Can Smarts Help Shield Folks from Obesity? Maybe Not

Dennis Thompson HealthDay Reporter

The brainpower of a teenager appears to be less important than their likelihood of becoming overweight or obese in adulthood.

According to a study published in the journal PLOS Medicine on April 13, British researchers discovered that on average, teens who were more intelligent weighed less as adults than their siblings with lower scores on thinking tests.

Liam Wright is a senior researcher in population health and the lead author of this study.

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He said, 'We found that there was a very slight association, which in practice means that on average, sibling with higher cognitive abilities are likely to weigh less than those with lower cognitive abilities.

This research contradicts previous studies which linked low cognitive scores among teens with a higher risk of obesity later in life.

Wright explained that this is because the earlier studies only looked at general populations and did not take into consideration other factors, such as intelligence, which could affect a person's body weight.

He said that 'the problem with comparing people in the general population based on their cognitive abilities and BMI, is that unobserved variables may explain the association'. Body mass index (BMI) is a measure of body fat that takes into account height and weight.

Wright and his co-workers analyzed data from 12,250 sibling households in the United States to account for these unknown factors. Four separate studies followed these sibs from adolescence until age 62.

Wright explained that comparing siblings can help identify hidden factors which could influence weight. Since brothers and sisters have a similar background, Wright suggested. They may share similar genetics or be raised in the exact same home.

He said that many studies are forced to use simple observational designs, where correlations could be explained by factors not measured. Sibling designs are better because they account for factors shared by siblings without the need to measure them.

Researchers first examined the data and discovered that teens with lower scores did appear to weigh more. Cognitive ability was assessed through math and literacy tests.

When researchers compared siblings specifically, the weight difference based on cognitive abilities all but disappeared.

David Knopman, a Mayo Clinic neurosurgeon, noted that teens who scored low in the study shouldn't be viewed as developmentally disabled.

This article did not mention cognitive impairment. Knopman explained that the article was simply comparing high and low scores on cognitive tests among presumably cognitively intact children or adolescents. I would never use the term impaired to describe the people who are performing poorly.

Andrew Brown, the biostatistics director for the Center for Childhood Obesity Prevention of the Arkansas Children's Research Institute, said that the findings contradict the common assumption that obesity is solely a self-control or decision-making condition.

This line of thought suggests that people who are more intelligent can better use nutrition and health information to prevent excess weight.

Brown explained that 'Implicitly', many people believe obesity is caused through choices. Choices are related to cognition. If you look at cognitive ability as an indicator of the ability to "make good choices", it's the ability for people to understand and think about choices.

Mental ability is also associated with higher wages and better education. This, in theory, could lead to people living in safer neighborhoods, where they have access to healthier foods.

Wright noted that factors other than intelligence likely have more of an impact on obesity.

He said that the heritability of BMI was high - greater than 50% - so genetics were important in a population. "But obesity rates also have increased massively in the last four decades. This is far faster than genetic changes that could have happened. It's clear, therefore, that environmental factors are important.

Wright suggested that one factor might be the increase in 'availability' of cheap and energy-dense food like processed foods and fast foods.

SOURCES: Liam Wright PhD, senior researcher, population health at University College London (U.K.); Andrew Brown PhD, biostatistics director of the Center for Childhood Obesity Prevention at Arkansas Children's Research Institute in Little Rock; David Knopman MD, neurology, Mayo Clinic Rochester, Minn.