The short answer is your BMI is very important. Body mass index (BMI) is a powerful tool used by health and fitness professionals the world over to measure levels of risk of ill-health. BMI is not a diagnostic method, it serves only to indicate risk.
How is BMI measured?
A person is weighed and this is then adjusted for their height. BMI does have some shortcomings in that it is not adjusted for stature, muscle to fat ratio, gender, age or ethnicity of an individual. Despite these weaknesses, BMI is a very useful indicator of underweight, normal, overweight or obese states. A range of values is given for each of these states. BMI is defined as an individual's body weight divided by the square of his or her height. The NHS provides a useful, easy to use link for calculating your BMI.
If an individual's BMI falls outside of the normal range, i.e. underweight, overweight or obese, the risk of ill-health increases significantly. The World Health Organisation categorises a BMI of less than 18.5 as underweight and an indication of potential malnutrition, eating disorders such as anorexia nervosa or other disease condition; a BMI greater than 25 is overweight and above 30 is obese. When BMI is greater than 35, the risk of premature death is doubled.
The risk of developing diseases associated with obesity does not increase significantly until BMI exceeds 27. There is then a graded increase in risk as BMI increases. For a woman 1.63 metres tall to have a BMI within the normal range her weight should be between 52.7 and 67 kg, but there is no significant health risk until her weight is more than 71.3 kg.
A weight excess or deficiency may, in part, be accounted for by an excess or absence of body fat, although other factors such as muscularity also affect BMI. For example, a body builder may have a BMI indicating they are obese when they not. This is because muscle weighs a lot more than fat. But for most people BMI is a true representation.
A study carried out in the US in 2007 found 63% of the population to have a BMI in the range 25-30 (overweight) and 26% having a BMI of 30 or above (obese). So, BMI is not only a measure of an individual's risk, it is also used to indicate the risk of a population and to observe trends within a population over time.
A BMI of over 25 is a risk factor for the following diseases: coronary heart disease; Type 2 diabetes; cancers (notably endometrial, breast, colon); high blood pressure; high cholesterol levels; stroke; liver and gall bladder disease; sleep apnea, respiratory problems; heart disease; osteoarthritis and gynaecological conditions. For example, nearly 9 out of 10 people who develop Type 2 diabetes have a BMI of over 25. In women, for every additional 10 BMI units there is more than double the risk of developing or dying from cancer of the uterus or throat.
So, what does all this mean for you? If your BMI falls within the normal range, that is desirable and it is important to maintain your healthy lifestyle. If your BMI is over 25 then your diet, exercise levels and lifestyle need careful consideration. Your GP or other health or fitness professional can offer you guidance.
What is a healthy diet?
Generally following a diet that regularly includes the following food types will ensure your body is getting a balance of nutrients: fruits, vegetables, whole grains, bread, potatoes, pasta and fat-free or low-fat milk and cheeses; lean meats e.g. poultry, fish, beans, eggs. Avoid foods that have high levels of saturated fats, trans fats, cholesterol, salt (sodium) and added sugars. As a general rule of thumb these are found in highly processed foods so try to steer clear of these and eat food that has had as little 'processing' as possible.
Regular physical activity is also important. When losing weight, increased physical activity increases the number of calories your body uses for energy. If you use calories by exercising and reduce the number of calories that you eat in food, then you will create a 'calorie deficit' that will result in you losing weight. You must exercise regularly to maintain your weight loss. It is possible to give guidance on the sort of activity levels that will result in weight loss but everyone is different in their needs. If your breathing and heart rate are increased but you can still talk with a friend while you exercise you are probably exercising at a 'moderate' level. Examples are walking briskly or playing football with the children. Your exercise level becomes vigorous when your heart rate is increased substantially and you can no longer converse with your friend! Examples are jogging or swimming lengths.
Knowing your BMI gives you an insight into your health status and importantly any health risks. You can then take any necessary measures to reduce these risks.
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