Body weight

Otherwise, take your weight (kg) and divide it by the square of your height (m).

For example, if you weigh 80kg and are 1.7m:

1. Multiply your height by itself 1.7x1.7=2.89

2. Divide your weight by this figure.

3. 80 ÷ 2.89= 27.7.

27.7 is the BMI

What determines my weight?
There are a number of factors that contribute towards your weight:

• hereditary factors
• hormonal abnormalities
• lack of exercise
• diet
• lifestyle.

Obesity is the fastest growing disease in the world, with related conditions such as high blood pressure, diabetes, heart disease and raised cholesterol all on the increase. If you are higher than the healthy range, you will reduce your risk of these diseases as you lose weight.

Being underweight can lead to irregular periods which can affect fertility, anaemia and fragile bones (osteoporosis). A lack of body fat can affect energy levels and your ability to keep warm. If you are below the healthy range, increasing the amount of nutrients you get will lower your risk of these problems.

If you are in the healthy range, but want a flatter stomach, your chances of getting a weight-related disease will remain low, but medically speaking won't change.

Weight loss and weight gain
Genes and hormones aside, weight gain is usually the result of an imbalance between calorie intake and the body's energy expenditure – you eat and drink more calories than your body can burn as you go about your daily life.

If you want to lose weight, you need to increase the amount of activity you do every day and knock 300-500 calories off your daily diet. Reducing calories alone (or increasing exercise alone) is not as effective for weight loss.

You should aim to lose about 1kg (2lb) a week. Losing more than this may mean you are only losing water, which will quickly go back on when you stop dieting. Large weight losses in a short time are usually followed by larger weight gain.

If you are underweight, the reverse is true.

You need to slow down if you have a lifestyle where you are constantly on the go, reduce the intensity of exercise sessions, say by swapping a stint on the running machine with yoga, and think about how to increase the amount of certain foods groups in your diet.

Healthy eating
Healthy eating is an aim in itself, regardless of whether you want to lose or gain weight.

A healthy diet should be based on a combination of complex carbohydrates, fibre and lean proteins, and include five portions of fruit and vegetables a day.

You also need to pay attention to the liquids you consume: caffeine, alcohol and fizzy drinks should be drunk in moderation.

Before you can adjust your diet to match your body's requirements, you need to understand how the different food groups react with the body and what they provide in terms of calories.

For example, fats are the most concentrated source of calories within the four main food groups. This is why controlling fat intake is the cornerstone of many diets.

However, your body needs fat for a whole range of tasks from tissue repair to transporting vitamins, so you shouldn't exclude them altogether. Equally, if you want to gain weight, don't exceed the daily recommended limits for saturated fat.

For detailed advice on the different food groups, plus tips for healthy living, read the other articles in this series.

Other articles in this series

• General lifestyle management
• Protein
• Fats
• Carbohydrates
• Fibre
• Soya
• Water
• Caffeine
• Smoking and nutrition
• Alcohol metabolism
• Exercise

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