The link between body mass index and Covid-19 is not clear, and frightening people into believing they will be protected if they lose weight may do more harm than good.
We’ve read the headlines and watched the prime minister’s address at the
Conservative party conference, where he said his experience of Covid-19 was worse because he was ‘too fat’. It seems an accepted fact obesity appears to be one of the biggest risk factors related to Covid-19 hospitalisations and critical illness. But this is not necessarily true and sweeping statements such as that made by Boris Johnson, with little
evidence, can be harmful.
When the health secretary stated ’everyone who is overweight should lose
at least 5lbs in order to save countless lives and spare the NHS a £100m
cost’, it became clear the Government believes ‘overweight’ and ‘obesity‘
was a choice for many. But this fat-shaming could lead to people with a higher body weight being terrified of dying and potentially developing habits that could lead to health issues, such as yo-yo dieting. Health is not a certain body size and it is more important for people to have a healthy relationship with food than to hit a certain weight.
The evidence so far
Given the conventional wisdom that obesity is harmful, assuming a higher body weight increases the risks with Covid-19 could be viewed as taking steps to protect the public.1 The actual evidence around the virus, however, remains inconsistent and it is possible an obesity survival paradox may exist, as is the case with other conditions.2, 3, 4
The published research linking body mass index (BMI) to Covid-19 is not yet conclusive and it appears much of the data has been taken at face value. The main flaw with most studies to date is they do not take into account the social determinants of health that more strongly predict our health outcomes, compared to body weight.5 Determinants like social class, racism, sexism, trauma and weight bias (which is negative weight-related attitudes toward an individual with a bigger body); these factors in a healthcare setting, which lead to cardiovascular disease, type 2 diabetes, cancer, asthma, or other chronic respiratory conditions, are what can increase the risk if you become Covid-positive, rather than weight or fatness itself. 6
As the majority of studies do not account for these diseases (as co-morbidities) in their design, the conclusions made about the links between obesity and this virus could be premature, despite knowing these disease states can be associated with worse outcomes for Covid-19.7
When social determinants and co-morbidities are accounted for, death rates appear lower in higher BMI groups 8 – hence the obesity survival paradox referred to earlier. The recent American study which leads me to conclude that shows obesity, black race, Hispanic ethnicity, chronic lung disease and hypertension were not associated with mortality due to Covid-19. The acknowledged limitation of this study, however, is the male subjects in the study had access to a national healthcare system and, therefore, may not be representative of the general US population.
A 2017 meta-analysis found that having a BMI of 30 or above was correlated with a significantly lower risk of dying from acute respiratory distress syndrome (ARDS), compared to those in the ‘normal’ category.9 A retrospective study published this August reported BMI >40 was more strongly associated with Covid-19 deaths in men, but not in women for the same BMI.10
Following the first epidemic wave across the UK, tabloid publications reported on data from the Intensive Care National Audit and Research Centre (ICNARC).11 For the first 200 critically ill patients, there was concern regarding the reasonably high percentage of Covid-19 patients with a BMI > 30. However, the percentages shown are simply reflective of the BMI spread of the general population and this does not mean BMI is therefore a risk factor.
Interestingly, data from China (where Covid-19 emerged) shows no correlation between a high BMI and the development of Covid-19. BMI is also not listed amongst any of the co-existing disorders among Covid-19 patients.12 This is noteworthy because China would likely have highlighted it if there was a link between high BMI and Covid-19 because weight management, as it is in the UK, is a public-health priority. Ultimately, there is a lack of consistency in findings and it is important to remember that correlation does not mean causation.
The dangers of associating a high BMI with Covid risk
Negative attitudes toward people in bigger bodies was already pervasive across the UK, pre-pandemic. When fatter people experience weight stigma, they are less likely to get the medical care they need which of course can negatively compromise their health.13 Therefore access to healthcare becomes another factor in the Covid-19 jigsaw. When discrimination exists in healthcare it is evident that fatter people are often not given the same quality of care because their conditions are automatically blamed on their weight. 14 This may also mean that fatter people avoid getting assessed for Covid-19 symptoms until their symptoms are already advanced (and perhaps this is one of the reasons they require hospitalisation). Weight stigma does not motivate individuals to adopt healthier behaviours. 15
Should weight loss be recommended?
Having said all of the above, and although it is not conclusively proven yes, it is still possible a high BMI is a risk factor for hospitalisation from Covid-19. But this does not mean that trying to lose weight will definitely lower the risk of hospitalisation or death from the virus. The main reason being there is still no proven, effective way to reduce BMI in the long term .16 It is well accepted in the field of weight science that many intentional weight loss approaches eventually result in weight gain (not weight loss) 95% of the time across all ages.17 Most will gain back more weight than originally lost due to the negative metabolic and psychological impacts of weight-centred approaches. A UK study from 2015 found people whose BMI>30 have < 1 % annual probability of moving into the ‘normal’ category.18 Strong evidence also shows weight cycling (or yo-yoyoing) increases the risk of hypertension, heart disease and type II diabetes, not body weight itself.19 It’s definitely time to challenge obesity research. 20 21
There is yet insufficient evidence to support the view that BMI is a significant risk factor for hospitalisation or death from Covid-19.
There is no convincing evidence to suggest that losing weight is a form of prevention or cure.
Recommending people focus purely on weight for weight loss is counter-productive and could cause more harm than good. It can ultimately lead to weight gain.
It would be more beneficial for healthcare professions to focus entirely on health behaviours (and not weight, through a weight neutral approach) to support people in improving their health. By encouraging healthy eating, sensible eating patterns and exercise people are likely to achieve any weight loss they wish to achieve in a more sustainable way.