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Does more leg fat protect women against heart attack and stroke?

Tuesday 2 July 2019

"Leg fat 'better than belly fat' for older women," reports BBC News.

Researchers looked at the body composition of 2,683 women in the US who were a healthy weight and had been through the menopause.

They found women who had a higher percentage of fat around their trunk were more likely to have a heart attack or stroke than women who had more fat on their legs, but less around their upper body.

Because of the nature of the study, we cannot be sure that body fat distribution directly caused the differences in risk of having a heart attack and stroke.

But previous studies have found people who are "apple-shaped" with more central body fat have a higher risk of cardiovascular disease than those who are "pear-shaped".

Scientists think this may be because fat on the legs is a harmless way of storing energy, while fat around the abdominal organs may affect metabolism and put people at risk of diabetes.

Interestingly, the study did not find that overall body fat affected women's risk of heart attack or stroke.

The study found body fat only made a difference to the results depending on where it was stored.

Many women find hormone changes during and after the menopause can affect where their body stores fat.

But as the researchers say, we do not know whether there are specific diets or exercises that can help retain leg fat while reducing fat around the trunk.

Until we know more, the best advice is to have a healthy, balanced diet and get plenty of exercise.

Where did the story come from?

The study was carried out by researchers from the Albert Einstein College of Medicine, Memorial Sloan Kettering Cancer Centre, the University of California San Diego, Oklahoma University Health Sciences Centre, the University of Iowa, State University at New York, Harvard Medical School and Stanford University School of Medicine, all in the US.

It was funded by the US National Institutes for Health and published in the peer-reviewed European Heart Journal on an open access basis, so the study is free to read online.

The BBC News article gave a comprehensive and accurate account of the study, although it did not point out that the type of study (observational) cannot prove that body fat storage caused raised cardiovascular risk.

What kind of research was this?

This was a cohort study, using information from the long-running Women's Health Initiative study in the US.

The researchers wanted to see if body fat composition in different areas of the body, measured by dual-energy X-ray absorptiometry (DEXA) scan, was linked to chances of having cardiovascular disease.

This type of study is good for spotting links between risk factors and disease, but cannot prove that one causes the other.

What did the research involve?

The researchers used information collected during the Women's Health Initiative study, which recruited postmenopausal women from the general US population from 1993 to 1998.

For this analysis, researchers included women who had a healthy body mass index (BMI) of 18.5 to 24.9 kg/m2 (who were not underweight, overweight or obese) at the study start, did not have cardiovascular disease, and had their body fat analysed by DEXA scan on their trunk (upper body) and legs.

They followed the women up at least once a year until February 2017 to see if they'd been diagnosed with or died from cardiovascular disease.

This included heart disease and stroke, or death from heart attack or stroke.

All outcomes were verified by medical records.

The researchers looked mainly at women's overall body fat percentage and their percentage of trunk fat and leg fat.

They calculated how the risk of cardiovascular disease compared between women with the highest and lowest body fat percentage in each of these body areas.

The researchers looked at how the results correlated with BMI, waist circumference, hip-waist ratio and lean mass.

They also took account of a number of potential confounding factors:

  • age and ethnic background
  • age at menopause
  • height
  • education
  • family income
  • smoking and alcohol consumption
  • physical activity levels
  • dietary intake in calories
  • family history of heart attack or stroke
  • use of HRT, statins, aspirin and NSAIDs

What were the basic results?

During an average 18 years of follow-up, there were 291 cases of cardiovascular disease among the 2,683 women in the study.

Researchers found no link between overall body fat percentage and risk of cardiovascular disease.

But they found:

  • women with the highest percentage of trunk fat were 91% more likely to develop cardiovascular disease, compared with those with the lowest percentage (hazard ratio [HR] 1.91, 95% confidence interval [CI] 1.33 to 2.74)
  • women with the highest percentage of leg fat were 38% less likely to develop cardiovascular disease compared with those with the lowest percentage (HR 0.62, 95% CI 0.43 to 0.89)
  • women with the lowest leg fat and highest trunk fat were more than 3 times more likely to develop cardiovascular disease, compared with those who had the most leg fat and least trunk fat (HR 3.33, 95% CI 1.46 to 7.62)

How did the researchers interpret the results?

The researchers said: "Normal BMI postmenopausal women who have higher trunk fat or lower leg fat are at elevated risk of CVD.

"These findings highlight the importance of fat distribution beyond overall fat mass in the development of CVD."

In an interview with BBC News, one of the investigators said that women past the menopause should be encouraged to reduce their trunk fat, but acknowledged: "It is unknown whether there might be some particular diet or exercise which can help relocate fat."

Conclusion

This study adds more evidence to the theory that carrying fat on your trunk is more harmful than carrying it on your thighs: that being "pear-shaped" is healthier than being "apple-shaped".

We already know that being overweight or obese increases the chances of having cardiovascular disease.

What's interesting about this study is that the women were all normal weight, which suggests that where fat is carried on the body is important, even if you're not overweight.

The study has some limitations. We cannot be sure that body fat distribution is the cause of the difference in cardiovascular disease risk because it's an observational study.

Though the researchers adjusted for various factors that may be influencing the links, other factors might be involved.

For example, the researchers found women with more leg fat and less central fat were less likely to have diabetes, which was not adjusted for in the analysis.

This may be relevant given that research has indicated that central body fat may be linked to poorer cardiovascular health because of its association with the risk of diabetes.

The study included mostly white postmenopausal women, so we do not know whether the results would apply to men, younger women or other ethnic groups.

Keeping healthy during and after the menopause means following a healthy, balanced diet and taking plenty of exercise.

As we do not know whether there are specific diets or exercises that can help retain leg fat while reducing fat around the trunk, the best advice is to continue eating a balanced diet and staying active.

Analysis by Bazian
Edited by NHS Website

Links to the headlines

Leg fat 'better than belly fat' for older women

BBC News, 1 July 2019

Links to the science

Chen G-C, Arthur R, Iyengar NM, et al.

Association between regional body fat and cardiovascular disease risk among postmenopausal women with normal body mass index

European Heart Journal. Published online June 30 2019