Surprising Swedish Study Finds Heavier Twins No More Likely To Have Heart Attacks

Can having a higher BMI protect you from heart disease? Probably not, but new research does present some pretty surprising results.

The study looked at over 4,000 identical twins and found that twins with higher body mass indexes were less likely to have a heart attack or die during the course of the study than their leaner siblings.

When researchers just looked at the data for the group of individuals (and didn't compare the siblings), they found that people with higher BMIs were more likely to have a heart attack or die during the study. But when the scientists compared twins to each other, they found that the twin with the higher BMI was at a lower risk of heart attack or death than their slimmer sibling.

Still, the study found that individuals with higher BMIs had a higher risk of developing diabetes, even when compared to their siblings.

The results, according to Dr. Peter Nordström, a professor of Geriatric Medicine at Umeå University in Sweden and the lead researcher on the paper, suggest that environmental factors that affect BMI — like diet and exercise — may not be responsible for an increased risk of heart attack or death. Other factors that affect BMI, like genetics, may be responsible for the risk of heart attack and death, he said.

Five percent of twins with higher BMIs had heart attacks and 14 percent died. Among siblings with lower BMIs, 5.2 percent had heart attacks and 16 percent died.

The results were unexpected, to say the least.

"I’m the first one to admit that I am very surprised,” Nordström said in an interview.

Nordström was so surprised by the results when he first got them, two years ago, that he waited until now to collect more data and publish the results.

The study was done using the Swedish Twin Registry. Participants self-reported their height and weight at the beginning of the study (which was used to calculate their BMI). They were then followed for heart attacks, diabetes and death for an average of 12 years, but their BMI was not retaken. A small group of participants did have a second BMI calculated, and the results from that group matched those of the study as a whole.

Some might be quick to point out that BMIs are a very blunt instrument, as they only look at height and weight and not measures like fat percentage or muscle mass. Many Olympic athletes would be considered “overweight” by a simple BMI.

It is also important to note that the average difference in the twins' BMIs was about two — a very small amount. To investigate this, the researchers analyzed a smaller group of the twins who differed by at least seven points in their BMI. Nordström found that as a whole, the twins in this group did have higher rates of heart attacks and death, but that the twins with the higher BMIs (i.e. the more overweight ones) had a lower rate (yes, you read that right, lower) of heart attacks and death than their thinner twins.

Nordström hopes to be able to expand the study to include more twins — and more diverse ones — to further support these results.

Don’t grab that bag of Oreos yet, though — the best way to stay healthy is still to stay in shape.