Overeating? Blame your genes


A gene could help prod people to overeat and gain excess weight, new research shows.

The finding probably won’t provide a ‘magic bullet’ for weight loss, but it does reinforce the value of good eating habits and exercise, especially for young people, scientists say.
The study, reported in the Oct. 17 issue of Science, is the latest in a series focusing on the brain’s response to food using the neurotransmitter dopamine. Cells in the brain’s ‘reward’ centers release dopamine when people eat, causing that feeling of pleasure, researchers explain.

Previous studies have shown that some people have fewer brain cell receptors for dopamine, which leads them to eat more to gain the same pleasurable effect. The new study used scans of the brain pleasure centers of a group of women. They revealed a sluggish dopamine response in the brains of some of the women.

‘This is the first imaging study which found less activation of dopamine receptors in [some] humans,’ said study lead author Eric Stice, a scientist at the Oregon Research Institute in Portland.

Women with one form of the D2 dopamine receptor gene had the lowest pleasure response when drinking a milkshake, the scans showed. They had to consume more of the shake to get the same pleasure response. Follow-up study found that these women were also more likely to gain weight over the following year.

The study was done in collaboration with researchers at Yale University and the University of Texas at Austin.

‘What is new here is that for the first time they have identified the consequences of this genetic polymorphism [type] in how the brain functions,’ said Dr. Nora Volkow, who worked on earlier studies at Brookhaven National Laboratory that established the role of the D2 gene in overeating. She is now is director of the U.S. National Institute on Drug Abuse.

Volkow noted that prior studies had linked this form of the gene to obesity, and the new work ‘shows an association in the brain region that governs pleasure. The response is different with this polymorphism.’

Studies of obese animals at Brookhaven National Laboratory have shown that dieting increases the D2 response to food, according to Peter Thanos, a neuroscientist at the lab. ‘If we could identify people who are more vulnerable, it would be fascinating to see what effect dieting has on their risk in terms of brain response,’ Thanos said. ‘No one has really done this in humans.’ Diet pills aimed at the dopamine receptors won’t work, Stice said. ‘These amphetamine-based diet pills are not the way to go,’ he said. Instead, Stice advocates early behavioral intervention that steers children away from fatty fast foods. ‘You want to change people’s behaviors before they become entrenched,’ he said. Exercise shouldn’t be overlooked, Volkow added.

‘Dieting is a complex process and people don’t like it,’ she said. ‘Physical activity, which also activates the dopamine pathway, may be a mechanism for reducing the compulsive activity of overeating.’ This work on obesity meshes nicely with drug-abuse studies, noted Volkow, who retains her laboratory position at Brookhaven. Both are instances of people engaging in compulsive behaviors, ‘even though they know it is very harmful,’ she said

Scientists hot on trail of new antibiotics: Researchers believe they are close to perfecting a new class of broad-spectrum antibiotics that could counter increasingly drug-resistant bacteria, a new study says. The new antibiotics compounds all of which are natural products produced by certain bacteria to battle other bacteria also show promise as a more effective and faster treatment for tuberculosis. One in three people worldwide carries TB, and today’s antibiotics are not efficient in combating it. The new research, published in the Oct. 17 issue of the journal Cell, is encouraging, because bacterial infectious diseases are responsible for a quarter of all deaths worldwide. For all major bacterial pathogens, strains resistant to at least one current antibiotic have arisen, according to one researcher. ‘For six decades, antibiotics have been our bulwark against bacterial infectious diseases,’ Richard Ebright, a Howard Hughes Institute investigator at Rutgers University, said in an interview issued by the journal’s publisher. ‘Now, this bulwark is collapsing. There is an urgent need for new antibiotic compounds and practical new targets.’ The new antibiotic compounds under study are myxopyronin, corallopyronin, and ripostatin. They block the action in bacteria of RNA polymerase, an essential protein in all organisms that is necessary to transcribe the genetic instructions in DNA into RNA, which in turn directs the assembly of proteins. ‘RNA polymerase has a shape reminiscent of a crab claw, with two prominent pincer-like projections,’ Ebright said. ‘Just as with a real crab claw, one pincer stays fixed and one pincer moves, opening and closing to keep DNA in place. The pincer that moves does so by rotating about a hinge. Our studies show that the three antibiotics bind to and jam this hinge.’ ‘It’s an amazing site,’ Eddy Arnold, also of Rutgers University, said of this hinge that the researchers refer to as a switch region. ‘It’s a drug designer’s dream, because it’s a pocket that can accommodate a variety of chemical inhibitors.’ Myxopyronin and corallopyronin appear to work against a broad range of infectious diseases including TB, according to the researchers. The current treatment for TB, rifamycins, requires six months to two years of therapy, depending on whether the person can tolerate the drugs or whether the strain of TB the person has is resistant to antibiotics. The researchers said that antibiotics targeting this RNA polymerase hinge cut treatment time down to as little as two weeks.

Exercise may cut uterine cancer risk in heavy women: In overweight or obese women, physical activity, even at light or moderate intensities, lowers the risk of cancer of the lining of the uterus (endometrial cancer), according to findings from the American Cancer Society’s prospective Cancer Prevention Study II Nutrition Cohort study. Dr. Alpa V. Patel and colleagues at the American Cancer Society in Atlanta identified 466 women who developed endometrial cancer between 1992 and 2003 among approximately 43,000 older ‘postmenopausal’ women. In the latest issue of the International Journal of Cancer, Patel and colleagues report that all measures of physical activity and ‘avoidance of sedentary behavior’ were strongly associated with reduced risk of endometrial cancer in women who were overweight or obese. Questionnaire responses showed that physically active women engaged primarily in low- to moderate-intensity activities, such as walking, biking, aerobics or dancing, equivalent to about 2 hours of moderately paced walking per week.

Patel’s team calls for more research into the link between light-intensity activity and endometrial cancer risk reduction in order to ‘strengthen public health recommendations in this regard.’ The News

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