A new study undertaken by a team at the University of Iowa, examining data from nearly 157,000 post-menopausal women over a 20-year period and published in the Journal of the American Medical Association, suggests that waist size – rather than body mass index (BMI) – is a better indicator of fundamental health in women.
BMI is calculated by dividing a person’s total mass by the square of their height – scores of 18 to 25 are considered healthy, 25 to 30 overweight, and above 30 obese. But given that fit individuals, including professional athletes with heavy muscle mass, often do not qualify as ‘healthy’ under these criteria, BMI has come to be regarded as a blunt instrument – “simple and cost-effective in terms of large group studies, but telling us little about individual health”, according to dietitian Paula Mee.
BMI does not look at where body fat is located, while the Iowa study indicates that abdominal fat in particular is an indicator of whether a person is more likely to develop serious illnesses, such as cardiovascular disease or cancer.
By way of example, the researchers found that those with a BMI reading of less than 25, but with a waist circumference of 35 inches or greater, were at a 31pc higher risk of dying during the study period than women of a normal weight and a waist of less than 35 inches.
Karl Neff is a consultant endocrinologist at St Vincent’s University Hospital in Dublin and principal investigator in UCD’s Diabetes Complications Research Centre.
“Fat distribution is determined by a number of factors,” he says, “and there is clear evidence that women’s fat distribution changes after menopause. There are many reasons as to why this might be the case. One possibility is that the changes in hormones like oestrogen and testosterone [women have testosterone too] may alter the distribution of fat cells.
“However, this is not definitely proven, and we cannot say for sure that the changes in hormones have any real effect on fat distribution. Likewise, there is no good evidence to say hormonal interventions like HRT change the distribution of fat after menopause. Pregnancy [a time when oestrogen concentrations are very high] is another risk time for weight gain and obesity in women. So it’s not as simple as hormone changes equal weight change.”
Neff says that it is more likely that genetics are primarily responsible for the distribution of fat.
“A combination of widespread changes in internal metabolism with a genetic code that predisposes to weight gain is probably why some women gain central weight after menopause,” he explains. “Scientific evidence to date has not been definitive as to the cause. This is most likely because there are many interacting causes, which makes it difficult to tease them all out.”
Neff points out that central adiposity – or ‘fat around the midriff’ to us lay-people – is known to be associated with worse health outcomes, and with a greater risk of heart and other diseases. “This does not mean that all women with weight around their middle get heart disease, but there is evidence that they would be at greater risk,” he says.
“This risk can be reduced with good blood pressure control, cholesterol control and lifestyle changes such as quitting smoking.
“The reasons for the increased risk are not entirely clear, but are again likely due to genetics. The same genetic code that makes it more likely that you put weight on around the middle could increase your risk of heart disease, diabetes and other conditions. So it’s not necessarily that the weight around the middle is directly causing increasing risk. It could easily be that the weight around the middle just is a sign that you have ‘higher risk’ genes.”
While Neff doesn’t think that we should abandon BMI completely, he agrees with Paula Mee that it is a crude measure of overweight and obesity, and does not correlate exactly with health outcomes.
“People can have a BMI of 60+ and have no diseases,” he says, “while conversely someone can have a BMI of 28 and have all the associated diseases, such as high blood pressure and diabetes.”
Any menopausal woman who struggles with fat around the middle knows that it is hard to shift, but Neff says that all fat is hard to lose, wherever it is stored and whatever age we are.
“The reason for this,” he says, “is that the body has multiple inbuilt mechanisms to defend against weight loss. We know that when people go on diets, the body tries to resist weight loss by reducing the amount of calories we burn and increasing our hunger. Internally, our body does not always know what weight it is, it only knows if weight is going up or down. If weight is going down, the internal interpretation is that we are in ‘famine mode’, so the body increases hunger to try to get us to eat whatever we can, and also simultaneously reduces our calorie burn.
“This is very likely to be an evolutionary mechanism that was a great advantage in Ireland during the Famine, but in modern Ireland is a disadvantage.
“This is the basis of the obesity epidemic. Obesity is a disease of unbalanced energy regulation. Most of us have a genetic code that does not defend against weight gain, but is really good at preventing weight loss. This is why we shouldn’t judge people for their weight. For the majority, menopausal or not, it is nearly impossible to achieve sustained weight loss, and there is abundant clinical trial evidence demonstrating this.”
Paula Mee and Karl Neff agree that when it comes to obesity or weight gain, prevention is better than cure. Their advice to women is to watch weight carefully around the time of menopause, and to act as soon as any weight gain is seen, as early intervention is key.
“Weight gain after menopause is not inevitable,” says Neff, “but given the changes in metabolism, there is an increased risk of obesity around the time of menopause. I would say women should view menopause as a risk time for obesity. Women should seek GP advice regarding medical and surgical options if diet and exercise intervention doesn’t work, but there is no conclusive evidence for medical interventions such as HRT in preventing weight gain.”
“The menopause is a time when women experience a wide range of different symptoms,” says Mee. “They are likely to be more fatigued, thanks to the sleep deprivation that accompanies night sweats, and there is a host of other factors at play that impact upon weight gain, including naturally declining metabolism and a reduction in male hormones leading to a decline in muscle mass.
“Many women report to me that they feel foggy-brained, moody, more anxious and simply ‘not themselves’. They may be juggling the competing demands of a career, relationship, teenage and young adult children, and ageing parents, with very little time to call their own. Unconsciously, they may be eating more for comfort, but it only takes a small increase in calorie intake to increase weight.
“Personally, I found gentle exercise such as yoga and other mindful practices very helpful for grounding me during that time. We can control the impact of changing hormone levels through our diet too – the drop in progesterone that comes with the menopause can lead to a sense of bloating and increased water retention, which can in turn affect blood pressure, so it’s good to keep an eye on salt, particularly hidden salts. To counteract the drop in oestrogen, eat a well-balanced diet with plenty of phytoestrogen-rich foods. It’s a time for more exercise and fewer calories.”
Mee says that menopausal women are at risk of leaning more heavily than they should on alcohol and recreational drugs to spike dopamine levels.
“If we abuse those substances, then our response to them becomes blunted and desensitised: there is a tendency to consume more to get the hit. We need to retrain our brains. I tell my patients to see the ‘pause’ in menopause as a chance to press the pause button and make more conscious decisions, to find other ways of getting the hit.
“For women spending long hours commuting and working, I advise them to be more conscious of the three Ps – posture, Pilates, which is great for the core, and the plank, which is a whole body workout that you can do in front of the TV.”
Mee says that if visceral fat is allowed to build up, it’s very hard to shift.
“There is a point at which it is very difficult to return to normal weight as the biochemistry has changed and hormones are so disrupted that there may be insulin resistance. With all the will in the world, it’s hard to get rid of it, but even losing 10pc of body weight will impact positively on blood pressure.
“We are not our weight, though, and we all set too much store by weight. How we feel, our confidence and eating well are much more important; it’s an anxious time for many women and the fact that we are talking about it more now can only be a good thing.”
For women who have taken BMI as the be all and end all, though, the findings of this new study may cause them to question whether science keeps moving the goalposts.
“Science is dynamic,” says Neff, “and our understanding of things is constantly evolving. There is a tendency for the media to report every little thing that’s found in every study [like ‘red wine is good, red wine is bad’-type stuff]. From a lay perspective, this can seem like shifting goalposts, but really it means that we should look at evidence as a cumulative.
“If 100 studies say red wine is good and 50 say it’s bad, then there’s roughly a 65pc chance that red wine is good. It’s not that red wine becomes bad or good every second or third week depending on the latest study – science doesn’t work like that. It is a holistic interpretation of whole bundle of scientific findings to come up with a plausible answer to a question.”
Health & Living