News & Views Outlook: Obesity

Weighing new Options to Measure Obesity

Researchers have identified a new way of determining whether or not a person is obese, according to a study published online March 3, 2011, in the journal Obesity. The scale is called the “body adiposity index,” or BAI, and relies on a ratio of hip and height measurements rather than body weight.

Lead author Richard Bergman, PhD, professor and chair of physiology and biophysics at the University of Southern California Keck School of Medicine, said the new index proved “a useful measure of percent fat” that can be calculated without using a scale—a major benefit for clinics in remote areas without access to reliable measuring devices.

Although the BAI measures body fat accurately, researchers wrote that more studies are needed to determine whether it is a better indicator of overall health and wellness than body mass index (BMI). Still, Dr. Bergman noted, the results show promise for more precise alternatives to BMI, which he said is “known to be of limited accuracy.”

Public health experts talk of the importance of achieving a “healthy BMI,” and the index is the international standard for measuring obesity; however, exactly what constitutes a healthy BMI is unclear. Because it makes no distinction between muscle mass and fat, the BMI often ranks top-form athletes in the same category as sedentary people with a high percentage of body fat.

Although it would require fine-tuning to implement, BAI has several advantages over BMI, researchers wrote. It can be easily calculated by a nurse or physician without a scale, and proved accurate when compared with precise values obtained through a dual energy x-ray absorptiometry scan. It could also be more accurate than BMI in measuring body fat among certain ethnic groups, according to the study.

Obesity in Pregnancy May Raise Infection Risk

New research shows that women who are obese before and during pregnancy have fewer infection-fighting immune cells than lean pregnant women. The results were presented May 1, 2011, at the Pediatric Academic Societies meeting in Denver, Colorado, and may affect how health care teams approach prenatal care among this patient population.

“Women who are obese before pregnancy have critical differences in their immune function during pregnancy compared to normal weight women, which has negative consequences for both mother and baby,” said Sarbattama Sen, MD, the study’s lead author and a researcher at Tufts Medical Center and Floating Hospital for Children.

For the study, “Obesity in Pregnancy Impairs Maternal Immune Function,” Dr. Sen and colleagues examined blood samples of 30 women who were 24 to 28 weeks pregnant. Half were obese before they became pregnant (BMI >30) and half had BMIs in the “normal” range (20-25).

Compared with normal-weight women, obese women had fewer cytotoxic T cells and natural killer cells. Obese pregnant women were also less able to produce infection-fighting cells than their normal-weight peers. The results may explain why obesity during pregnancy is associated with an increase in certain types of infections, researchers noted.

Dr. Sen said the findings call for further investigation of obesity’s impact on pregnancy. “Maternal obesity has consequences for the mother and baby, which we are only beginning to understand,” she said.

Given the growing prevalence of obesity, she added, “it is critical to understand the repercussions of this disease for future generations.”

Study Links Late Nights and Extra Calories

Insufficient sleep has been tied to obesity and poor overall health, and a small new study suggests that eccentric sleepers also face a higher risk of weight gain. Writing online in the journal Obesity, researchers at Northwestern University reported that people who stay up late and sleep in eat more calories and more fast food than those who don’t.

Those who keep odd hours also eat half the fruits and vegetables, consume more nondiet sodas, eat more of their calories at night, and have a higher BMI than normal sleepers, according to the study of 51 individuals. The researchers identified participants who went to bed by 3:45 am and woke by 10:45 am as “night owls,” whereas “normal sleepers” were those who were asleep by 12:30 am and awake by 8:00 am.

The study did not explain the nature of the relationship between overeating and staying up late, but the authors did note that the extra calories—250, on average—were enough to cause weight gain of about 2 lb per month. Further, said senior author Phyllis Zee, MD, of the Northwestern University Feinberg School of Medicine, staying up and eating late meals are habits that disrupt the body’s natural rhythms.

“Human circadian rhythms in sleep and metabolism are synchronized to the daily rotation of the earth, so that when the sun goes down you are supposed to be sleeping, not eating,” Dr. Zee said. “When sleep and eating are not aligned with the body’s internal clock, it can lead to changes in appetite and metabolism, which could lead to weight gain.” PT