Sunday, 6 November 2011

Is BMI the best indicator of health?

I’m doing some research for a weight management programme today and have been busy looking at the ins and outs of the Body Mass Index (BMI) which is one of the most common methods used to assess weight in relation to height.  The BMI calculation involves dividing the weight in kilograms, by the square of the height in metres.

For example, weight 80kg, height 1.85m, then the BMI is 80/(1.85 x 1.85)  = 23.37

(Note that BMI applies to adults between the ages of 18 and 65 years of age, and should not be used by pregnant or nursing mothers and might not apply to serious athletes which higher muscle masses).

BMI classifications were decided by The World Health organisation in 1995 who originally recommended three cut off points, 25, 30 and 40, based on anthropometric international data examining populations, weight and disease risk.  These classifications have now been refined and are as follows:

18.5 or less  Underweight
18.5 to 24.99  Normal Weight
25 to 29.99   Overweight
30 to 34.99  Obesity (Class 1)
35 to 39.99  Obesity (Class 2)
40 or greater  Morbid Obesity

These ranges apply to both men and women, and are meant to take into account build and muscle mass.

The health issues associated with having a BMI in the higher ranges include cardiovascular disease, diabetes, joint issues and a possible higher risk of cancer.  However BMI may not necessarily give us the best picture of our health for the following reasons:
  • It is possible to be fit, well muscled and well built (yup - those ‘heavy bones’ we inherited!) and have a BMI of overweight, despite having a low level of body fat.  In contrast a skinny, low muscled, unfit individual might have a normal BMI.  
  • There are some studies which actually show no greater risk of overall mortality for individuals who sit in the overweight category (BMI of 25-29.9) while being underweight is linked with being more dangerous for our health.  This could possibly be for the reason above, while the underweight category will include people with underlying disease processes - such as heart disease, lung disease, cancer or infection, which can cause weight loss.  Some researchers have highlighted that despite the conflicting evidence being overweight is still a risk to health because excess weight tends to progress and can also be hard to lose. Many overweight people can go on  to become obese which is linked with definite health risks.  
[(Lewis et al (2009) Mortality, Health Outcomes, and Body Mass Index in the Overweight Range American Heart Association 119: 3263-327]
  • One of the most important points to make about BMI is it that does not take into account fat composition and where fat is deposited in our bodies. Lean muscle weighs more than fat!  Research shows that it is far more dangerous to store the fat around the middle, where it is known as ‘visceral fat‘ which is strongly linked with cardiovascular disease and type 2 diabetes.  Visceral fat is not more dangerous because it sits closer to our hearts (as many people seem to think!), but because abdominal fat is ‘metabolically active'.  It  produces chemical substances which trigger inflammatory processes, and these processes then damage our blood vessels and interfere with blood sugar regulation. Better measures to assess fat composition are hip to waist measurements and skin-folds tests.  Ideally the waist circumference should not be more than 80cm for women and 94cm for men.  The waist hip ratio is calculated by dividing your waist measurement by your hip measurement and should not be more than 1.0 for men and 0.8 for women. 
It is interesting that fat stored on the thighs and bottoms seems to play a protective role, so all your lovely Rubenesque pear shapes should celebrate!  Research now links fat on the lower part of the body (known as gluteofemoral body fat) to playing a protective role in managing long term fat storage (it ‘traps’ excess fats and prevents them floating around your body causing mayhem!) and reducing inflammation.

[Manolopoulos et al (2010) Gluteofemoral body fat as a determinant of metabolic healthInternational Journal of Obesity 34, 949-959]

So, while BMI is probably ok as a health indicator for those at the upper and lower ends, it is less clear cut for those individuals in the overweight range.  In this case, waist circumference and other measurements to assess fat composition will give a more accurate picture of health.  

As always, a recipe.  Adapted from 101 cookbooks ( ) a fantastic blog and given to me by my friend Janelle who runs ‘Big Apple Yoga’ at Villennes

Chinese cabbage salad

The dressing is incredible and can be used pretty much with any salad.  I like to use red cabbage rather than the white cabbage the original recipe suggests.  I love the colour which to me screams of autumn (a bit like red wine!).  It is a great source of Vitamins A and C, and like all the cruciferous family a source of substances called ‘indoles’, compounds linked to a reduction in cancer risk.

Lovely served as a side dish with cold roasted meat.  I ate it last night with salmon brochettes - salmon strips marinated in teriyaki sauce.  

3 large shallots, skinned and thinly sliced
splash of extra-virgin olive oil
pinch of salt
1 tablespoons miso
1/2 teaspoon powdered mustard (or a bit of whatever mustard you have around)
2 tablespoons brown sugar (or honey or agave)
50ml (brown) rice vinegar
70ml cup mild flavored extra-virgin olive oil
1 teaspoon pure toasted sesame oil (optional)
1/2 of a medium-large red cabbage
75g slivered almonds, toasted
2 large grated carrots
large chunk of grated radish (radis noir)

Stir together the shallots, splash of olive oil and big pinch of salt In a large frying pan over medium heat. Stir every few minutes, you want the shallots to slowly brown over about 15 minutes. Let them get dark, dark brown (but not burn). if needed turn down the heat. Remove them from the skillet and onto a paper towel to cool in a single layer. they should crisp up a bit.

Make the dressing by whisking the miso, mustard, and brown sugar together. Now whisk in the rice vinegar and keep whisking until it's smooth. Gradually whisk in the olive oil, and then the sesame oil. Two pinches of fine grain salt. Taste and make any adjustments if needed.

Cut the cabbage into two quarters and cut out the core. Using a knife shred each quarter into whisper thin slices. The key here is bite-sized and thin. If any pieces look like they might be awkwardly long, cut those in half.

Gently toss the cabbage, carrots, shallots, almonds and radish in a large mixing/salad bowl. Add a generous drizzle of the miso dressing and toss again - until the dressing is evenly distributed. Add more a bit at a time if needed, until the salad is dressed to your liking.


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