New Study Supports Weight-Neutral Health

Weeldryer et.al. Cardiorespiratory fitness, body mass index and mortality

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Today we’re going to talk about a new study called Cardiorespiratory fitness, body mass index and mortality: A systematic review and meta-analysis whose goal was to assess the “relationship of cardiorespiratory fitness (CRF) and Body Mass Index (BMI) on both cardiovascular disease (CVD) and all- cause mortality risk” by Nathan R Weeldreyer, Jeison C De Guzman, Craig Paterson, Jason D Allen, Glenn A Gaesser, and Siddhartha S Angadi.

Before we dig into this new study, during launch week for this newsletter I wrote about Gaesser and Angadi’s 2021 study “Ob*sity* treatment: Weight loss versus increasing fitness and physical activity for reducing health risks” which was a huge analysis of 225 other papers, analyses, and meta-analyses that drew four main conclusions:

The mortality risk associated with ob*sity is largely attenuated or eliminated by moderate-to-high levels of cardiorespiratory fitness (CRF) or physical activity (PA)

most cardiometabolic risk markers associated with ob*sity can be improved with exercise training independent of weight loss and by a magnitude similar to that observed with weight-loss programs

increases in CRF or PA are consistently associated with greater reductions in mortality risk than is intentional weight loss

weight cycling is associated with numerous adverse health outcomes including increased mortality

Before we dig into all of this, I said it then and I’ll say it now:

Health is not an obligation, a barometer of worthiness, or entirely within our control. Further, while physical activity is one option for weight-neutral health-promoting behavior, there are many other options for weight neutral care that aren’t explored here (including things like sleep, stress management, and social connection not to mention larger issues like thriving wages, ending oppression, access to physical and mental healthcare and more.) It’s also important that public health focuses on things like removing barriers to access and improving social determinants of health (including ending oppression) rather than fixating on the choices of individuals, or trying to make the individual’s choices the public’s business. My goal is always to give people accurate information so that they can make decisions based on their situation and priorities.

As a reminder, fitness/exercise is also not an appropriate health intervention for some people for a variety of reasons, and often higher-weight people experience stigma, mistreatment, and trauma around physical activity that negatively impacts their relationship with, and desire/ability to participate in, movement. Finally, many fitness activities are not available to higher-weight people at all due to lack of accommodation including in clothing, equipment, and instructor knowledge. These issues will always do the most harm to those of the highest weights and those with multiple marginalized identities. It’s very important that we not blame higher-weight bodies for those harms, but are clear that they are due to the inequalities and mistreatment that higher weight people face.

And regardless of the possible health benefits, participation in movement/fitness is never an obligation or barometer of worthiness for anyone of any size.

This new study analyzed data from 20 studies that included 398,716 observations. They divided the groups into “normal weight, “overw*ight,” and “ob*se” and subdivided each group into “fit” and “unfit” based on the highest and lowest levels of cardiorespiratory fitness shown in each of the articles. They used “normal weight fit” as the reference group and compared the other five groups in terms of cardiovascular disease and all cause mortality (a measure of the mortality rate for a population across all causes.)

Their conclusion was

Our analyses found that those classified as fit, regardless of BMI status, showed no statistically significant increase in CVD or all-cause mortality risk compared with normal weight-fit individuals.

In contrast, all BMI classifications who were “unfit” showed twofold to threefold increases in risk of CVD and all-cause mortality compared with normal weight-fit individuals.

Said another way in the discussion section:

The major finding of the present meta-analysis was that once CRF was accounted for, there were no significant increases in all-cause or CVD mortality risk for overwight or ob*se individuals. Importantly, these data extend prior findings to a pooled cohort with greater representation of females (33%). Our findings demonstrate that individuals with higher CRF who are overw*ight or ob*se are not at a higher risk for all-cause or CVD mortality when compared with normal weight-fit individuals. Importantly, individuals who were unfit had a ~2-fold increase in the risk of all-cause mortality and a ~2–3-fold increase in the risk of CVD mortality.

So what level of cardiorespiratory fitness is required? They explain:

It is important to note that a majority of these studies demonstrated that individuals only needed to exceed the CRF of the study population 20th percentile in order to be considered fit, which suggests that significant reductions in mortality risk may be attained with moderate levels of age-adjusted CRF regardless of BMI status

That said, cardiorespiratory fitness (CRF) does not directly transfer to specific time and/or movement types. In the included studies, CRF was measured using maximal oxygen uptake (VO2Max - the maximum amount of oxygen one can use during intense activity) or Bruce Protocol Treadmill Time, which is a test of aerobic endurance used to estimate V02Max in which the participant is typically put on a treadmill and every three minutes speed and incline are increased (unless heart rate changes greater than 6 beats per minute between minute to and three of any given stage, at which point speed and incline remain the same for an additional minute) until the person reaches 85% of their maximum heart rate, heart rate exceeds 115 beats per minute for two stages, or something occurs that causes those running the test to decide that it shouldn’t continue.

That said, any activity that increases breathing and heart rate can help to increase CRF.

They explain that their findings are not new information. As they point out:

In the past three decades, a multitude of prospective studies have investigated the joint associations of CRF and Body Mass Index (BMI; kg/m2) categories on mortality. These studies consistently show that CRF has a stronger association with mortality risk than does BMI.

They also performed analyses around other variables and found:

Within each of the subgroups, there were no significant effects of sex, age, chronic disease status or length of follow-up(all p>0.05). This indicates that the effects of fitness appear to show benefit in all-cause mortality risk for each BMI class regardless of these population characteristics.

They also point out that, when it comes to higher-weight people:

The public health strategy has largely focused on weight loss; however, this has a recidivism rate of ~100% at 10 years follow-up. In addition, intentional weight loss alone has not consistently shown improvements in mortality risk in observational studies or randomized controlled trials.

As someone who spends a decent amount of her time either saying this to people, typing it out, or yelling it at my computer screen, I cannot tell you how refreshing it is to read this.

I am grateful to these authors for their work around this.

There are some thing I want to discuss here:

They write:

Cardiorespiratory fitness (CRF) has been shown to be inversely related to both all-cause and CVD mortality risk. Due to this, CRF has been proposed as a vital sign but is not part of risk management guidelines in overw*ight and ob*se individuals.

I’ve seen this idea before and I believe it’s well intentioned. And while I think giving patients accurate information about health supporting behaviors is important, I strongly disagree with making cardiorespiratory fitness a vital sign. As I said above, there are many people who aren’t interested in participating in fitness, including because of the mistreatment/trauma they’ve experienced when they tried. There are also people for whom exercise is contraindicated for any number of reasons, some of which they might not be comfortable disclosing to every healthcare provider. Regardless, having their doctor’s office insist that people discuss (or somehow test!) their cardiorespiratory fitness could cause direct harm as well as delayed appointments and patient disengagement.

Note that they also qualify this by writing “but is not part of risk management guidelines in overw*ight and ob*se individuals” Their own findings showed that people of all sizes who were in the “unfit” category had higher rates of CVD and all-cause mortality so, while I agree that it’s certainly better than weight loss as a recommendation for higher-weight people, I would argue that it would be better to stop focusing on making recommendations based on body size and, instead, just give accurate information about cardiorespiratory fitness to people of all sizes.

In general, I feel that they had an opportunity to suggest a parting from the current practice of pathologizing bodies based on size, but they did not take that opportunity.

They point out that when taking into account other study results:

This suggests that CRF may substantially attenuate, but not entirely eliminate, the CVD mortality associated with elevated BMI. The reasons for this are unclear but may be related to the association between ob*sity and CVD risk factors and type 2 diabetes, which increases the risk of CVD. It is also possible that higher levels of CRF are necessary to further attenuate CVD mortality risk associated with high BMI

This represents a recurring issue in this paper (and, honestly most, if not all, of the literature) there is no discussion (or even mention) of the fact that being higher-weight is also correlated with weight stigma and weight cycling, both of which are independently associated with increased CVD mortality and all cause mortality.

Again, I’m grateful for this paper and this work is incredibly important. What we absolutely need is more analyses and randomized controlled trials that look at the impact of weight-neutral health supporting behaviors (including things like high-quality sleep, social connection, resilience against - and better yet lack of - weight stigma etc.) and weight-neutral healthcare for higher-weight people - and people of all sizes.

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More research and resources:
https://haeshealthsheets.com/resources/

*Note on language: I use “fat” as a neutral descriptor as used by the fat activist community, I use “ob*se” and “overw*ight” to acknowledge that these are terms that were created to medicalize and pathologize fat bodies, with roots in racism and specifically anti-Blackness. Please read Sabrina Strings Fearing the Black Body – the Racial Origins of Fat Phobia and Da’Shaun Harrison Belly of the Beast: The Politics of Anti-Fatness as Anti-Blackness for more on this.