Diet

Diet

Facts

• Today, in the UK, there are approximately 24 million overweight or obese people and, if this trend continues, one in four people will be obese by 2010. This is largely due to unhealthy eating and lifestyle.
  
  
• Over 200,000 people die prematurely in the UK every year as a result of coronary heart disease, stroke, and other illnesses related to poor diet and unhealthy lifestyle. Those who survive these conditions may be left with pain, long-term disability, and a restricted lifestyle.
  
  
• In the UK, over 80% of men, and nearly 70% of women, eat too much salt. Many people only think of salt in terms of the white condiment that they sprinkle on food, and are unaware that they eat too much. As much as 75% of the salt that we eat is already in the food we buy.
  
  
• By eating a healthier diet, you could help protect yourself from a third of all cancers, diabetes, osteoporosis (thinning bones), heart disease, strokes and tooth decay, as well as many other diet related conditions.

POOR DIET

Some effects of a poor diet

If you have too little of a particular nutrient, we say that you have a deficiency in that nutrient. For example, fibre is needed to keep food moving through the intestines easily, and people who have a fibre deficiency in their diet may get constipation.

Mineral deficiencies

People with iron deficiency may get anaemia and have too few red blood cells. People with iodine deficiency may get a swelling in the neck called a goitre (pronounced "goy-ter").

This person has a goitre

Vitamin deficiencies

Although we only need small amounts of the different vitamins in our diet, we become ill if we don't get enough. For example, vitamin A deficiency can cause blindness. Vitamin C deficiency causes scurvy, which makes the gums bleed, and vitamin D deficiency causes rickets, which makes the legs bow outwards in growing children.

Too thin, too fat

Food is a store of chemical energy. If you look on the side of food packets you will see the food's energy content. This is usually measured in kilojoules, kJ. If we eat too little food, we will use up our store of fat and become too thin. If we eat too much food, especially foods rich in sugar and fat, we will increase our store of fat and become too fat.

It is important to balance the amount of food we eat with who we are and what we do. The amount of energy we need from our food depends on our age, our height and how much exercise we get. For example, a one-year old baby needs 3850 kJ each day to continue to grow, whereas an adult Olympic swimmer in training needs 15,600 kJ each day. Someone who sits at a desk all day will need less food than their twin who climbs ladders all day to wash windows.

A balanced diet

A balanced diet contains the different nutrients in the correct amounts to keep us healthy. Certain foods are not necessarily 'bad' for us, but eating too much of them could be.

Nutrients

There are seven different nutrients:

• carbohydrates
• proteins
• fats
• minerals
• vitamins
• fibre
• water

Some foods are particularly rich in certain nutrients. The table shows why we need each nutrient, and some good sources of each.

Nutrient	Use in the body	Good sources
Carbohydrate	To provide energy	Cereals, bread, pasta and potatoes
Protein	For growth and repair	Fish, meat, eggs and dairy products
Fat	To provide energy. Also to store energy in the body and insulate it against the cold	Butter, oil and nuts
Minerals	Needed in small amounts to maintain health	Salt, milk (for calcium) and liver (for iron)
Vitamins	Needed in small amounts to maintain health	Dairy foods, fruit, vegetables
Fibre	To provide roughage to help to keep the food moving through the gut	Vegetables, bran
Water	Needed for cells and body fluids	Fruit juice, milk, water

Healthy Diet

What is a healthy, well-balanced diet?

A well-balanced diet includes food from the five main food groups. These are:

• bread, cereal (including breakfast cereals) and potatoes (starchy foods),
• fruit (including fresh fruit juice) and vegetables,
• meat and fish,
• milk and dairy foods, and
• fat and sugar.

Most people should be eating three main meals a day. Most people need to eat more starchy foods and more fruit and vegetables, as well as reduce their fat intake, drink less alcohol and eat less salt. Look for labels that say food is low in fat (particularly saturated fat), low in salt and sugar-free.

Fruit and vegetables are packed with vitamins and minerals, low in calories and high in fibre. Eating lots of fruit and vegetables keeps the HEART and body healthy. They are also an ideal alternative to eating crisps and chocolate as snacks between meals.

Diet - Definition

Diet

Definition

Healthy eating is about maintaining a balanced diet. This means eating foods from all the different food groups in the right amounts.

There are five main food groups, and each one contains nutrients that are essential for your body's growth, energy and body maintenance. Nutrients are vitamins and minerals that regulate your body's chemical processes and functions and help to keep you fit and healthy.

The five main food groups are:

Carbohydrates

Carbohydrates include foods like bread, pasta, potatoes, cereals, low fat oven chips, rice, oats, noodles, couscous, maize and cornmeal. They provide energy and should make up about one third of your diet.

Carbohydrates are divided into two groups - refined and unrefined. Refined carbohydrates include white bread and sugary cereals that have had the fibre removed. Unrefined carbohydrates include brown and wholemeal bread, pasta and rice, and you should choose these options whenever possible.

Some people think starchy foods are fattening. However, it is the fats that are added to them, such as butter and cheese, which can make them unhealthy. Avoid frying these foods and choose healthier alternatives, such as low fat oven chips rather than fried chips.

Fruit and vegetables

Fruit and vegetables are rich in vitamins and minerals which are essential nutrients that your body needs in order to work properly. As well as keeping your skin and hair healthy, they can reduce your risk of getting heart disease and some cancers.

You should aim to eat five portions of fruit and vegetables each day. They can be fresh, frozen, canned or dried. One portion counts as a large piece of fruit, such as an apple or banana, three heaped tablespoons of vegetables, or one glass of 100% fruit or vegetable juice (although this only counts as one portion regardless of how much you drink). Beans and pulses, such as baked beans or lentils, also contribute to this group, but they only count towards one portion no matter how many different types you eat.

Protein

Protein helps to build and repair your body. Foods rich in protein also contain minerals, such as iron, zinc and magnesium, as well as important B vitamins. They should make up about one fifth of what you eat each day.

Sources of protein include meat, fish and eggs, as well as non-animal products, such as beans and nuts. To keep it healthy, trim fat from meat, remove the skin from chicken, drain fat away after cooking, and try to eat two portions of fish each week. One of these fish portions should be oily fish, such as salmon, mackerel or fresh tuna. Canned tuna does not count as oily fish because the canning process removes the beneficial oils. Avoid frying meat and fish, and try to grill, roast or microwave instead.

If you are a vegetarian, you can get the protein that you need by including seeds, nuts, tofu, soya products and beans in your diet. These foods provide protein, fibre and iron but, unlike the non-vegetarian examples, they do not provide much zinc or vitamin B12 unless they are fortified (have had vitamins or minerals added to them).

Dairy

Cheese, milk, yoghurt and calcium fortified soya alternatives are all examples of dairy foods (cream and butter are in the fats group, and eggs fall under protein). Dairy products are rich in calcium, which is important for strong bones and teeth. You should aim to get 700mg of calcium each day, which is roughly the same as a pint of milk, or two small yoghurts. Choose lower fat versions, such as semi-skimmed milk, low fat yoghurt and reduced fat cheese.

If you do not drink cow's milk or eat dairy products, you can get calcium from soya milk and yoghurts with added calcium, and from vegetables such as broccoli and cabbage.

Fat and sugar

Fats and sugars contain more energy than any other food group and should make up the smallest part of your diet. Foods such as butter, mayonnaise, chocolate, crisps, cakes, soft drinks, jam, sweets and ice cream, all usually contain high amounts fat.

Fats are divided into two groups - saturated and unsaturated. Saturated fat is found in cream, margarine, and fried foods. This type of fat can contribute to heart disease. Unsaturated fat is found in vegetable oils and oily fish. Eating a small amount of unsatuated fat will help to keep your IMMUNE SYSTEM healthy and can reduce CHOLESTEROL levels.

Sugary foods are bad for your teeth and are full of calories. You should therefore eat them sparingly, as a special treat.

DIET - INTRO

Diet

Introduction

Good health is fundamental to leading a full and active life, and getting the right nutrition is an important step towards good health.

The word diet is often used to describe an eating plan intended to aid weight loss. However, diet really refers to the foods a person eats in the course of a day, or week. The more balanced and nutritious the diet, the healthier the person can expect to be. A balanced diet means eating the right amount of foods from all food groups.

The benefits of a balanced diet are numerous. No single food contains everything the body needs so it is important to eat a wide variety. The right amount of vitamins and nutrients can increase life expectancy by keeping the HEART and body healthy, and preventing many long-term illnesses.

Body weight can also be kept to an acceptable level through healthy eating, leading to a fitter and more active lifestyle.

Magnetism

Magnetism

This Revision Bite is about magnetism. It has these parts in it: Bar magnets Magnetic fields The Earth's magnetic field Electromagnets Using electromagnets

Bar magnets

Bar magnets are permanent magnets. This means that their magnetism is there all the time and cannot be turned on or off. They have two poles:

• north pole (short for north-seeking pole)
• south pole (short for south-seeking pole).

The north pole is normally shown as N and the south pole is normally shown as S.

A bar magnet

Magnets are made from magnetic materials. These are metals that can be magnetised or will be attracted to a magnet. Most materials are not magnetic, but iron, cobalt and nickel are magnetic. Steel is mostly iron, so steel is magnetic too.

Attract and repel

If you bring two bar magnets together, there are two things that can happen:

• if you bring a north pole and a south pole together, they attract and the magnets may stick together;
• if you bring two north poles together, or two south poles together, they repel and the magnets push each other away.

We say that unlike poles attract, and like poles repel.

Remember that unmagnetised iron, steel, cobalt and nickel objects will be attracted to either pole of a magnet. This means you can only show that an object is a magnet if it repels a known magnet.

Magnetic fields

Magnets create magnetic fields. These cannot be seen. They are the space around a magnet where magnetic materials are affected by forces, and so may be attracted or repelled.

Although we cannot see magnetic fields, we can detect them using iron filings. The tiny pieces of iron line up in the magnetic field.

It would be difficult to draw the results from the sort of experiment seen in the photograph, so we draw simple magnetic field lines instead. In the diagram, note that:

• the field lines come out of N and go into S
• the field lines are more concentrated at the poles.

The magnetic field is strongest at the poles, where the field lines are most concentrated.

Attraction and magnetic fields

Iron filings can show the magnetic field between two magnets where unlike poles face each other, and so attract.

If we look at the field lines, we see that they go from the north pole of one magnet to the south pole of the other magnet.

Magnetic field lines between two attracting magnets

Repulsion and magnetic fields

Iron filings can also show the magnetic field between two magnets where like poles face each other, and so repel.

If we look at the field lines, we see that they do not go from one magnet to the other, and they do not cross.

Magnetic field lines between two repelling magnets

The Earth's magnetic field

The Earth does not contain a giant bar magnet, but it behaves as if it does. The Earth has a magnetic north pole and a magnetic south pole. Compasses work because bar magnets can line up in the Earth's magnetic field and point north. Make sure you understand these things:

• the north pole of a bar magnet is actually called the 'north-seeking pole', and it points to the Earth's magnetic north pole;
• the south pole of a bar magnet is actually called the 'south-seeking pole', and it points to the Earth's magnetic south pole.

Compasses point towards the Earth's magnetic north pole

Small compasses called plotting compasses can be used to show the magnetic field around a bar magnet, instead of using iron filings. The needle in each compass turns and lines up along the field lines.

A line of plotting compasses follows a field line

If we arrange some plotting compasses around a bar magnet, we see that the needles point away from the magnet's north pole and towards its south pole.

Plotting compasses in a circle

When you do this experiment, it is important to keep iron or steel objects away, otherwise the compass needles might point to them instead

Electromagnets

A magnetic field is produced when an electric current flows through a coil of wire. This is the basis of the electromagnet. We can make an electromagnet stronger by doing these things:

• wrapping the coil around an iron core
• adding more turns to the coil
• increasing the current flowing through the coil.

How to make a simple electromagnet

The magnetic field around an electromagnet is just the same as the one around a bar magnet. It can, however, be reversed by turning the battery around. Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off just by closing or opening the switch.

Using electromagnets

Many objects around you contain electromagnets. They are found in electric motors and loudspeakers. Very large and powerful electromagnets are used as lifting magnets in scrap yards to pick up, then drop, old cars and other scrap iron and steel.

An electromagnet in a scrap yard

Electric bell

Electric bells like the ones used in most schools also contain an electromagnet.

• When the current flows through the circuit, the electromagnet makes a magnetic field.
• The electromagnet attracts the springy metal arm.
• The arm hits the gong, which makes a sound and the circuit is broken.
• The electromagnet is turned off and the springy metal arm moves back.
• The circuit is complete again.

ELECTRICAL ENGINEERING FOR HEALTH

Magnetic Resonance Imaging for Medical Diagnostics

Today's medical professionals use a variety of diagnostic tools to probe the condition of biological entities. One such technique is that of magnetic resonance imaging (MRI).

MRI works in the following manner. The patient is first placed in a strong magnetic field. The paramagnetic atoms become aligned with the direction of the field. The aligned hydrogen atoms take on resonance characteristics; that is, they can absorb energy and re-emit the energy as electromagnetic radiation at a specific frequency. A short pulse of radiofrequency (RF) waves is then sent to the body. The aligned protons (hydrogen) are excited and become deflected. Once the RF pulse is stopped, the protons realign with the magnetic field while emitting RF waves that are measured. The emitted RF waves contain information on both the physical and chemical characteristics and spatial distribution of body materials. For instance, an image representing the density of hydrogen nuclei within the body is produced.

The electromagnet experiment serves to illustrate just a fraction of the physics behind MRI. The electromagnet interacts with metal objects on a macroscopic scale whereas the object of MRI is to take advantage of interactions on an atomic scale.

The electrical engineer is involved in the development of medical diagnostic procedures in a variety of ways, including: Radiofrequency (RF) waves are studied in electromagnetics Instrumentation is developed to measure the emissions Signal processing techniques are used to analyze and enhance the images