Don’t feel guilty about BMI – there’s a new definition of obesity
Which of your own health statistics are you aware of? Perhaps a tally of how many steps you do in a day and your weight? But medical science is increasingly telling us that having a working knowledge of a stack of other numbers is key to a healthier life. In fact, a new global report even calls for an entire rethink in the way we diagnose obesity – abandoning BMI classifications and taking other health measures into account, too.
“We no longer have a patriarchal system where the doctor is in charge and the patient sits there in the dark without knowing what’s going on in their body,” says Dr Eve Wijayanayagam, a GP who practises at the Sarum Road Hospital, Winchester. “There’s been a natural shift to patient responsibility. These days, it’s important to discover your ‘numbers’ and have an idea of them in your head so you can take some responsibility for your own health and enjoy an element of autonomy.” Here are the health numbers it makes sense to count on.
Your waist-height ratio (or Body Roundness Index)
For almost 200 years, medics have relied solely on the Body Mass Index (or BMI) to determine whether a person is a healthy weight. The formula for BMI – weight in kilograms divided by your height in meters squared – was invented in the early 19th century by Belgian mathematician Lambert Adolphe Jacques Quetelet.
And while health professionals still use BMI to determine whether a person has a healthy amount of body fat – an ideal BMI is between 18.5 to 24.9 – the system is increasingly being seen as out of date. In fact, a new global report argues that obesity should be defined by a range of other factors as well as your BMI, and suggests that a new diagnosis of “pre-clinical obesity” be given to anyone who is living with obesity but is free of chronic illnesses.
“Though it can be useful to measure general obesity, BMI measures both muscle and fat, so does not distinguish between overmuscled and overweight people,” says Dr Margaret Ashwell, a biochemist and past president of the Association for Nutrition.
The most important measurement, says Dr Ashwell, is the waist-to-height ratio, which is a person’s waist circumference divided by their height. A too-large waist is a marker that you might have visceral fat, which wraps around your organs and raises the risk of certain conditions. “It’s long been known that central obesity raises the risk of heart disease, type 2 diabetes and strokes,” says Dr Ashwell. “And one in three people who have a ‘normal’ BMI could have too high a percentage of visceral fat.”
A recent report in The Journal Of American Medicine suggested that a new metric, the Body Roundness Index, was a more accurate measure of your health than the BMI.
To calculate your BRI, measure your height, waist circumference and hip circumference, then enter the results into an online BRI calculator. A BRI score of 2.5 or less shows you have a healthy shape and lower levels of hidden belly fat.
Otherwise, just grab a tape measure, measure your waist circumference (just above the belly button) and divide this by your height. The general guidance is that a waist-to-height ratio between 0.4 and 0.49 is considered healthy.
Your QRISK
Probably the most effective and reliable overall view of your health is an algorithm called the QRISK, a number which suggests your risk of a cardiac “event”, such as a heart attack or stroke in the next 10 years.
You’ll be given your QRISK when you visit your GP surgery for your over-40s health check, an examination available every five years for everyone aged between 40 and 74.
A health professional will measure your blood pressure, cholesterol, height, weight and waist circumference, and ask questions about smoking, alcohol consumption and exercise. These are put into a computer, which will work out your QRISK.
A low QRISK score of less than 10% means that you have less than a one in 10 chance of having a stroke or heart attack in the next 10 years and a higher QRISK score of more than 20% means that you have at least a two in 10 chance of having an event in the next 10 years. Depending on your QRISK score, you’ll be offered advice on how to change your lifestyle – and possibly medication, which could stop any condition becoming more serious.
Blood pressure
If you don’t know your blood pressure readings – and check them – regularly, you should. Around one in three adults have high blood pressure, and 6m people have it but are unaware of it. “High blood pressure (or hypertension) does not always have any noticeable symptoms, but if left untreated raises the risk of so many conditions, from kidney disease to stroke and heart attacks,” says Dr Wijayanayagam.
The blood pressure machine (an inflatable cuff, placed on your upper arm) measures the force of the blood being pushed against the walls of the arteries. The first number is the systolic pressure and the second, diastolic pressure. Systolic measures the force when your heart beats and diastolic is when it rests. Those numbers – particularly systolic pressure – can increase as we age and arteries stiffen. Regular home testing is increasingly recommended, as is being tested at the local pharmacy.
A normal blood pressure reading is when the systolic pressure (upper number) is lower than 120mmHg and the diastolic pressure (lower number) is lower than 80mmHg. When these levels climb to 130mmHg or higher for systolic pressure, or 80mmHg or higher for diastolic pressure, this is considered high blood pressure, or hypertension.
Cholesterol
Cholesterol is a waxy, fat-like substance found in the blood or cells of the body. All the experts agree that having some cholesterol in your body is necessary and healthy, but having too much of the “wrong” type of cholesterol (known as LDL cholesterol) over time can clog a person’s arteries and lead to problems such as stroke, kidney disease and dementia.
High-density lipoprotein (HDL) cholesterol is known as the “good” cholesterol because it helps remove other forms of cholesterol from the bloodstream. A higher level of HDL cholesterol is linked to a lower risk of heart disease.
Cholesterol is measured with a blood test, ideally after a patient has fasted for eight hours. “Results can be confusing, but the easiest to understand is looking at total cholesterol,” says Dr Wijayanayagam. “Your HDL cholesterol should have a healthy ratio to your LDL.”
“Total” cholesterol should be lower than 5.0, while your LDL cholesterol should be lower than 3.0. Your HDL cholesterol should be as high as possible, ideally 1.4. A total cholesterol to HDL ratio of above 6 is seen as high-risk.
The good news is that many people can lower their cholesterol by losing weight and eating a diet rich in wholegrains, which have been shown to lower cholesterol. “But if lifestyle changes are ineffective, a patient has a strong family history of cardiovascular disease or has had a heart attack under 55, we will strongly recommend starting on statin medication,” says Dr Wijayanayagam. “The same goes if you have familial hypercholesterolemia – a genetic predisposition to high cholesterol.”
Blood sugar (and type 2 diabetes)
Type 2 diabetes is a condition where a person has high blood sugar levels due to their body not making enough of the insulin hormone. Consistent high blood sugar can lead to heart attacks and strokes, as well as problems with your eyes, kidneys and feet.
We’re heading for a type 2 diabetes epidemic: according to Diabetes UK, an estimated more than 3.2m people in this country are at an increased risk of type 2 diabetes, and 1.2m people are currently living with the condition but are yet to be diagnosed.
So, how is it tested? “The most up-to-date test is the HbA1c, a blood test which is traditionally done after an overnight fast,” say Dr Wijayanayagam. “This measures your blood sugar over the past six weeks. Over a certain figure, a person is at risk of diabetes.” An ideal HbA1C reading is between 20 and 38. Prediabetes starts at 42, and diabetes at 48.
The good news is that research has consistently shown that for many people, combined lifestyle interventions including diet, physical activity and sustained weight loss can be effective in reducing the risk of type 2 diabetes by about 50%.
The jury is still out on the usefulness of continuous glucose monitor (CGM) for non-diabetic patients. A CGM is a wearable device that tracks blood sugar in real time and, increasingly, you’ll see non-diabetic people out and about wearing, for example, the little circular yellow ZOE patches. “The idea is that these patches tell you what your body can tolerate by way of monitoring a sugar spike after you’ve eaten a specific food,” says Dr Wijayanayagam. “For example, you might tolerate apples better than bananas.”
But are they clinically helpful? “People love instant feedback, but this sort of thing comes at a cost,” says Dr Wijayanayagam. “The problem is that it’s the ‘worried well’ who tend to use health technology, rather than the people we really need to see.”
Bone density
“Bone density (or DEXA) scans are not routine on the NHS, but certain sets of patients will be able to get them,” says Dr Wijayanayagam. “For example, if you’re in your 40s and 50s and have had a fall followed by a fracture, have had an early menopause or have a BMI under 19.”
Bone density figures are reported as t-scores, which compare a person’s bone mineral density (BMD) to the average BMD of a young adult: a t-score of -1 or higher means bone density is healthy; a t-score of -1 to -2.5 means bone density is low (a condition called osteopenia); a t-score of -2.5 or lower means bone density is low enough to be categorised as osteoporosis.
You can pay privately for a DEXA scan – the price of which ranges from £110 to £300, depending on the scanner. “While private providers may offer this service, it’s important to see a doctor to interpret the results and decide on the most appropriate treatment,” says Dr Wijayanayagam.
Resting heart rate (RHR)
“Normal is between 60 and 100 beats a minute,” says Dr Wijayanayagam. “But resting heart rate depends so much on the individual.” Wearing a heart rate monitor over a few days should give you a good idea of RHR. An ultra-fit person may have a resting heart rate of 40bpm, but on another person, it may be cause for concern. An RHR of over 100 is worrying as this could be a sign of heart trouble, fever or thyroid issues.”
Thyroid, iron, vitamin D
These checks are not done as part of your over-40s health check, but you can pay privately for them or speak to your GP if you have concerns such as feeling tired or hair loss.
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