“Fat but fit” is a myth, suggests new study

15 Aug 2017 --- Carrying extra weight could raise the risk of a heart attack by more than a quarter, even in those who are otherwise healthy. This is according to a group of researchers at Imperial College London and the University of Cambridge, who found that this overweight group is still at increased risk compared to those with a healthy weight.

The researchers’ findings suggest that being overweight or obese increases a person’s risk of coronary heart disease (CHD) by up to 28 percent compared to those with a healthy body weight, even if they have healthy blood pressure, blood sugar and cholesterol levels.

The findings add to a growing body of evidence that suggests being “fat but fit” is a myth, Imperial College London reports, with the evidence also suggesting that people should aim to keep their body weight within a medically healthy range.

“[The study reinforces] the need for population-wide efforts to tackle obesity and overweight through current nutritional advice,” Dr. Ioanna Tzoulaki, from Imperial’s School of Public Health, tells NutritionInsight. “Medical professionals should look at metabolic health and overweight or obesity independently as both are associated with future cardiovascular events.”

The largest study yet
Storing too much fat in the body is associated with a number of health problems, including increased blood pressure, high blood sugar and altered cholesterol levels. However, previous studies had revealed that some overweight people who seemed not to experience the adverse health effects of excess weight. This led to them being called “metabolically healthy obese” in medical literature and “fat but fit” in the media.

In the largest study of its kind to date, published in the European Heart Journal, scientists used data from more than 500,000 people in 10 European countries – taken from the European Prospective Investigation into Cancer and Nutrition (EPIC) – to show that excess weight is linked with an increased risk of heart disease, even in those who have a healthy metabolic profile.

Researchers looked at the link between excess weight and risk of CHD, a condition which means that not enough blood gets through to the heart due to clogged arteries, leading to heart attacks.

After a follow-up period of more than 12 years, a total of 7,637 people in the EPIC cohort experienced CHD events, such as death from heart attack. Researchers then selected a representative group of more than 10,000 individuals as controls, for analysis.

Body weight was classified according to definitions from the World Health Organization. Those with a body mass index (BMI) over 30 were classed as obese, while those with a BMI of 25-30 were classed as overweight, and 18.5-25 as normal weight. More than half of the control group (63 percent) were female, with an average age of 53.6 and an average BMI of 26.1.

Participants were categorized as “unhealthy” if they had three or more of a number of metabolic markers, including high blood pressure; blood glucose or triglyceride levels; low levels of HDL cholesterol; or a waist size of more than 37 inches (94cm) for men and 31 inches (80cm) for women.

After adjusting for lifestyle factors such as smoking, diet, exercise and socioeconomic status, the researchers found that compared to the healthy normal weight group, those classed as unhealthy had more than double the risk of CHD, whether they were normal weight, overweight or obese.

However, the analysis also revealed that within the apparently healthy group, there was a significant difference in outcomes for people depending on their weight. The research found that compared to those at a normal weight, people who were classified as healthy but were overweight had an increased CHD risk of 1.26 (26 percent), while those who were healthy but obese had an increased risk of 1.28 (28 percent).

Challenging “healthy obese”
“Our findings suggest that if a patient is overweight or obese, all efforts should be made to help them get back to a healthy weight, regardless of other factors. Even if their blood pressure, blood sugar and cholesterol appear within the normal range, excess weight is still a risk factor,” says lead author Dr. Camille Lassale from Imperial’s School of Public Health, now based at University College London.

“I think there is no longer this concept of ‘healthy obese,’” agrees Dr. Tzoulaki. “If anything, our study shows that people with excess weight who might be classed as ‘healthy’ haven't yet developed an unhealthy metabolic profile. That comes later in the timeline, then they have an event, such as a heart attack.”

According to the researchers, the excess weight itself may not be increasing the risk of heart disease directly, but rather indirectly through mechanisms such as increased blood pressure and high glucose. They add that no follow-up measurements were taken, so they cannot show how the group’s health status changed over time.

British Heart Foundation (BHF) Senior Dietician Victoria Taylor urges some caution: “There were limitations to this study in that it only assessed physical activity at the start of the study and didn’t look at other important risk factors like smoking.” But, she adds: “Nonetheless, it’s a good reminder that addressing one risk factor does not necessarily cancel another one out.”

Tzoulaki also tells NutritionInsight that she believes the findings should not encourage unhealthy forms of dieting, as: “metabolically unhealthy lean individuals were also at increased risk of cardiovascular disease.”

The research was funded by the European Union and supported by the UK Medical Research Council (MRC), the BHF and the National Institute for Health Research (NIHR). “Separate and combined associations of obesity and metabolic health with coronary heart disease: a pan-European case-cohort analysis” by Lassale, C. et al, is published in the European Heart Journal.

By Paul Creasy

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