The basic measure of classification of weight from underweight through normal to overweight and obesity is the Body Mass Index (your weight in kilograms divided by your height in metres squared). This classification is used worldwide but the various figures may be interpreted differently by different organisations.The World Health Organisation for example describes normal weight as a BMI of between 18.5 and 24.99. Some experts prefer to describe BMI 20 - 24.99 as normal.
in fact, a BMI of between 18 - 25 is associated with lowest risk of death. And again other experts say that a BMI of up to 27 is alright healthwise as the health risks don't really begin to show to a great extent until then.
As you can see there is a lot of room for quite large differences in weight between two people of the same height using the BMI as your basis. For example someone of 5ft 7ins can weigh from as little as 114lb to as much as 154lb and still be within the 18.5 - 24.99 limits.Perhaps the halfway point between 20 and 25 could be considered the 'perfect' weight - a BMI of 22.5. This is an idea endorsed by the American Heart Association which says that 'A BMI of about 25 corresponds to about 10% over ideal body weight'. Indeed a BMI of just 22 has been cited by some as the ideal weight for males, and in another study by the America Cancer Society in the early '90s desirable BMIs for women were listed as between 21.3 - 22.1 and for men as between 21.9 and 22.4. Other experts feel such guidelines are too specific.
In truth there is no such thing as a perfect weight for everyone at every time in their lives. Lastly, expert advice is that the size of your waist should also be considered when deciding whether or not you are 'ideal' weight as a disproportionately large midriff is an indicator of increased health risks.
To find out your Body Mass Index:
1. Find out your weight in kilograms (kg = lbs divided by 2.2).
2. Find out your height in metres (metres = height in inches x 0.025).
3. Square your height (height x height).
4. Divide your weight by your squared height.
The result is your Body Mass Index.
Is there any very quick and easy way to tell if I am overweight?
If you have a tape measure handy you can get a very good indication of whether or not you are health-risk-related overweight by measuring your waist size. If you waist is over 34.5ins (88cm) for females or 40ins (102cm) for males, then you are almost certainly overweight.
You can also try the old-fashioned 'pinch test' - if you can pinch a fold of flesh around your midriff at least one inch thick you are probably overweight (but this isn't exactly scientific). Lastly, another quick rule of thumb is this: if you were at an ideal weight (BMI around 22 - 23) at age 25, add on 5lb for every decade over that and you can assume that you are not overweight. E.g. at 55 you could be 15lb heavier than at 25 and consider yourself as having done well at keeping your weight within bounds.
Is it true that dieting will slow my metabolic rate?
Yes. If you are successful at losing weight your metabolic rate will quite naturally slow down. This is mostly because when your body weighs less, it has less work to do (carrying its new, lighter weight around) and so it needs less energy to do the work, and so it will naturally use up less calories - which is another way of saying that its metabolic rate will be slower.
This means that if, as an example, you weighed 12 stone when you were overweight and now you weigh 10 stone, all other factors (e.g. your levels of activity) being equal you will need to eat less to maintain your new weight of 10 stone than you did to maintain your weight of 12 stone.
This is not, in essence, because the dieting has adversely affected your metabolism but because you weigh less. Research carried out at Cambridge several years ago found that people who had dieted down to a particular weight, had similar metabolic rates to people of that same (lower) weight who had never dieted. (If you put on weight again, your metabolic rate will rise again.)
There may also be other factors at work here tending to put the brakes on your metabolism, too. The World Health Organsation says that the body seems to want to defend a high weight against weight loss, more readily than it does a low weight against weight gain, so that a 3500 calorie reduction in your food intake doesn't necessarily always translate itself to 1lb of fat lost off your body, which in theory is the equation.
This means that weight loss over time will progressively become harder as the metabolic rate appears to slow down more than would be predicted from the weight loss.
People who take up regular physical activity including aerobic work and some strength training will find that dieting doesn't tend to alter the metabolism so much. Regular aerobic exercise can increase your metabolic rate a little for several hours after exercise, as well as burning up extra calories during the course of the exercise. And weight training will help to avoid the loss of lean
tissue (muscle) for the dieter, and may even add some. Lean tissue is heavier and uses up more calories than other tissue (e.g. fat) and so a good proportion of lean tissue to fat in the body is essential to maintain a good metabolic rate. Crash or very low calorie diets tend to lose a fairly high proportion of muscle as well as fat, whereas moderate energy restriction loses proportionately more fat, which is why steady slimming is the best way to go.
Will my percentage of body fat increase each time I diet?
No, when you diet to lose weight you will decrease your percentage of body fat. But the question implies that you are a yo-yo dieter (sometimes called 'weight cycling') and it is probably true that with repeated bouts of yo-yoing, every time you return to a high weight, your percentage of total fat may have increased a little. This is because when you lose weight, some of the weight loss is lean tissue (particular if you 'crash' diet) and when you put the weight back on, the
lean tissue isn't replaced. So you'll be your old weight, but may have less lean tissue and therefore may have a little higher percentage of body fat. Compared with the last time you were at this same high weight, your overall resting metabolism will then have decreased slightly because of the lower proportion of lean tissue, so this time it may be a little harder to lose the weight.
Avoid yo-yo dieting, avoid crash dieting, and always exercise when slimming to retain as much lean tissue (muscle) as you can.
How can I avoid regaining all the weight I've lost?
First of all, let's hope that you have settled on a reasonable 'target' weight, which is always easier to maintain than a too-low one. For young adults, a target Body Mass Index (BMI) of around 22 - 23 is as low as you want to go - but 25 would be fine if your starting level was highr than 28, especially if you are over 40. For older adults, a target around BMI 24 -25 is often reasonable. Use your common sense. If you go too low, your will need to reduce your regular calorie intake
low as well and this may be too hard to do (see previous question).
Secondly, let's hope that you dieted slowly so that you didn't lose too much lean tissue (muscle). The more muscle you have on your body, the more calories you will burn up every day rather than storing them as fat. Research shows that very fast (crash) dieting does lose more lean tissue than slow dieting.
Thirdly, you need to eat a healthy balanced diet and keep the total fat content fairly low, while filling your plate with more of the complex carbohydrates, vegetables, fruits and low-fat proteins. You need to eat smallish, regular meals and snacks - portion control is a simple method of watching total calorie intake.
Fourthly, you need to look at your lifestyle and try to adjust it so that you are less inclined to overeat.
And last but definitely not least, you need to take regular exercise - preferably both aerobic (e.g. walking, cycling) and weight training (e.g. with free weights or at a gym).
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