‘To know that we know what we know, and that we do not know what we do not know, that is true knowledge’ (Henry David Thoreau (1817-1862): American historian, essayist, poet and philosopher)
There was much coverage by the media of the research findings by the University of Birmingham; presented at the European Congress on Obesity in Portugal last month (but as yet, unpublished) regarding the health implications of obesity on health.
A 10-year cohort study (1995-2005) of 3.5 million British Peoples’ GP health records tested whether the risk of developing coronary heart disease, stroke, peripheral vascular disease, and heart failure was different for normal weight people (BMI of 18.5-24.9) or people who were obese (BMI over 30), but “metabolically healthy”.
In this study, the term “metabolically healthy” was used to describe people who had ‘no evidence of diabetes, high blood pressure, or abnormally high levels of blood fats (Hyperlipidemia)’.
The results demonstrated that compared to people of normal weight/BMI – the risk of heart failure doubled, the risk of coronary heart disease increased by 50% and the chances of having a stroke increased by 7%.
So, it would seem the term “metabolically healthy” is odds-on to mean anything but, and arguably a poor choice of words considering the findings, but, when we also consider the World Health Organisation and their definition of health, which includes the descriptor ‘…not merely the absence of disease of infirmity’, it also seems to be a very misleading.
Nevertheless, it is a common term used in studies. An interesting example is a 2015 study; people described as ‘metabolically healthy obese’ (or “MHO” for efficiency) were defined by a criteria which included high levels of insulin sensitivity, low prevalence of hypertension and favourable fasting glucose, lipid and inflammation profiles. Furthermore, the study cited that, depending on how MHO is defined, anywhere between 10-40% of obese individuals fall into this category. But there lies a problem, given how seemingly broad the definition of it is, only seems to mislead even more.
It also remains the subject of intense debate, not least because of certain variations, as well as contradictions, in the findings of numerous studies on obesity and the risk of adverse health outcomes.
Consider the findings of a 2013 study, which tested fitness as well as health records, with results demonstrating that when fitness was factored in to the study, MHO individuals showed a significantly lower risk (30-50%) of all-cause mortality, non-fatal/fatal cardiovascular disease and cancer compared to metabolically unhealthy obese participants – which may be of little surprise, although the size of the risk-gap might – however, the real surprise was findings indicating there was no significant difference in risk between MHO individuals and metabolically healthy individuals of normal weight. Being overweight, obese even, and making sure you stay fit seems to carry a raft of risk-reducing benefits according to this study.
And these findings are certainly not unique when uncovering a seemingly low level of risk - particularly for issues such as all-cause mortality amongst others - of being overweight and/or grade 1 obese (however, above grade 1 obesity did demonstrate definite and substantially increased risk) as defined by Body Mass Index (BMI), such as the following studies; (2013, 2013, 2008, and 2006).
These studies, amongst others, have given rise to the notion of the “obesity paradox” which implies that for certain medical conditions and certain people with said medical conditions (old age, wasting diseases, heart diseases or those undergoing renal dialysis, being major examples), study outcomes demonstrate that being overweight, even obese, could impart some protective benefits. We emphasise the word could.
But caution is very much advised. Numerous articles by experts reinforce each other with similar messages; that the ‘protective effects’ observed remain uncertain, ambiguities and biases abound in the studies revealing these results and for the vast majority of us, to consider these findings and conclude that being overweight or obese doesn’t carry health risks, or can even have positive health outcomes, is akin to adding 2 and 2 together to get 22! Despite the findings, the key message remains the same; it would be prudent to adopt the conventional, mainstream thinking on this - being overweight or obese increases the risk of developing numerous chronic diseases and/or premature death for the general population.
Maintaining a healthy weight throughout your life is still the recommendation of every public health organisation you care to name.
But you certainly could be forgiven for wondering how so many studies have resulted in so many contradictory results. How can it be that the very factors that put people at risk of various metabolic health disorders have been found – consistently or not - to have seemingly protective benefits in some circumstances?
Ultimately, there is a lot of speculation but very few definitive answers. Studies, no matter the size or length of time over which they are conducted, the rigour adopted in testing, or the number of variables tested, can ever truly capture all the variables, lifestyle factors and complexities each individual participant studied has.
Numbers just cannot crunch such complex issues into a neat, predictable algorithm and outcome. Because as well as the complexities of those studied, there seems to be a growing body of evidence indicating that perhaps a particular measurement – key in virtually all of the studies referenced here, is not exactly without flaws, nor without its critics, as well as a growing body of evidence to indicate that it may be far too vague a tool for such a complicated problem.
This measurement is Body Mass Index (or BMI) and in the next blog, we will be discussing the growing evidence to support its criticism.
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