TUESDAY, Jan. 20 (HealthDay News) -- New research on the brain suggests that women unconsciously have a tougher time resisting their favorite foods than men do.

"This gives us another piece to put into this puzzle," said Dr. Gene-Jack Wang, the study's author, who speculated that women may have more trouble saying no to food because they sometimes have to eat for two.

"Maybe evolution leads them to this because of their important mission to have a baby," said Wang, a senior scientist at Brookhaven National Laboratory and professor of psychiatry at Mount Sinai School of Medicine in New York.

According to Wang, the new study aimed to understand why some people don't stop eating when they're full. Your body tells you that you've eaten enough by sending a signal to your brain from the gut, he explained, "but if you go to the buffet, sometimes you just cannot stop."

This wasn't a big problem throughout history because people rarely had a chance to eat more than they needed, Wang said. But modern society has changed that, he said, especially over the past 30 to 40 years as obesity has become much more common in the United States.

For the study, which appears in this week's issue of the Proceedings of the National Academy of Sciences, the researchers asked 13 women and 10 men about their favorite foods. The participants said they liked a variety of dishes and desserts, including lasagna, pizza, brownies, ice cream and fried chicken.

Then, after they fasted for 20 hours, the researchers presented them with their favorite foods; the dishes were even warmed up, if appropriate, to make them more tempting. The men and women were allowed to smell and taste the food but not eat it. Then, in an experiment, they were told to try to inhibit their desire to eat the food.

Meanwhile, PET scans examined their brain activity.

The researchers found that certain areas of the brain became more active in both the men and women when they were tempted with food. The brain areas that lit up control emotions such as motivation.

Also, both men and women succeeded in making themselves feel less hungry by inhibiting their desire to eat the food. But the brain scans suggested that the women's brains were still acting as if they were hungry.

In other words, the women may have thought they were less hungry, but their brains didn't seem to be entirely on board.

What's going on? Hormones could play a factor in women, Wang said, because they need to eat more when they're pregnant.

The research could help scientists understand why some people can't resist certain kinds of high-calorie food, Wang said. "Some people cannot inhibit themselves, and we need to help those people."

More information

Learn more about obesity from the National Heart, Lung and Blood Institute.

TUESDAY, Jan. 20 (HealthDay News) -- Physical fitness may be as good for the brain as it is for the body in old age, a new study says.

A study of Canadian women older than 65 found that those who took part in regular aerobic activity had cognitive function scores 10 percent higher than their peers who did not exercise. The active women also had lower blood pressure (at rest and during exercise) and better vascular responses in the brain, suggesting that better blood flow aids the ability to think, the study found.

The findings were published in the journal Neurobiology of Aging.

"Being sedentary is now considered a risk factor for stroke and dementia," study author Marc Poulin, an associate professor in the Faculties of Medicine and Kinesiology at the University of Calgary, said in a news release issued by the Alberta Heritage Foundation for Medical Research. "This study proves for the first time that people who are fit have better blood flow to their brain. Our findings also show that better blood flow translates into improved cognition."

"The take-home message from our research is that basic fitness -- something as simple as getting out for a walk every day -- is critical to staying mentally sharp and remaining healthy as we age," Poulin said.

More information

The U.S. National Institute on Aging has more about exercise for older adults.

FRIDAY, Jan. 9 (HealthDay News) -- Parents may not always be the best barometer of their child's eating and exercise habits, a new study shows.

Researchers reported in the January/February issue of Journal of Nutrition Education and Behavior that mothers of preschool-aged children thought their kids ate and exercised well, while those with older children did not. But when the children and their actual habits were examined more closely, there was little difference between the two age groups.

When comparing the questionnaire answers with the child's height and weight, the researchers found younger children weren't much better off their older peers.

"Although preschool-aged children engaged in more healthful behaviors according to parent recall, the preschool-aged children only met 2 dietary recommendations, fruit and low-fat dairy intake. All other parent-reported eating and leisure-time activity patterns did not meet current recommendations," Hollie A. Raynor, from the department of nutrition at the University of Tennessee, Knoxville, wrote in a journal news release.

"Surprisingly, other than fast-food consumption, this study found few parent-reported eating and leisure-time behaviors related to weight status, which may be a consequence of the overall poor diet quality and relative inactivity reported in this diverse sample. Thus, interventions designed to help children meet dietary and leisure-time activity recommendations should begin by assisting parents with preschool-aged children in developing skills to provide the structure and the environment necessary for their young children to develop healthful lifestyles," she wrote.

The survey, in which researchers from the Knoxville, Tenn., school and Brown University Medical School questioned 172 mothers, found more of those with younger children thought their child was as active, or a bit more than, his or her peers and watched less TV on weekends than mothers of older children.

Older children, according to their mothers, also consumed more sweetened drinks and salty and sweet snacks than the younger ones. They also didn't eat dinner with parents as often as the preschoolers did, a factor generally thought to lead to kids making poorer food choices.

More information

The U.S. Centers for Disease Control and Prevention has more about childhood obesity.

TUESDAY, Jan. 6 (HealthDay News) -- Brain circuitry involved in regulating impulsive behavior seems to be less active in women suffering from the eating disorder known as bulimia nervosa.

The frontostriatal regulatory circuits implicated in this study are mediated by both the neurotransmitter dopamine and the neurotransmitter serotonin.

So far, serotonin has been widely implicated in bulimia, which is often treated with antidepressants known as selective serotonin reuptake inhibitors (SSRIs). However, dopamine has not been studied closely in relation to bulimia nervosa.

"These findings argue for looking more directly into dopamine systems in eating disorders," said study author Rachel Marsh, an assistant professor of clinical psychology in the division of child and adolescent psychiatry at Columbia University in New York City.

"It's definitely preliminary . . . but it's not something to ignore," added Mary Tantillo, director of the Western New York Comprehensive Care Center for Eating Disorders. "We need to study this on adolescents who are closer to the onset of illness [Marsh has already started such a study]."

"This is pretty new stuff... We have a fair degree of understanding of the neurochemistry of eating disorders [but this study looked at] what actually happens in the brain when you engage in certain decision-making tasks or activities," said Daniel le Grange, director of the Eating Disorders Program at The University of Chicago and author of Help Your Teenager Beat an Eating Disorder and Treating Bulimia in Adolescence. "The main interest [of the study] at this time would be to understand how these disorders develop. Does the abnormality occur because someone has bulimia nervosa, or does it contribute to developing it?"

At this point, it's not clear if the brain differences are a cause or an effect of the disorder.

"These were adult women who had had the illness for a median of nine years," Marsh said. "We don't know if [the changes are] the product of having the disorder for nine years, or if something determines development of the disorder."

The study was expected to be published in the January issue of the Archives of General Psychiatry.

Bulimia nervosa, characterized by alternating binging and purging episodes (vomiting and taking laxatives being among the more common behaviors), primarily affects girls and women.

Researchers are just beginning to untangle the neurochemistry of eating disorders.

"Patients with bulimia nervosa are very impulsive, not only in an inability to stop eating everything in front of them, but there is also a high prevalence of shoplifting and drug abuse in this population," Marsh said. Mood disorders are also common in these women, indicating that problems with behavioral self-regulation might be at play.

The researchers compared results from fMRI on 20 women (average age about 26) with bulimia nervosa and 20 age-matched controls.

Participants were shown pictures with arrows pointing either left or right and were asked to identify which way the arrows were pointing. In the simple version of the task, the arrows pointing left were on the left side of the screen and the right-directed arrows on the right side of the screen.

For the more difficult component of the task, the leftward-pointing arrow was positioned on the right side of the screen.

"When individuals are performing correctly, they need to engage self-regulatory control or cognitive control. They need to hold back the automatic response strategy in order to perform correctly," Marsh explained.

Women with bulimia nervosa performed faster on the difficult trials and made more errors and, when they were performing the task, they did not engage the same brain circuitry as the controls.

Participants with the most previous bulimic episodes and the highest rates of preoccupation with shape and weight performed the worst on tasks and engaged the frontostriatal circuits the most.

Healthy controls activated the anterior cingulated cortex region of the brain more when making correct responses and the striatum more when delivering incorrect responses.

More information

The U.S. National Institute of Mental Health has more on eating disorders.