The negative health implications of obesity may not be counteracted by high aerobic fitness, according to new research.

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Researchers say their findings contradict the idea that aerobic fitness can offset the health implications of obesity.

Obesity increases the risk of a number of serious health conditions, including type 2 diabetes, heart disease and stroke, and with obesity affecting more than a third of American adults, it has become a major public health concern.

One of the main contributors to overweight and obesity is lack of physical activity; individuals who are physically inactive do not burn as many calories taken in from food and drink as those who exercise regularly.

But can a person be obese yet physically healthy? Some previous studies say so, suggesting that individuals who are obese but who engage in regular exercise are at lower risk for heart disease and other obesity-related complications than obese people who are physically inactive.

In October, Medical News Today reported on a study published in the journal Diabetes Care, which claimed this “fat but fit” theory is misleading.

Now, a new study published in the International Journal of Epidemiology builds on this claim, finding that men of a normal weight – irrespective of their level of aerobic fitness – were at lower mortality risk than obese men with high aerobic fitness.

Study coauthor Peter Nordström, of the Department of Community Medicine and Rehabilitation, Geriatric Medicine at Umeå University in Sweden, and colleagues analyzed data of 1,317,713 men of an average age of 18.

To assess the men’s aerobic fitness, each participant was required to take part in a cycle test, in which they were asked to cycle until they had to stop due to tiredness.

Over an average 29 years of follow-up, men who were in the highest fifth of aerobic fitness were found to be at 48% lower risk of all-cause mortality than those who were in the lowest fifth, according to the researchers.

Deaths associated with suicide and alcohol and drug abuse were most commonly seen among men with lower aerobic fitness, and the team identified a strong link between trauma-related death and low aerobic fitness.

Fast facts about obesity
  • Around 78.6 million adults in the US are obese
  • In 2008, obesity cost the US around $147 billion
  • Middle-aged adults (aged 40-59) have higher rates of obesity than younger adults (aged 20-39).

Learn more about obesity

Though Nordström says the team is unable to explain these findings, he suggests “genetic factors could have influenced these associations given that aerobic fitness is under strong genetic control.”

However, on analyzing the results by obesity status and fitness of the men, the team uncovered some data that may oppose the fat but fit theory.

While aerobic fitness was linked to reduced mortality in both normal-weight and overweight men, the researchers found that the mortality benefits were lower for aerobically fit obese men, with no lower risk of death identified at all for men who were extremely obese with high aerobic fitness.

Additionally, compared with aerobically fit obese men, the researchers found normal-weight men with low aerobic fitness were still at 30% lower risk of death.

While a key limitation of the study is that all participants were male, the researchers believe their results help disprove the idea that aerobic fitness can eliminate the health implications of obesity.

MNT recently reported on a study suggesting lack of sleep may contribute to obesity, causing people to eat and drink more.