It’s the New Year, and this time usually brings with it an upsurge in the numbers of people wishing to shed excess weight. Some of these may even have been urged to take steps to lose weight by their doctor or other health professional. Governments and the medical profession frequently warn that being ‘overweight’ or ‘obese’ puts us in mortal danger, and encourage us to conforms to weight norms defined by a measure known as the body mass index (BMI).
The BMI is calculated by dividing someone’s weight in kilograms by the square of their height in metres (kg/m2). According to conventional wisdom, a BMI of 18.5 – 24.9 is regarded as ‘normal’ or ‘healthy’, while BMIs of 25.0-29.9 are considered ‘overweight’, and those of 30.0 or more are classified as ‘obese’. While the BMI usually forms the basis of the advice health professionals give to individuals about their weight, does the advice stand up to scientific scrutiny?
When considering the relationship between BMI and health, it pays to take as wide a view as possible. The way to do this is to assess its relationship, not with the risk of individual conditions, but with overall risk of death. Ultimately, risk of death is 100 per cent, of course. In studies ‘risk of death’ (sometimes termed ‘overall mortality’ or just ‘mortality’) refers tolikelihood of death over a specified period of time (usually many years).
A study just published in the Journal of the American Medical Association should cause us to consider whether making health recommendations based on the current bands makes good sense. In this study, US researchers amassed evidence from 97 studies which assessed the relationship between BMI and overall mortality. The studies taken together involved 2.88 million people and a total of 270,000 deaths. This is the biggest ever study of its kind.
Individuals with a BMI of 25 – <30 (‘mildly overweight’) relative risk of death was 0.94 (a 6 per cent reduction compared to those of ‘normal’ weight: BMI18.5-<25 – this result was statistically significant).
Individuals with a BMI of 30 – <35 (‘grade 1 obesity’) had a relative risk of death of 0.95 (a 5 per cent reduced risk that was not statistically significant.
Some have suggested though that these results are skewed by two basic facts:
1. smoking overall tends to shorten life and smokers tend to be lighter in weight
2. when people get sick they can lose weight before they die
The idea here is that the presence of smokers and individuals with long-term illness in these studies makes being a bit heavier look healthier than it is in reality.
The authors of this latest study address this and say this:
“The results presented herein provide little support for the suggestion that smoking and preexisting illness are important causes of bias. Most studies that addressed the issue found that adjustments or exclusions for these factors had little or no effect.”
We should not be too surprised by these results, though, as time and again, previous evidence has found pretty much the same thing. One thing that has come out of the research is that the relationship between BMI and mortality is influenced, to some degree, by age. In one study , being ‘overweight’ was associated with an enhanced risk of death in individuals under 60 years of age, but not after this. Other studies have yielded findings that support the idea that as we age, being technically ‘overweight’ is not a concern in itself, and may in fact signal superior survival.
For instance, in a study of Japanese men and women aged 65 years and older, having an overweight BMI was not associated with an enhanced risk of death, and this was even true for men technically classified as obese . In another study, lowest mortality in was found in older Norwegian men and women with BMIs of 25.0-29.9 (overweight) and 25.0-32.4 (overweight/obese) respectively.
One theory that has been put forward to explain why larger BMIs are associated with improved survival in the elderly is that some surplus fat can be used as a store of energy which individuals can draw on in times of need – such as during a critical illness. In one study, researchers assessed the relationship between ‘fat mass’ (overall levels of fat in the body), and risk of illness and mortality in individuals aged 65 and older . Over time, compared to those with the lowest fat masses, individuals with most fat had a 70 per cent reduced risk of mortality. These findings provide support for the idea that decent fat stores can come in handy in later life.
Also, it’s a pain a simple fact that BMI tells us nothing about body composition, so that individuals of big build who are quite heavily muscled and maybe very healthy and robust are penalised if judged by weight or BMI alone.
Overall, the evidence suggests that the hazards of being overweight (and possibly even obese) have been overstated. It seems some individuals may have less need to lose weight on health grounds than conventional wisdom dictates. This applies particularly to elderly individuals, as well as those who are of ‘big build’ and relatively muscular.
Also, even if someone is carry extra fat, the distribution of that fat appears to be important in terms of its likely impact on health. ‘Visceral’ fat (fat within the abdomen and organs) appears to be particularly toxic, and a decent proxy for this is an expanded waist size. More details about this sort of fat and how to get rid of it can be found in my last two books Waist Disposal – the ultimate fat loss manual for men and Escape the Diet Trap – lose weight for good without calorie-counting, extensive exercise or hunger.
1. Flegal KM, et al. Association of All-Cause Mortality With Overweight and Obesity Using Standard Body Mass Index CategoriesA Systematic Review and Meta-analysis JAMA 2013;309(1)
2. Berrington de Gonzalez A, et al. Body-mass index and mortality among 1.46 million white adults. N Engl J Med. 2010;363(23):2211-9
3. Tamakoshi A, et al. BMI and all-cause mortality among Japanese older adults: findings from the Japan collaborative cohort study. Obesity (Silver Spring). 2010;18(2):362-9
4. Kvamme JM, et al. Body mass index and mortality in elderly men and women: the Tromso and HUNT studies. J Epidemiol Community Health. 2011 Feb 14. [Epub ahead of print]
5. Flicker L, et al. Body Mass Index and Survival in Men and Women Aged 70 to 75. Journal of the American Geriatrics Society 2010;58(2): 234-241
6. Bouillanne O, et al. Fat mass protects hospitalized elderly persons against morbidity and mortality. Am J Clin Nutr 2009;90(3):505-10
By failing to measure the individuals actual body fat & correlate that with death rates & bmi these researchers have surely just muddied the water . The only person I know who died of a heart attack under 55 (an employee of our business) had a horrific diet but probably only a BMI of 25-30 as he was fairly active , he would doubtless have seen this as a green light to continue living on chips…..
Such a coincidence.
Only last evening I had to see a surgeon, in order for him to decide if I needed a knee replacement. Indeed I do, but before I can be admitted to the hospital their rules state, I must lose weight. And how did they come to this conclusion? By working out my BMI of course. BMI is something I have long considered out of date, and pretty much useless. Especially when I found out that Arnold Schwarzenegger (in his heydey) would likely have had a BMI that classed him as obese! The problem is in ignoring what they say Dr. John. Whatever I think, until my BMI suits them, they won’t give me the go ahead for surgery, and I will continue to be in agony. This is all despite having lost almost four stones since I first came across your ‘Waist Disposal.’ When I got home last night, I also watched an episode of the ‘Hairy-Dieters’ re-run yesterday. It is mind boggling that health Professionals can get away with some of the things they say about
1) Calories. 2) Fat, and 3) Exercise. With all the evidence that’s available now, to show that current thinking is wrong, just how long will it take for these dogmatic people to accept they are wrong? The fact is they are spouting nonsense, and they are also spouting it in schools, and other places where they shouldn’t be allowed to set foot, let alone teach. I fear it’s going to be a long, long time before the truth is out and is accepted as ‘Gospel’.
Interesting stuff. I agree that bmi doesn’t say anything for body composition but I think it would be reasonable to assume that the majority of american people in the 25-29.9 range are not there because of their muscle mass.
I like the theory regarding accumulated fat stores in elderly people being beneficial for survival in times of illness. I guess in the modern era this also helps with cancer survival, enabling people to withstand the weight loss caused by the malignancy (and the treatment), possibly long enough to recover from it.
I wonder what the figures would look like if the all cause mortality were broken down into smaller ranges, whether the 25-27.4 range would have a lower mortality than the 126.96.36.199 range.
Also I think you might have typed the ranges incorrectly in the 5th and 6th paragraphs.
Another thought, it seems strange that bmi categories correlating with research derived mortality would fit into such neat little ranges. It seems obvious that these ranges are there for simplicity, and it would it be far more useful to reevaluate the ‘normal’ bmi reference range based on actual evidence.
Being overweight is also a sign on inactivity and *perhaps* stress, sugary diet etc. I agree that waist circumference is most important. But hard to measure sometimes as waist may have ‘dropped’ in those who are very overweight….
Spare a thought for ladies who have lipoedema as their legs are grossly disproportionate to their upper body. Working out a BMI in these cases in no indicator of health.
I have long wondered about the connection of obesity as a cause of death. Given that so many very large people are being told they won’t live past …. (Embarrassing Fat Bodies again last night was scaring people with this). So how is it that actually they seem to manage to live for quite some time, Cyril Smith springs to mind for just one example and then there’s the man who was 70 stone. I’m sure they aren’t without health problems but not as life threatening as one is led to believe.
Watching Embarrassing Fat Bodies and a string of other such programmes, I am still saddened to hear the “experts” trotting out the same out of date advice about fat, calories and exercise. Having read in The Times recently about how the recommended number of alcohol units was arrived it, it tells me that actually, most of the medical profession is way behind the times and when they decide to dish out their wisdom, they base it on very little in the way of facts.
What gets me is that most GPs and practice nurses have such a limited ‘training’ on nutrition and it’s effects on health, there is little any of them can say that cuts any ice with me. I know of one health visitor who was very overweight and doing nothing about it, yet was advising parents about their children’s diets and giving really bad advice, e.g. a four year old should eat no carbohydrate at all because she was ‘chubby’, yet within that child’s diet plan she was told to eat lots of pasta??????
I agree with John Walker’s comments re so called ‘health professionals’ being allowed to continue to spout all this rubbish. They seem to be everywhere: schools, hospitals, supermarket magazines and shelves So, Dr Briffa, when are you going to make a tv programm to put the record straight? I look forward to it.
Most importantly even if this study is right it says nothing about the affect on quality of life. My mother is 82 and weighs 100kg (height 5ft2), blood pressure 115/80, pulse 65 and seems like she could go on for ever. BUT she has severe arthritis and at 100kg is virtually immobile so her quality of life is extremely poor.
She is lucky enough to live in a residential village which mitigates this and perhaps it is some consolation that nearly all the people iin the village have the same problem with mobility that is aggravated by weight. Oh and they all have type 2 diabetes like my mum!!
Fustratingly I cannot get any of the health care professionals mum sees (GP, Consultant for arthriitis, haematologist etc ) to talk to her about her diet and her weight!! Funnily enough both her GP and her main consultant are obese too.
My husband had to cope with a week in hospital at end of chemotherapy due to infection. They were brilliant but dietetically hopeless as he is low carb to control type 2 diabetes. I had to take meat and cheese in every day to fill the hunger gap. Every meal was carbohydrate based on epic scale
We challenged it at chief exec level and our request for a protein choice at every meal will be done if he is in there again. The dietitian trotted out Nice guidelines. !! His Hba1c is 6 at the moment. He is borderline slightly overweight. But doing ok beware hospital food. Carbohydrate heaven, also fresh fruit and sugar sugar sugar
Must agree with Sue it’s time the so called “professionals” get up to date and that you Dr Briffa put things straight. Bring the calorie in/calorie out theory to where it belongs – the rubbish heap.
I certainly agree that in general, the medical profession has overplayed the association between obesity and mortality. As Dr. Briffa points out, abdominal obesity does seem to be correlated with increased mortality because it is associated with insulin resistance and type II diabetes. Patients with total body obesity often are relatively free of these dangerous metabolic disorders, especially in the elderly.
We have also noticed that patients with the more dangerous type of central obesity are also more prone to a form of food-induced brain dysfunction called Carbohydrate Associated Reversible Brain syndrome or CARB syndrome. CARB syndrome associates dangerous metabolic states with some common brain disorders. Recent studies have found that the combination of depression and obesity is especially deadly:
What I find interesting is that up to about 50 years ago, major depression was always associated with a loss of appetite and weight loss. In recent decades many cases of depression seem to be associated with an increased appetite, carbohydrate cravings and weight gain. We believe that this is CARB syndrome, not true hereditary major depression. CARB syndrome appears to be triggered by the long-term exposure to excessive fructose mainly from sugar and HFCS and high glycemic carbohydrates mainly from grains—two dietary elements that form the core of our modern diet.
Thus the form of obesity associated with simply overeating healthy foods is often not associated with metabolic problems and brain dysfunction, indicating that it is a somewhat benign condition. Central obesity associated with brain dysfunction symptoms like we see in the weight gain type of depression clearly does increase morbidity and mortality. Dr. Briffa’s approach seems to be targeted to reversing this more dangerous type of obesity and I share many of his treatment recommendations.
The bottom line is that if you have obesity (excessive body fat) regardless of your size or weight and have been diagnosed with common brain disorders like depression, ADHD, PTSD, anxiety disorders, eating disorders, fibromyalgia, OCD or similar conditions, you may be prone to increased mortality. Limiting your intake of sugar, HFCS and high glycemic carbohydrates is the first step in reversing this dangerous situation
I wonder how this might tie in with the fact, that I think is well established, that calorie restriction leads to longer life.
Any ideas on this?
There might be a lot in what you say. I do imagine our ‘hunter-gatherer’ ancestors must have eaten far less than we eat today. If only because they had to pursue and catch their protein, and were reliant weather patterns to have good ‘harvests’ of nuts and berries etc. Even if they ate well, almost certainly they would have gone for longer periods between meals. Maybe that might bolster the idea that fewer calories means better health. But that is only conjecture on my part.
Eric, I never seen a large scale study investigating this. There is a ready made sample – flat racing jockeys – if anyone is interested. Around 30 years each of calories restriction.