Getting fit may benefit obese people even if they don't lose weight

Thursday January 18 2018

Exercise "can protect against a heart attack, stroke and cancer – even if you're obese," reports the Mail Online. Researchers in Denmark who studied almost 11,000 people found that those with better heart and lung function had lower levels of inflammatory markers in the blood.

The relationship between fitness, weight, body fat and disease is complex. Persistently high levels of inflammation in the body increase the risk of long-term illnesses, such as heart disease, some types of cancer and type 2 diabetes. Also, fat around the waist has been linked to increased inflammation. People who are overweight or obese are likely to have larger waists, higher levels of inflammation and lower fitness – although this varies from person to person.

Researchers found that people with better fitness levels (measured using an exercise test) were likely to have lower levels of inflammation and smaller waists, even if they were overweight or obese.

Does this mean that people can forget about weight? Not really, because many people who are overweight have poor fitness levels. However, it does show that taking exercise to improve your fitness can be good for your health, even if you are overweight.

Read more advice about getting started with exercise and how a combination of exercise and healthy eating can help you lose weight.

Where did the story come from?

The researchers who carried out the study were from the University of Copenhagen and the University of Southern Denmark. The work was funded by the research foundation Trygfonden and the Danish National Research Foundation.

It was published in the peer-reviewed journal PLOS One, which is an open-access journal that can be read for free online.

The Mail Online provided a reasonable overview of the study, but took a leap by saying: "Going for a brisk walk or bike ride each day," would protect against disease. Although these activities might improve your fitness (and certainly can't hurt), we don't know from this study how much exercise would do the job. It may be more than a daily walk or bike ride. The study only looked at people's measured fitness levels, not at how much activity or exercise they reported doing.

What kind of research was this?

This was a cross-sectional study which is useful for investigating links between factors – in this case, fitness, waist circumference, body mass index (BMI) and inflammation markers. However, because it gives us just a one-off snapshot in time, we can't tell exactly how these factors are related, or whether one factor causes another.

What did the research involve?

More than 180,000 adults taking part in a survey of health in Denmark were invited for a health examination. About 10% of them attended.

Researchers took blood samples to measure C-reactive protein (CRP) levels (an indicator of inflammation in the body). They also measured people's height, weight and waist circumference.

Some people were invited to take part in a fitness test using an exercise bike and a mask to measure oxygen uptake, resulting in 10,976 fitness test results.

Researchers then looked for links between people's waist circumference, fitness levels and CRP levels.

People didn't do the fitness test if they were pregnant, or if they had a range of conditions including high blood pressure, muscle or joint problems, heart disease or chest pain.

Researchers adjusted their figures to look for the potential confounding effect of:

  • BMI
  • age
  • education level
  • smoking
  • self-rated health
  • alcohol consumption

BMI was the most important of these, as researchers wanted to see whether fitness, inflammation and waist measurements were linked even for people who were overweight or obese.

What were the basic results?

For both men and women, researchers found people who were of healthy weight, overweight or obese all had:

  • Lower waist measurements if they had better fitness levels (1.5cm lower for men per unit of fitness and 1.26cm for women).
  • Higher levels of inflammation if they had larger waist measurements (0.03mg/L higher CRP for each additional 1cm of waist circumference in men, and 0.025mg/L in women).
  • Lower levels of inflammation if they had better fitness levels (0.19mg/L lower CRP for each additional unit of fitness in men and 0.25mg/L in women).

For the last finding, fitness had a stronger effect on CRP levels for people with higher BMI. In other words, people of normal weight had reduced CRP levels if they were fitter than if they were not, but people who were obese had far lower CRP levels if they were fit, compared to unfit people who were obese. The results found that people with high fitness levels had "negligible" levels of CRP, even if they were obese.

For men, low waist measurement was linked to lower CRP levels regardless of their BMI, while for women, even a low waist measurement didn't completely wipe out the increase in CRP associated with being overweight.

However, people with higher BMI in the study were likely to have higher waist circumference and higher CRP levels.

How did the researchers interpret the results?

The researchers say that their results show "high fitness levels are inversely associated with the amount of visceral fat and the level of chronic systemic low-grade inflammation, regardless of BMI" – in other words, that people with high fitness have less fat around their waist and lower CRP levels, at any level of BMI.

They go on to say that the study may help doctors identify people who are "healthy despite obesity" and "at metabolic risk despite normal weight", by measuring their waist, CRP and fitness levels.

Conclusion

The question of whether you can be "fat but fit" as the Mail Online puts it, has been around for many years. This study adds to evidence that suggests it is possible – but unlikely for most people.

The study suggests that good cardiovascular fitness protects against inflammation at any weight. But at the same time, people in the study who were overweight or obese were likely to have higher inflammation and waist measurements, suggesting they were probably less fit, too.

Unfortunately, the study doesn't show fitness results by BMI, so we don't know how many people who were overweight or obese had a good fitness score on the exercise test. We also don't know what type of exercise or level of physical activity the "fat by but fit" reported doing.

There are other limitations to the study:

  • Only 10% of those invited for a health examination attended, so we don't know how well that represents the general population. People who were healthier might have been more likely to attend.
  • People with conditions such as high blood pressure did not do the fitness test, which means the people who took the test were likely to be healthier than the general population.
  • The study didn't follow people up to see what happened to them – so we don't know whether, for example, people in the study who were obese with good fitness and low CRP were more or less likely to go on to have heart attacks or other illness, compared to others in the study. The study certainly shows the benefits of being fit, which should encourage people to take exercise and improve their fitness levels. However, it's also a good idea to aim for a healthy weight.

The NHS weight loss plan is designed to help you lose weight over the course of 12 weeks through a combination of healthy eating and exercise. Find out more about getting started on the 12 week plan

Analysis by Bazian
Edited by NHS Website