How Important is BMI when assessing Obesity Status ?

 

The obesity epidemic is steadily gaining ground in the western world, and the UK is no exception. The proportion of adults in the UK population classified as obese (i.e. BMI >30) virtually doubled between 1993 (14.8%) and 2023 (29.8%). Of even more concern was the statistics in our children, with obesity classifications rising in 10-11 year-olds from 17.5% in 2008 to a whopping 25.5% at the peak of the pandemic in 2021, before falling back a little to 22.7% in 2023. Can we really ignore the fact that more than a quarter of our adult population is clinically obese, and perhaps even more worryingly, almost as many of our children have already succumbed to the same problem ?

First, how do we define obesity ? The key parameter is body mass index (BMI), and anyone with a BMI of more than 30 is classified as obese. There is some argument as to whether using  BMI alone is the best way of assessing whether someone is clinically obese (see below for some of the arguments for and against), but the fact remains that going by this criterion, well over a quarter of us are seriously overweight, with all the potential health issues (and thus pressures on our NHS) that will result. 

Read on for some background to the problem, and a discussion on how we can all monitor and improve our diet and health....and help solve it.

Introduction

Heart disease and stroke are two of the major causes of death in the UK population. Type 2 diabetes is also a growing scourge, and the uncontrolled high blood sugar it causes has many adverse effects.

Maintaining healthy blood pressure, glucose, cholesterol and lipid levels, and a healthy Body Mass Index (BMI), is crucial to avoiding falling victim to these modern-day ills, particularly later in life. Our highly-processed modern Western diet, which is high in fat and carbohydrate, and our increasingly sedentary and exercise-poor lifestyles, both serve to increase the risk. How has this happened ?

Millions of years of evolution has optimised our physiology and metabolism for a low fat, high roughage diet and an active lifestyle. This is because our ancestors were faced with a restricted diet at best, with recurrent bouts of near-starvation when times were really lean. Those who could hunt and make best use of what little food was available were the ones who survived to reproduce - the others didn't.

Hence evolution favoured those who were best able to chase their prey, were able to survive the frequent 'lean' times and who had the appetite to consume as much as possible when their hunts were successful. It was also vital for them to be able to escape any predators themselves. This has left many of us with a legacy of a strong appetite, a low resting metabolic rate, and a need to exercise regularly - all of which are completely out of tune with the way modern society and its commercialism now encourage us to live.

As a result, our largely sedentary 21st century existence, lack of the incentive to exercise, and a high intake of cheap and heavily-processed high-calorie food, sets up an imbalance between energy input and output, and can also compromise our gut health through lack of roughage in the diet. Our busy lifestyle also often mitigates against getting enough exercise to burn off the excess calories we consume. Sadly, it takes a surprising amount of vigorous physical effort just to burn off the calories in a single Mars bar, and most of us just don't have the time or the inclination to keep things in balance. Our 'express' lifestyle also mitigates against preparation of healthier food, which takes time and effort to prepare than the 'fast food' many of exist on. This ‘perfect storm of adverse factors affects those with a ‘strong’ appetite most, and puts them at the highest risk of becoming obese. We should therefore regard them more as victims of their genes and circumstances, rather than weak-willed gluttons.

Could we not all just switch to a 'healthier ' diet ?,   you may ask.

Sadly, such a typical 'healthy' mediterranean-style diet, rich in fresh fruit and vegetables, is usually a more expensive option to buy and prepare, and is now simply beyond the means of some of the poorest in our society, where, sadly,  the UK's obesity epidemic is the most prevalent. It is also not as attractive to the NW European palate as the high carbohydrate + fat combination found in many of our fast food items. It is no coincidence that the food industry has hitherto promoted these fast foods, since they are more saleable, cheaper to manufacture en masse, and generate more profit.  Although there are some signs of change, both from regulators and more health-aware consumers,  this is a slow process, and hasn't been helped by the cost of living crisis. All that regulation has managed so far are marginal decreases in salt and sugar content, and some reductions in portion sizes which manufacturers would have introduced themselves anyway on cost grounds.

The real problem from a health point of view is that hypertension, atherosclerosis and other consequences of obesity such as Type 2 diabetes, are all 'silent' killers, since they are often asymptomatic until a life-threatening problem occurs. And they affect all levels of society - no one is immune.

Early diagnosis of any abnormalities will pay dividends in later life, and continued monitoring will help ensure the advantage is maintained in later years, and is likely to prolong 'good quality' life.

For those who are unable to control their food intake effectively via diet and exercise alone, the possibility of some help has recently emerged in the form of the GLP-1 analogues, notably semaglutide, which is marketed by Novo Nordisk as Wegovy (see Figure 1 for structure). This class of 'peptide mimics' was originally developed as a therapy for type 2 diabetes, and work by binding to and activating the GLP-1 receptor, thereby stimulating insulin secretion and reducing blood glucose. They were also found to have a notable side-effect in reducing appetite. Semaglutide therapy effectively resets the 'appetite stat', but unfortunately doesn't do this on a permanent basis, and weight lost is usually regained when therapy is stopped. Thus effective weight control is likely to require lifelong treatment. Like all potent drugs, it also has some side effects. Semaglutide has been licensed as a weight reduction therapy but is only available on the UK NHS in conjunction with an approved diet modification and exercise treatment programme. Its primary role as a treatment of Type 2 diabetes, which is a common consequence of obesity, is also beneficial in reducing the disease burden. 

The 'holy grail' of a permanent appetite-stat reset, however, still eludes us.

Can I Monitor and Assess My Own Health Effectively ?

The short answer is ‘Yes’….a lot can be done by the individual to monitor and improve their own health. This is particularly important at a time when the UK health service is under severe strain, with both GP and dental appointments 'like gold dust' and often only available many weeks or even months after you really need them. The NHS is now actively promoting 'self-help' as a way of reducing demand. GP practices are introducing more 'holistic' medical strategies to encourage this, in an attempt to reduce GP workloads and improve outcomes. We are all being encouraged to take care of our own health to prevent the need for expensive and resource-hungry treatment interventions. Merely accepting the need to look after your health is half the battle and can ‘reset’ behaviour in the direction of a more healthy outcome.

Where do I start ?

You can help maintain good health by generating your own blood pressure, heart rate and BMI assessments at home. You can do this easily and with a minimum of equipment; heart rate can be measured with a watch showing seconds and a knowledge of how to take your own pulse; digital blood pressure monitors can be purchased for £10-20, and will measure haert rate for you. A set of digital scales and a tape measure is all that's needed for BMI.

Cholesterol and lipid profiling and blood glucose testing is widely available in pharmacies and is often included in routine GP health screens, particularly in the older age groups. By monitoring all these key health parameters, and acting on them where necessary, you can do much to reduce your risk of poor-quality life in old age and avoid suffering chronic illness and a premature death.

Childhood obesity is a particular worry, since it has already reached near epidemic proportions in UK, and spells trouble ahead for tomorrow's adults. It's well known that bad dietary habits are most easily established (and broken!) in early childhood. If you are a parent, check out your children’s status now - it may save them from much angst in later life. Read on for some practical suggestions.

Some Practical Suggestions for Monitoring Your Own Health

Having experienced routine GP health checks myself in the recent past, and with a  background in Clinical Chemistry, it occurred to me that it might be useful to produce an easy-to-use health checker designed to help others to interpret their own health-related test results.

As discussed, many of the tests described above can be done at home with inexpensive equipment. Other more complex tests, that involve blood sampling are normally done at clinics or GP surgeries, but should be available to you (although you may need to ask for them specifically).

Check them out and see if you're really as healthy as you think....

You can download the Health Checker app to find out how best to generate and interpret your data. This requires MS Excel (2010 onwards) running on a Windows pc. Just key in your home readings and other test results and the software will calculate your BMI and provide assessments of each parameter against recommended normal ranges.

The assessments and recommendations used are based on current NHS guidelines, and links to these and a BMI calculator designed specifically for children are provided within the workbook. Apart from the links I've provided to NHS web pages, the stand-alone calculator runs entirely offline and your data is therefore kept confidential. You can even build up a database of your own results over time if you wish, using the results transfer button for each set of results.

Always consult your GP if you have concerns about any of the results, before considering any self-treatment.

How Important is BMI when assessing my Obesity Status ?

The are now increasing numbers of clinicians who advocate that the current exclusive reliance on BMI should be dropped. Their argument is that it is the distribution of excess body fat that is important in determining future health rather than merely the overall quantity (as used by BMI). In particular, excess fat surrounding the abdominal organs is known to have a poor prognosis for health, but this is not specifically assessed by a simple BMI calculation. Mike Tyson, ex-World Heavyweight Boxing Champion has a BMI over 30,  which technically classifies him as obese. Although this is an extreme anomaly, and is caused by his size and very high muscle:fat ratio, it illustrates the need to assess other factors. 

An additional, and informative, measurement that's easy to make yourself is your 'Waist to Hip' ratio. This simple parameter gives an indication of whether you might be carrying too much fat around the middle. This can be harmful since excessive amounts can interfere with the functioning and health of your internal organs.

To assess, simply use a tape measure to generate a waist measurement and one at the widest part of your hips.

Ratios vary between the two sexes, as females tend to have wider hips, so you will need to enter your sex to complete the assessment.

Another more complex index used by clinicians, which is based on similar assumptions, is the Body Roundness Index (BRI). Like Waist:Hip ratio, this takes into account excess fat stored around the middle. This parameter is becoming more popular as a supplement to BMI in obesity assessments and you'll find it's calculated and assessed for you in the Health Check.xlsm workbook if you enter your data on the BMI worksheet of the app.

So, returning to our original question, BMI remains a useful index of overall obesity risk, but should not be relied on exclusively to define obesity. Many other factors contribute to the health risks of being overweight, most notably the distribution of body fat, and these should always be taken into account in any health assessment.

I hope this article will provide 'food' for thought, and some practical suggestions on monitoring and assessing your own health. Constructive suggestions on how it might be improved are of course welcome via the comments page.

First Published 15.1.25

Revised 21.1.25

                            Figure 1: Semaglutide Structure