Can you be both fat and fit? That question has been the core of a lengthy scientific debate that basically boils down to this: Are cardiovascular problems associated with high weight attributable to the weight itself? Or can they be mitigated by fitness?

Many on the “no” side probably felt vindicated by the results of a widely publicized study of 527,662 Spanish adults released in January. The study examined associations among body mass index (BMI), physical activity and cardiovascular disease factors, and it concluded that the government needed to make weight loss, as well as physical activity, a primary target of health policies.

But although this study stirred the pot and grabbed some headlines, such as “ ‘Fat but fit’ is a myth when it comes to heart health, new study shows,” it had some major shortcomings. The design of the study can’t establish cause and effect, let alone present a well-rounded picture of health risks. Perhaps worse, it goes on to propose unrealistic public policies.

To conduct the study, researchers drew data from insured active workers across Spain, including their BMI, self-reported leisure-time physical activity levels and information from medical examinations on the presence of Type 2 diabetes, high cholesterol and high blood pressure. They concluded that being active was associated with lower risk of having those health issues within each BMI category — “normal weight,” “overweight” and “obese” — but that individuals in the higher weight groups had more cardiovascular risk factors than their “normal weight” peers, regardless of activity level.

The study was published in the European Journal of Preventive Cardiology as a “research letter,” which means it lacks the details found in full research reports and was subject to less scrutiny. Although the study included an impressive number of participants, it’s notable that the authors did not look at eating habits, and that the activity levels were self-reported. But the cross-sectional design of the study — looking at data from a specific population at one point in time — brings up other issues.

“Specifically, from a cross-sectional study, you cannot know what came first. Did the health issue lead the individual to engage in more activity, or did the lack of activity lead to disease?” said Jennifer Kuk, an associate professor and researcher at York University in Toronto who specializes in how obesity, diet and physical activity relate to health. Kuk said it’s also unclear whether factors such as income or socioeconomic status, ethnicity or a family history of chronic disease are affecting these results. 

“A more accurate headline would have been: ‘Another study confirms that cardiovascular disease risk factors are related to each other,’ ” said Fiona Willer, a Queensland, Australia-based dietitian and researcher and the host of the podcast “Unpacking Weight Science.” “This study offers nothing really new or interesting. High blood pressure, high blood cholesterol, diabetes, higher BMI and a sedentary lifestyle are all well-established as cardiovascular disease risk factors, and some of them share common metabolic origins, particularly diabetes and higher body weight.”

Willer said research has already established that being physically active does not fully counteract those risk factors. “If that were the case, the only risk factor we’d care about would be physical activity level,” she said, adding that, ironically, the new study did show that being physically active may lessen those risk factors, regardless of body size. She said that without information about who actually developed cardiovascular disease or experienced adverse health events over time, it is impossible to know how weight and activity level might influence the things we really care about, such as actual heart attacks. She also points out that an individual’s physical fitness levels can fluctuate over a lifetime, but this study does not capture that information.

Alejandro Lucia, a professor at the European University of Madrid and one of the study’s authors, acknowledged the study’s limitations but said it still contributes valuable evidence. “In a world full of inactivity and obesity, with the figures even more worrying in the younger population segments, most adults don’t seem to follow that advice of being active and thin. And policies in these matters have not been too successful in general,” he said via email. He said the study’s findings that active “obese” participants were more likely to have high cholesterol, high blood pressure and diabetes support fighting or preventing excess body weight, “which, to the best of my knowledge, can only achieved by losing body weight, per se!”

However, although engaging in physical activity is a behavior, weight change is not. It’s something that may or may not happen as a result of our behaviors, our genetics and other factors. Other researchers question how promoting weight loss as a health policy is realistic, given the fact that, despite decades of trying, no one has come up with a way to help people maintain weight loss for the long term.

Willer said statements recommending weight loss are common in the conclusion sections of these kinds of “fat/fit” papers, even when the study didn’t investigate intentional weight loss — something that, as a researcher, she finds disappointing. “The fact that it appears in this paper and that this very brief paper was deemed headline-worthy demonstrates the huge problem we have, not with weight itself, but with weight bias in scientific research and journalism.” She said that if the authors had used all of the data at their disposal, including information from routine medical examinations, which would have included weight-related goals, it’s likely that they would have found what other long-term studies have concluded: that lasting weight loss is unlikely beyond two to five years for most people who lose weight voluntarily.

“Public health policies have a moral and civic obligation to be feasible, achievable and effective for the target population,” Willer said. “Weight loss targets have been at the center of public health chronic disease prevention campaigns for years. We have diligently observed the outcomes of these efforts for decades. We now know them to be unsuccessful at a population level, and for some, they have led to the experience of weight stigma, discrimination, disordered eating and eating disorders.” She said the intention of these policies — improved health — was good, but it’s time to recognize that they don’t work.

Even though most people who lose weight don’t maintain those losses long term, a small percentage of people do. Is there something we can learn from these outliers about whether weight loss leads to a longer, healthier life?

“The study of statistical outliers means that, by definition, we cannot generalize their experiences to the broader population,” Willer said. She points to the Look AHEAD trial, which randomly assigned participants with Type 2 diabetes to receive either an intensive lifestyle intervention with a weight loss goal, or simply diabetes support and education. The trial was stopped after 10 years, because its researchers discovered that participants who lost weight were just as likely to have a heart attack or stroke — or to die — as those who didn’t lose weight.

In a 2013 review of long-term, randomized controlled diet studies, researchers from UCLA and the University of Minnesota found no clear relationship between weight loss and health outcomes. They said this called into question whether weight change actually caused the few improvements observed in some studies; other factors, such as increased exercise, healthier eating, engagement with the health-care system and social support may have played a role instead.

Given that most people cannot sustain their weight loss for the long term, this begs another question: Instead of asking people in larger bodies to continually “fail” at losing weight, which could be even worse for their health, why not focus on helping everyone be more active, which, in some cases, may include making neighborhoods, towns and cities more walkable or bikeable? If we can’t all be lean and fit, can we at least be fitter? Abundant research demonstrates that physically active people of all age groups and ethnicities have higher levels of fitness, health and wellness, and a lower risk of developing cardiovascular disease and several other chronic diseases, compared with people who are physically inactive.

“The main message is that physical activity and other lifestyle factors can have substantial health effects beyond changes in obesity,” Kuk said. “This is particularly important for physical activity, because exercise is typically associated with very small, if any, differences in body weight, but still can cause improvements in body fat and health.”

She said health experts should recommend a combination of lifestyle improvements to help lower the likelihood of developing obesity-related chronic conditions. “But even with a perfect lifestyle with wonderful diet, lots of physical activity, the right amount and good-quality sleep, not too much stress, etc., there will still be those who develop obesity and associated chronic diseases.” 

The bottom line is that being physically active is better for your health than not being active. There’s no one-size-fits-all solution, but a good place to start is to find types of activity that you enjoy, suit your current fitness level and mesh with your schedule. This includes both “formal,” planned exercise and incidental daily movement that helps you spend less time simply sitting — something many of us may have been doing more of during the past year.

Dennett is a registered dietitian nutritionist and owner of Nutrition by Carrie.