 kJ
Protein: 15.9 g
Carbohydrates: 0 g
Fat: 30.2 g
Calcium: 7 mg
Iron: 1.3 mg
Vitamin C: 0 mg
Vitamin D: 0 $\mu$g
Milk
Energy: 274 kJ
Protein: 3.3 g
Carbohydrates: 4.8 g
Fat: 3.8 g
Calcium: 120 mg
Iron: 0.1 mg
Vitamin C: 1 mg
Vitamin D: 0.05 $\mu$g
Cheese 1 (Cheddar)
Energy: 1549 kJ
Protein: 25.4 g
Carbohydrates: 0.8 g
Fat: 43.0 g
Calcium: 810 mg
Iron: 0.6 mg
Vitamin C: 0 mg
Vitamin D: 0.4 $\mu$g
Cheese 2 (Cottage)
Energy: 1531 kJ
Protein: 15.3 g
Carbohydrates: 4.5 g
Fat: 4.0 g
Calcium: 80 mg
Iron: 0.2 mg
Vitamin C: 0 mg
Vitamin D: 0.02 $\mu$g
Butter
Energy: 3006 kJ
Protein: 0.5 g
Carbohydrates: 0 g
Fat: 81.0 g
Calcium: 15 mg
Iron: 0 mg
Vitamin C: 0 mg
Vitamin D: 1.25 $\mu$g
Chicken
Energy: 870 kJ
Protein: 20.8 g
Carbohydrates: 0 g
Fat: 6.7 g
Calcium: 11 mg
Iron: 1.5 mg
Vitamin C: 0 mg
Vitamin D: 0 $\mu$g
Egg
Energy: 590 kJ
Protein: 12.3 g
Carbohydrates: 0.9 g
Fat: 10.9 g
Calcium: 54 mg
Iron: 2.1 mg
Vitamin C: 0 mg
Vitamin D: 1.50 $\mu$g
Fish 1 (White fish like Cod)
Energy: 274 kJ
Protein: 17.4 g
Carbohydrates: 0.7 g
Fat: 0.7 g
Calcium: 16 mg
Iron: 0.3 mg
Vitamin C: 0 mg
Vitamin D: 0 $\mu$g
Fish 2 (Oily fish like Herring)
Energy: 970 kJ
Protein: 16.8 g
Carbohydrates: 0.3 g
Fat: 33 g
Calcium: 33 mg
Iron: 0.8 mg
Vitamin C: 0 mg
Vitamin D: 22.2 $\mu$g
Apple
Energy: 197 kJ
Protein: 0.3 g
Carbohydrates: 12.0 g
Fat: 0 g
Calcium: 7 mg
Iron: 0.3 mg
Vitamin C: 5 mg
Vitamin D: 0 $\mu$g
Banana
Energy: 326 kJ
Protein: 1.1 g
Carbohydrates: 19.2 g
Fat: 0 g
Calcium: 4 mg
Iron: 0.4 mg
Vitamin C: 10 mg
Vitamin D: 0 $\mu$g
Orange
Energy: 150 kJ
Protein: 0.8 g
Carbohydrates: 8.5 g
Fat: 0 g
Calcium: 41 mg
Iron: 0.3 mg
Vitamin C: 50 mg
Vitamin D: 0 $\mu$g
Notes for Tables 4.2 and 4.3
Vegetables are raw; the bread is wholemeal bread.
Cheese 1 is Cheddar cheese.
Cheese 2 is cottage cheese.
Fish 1 is a white fish such as cod.
Fish 2 is an oily fish such as herring.
Let's Talk đŖī¸
In groups, answer the following questions:
1. Which foods are vegetarian? What foods would a vegetarian eat?
2. What foods would a vegetarian not eat?
3. Which foods would you expect to contain a lot of nutrients?
4. Which foods provide all the nutrients that humans need?
5. Why might you expect this?
6. What percentage of the nutrients does an apple contain?
Minerals
The body needs 20 different minerals to keep it healthy.
Two minerals are very important: iron and calcium.
Calcium is needed to make strong bones and healthy teeth.
Iron is needed to help form red blood cells and to help them carry oxygen around the body to the cells.
Did You Know?
A meal contains protein, vitamin D, iron, calcium, fat, and carbohydrates.
The tiny amounts of these minerals in food are needed to keep the body healthy.
Anemia (or anaemia) can be cured by eating more iron in the diet.
Water is very important for the body.
About 70% of the human body is water.
The body can survive for only a few days without a drink of water.
All the substances that the body needs for life dissolve in water.
Water is found in all cells and is where all the chemical reactions (changes) between the substances take place to keep us alive.
The blood is made mainly from warm water. It is the liquid that carries all the substances we need.
Water is also used to cool down the body by the evaporation (turning to gas) of sweat from the skin.
The blood must clot (thicken) when you cut yourself. This is the body's way of stopping blood loss.
Energy in food âĄ
A piece of equipment called a bomb calorimeter is used to find out how much energy there is in food.
A food item is placed inside it and oxygen is pumped in.
Then the food is set on fire, and all the heat that is produced is measured.
Finally, the energy in 100g of food is calculated in kilojoules (kJ), and tables are produced, like the ones shown here.
Table 4.3 The energy values of some common foods.
Table 4.3 The Energy Values of Some Common Foods (per 100g)
Butter: 3006 kJ
Peanut: 2428 kJ
Cheese 1 (Cheddar): 1708 kJ
Spaghetti: 1549 kJ
Rice: 1531 kJ
Lamb: 1388 kJ
Lentil: 1256 kJ
Jam: 1116 kJ
Bread: 1025 kJ
Fish 2 (Oily fish): 970 kJ
Chicken: 602 kJ
Cheese 2 (Cottage): 480 kJ
Banana: 326 kJ
Potato: 324 kJ
Fish 1 (White fish): 321 kJ
Milk: 274 kJ
Pea: 273 kJ
Apple: 197 kJ
Carrot: 130 kJ
Orange: 150 kJ
14. Foods shown in Table 4.3:
a. Put the nine foods with the highest energy values in order, starting with the highest and ending with the lowest.
b. Look at the nutrient content of these foods in Table 4.2. Put the nine foods from question 14.a into food groups based on whether you think the Energy/kJ figures show the amount of fat and carbohydrate in the food.
c. Do fats and carbohydrates store the same amount of energy (see also pages 26â27)? Explain your answer.
d. Why might people who are trying to lose weight eat cottage cheese instead of Cheddar cheese? Explain your answer.
e. Describe the nutrients you would expect it to contain.
f. Milk is an oily fish. Describe the nutrients you would expect it to contain.
g. Look again at the eating pattern you prepared for Question 1 on page 26.
h. Look closely at your diet and divide it up into the food groups shown in Table 4.5 (page 36). How well does your diet give you all the nutrients you need?
How the body uses nutrients đ§Ē
Vitamins
Vitamins are needed by the body in much smaller amounts than carbohydrates, fats, and proteins.
When vitamins were first found, they were named after the letters of the alphabet.
Later, when scientists knew more about them, they were also given chemical names.
Each vitamin has one (or more) job inside the body.
Vitamin A helps the eyes to see in dim light. It also helps make a mucus lining for the breathing, digestive, and excretory systems, which protects against germs.
A lack of vitamin C causes the deficiency disease called scurvy.
As the disease gets worse, bleeding occurs in the gums in the mouth, under the skin, and into the joints. If it is severe, death may happen because of a lot of bleeding in the body.
Vitamin D helps the body take up calcium from food to make bones and teeth strong.
Children who lack vitamin D in their diet may get the deficiency disease called rickets.
In rickets, the bones do not grow to their full strength and may bend.
This is seen most often in the leg bones.
This child has rickets. It can be stopped by adding supplements with vitamin D to the diet.
Table 4.1 Vitamins and Their Uses
Vitamin A
Effect on body: Helps eyes to see in the dark.
Good sources: milk, liver, cod-liver oil.
Vitamin C
Effect on body: Prevents the disease scurvy, which causes gums to bleed and the circulatory system (blood flow) is damaged.
Good sources: Blackcurrant, orange, lemon, papaya, guava.
Vitamin D
Effect on body: Prevents the disease rickets, in which bones become soft and leg bones of children may bend.
Good sources: egg yolk, butter, cod-liver oil, pilchard, herring, sunlight.
4. In a person with rickets, why do the leg bones bend more than the arm bones?
Science in context đ¨âđŦ
Thinking and working scientifically to discover a vitamin
There are many stories about the discovery of vitamins. They show how scientists used scientific thinking and work to make their discoveries.
Finding the cause of a disease called beriberi is one example.
The illness beriberi causes great loss of movement and weakness, especially in the legs.
Most people with the disease had a very high chance of death.
All attempts to find a tiny germ (microorganism) that caused the disease failed.
In 1886, a scientist named Christiaan Eijkman (1858â1930) was a Dutch doctor who worked at a medical school in the East Indies (now Indonesia).
He investigated the disease called beriberi.
Eijkman began to look for a reason for the disease using chickens.
He wanted to see if the disease could be passed from one chicken to another with a small germ (microorganism).
He had no success in connecting the disease to the microorganisms he thought existed.
Eijkman tested the chickens for signs of the symptoms of beriberi.
Then one day, a group of chickens kept at the medical school began to show the symptoms of beriberi.
Eijkman began to search for a reason for the disease.
He found out that the chickens were usually fed on unpolished rice (brown rice), but a new cook at the school had stopped using the usual chicken feed.
This cook had extra cooked, polished white rice (rice with the brown outer layer removed) from the patients who would not eat the rice.
He fed this white rice to the chickens.
The chickens again developed beriberi.
When Eijkman fed the chickens unpolished rice again, they recovered from the disease straight away.
The rice fed to the patients and the chickens was polished rice. This meant that the outer skin, called the bran, had been taken off.
This outer skin contains vitamin B1 (thiamin).
Eijkman, with another scientist named Gerrit Grijns, showed later that the skin of rice contains vitamin B1 (or thiamin).
This vitamin is needed to keep nerves healthy and prevent beriberi.
More scientific work on vitamin B1 showed it to be important in preventing diseases of the stomach and intestines.
It is found in bread, milk, brown rice, soya beans, and potatoes.
Let's Talk đŖī¸
Eijkman did his experiments on animals. Question 11 asks you to plan an investigation to check his work. Your plan may have also included studying animals. A lot of information that helps humans has been gathered by studying animals in experiments. Are there any general rules that you would want scientists to follow in experiments involving animals?
Challenge Yourself đ§
A watermelon can be over 90% water. What experiment could you do to find out what percentage of a watermelon is water? If your teacher approves, try it.
Science extra: Treating iodine deficiency đ§
Iodine is a mineral that the body needs.
The body needs it to make a chemical (hormone) that controls the speed at which the body uses energy.
This chemical also helps with growth and development.
If a person's diet does not have enough iodine, they can get a condition called iodine deficiency.
One place where the body changes due to iodine deficiency is the thyroid gland in the neck.
A lack of iodine can cause the thyroid gland to swell up. This swelling in the neck is called a goitre.
Iodine goes into the roots of plants from the soil, but in places where the soil has been washed out over a long time, there is very little iodine in the food.
This lack of iodine in the diet can cause tiredness and dizziness.
A bigger problem is that a lack of iodine can stop the heart from beating and prevent the brain from developing properly.
Scientists in Africa noticed an increase in a problem called universal salt iodisation (USI). This means adding iodine to all salt used.
They helped by giving people salt that contained iodine through a program in Tanzania.
The health of the people can improve the amount of iodine the plants take up.
Science in context đŠââī¸
Dietitians
A dietitian is a person who has studied the science of food and nutrition in great detail.
They use this knowledge to help others eat healthy food, especially people with health problems, such as those who are very heavy, people who work in hospitals, health centres, and areas where they advise people about diet and lifestyle in order to make improvements in their health.
The dietitian usually works in a hospital where they help people who have a wide range of problems, from diabetes (too much sugar in the blood) and food allergies, to eating disorders and kidney failure.
They help people to improve the health of their people.
In addition to a good knowledge of food and nutrition, a dietitian needs to think and know about people and their needs to be successful.
Let's Talk đŖī¸
Could you be a dietitian? Explain your answer.
A healthy diet (continued)
We have seen that the body needs many different nutrients to keep it healthy.
These nutrients can be provided by a balanced diet.
Everyone should try to eat a balanced diet. But diets can be unbalanced, even by some eating habits that seem small, such as regularly eating high-energy snacks like sweets, chocolate, crisps, and ice cream between meals.
These habits can lead to a number of unhealthy conditions such as obesity (see page 43) and tooth decay.
Did You Know?
It shows that you can eat large amounts of the foods shown at the base of the food pyramid, but should eat very small amounts of the foods shown at the top.
There are ways to eat well while still enjoying your favourite foods.
You can cook food using different methods, such as steaming or boiling, rather than frying, to put less fat in your diet.
Figure 4.9 A pyramid of food.
24. The food pyramid tells you:
a. Foods rich in carbohydrate (like bread, rice, pasta) are at the high bottom.
b. Foods rich in vitamins and minerals (like fruit and vegetables) are in the middle.
c. Foods rich in protein (like meat and fish) and dairy products (like milk and cheese) are also in the middle.
d. Meat and fish are at the small top.
e. A large amount of fat and sugar (like butter and sweets) are at the very top.
25. Make a pyramid of food that shows your diet. How does it compare with the pyramid in Figure 4.9?
Keeping a balance âī¸
To remain healthy, a diet has to be balanced with the body's needs.
A balanced diet is one in which all the nutrients are present in the correct amounts to keep the body healthy.
You do not need to know the exact amounts of nutrients in each food you eat, but whether you have a healthy diet.
One simple way is to look at a chart (like Table 4.5) that groups different foods.
With the main nutrients of each group displayed (see Table 4.5), you can then see if you eat at least one portion from each group each day and more portions of the food groups that lack fat.
Remember that you also need to include fibre, even though it is not digested. It is essential for the efficient movement of food through the large intestine. Fibre is found in cereals, vegetables, and pulses, such as peas and beans.
Table 4.5 The groups of foods and their nutrients.
Table 4.5 The Groups of Foods and Their Nutrients
Vegetables and Fruit
Nutrients: fibre, vitamin C, vitamin A, minerals, calcium, iron.
Cereals
Nutrients: carbohydrate, fat, protein, B vitamins, minerals, fibre.
Pulses
Nutrients: protein, carbohydrate, fat, B vitamins, minerals, fibre.
Meat and Eggs
Nutrients: protein, fat, vitamin A, B vitamins, iron, minerals, fibre.
Milk Products
Nutrients: protein, fat, carbohydrate, calcium, vitamin C, B vitamins, vitamin A.
18. The following table shows how the energy used by an average male person and an average female person changes between the ages of 2 and 25 years.
Table 4.4 Daily Energy Used by Males and Females
Age 2 years:
Males: 5500 kJ
Females: 5500 kJ
Age 5 years:
Males: 7000 kJ
Females: 7000 kJ
Age 8 years:
Males: 8800 kJ
Females: 8800 kJ
Age 11 years:
Males: 10000 kJ
Females: 9200 kJ
Age 14 years:
Males: 12500 kJ
Females: 10500 kJ
Age 18 years:
Males: 12100 kJ
Females: 8800 kJ
Age 25 years:
Males: 12100 kJ
Females: 8800 kJ
a. Plot the information given in the table as a single graph.
b. Explain what the graph shows.
c. Explain the difference between the amounts of energy used by a 25-year-old man and a 25-year-old child.
d. Explain why there is a difference between the amounts of energy used by an 18-year-old male and an 18-year-old female.
e. Explain why there is a change in the amount of energy used as a person ages from 18 to 25.
19. What changes would you expect to see in the amount of energy used by:
a. A 25-year-old person who changed from a job delivering letters and parcels to a job working with computers?
b. A 25-year-old woman working with computers and took a job on a building site that involved carrying heavy loads?
c. A 25-year-old female during pregnancy?
Science in context đ§Ē
Treating malnutrition and famine
Malnutrition occurs when a diet has too few or too many nutrients.
For example, anemia is caused by having too little iron in the diet, while obesity (see page 43) can be caused by having too much fat in the diet.
Famine is a lack of all foods, which can be caused by crop failure, but also by human activities such as war, where people have to move away from their crops and food sources.
The lack of food affects the health of everybody, no matter their age.
It stops growth and development, so young bodies will grow and develop much more slowly than normal, and over time, their bodies will be smaller and less well-developed than people with healthy diets.
In areas of famine, aid workers give children with no food two types of powdered milk, called F75 and F100.
Children are first given F75, which is powdered milk mixed with water.
Then, after a few days, they are fed F100.
This contains more proteins and energy to help the body begin to build itself up.
The children must be able to start digesting food again.
Then, after a few days, they are fed Plumpy'Nut, which is made from peanut paste, powdered milk, and minerals.
A woman feeds her child in a clinic for malnourished children.
26.
a. Look at Table 4.2 on page 32 and compare the nutrients in rice and peanuts.
b. Why do you think a food based on peanuts is better than one based on rice in order to help people recovering from starvation and malnutrition?
Challenge Yourself đ
Look at a world map that shows the number of people per country who do not have enough food (malnutrition) and find out where iodine intake is not enough.
Go to the Global Network's website to see if the population's iodine intake is enough or not.
Survey the map to find at least six countries where the intake is not enough.
27. Do you see a pattern in the countries where iodine intake is not enough, according to the Iodine Global Network? For example, is the country an island, or in the middle of a continent, or does it have a coast (sea line)? Explain your answer.
Let's Talk đŖī¸
Is it right to add nutrients to people's diets in addition to the ones they get from eating their own foods? Explain your answer.
How the body uses nutrients đ§Ē
21. Look again at the food labels from the start of the inquiry. Choose the labels of the foods you regularly eat, and look at the amounts of protein, fat, and carbohydrate listed on them. Do they show evidence of a balanced diet? Explain your answer.
22. Now look at the amounts of energy the food labels from the inquiry. Explain your answer.
23. Look at the foods you regularly eat. Do they show evidence of a high-energy diet or a low-energy diet? Explain your answer.
Obesity đ
Obesity is a condition where children (and adults) have too much body fat.
The diet may be made up of lots of sweets, high-energy, high-fat foods, chips, pizza, or other foods with a lot of carbohydrate and fat content.
The person uses less energy than they take in from food, and the increased body mass makes the person tend to move around less than normal.
As the person uses less energy than before but continues to eat the high-energy diet, even more body fat is produced.
This can affect the working of the heart and the increase in blood pressure.
Obesity can also lead to a disease called diabetes (where the body has trouble with sugar).
This happens when the pancreas (an organ) stops making enough of a substance called insulin, which helps the body to take extra sugar out of the blood and store it in the liver.
The blood is left with a high sugar content.
Normally, the body controls the amount of digested sugar in the blood.
This can eventually cause damage to the nerves and blood vessels in the feet, which can only be treated by amputation (cutting off a part of the body).
It can also cause kidney damage, which can be fatal (cause death).
This is an example of a diet containing too much energy.
2. How do obese people put their health and lives at risk?
Anorexia nervosa đ
In the condition anorexia nervosa, a person eats very little and is very scared of gaining weight.
They are often wrongly sure that they are overweight.
This disease happens more in teenage girls and young women.
It causes the body to use up the energy stored as fat.
Energy stored as protein may also be used up.
As the body's energy is used up, the person loses a lot of weight.
This happens because of eating too little high-energy food.
This causes them to lose body weight and may affect their general health.
In the worst cases, this disease can result in death.
Anorexia nervosa needs special talking and treatment from a doctor to give them the best chance of getting completely well.
Treating obesity đââī¸
Treating obesity is done in two main ways for children and adults.
One way is to go back to eating a balanced diet.
The second way is to do a lot of exercise to burn up the extra fat.
The aim is to help the person's body grow into the right size so that their weight and appearance become more normal.
The treatment for adults and children is a little different because children are still growing.
3. Could you be a dietitian? Explain your answer.
Science in context đŠââī¸
Dietitians
A dietitian is a person who has studied the science of food and nutrition in great detail.
They use this knowledge to help others eat healthy food, especially people with health problems, such as those who are very heavy, people who work in hospitals, health centres, and areas where they advise people about diet and lifestyle in order to make improvements in their health.
The dietitian usually works in a hospital where they help people who have a wide range of problems, from diabetes (too much sugar in the blood) and food allergies, to eating disorders and kidney failure.
They help people to improve the health of their people.
In addition to a good knowledge of food and nutrition, a dietitian needs to think and know about people and their needs to be successful.
Let's Talk đŖī¸
Could you be a dietitian? Explain your answer.
A healthy heart â¤ī¸
Your heart is about the size of your fist and is a strong muscle.
It beats about 2.5 billion times during a person's life!
It works to pump blood all around your body.
It sends about 5 litres of blood around every minute.
The blood goes to all the small blood vessels (like tubes) in the body.
Blood vessels are like a network of tubes that carry the blood.
The heart's beat pushes the blood out of the heart and into the arteries (the largest blood vessels).
This push is called blood pressure.
When you push your finger on a drawing pin into a board, you use pressure. This is similar to the force used by the heart to pump blood around the body.
The walls of the arteries are strong and can stretch when the heart pumps the blood.
In young people, the arteries are wide open, so the blood flows easily without much pressure.
As the body gets older, the walls of the arteries become less stretchy.
The heart has its own blood vessels called the coronary arteries and veins.
These vessels bring blood to and from the heart muscle itself.
Did You Know?
Your heart is the size of your fist and is a muscle.
Cholesterol and the circulatory system đŠ¸
Over time, fatty things like cholesterol stick to the inside walls of the arteries.
Cholesterol is a waxy, soft substance that is part of every cell.
When this sticky plaque builds up, it makes the artery smaller.
This makes it harder for the blood to push through the artery, and the blood pressure goes up.
The artery has less space for the blood to flow through.
The blood can get sticky and form a small clot called a thrombus (many are called thrombi).
A thrombus can block the artery and stop the blood from getting to a body part.
If this happens in a coronary artery (a vessel of the heart), it stops the oxygen and nutrients from getting to the heart muscle. This causes a heart attack.
The word "coronary" is used to describe a heart attack.
Did You Know?
A thrombus (blood clot) in an artery in the brain causes a stroke.
A stroke means a part of the brain is damaged because it can't get oxygen and nutrients (food).
Science in context đ¨âđŦ
A long time ago, in the early 1900s, a Russian scientist named Nikolay Anichkov (1885-1964) was studying things that cause heart disease.
He fed rabbits a diet with lots of cholesterol and found that patches of a fatty substance formed inside their arteries.
Other scientists did not pay attention to his work because they thought it was only true for rabbits.
About 40 years later, an American scientist named John Gofman (1918-2007) started working on a similar problem: how to connect cholesterol in human blood to heart disease.
He created ways to separate the different fatty substances that carried cholesterol in the blood.
He did experiments to test his ideas and found proof that they were right.
Again, other scientists did not listen to his work, but his ideas were shown to be correct by new proof later on.
After some time, another American scientist named Ancel Keys (1904-2004) started a study that looked at heart disease in different countries.
He set up a big investigation called the Seven Countries Study.
The results of this study supported the idea that high levels of cholesterol in the blood were a cause of patches forming in the arteries and causing heart disease.
Activity and the heart đââī¸
The heart is made of muscle, just like all other muscles in the body.
It needs exercise to stay strong and healthy.
The heart muscle squeezes when you exercise, making it stronger.
Doing exercise often makes many of your organ systems (groups of organs that work together) better.
It helps you lose weight because it burns up the extra fat you've stored.
Exercise helps your body use oxygen better.
More blood is pumped to your muscles when you exercise.
The muscles need more blood to work hard.
The heart beats faster and harder during exercise than when you are resting.
This makes your body more flexible and strong and increases your endurance (how long you can keep doing an activity).
Table 5.1 Levels of Fitness Required for Different Activities
Basketball: High Strength, High Flexibility, High Endurance.
Dancing: Medium Strength, High Flexibility, High Endurance.
Golf: Medium Strength, Medium Flexibility, Low Endurance.
Long-distance running: Low Strength, Low Flexibility, High Endurance.
Rugby: High Strength, High Flexibility, High Endurance.
Soccer: Medium Strength, Medium Flexibility, Medium Endurance.
Squash: High Strength, High Flexibility, High Endurance.
Swimming: High Strength, High Flexibility, High Endurance.
Tennis: Medium Strength, High Flexibility, High Endurance.
Walking: Low Strength, Low Flexibility, Medium Endurance.
Care with exercise đ¤¸
When people want to get fit, they can choose activities that they like.
But sometimes people try to exercise too hard or too much when they first start.
This can cause a sprain (a stretch or tear of a strong band called a ligament) or pain in a joint (where bones meet).
It takes a long time for the body to get used to new activities.
The skeleton (bones) and muscles have to work together to move your body.
It is very important to start exercising slowly and build up the time you spend exercising.
This helps your muscles and joints get used to the movement slowly.
If someone gets hurt (an injury), they might not want to continue exercising.
But it's important to remember that the body gets stronger and fitter over time.
Is there a link between pulse rate and exercise? đââī¸
15. What did you conclude from your previous experiment about breathing rate and exercise?
In Chapter 3, you looked into the breathing rate when at rest and after exercise.
Find out if there is a link between pulse rate (heartbeat) and exercise in the following inquiry.
You will need:
A stopwatch or timer and an open space for exercise.
Hypothesis
The breathing rate changes after exercise, so the pulse rate (and heart rate) may also change after exercise.
Plan and investigation
Make a prediction based on the hypothesis.
Make a plan to test the hypothesis and prediction and, if your teacher approves, try it.
Examining the results
Examine the data you have collected. Do you have enough proof to support your conclusion? Explain your answer.
Conclusion
Draw a conclusion. Was your hypothesis testable? Explain your answer.
Smoking and health đŦ
We all need a healthy respiratory system (lungs and airways) to exchange oxygen and carbon dioxide.
A healthy respiratory system is important for good health.
The respiratory system is easily damaged by smoking.
There are over a thousand different chemicals (bad things) in cigarette smoke.
One of these chemicals is nicotine, which is highly addictive (it makes you want to keep smoking all the time).
Smoking and growth and development đļ
We have seen that smoking can damage the lungs and affect a person's growth and how they develop.
The damage to the lungs makes them less good at taking in oxygen and giving it to the body's cells.
Pregnant women who smoke take in less oxygen, which is bad for the baby they are carrying.
This can cause the babies to be born smaller and less developed.
Adults who smoke may not feel like eating as much, so they get less food and fewer nutrients.
This can also lead to heart disease and other health problems.
Emphysema đ¨
In the air sacs of the lungs (called alveoli), the smoke causes damage to the walls.
This makes it harder for oxygen and carbon dioxide to exchange (switch places).
The alveoli burst and merge (join together) to make bigger, less helpful air sacs.
This disease is called emphysema.
It causes people to breathe faster than healthy people.
18. Someone with emphysema breathes more quickly than a healthy person. Why do you think this is?
19. How does a reduced number of alveoli affect the exchange of oxygen and carbon dioxide?
Chronic bronchitis đˇ
Chronic bronchitis is another disease caused by smoking.
In the airways of the lungs (called bronchi), the smoke causes the lining to get swollen (inflamed).
The airways make too much mucus (a sticky liquid).
The bronchi get smaller and smaller, making it hard to breathe.
It also causes a lot of coughing.
17. Why may chronic bronchitis lead to other diseases?
Cancer of the lung đĻ
The tiny hairs inside the airways (called cilia) move mucus and small pieces of dirt out of the lungs.
The chemicals in cigarette smoke damage these cilia, so they can't do their job well.
This means small bits of dirt and mucus stay in the throat.
The smoker tries to get the dirt and mucus out by coughing. This is the smoker's cough.
The cells lining the air passages are hurt by the chemicals in the smoke.
Some of these damaged cells may change and become cancer cells.
These cells start to divide (copy themselves) very quickly and form a tumour (a lump of bad cells).
The tumour can block the airway or spread to other parts of the lung where more tumours can grow.
20. How are cancer cells different from every other part of the lung tissue?
21. Why do cancer cells make the organ less efficient?
22. Why might the amount of cancer cells in an organ have fatal results?
Helping smokers stop đ
People smoke because they become addicted (their body needs) to the nicotine in the tobacco.
Addiction is a condition where a person can't live a normal life without a substance.
Some ways to help smokers stop are by giving them something that has nicotine but not the other harmful chemicals in smoke, like nicotine patches (sticky pads) or nicotine gum.
This helps them slowly stop needing the nicotine while not smoking.
They may also get medical help or support from others who want to give up and break an unhealthy drinking alcohol or taking drugs habit.
Smokers who wish to give up and break the addiction need a lot of support.
Some people need special help and support to stop smoking, like from a doctor or counselor.
In some countries, smoking in public places and smoking cigarettes are not allowed.
Some research suggests that e-cigarettes (vapes) are dangerous and do not help people stop smoking.
End of chapter questions â
1. What does the body need the following for?
a. Glucose (sugar)
b. Fats
c. Proteins
2. Why does the body need:
a. Calcium
b. Iron
3. What foods should people eat to prevent them getting scurvy?
4. What foods should people eat to prevent them getting rickets?
5. Imagine you knew of someone who ate a lot of high-energy snacks.
a. What could happen to them if they continued with this habit?
b. What advice would you give them to keep them healthy?
6. What is a balanced diet?
a. Give examples of the quantities of different foods you would eat to keep your diet balanced.
7. How does smoking affect the lungs?
a. Iron
b. Vitamin C
c. Vitamin D
8. Your teacher will put an inquiry question on the board. You will need a stopwatch or timer. Use your pulse to measure your heartbeats per minute (bpm).
a. Plan, investigation and recording data:
1. Hold out your right hand with the palm up.
2. Put the thumb of your left hand under your right wrist.
3. Put the first two fingers of your left hand on your wrist.
4. Feel around on your wrist with these two fingers to find a throbbing artery (this is your pulse).
5. You can measure your pulse rate by counting how many times your pulse beats in a minute.
Here is a reminder: You learned how to measure your pulse rate last year.
Some people count the beats for 15 seconds, then multiply the number by 4 to check the beats per minute. This helps you be more accurate.
The teacher will ask you to:
1. Plan a way to record your results.
2. Take your pulse while sitting down for 1 minute and record the beats per minute.
3. Take your pulse for 15 seconds, then multiply the number of beats by 4 and record the beats per minute.
4. Construct a plan in which someone else takes your pulse to test your results, if your teacher approves, try it.
b. Examining the results:
1. Compare the data from your own measurements and from the measurements of someone else.
c. Conclusion:
1. Draw a conclusion. Which method is the most accurate, or are they equally accurate?
2. Is your conclusion limited in some way? Explain your answer.
3. What improvements could be made? Explain the changes that you suggest.
d. Anwari, Baylee, Chumbo, and Daisy used their pulse to test their probable heart monitor results.
e. They monitored their pulse rate when resting, 1 minute after exercise, 2 minutes after exercise, and 3 minutes after exercise.
f. Here are their results (beats per minute):
Student Pulse Rate (Beats Per Minute)
Anwari
Resting: 71
1 Minute After Exercise: 110
2 Minutes After Exercise: 90
3 Minutes After Exercise: 79
Baylee
Resting: 74
1 Minute After Exercise: 115
2 Minutes After Exercise: 88
3 Minutes After Exercise: 77
Chumbo
Resting: 80
1 Minute After Exercise: 107
2 Minutes After Exercise: 98
3 Minutes After Exercise: 87
Daisy
Resting: 69
1 Minute After Exercise: 80
2 Minutes After Exercise: 77
3 Minutes After Exercise: 72
g. The teacher will ask you to:
1. Make a table of the results.
2. Make a graph of the results.
3. What trend (pattern) can you see in the results?
4. When did Anwari and Baylee's hearts beat at the same rate?
5. Anwari claims to be fitter than Chumbo. Do you think the results support his claim? Explain your answer.
6. Which result does not follow the trend? Explain why this may be so.
9. What can happen in an artery if there is too much cholesterol in the diet?
10. What is a thrombosis?
11. What causes a heart attack?
12. What causes a stroke?
13. What should you include in your diet to stop you getting a high level of cholesterol?
14. What disease could you develop if your diet lacks vitamin C?
15. How does smoking affect the lungs?
Summary â¨
A balanced diet is made up of proteins, carbohydrates, fats and oils, water, minerals, and vitamins in the correct amounts.
Nutrients are needed by the body to keep it healthy and can be split up into water, minerals and vitamins in the right quantities.
Carbohydrates and fats can be used to store energy and nutrients in animals.
Animals consume food to get energy and nutrients.
Fibre is important in the diet.
You can treat malnutrition using foods such as powdered milk.
Scientists can discover a vitamin by thinking and working like scientists.
Dietitians help people make healthy food choices.
The energy in food is made up of the fat and carbohydrate it contains.
Poor blood pressure or high cholesterol can lead to heart problems and illnesses, such as blood clots, thrombosis, or a stroke.
Regular exercise makes many of the organs (like the heart and lungs) work better. It also makes you less likely to get hurt or sick.
Smoking is bad for health, growth, and development and can cause sicknesses such as cancer, emphysema (bad lungs) and 'smoker's cough'.
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