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'Fat but fit' people may still be at risk of heart disease

4:45pm Tuesday 15th August 2017 content supplied byNHS Choices

"Concept of being 'fit but fat' is a myth, researchers say," ITV News reports after a Europe-wide study looked at associations between body weight, metabolic health and heart disease.

The term "fat but fit" is used to describe people who are overweight or obese but don't have any of the symptoms of metabolic syndrome.

This is a common complication of obesity, and symptoms include high cholesterol, high blood pressure and an inability to control blood sugar levels (insulin resistance).

The study involved 17,640 people. Body weight was used to calculate each person's body mass index (BMI) and various tests were used to assess each person's metabolic health. They were then followed for 12 years to look at the development of heart disease.

The findings showed that BMI was an independent risk factor for heart disease, regardless of metabolic health.

Obese people who were metabolically healthy - the "fat but fit" - had a 28% higher heart disease risk than their normal weight, metabolically healthy counterparts.

But metabolic risk factors still seem to carry the highest risk for heart disease. People who were a normal weight but metabolically unhealthy had a more than doubled risk of heart disease. So despite being a normal weight, their risk was actually higher than the "fat but fit".

The good news is that certain lifestyle changes can prevent or reverse metabolic syndrome and reduce your risk of heart disease.

This includes quitting smoking if you smoke, getting regular exercise, eating healthily, trying to achieve a healthy weight, and cutting down on alcohol

Where did the story come from?

The study was carried out by researchers from Imperial College London, University College London, and an extensive number of other institutions across Europe. 

It was primarily funded by the European Union Framework, the European Research Council, the UK Medical Research Council, the British Heart Foundation, and the UK National Institute of Health Research.

The study was published in the peer-reviewed European Heart Journal.

The UK media's reporting of the study was accurate.

What kind of research was this?

This was an analysis of a random sample of people taking part in the large European Prospective Investigation into Cancer and Nutrition study (EPIC).

As the title suggests, EPIC is an ongoing cohort study looking at the links between diet and cancer. Because of the large amount of data the EPIC study gathers, researchers can also use the data to look at other associations by focusing on smaller groups (a sub-cohort).

Within this sub-cohort, known as EPIC-CVD (cardiovascular disease), the researchers compared cases of people who developed heart disease with those who didn't in a case-cohort study.

The aim was to investigate the theory of "metabolically healthy obesity". This is the idea that people who have excess body fat can still be healthy if they don't have other metabolic risk factors like high blood pressure, high cholesterol and poor blood sugar control.

To date, there's been conflicting evidence about whether the metabolically healthy obese have a higher or lower risk of heart disease and type 2 diabetes.

This study aimed to use the large body of data collected from the EPIC-CVD cohort to better look into this.

What did the research involve?

Between 1991 and 1999 EPIC recruited 366,521 women and 153,457 men aged 35-70 from 10 countries across Europe.

The sub-cohort for the EPIC-CVD project consisted of a random sample of 17,640 adults who were free from stroke or heart disease at baseline.

Participants completed questionnaires on medical history, diet and lifestyle at the start of the study.

They gave blood samples to measure total cholesterol and blood sugar, and their blood pressure, weight, height and waist circumference was also measured.

Being metabolically unhealthy or having metabolic syndrome was defined as having three or more of the following at baseline:

  • high blood pressure, use of blood pressure medications, or self-reported history
  • high triglycerides (a type of fat) or use of lipid-lowering medication like statins
  • low HDL (good) cholesterol
  • high blood sugar, use of diabetes medications, or self-reported history
  • high waist circumference

Researchers looked for the new development of heart disease during follow-up, either self-reported or through data from GP and hospital registers and mortality records. Last follow-up ranged from 2003-10, with an average of 12.2 years.

Researchers looked at the link between body fat, metabolic markers and developing heart disease, adjusting for baseline variables of country, gender, age, education, smoking status, alcohol intake, diet and physical activity.

What were the basic results?

There was a total of 13,964 cases of heart disease during the 12-year follow-up, 631 of which were within the sub-cohort.

Almost two-thirds of the sub-cohort was female, with an average age of 54 and an average BMI of 26.1, which is classified as being overweight.

Of these, 16% were obese - 45% of obese people were classed as metabolically healthy and had no features of metabolic syndrome.

BMI was linked with heart disease risk, with each standard deviation increase in BMI increasing risk by 25% (hazard ratio [HR] 1.25, 95% confidence interval [CI] 1.19 to 1.32).

Adjusting for metabolic risk factors of blood pressure, cholesterol and diabetes substantially reduced the link with BMI, showing the importance of these factors. But the link was still statistically significant (HR 1.05, 95% CI 1.01 to 1.10).

Waist circumference was similarly associated with heart disease risk (HR 1.32, 95% CI 1.24 to 1.41). Again, adjusting for blood pressure, cholesterol and diabetes similarly reduced the link so it was on the threshold of significance (HR 1.06, 95% CI 1.00 to 1.13).

Metabolically healthy obese people had a 28% increased risk of heart disease compared with metabolically healthy normal weight people (HR 1.28, 95% CI 1.03 to 1.58).

But metabolic health still seemed to be the most important factor. Normal weight people who were metabolically unhealthy had a more than doubled risk of heart disease than metabolically healthy normal weight people (HR 2.15, 95% CI 1.79 to 2.57).

Metabolically unhealthy obese people had an even higher risk compared with metabolically healthy people of a normal weight (HR 2.54, 95% CI 2.21 to 2.92).

How did the researchers interpret the results?

The researchers concluded: "Irrespective of BMI, metabolically unhealthy individuals had higher CHD [coronary heart disease] risk than their healthy counterparts. Conversely, irrespective of metabolic health, overweight and obese people had higher CHD risk than lean people."

They say that their findings "challenge the concept of 'metabolically healthy obesity', encouraging population-wide strategies to tackle obesity". 

Conclusion

This large, valuable study confirms that - as has long been thought - an increased BMI is linked with an increased risk of heart disease.

It shows that people with an obese BMI had a higher risk of heart disease, even if they didn't have other risk factors like high cholesterol and high blood pressure, proving that body fat is an independent risk factor.

That said, this study does have some limitations. For example, definitions of being metabolically unhealthy aren't entirely consistent with other definitions of metabolic syndrome.

This was also only assessed at the start of the study, and risk factors may have varied among individuals during follow-up.

And not all participants in the centres across Europe were general population samples. They may have included a higher proportion of those with risk factors.

Nevertheless, the study on the whole supports our understanding of the modifiable risk factors for heart disease, and shows that being obese in itself increases your risk, regardless of your metabolic health.       

More importantly, it also shows it's possible to be "not fat but unfit" if your BMI is within the recommended range but you have one or more metabolic risk factors.

The best way to prevent heart disease, reduce your BMI, and prevent or reverse the symptoms of metabolic syndrome are quitting smoking if you smoke, getting regular exercise, eating healthily, trying to achieve a healthy weight, and cutting down on alcohol.

Summary

"Concept of being 'fit but fat' is a myth, researchers say," ITV News reports after a Europe-wide study looked at associations between body weight, metabolic health and heart disease.

Links to Headlines

Concept of being 'fit but fat' is a myth, researchers say. ITV News, August 15 2017

'Fat but fit' still risk heart disease. BBC News, August 15 2017

How 'fit but fat' is a myth: Overweight people are still at greater risk of heart problems even if other markers suggest they are healthy. Mail Online, August 15 2017

People who are 'fat but fit' still face higher risk of heart disease, finds study. The Independent, August 15 2017

Links to Science

Lassale C, Tzoulaki I, Moons KGM, et al. Separate and combined associations of obesity and metabolic health with coronary heart disease: a pan-European case-cohort analysis. European Heart Journal. Published online August 14 2017

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