First devised by Adolphe Quetelet more than 150 years ago, BMI is calculated by taking your weight (in kilograms) and dividing it by your height squared (in metres). In simple terms, it is a way to compare the weights of groups of people of different heights. However, the one obvious weakness of the BMI is that it doesn’t distinguish between fat and muscle. How often have we heard that Brad Pitt at the time of Fight Club, and England rugby player Jonny Wilkinson in his prime, were “overweight” – according to their BMI? This is a MAJOR flaw in the BMI system and for this reason I consider it to be a largely worthless indicator, even an unnecessary “distraction”, particularly for those starting out trying to lose weight.
Your weight is of course relevant to weight loss but taken on its own without any context it too can be misleading/irrelevant. To say “I weigh x kg” without also putting it into the context of your height tells us nothing. For example, a person who weighs 90kg but is only 1.60 m tall is more than likely to be overweight by any definition, whereas the same weight for a person of 1.95 m means their weight is OK. BMI in theory takes care of this problem but, as discussed above, it’s also a flawed indicator, which brings us onto our final and most definitive measure, your waist..
Your waist measurement, as measured around your navel, is the single true indicator that determines whether or not you are overweight. Why? Because it is totally independent of your height or body composition, and it is the one thing that just about all government health agencies across the globe can agree on when it comes to weight management. It is a direct measure/indicator of your visceral fat levels, the most dangerous when it comes to CVD. To put it simply, stored fat around your waist indicates that you also have fat around your organs, in particular your heart and hence an associated increased risk of CVD, diabetes, stroke, etc., etc. The guidelines also take into consideration your ethnicity e.g. for African-Caribbean, South Asian and some other minority ethnic groups, waist measurements are more restrictive than for white Europeans i.e. they are in a higher risk group.
Here are some simple, practical tips on weight management that I used during my weight loss phase and continue to use to this day to ensure I am managing my weight correctly:
- You can largely forget about BMI, it’s irrelevant.
- Weight: During weight loss phase, check your “dry weight” every morning before breakfast. Weight loss is a “leading indicator” before waist and will give you confidence that you are doing the right things. I also check my weight daily in the mornings during the so-called “maintenance phase”. If you are inflamed in any way at all, your weight will almost immediately shoot up before you see any reaction in your waist measurement, thereby giving you plenty of time to sort the problem out. If you are getting things right during the maintenance phase, and assuming you are not resistance training for muscle mass, you should see your weight fluctuate no more than +/- 1-1.5kg throughout the year. Any more than this you need to check your diet.
- Waist: check this at least once/week during both weight loss and maintenance phases. Use this as your principal measurement. Assuming that you are fully ketogenic at all times, and even if you are resistance training for muscle mass, your waist measurement should not increase, even if your weight does. Aim to be within the limits defined here according to your ethnicity.