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Body Mass Index: a Poor Indicator of Health

Body Mass Index (BMI) has for at least the past 40 years been used as the gold standard to indicate whether you are overweight and, if so, then as an indicator as to whether or not you will get heart disease or an obesity-related illness.

Unfortunately, BMI is NOT to be relied on!

At Ambition we have never used BMI as anything more than an opportunity to expose the failure of conventional wisdom/advice. We will then proceed with a more accurate measurement such as a Body Composition Measurement - this will tell you what percentage body fat you have, and how much lean muscle you have.

Medical studies indicate strongly that the problem of heart disease and obesity-related illness is not associated with having muscle, but instead with having excess fat - and exactly where that fat is located.

BMI Measurement

When your BMI is measured, three things are taken into consideration: your age, your height, and your weight. Let's take two examples to illustrate how misleading BMI actually is.

These are both people that came to see us recently, having also seen their GP. 

Apparently Slim - but actually FAT

'Mrs Smith' came to us for an assessment and told us before we started that her BMI was perfect and that she had nothing to worry about. She weighed 65kg, had a body mass index of 22.5 and - as far as the NHS is concerned - is the perfect picture of heart health.

We measured her Body Composition and this came out at a whopping 38% body fat, putting her in the 'dangerous' category for obesity even though she appeared slim - apart from an obvious abdominal bulge.

She was obviously shocked, and immediately told us that this cannot be correct. We then measured her three further times, using three different methods (talk to us about these) and the results were roughly the same.

The truth that BMI missed

Mrs Smith is what is called a 'slim fat person'. She may look petite but - when measured correctly - proportionally she has very low levels of lean muscle and very high levels of body fat. This puts her at a high risk from obesity related illness and heart disease.

Muscular and Lean - but NOT 'BMI healthy'

'Mr Jones' weighed 92kg with 12% body fat (N.B this is an athletic level of body fat) and had good levels of lean muscle. However his BMI measurement was 28. This is (according to the NHS) bordering on obese, and traditional advice would be that he needs to lose 21kg. This is a HUGE amount of weight to lose - 22% of his entire body weight.

The problem is that, with 11kg of body fat, he would need to lose ALL his body fat and a further TEN KILOS. This is clearly impossible! His body fat is already what we would regard as excellent, so even if we allowed for him to shed every ounce of that, he'd still need to starve himself until his muscles waste away. He will never become the picture of 'heart health' (as defined by BMI and the  NHS) without becoming a shadow of his former self - and we pray he never tries!

PLEASE don't trust BMI!

If Mrs Smith hadn't come to see us she would have continued on her way, oblivious to this serious danger to her health. She would likely end up having a stroke or heart attack.

Mr Jones is a healthy individual but his GP would likely tell him that he needed to lose 21kg and probably go on statins. He would be risking exhaustion and malnutrition at the very least.

Jeff says: This was a terrible outcome for both people. Please do beware of BMI measurements - they are misleading and could be fatal. Instead, please read up on our 'Live Long Strong Heart' program.

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