Is Obesity Bad For the Brain, but OK for the Heart?

Two new studies report good and bad news about obesity. The first study suggests that obesity doesn't appear to raise the risk of dying for men who have had heart attacks. The second found that being overweight is harmful to women's brains.

Study 1: Men And Heart Attack

Obesity is a well-known risk factor for heart disease, but a study of 5.010 middle-aged and older men who participated in the Physicians' Health Study found that obesity did not increase the risk of death in men who had already had a heart attack.

The researchers found that men who had a body mass index (BMI) of 28 or higher and who had had a heart attack or stroke did not have a significantly greater risk of death from cardiovascular disease compared with thinner men.

BMI is a height-to-weight ratio that is used to determine if someone is at a healthy weight. A person who has a BMI of 25 or above is considered to be overweight; a person who has BMI of 30 or higher is obese.

The finding is surprising, says co-author Howard D. Sesso, an assistant professor of medicine at Harvard Medical School in Boston. "One always assumes that when we deal with obesity, higher is always worse," he says.

Implications

"Our finding doesn't suggest that there are benefits to being heavier," Sesso notes. "But that there was no added risk was surprising."

Sesso believes that some of these men may have lost weight since their heart attack or stroke. In addition, treatment with medication to prevent a second heart attack or stroke may play a role in their reduced risk of death, he notes.

"It is not our desire to downplay the role of being heavy," Sesso says. These are men who had likely felt the impact of being obese in the first place."

It is not clear if the effect is the same for obese women after having a heart attack or stroke, Sesso says.

Study 2: Women’s Brain Health

Swedish researchers say that women who have been obese throughout their lives are more likely to lose brain tissue in the temporal lobe compared with women of normal weight. Loss of brain tissue has been linked to cognitive decline and an increased risk of Alzheimer's disease.

Lead researcher Deborah Gustafson, a psychiatrist at Sahlgrenska University Hospital in Göteborg, and her colleagues collected data on 290 Swedish women born between 1908 and 1922. Each woman had four exams between 1968 and 1992. At the last exam, they underwent a computed tomography (CT) scan to determine if they had lost any brain tissue during the 24 years of follow-up.

The only significant relationship between BMI and brain atrophy was found in the temporal lobe, Gustafson reports. "The temporal lobe is important for a number of reasons, including hearing, speech, language, comprehension, naming, memory and visual processing of, for example, faces," she says.

Increased BMI accounted for approximately 8% of all dementia, Gustafson adds.

The Swedish paper is the first study to show a higher body mass index is related to brain atrophy," says Gustafson. "BMI was related to 11% to 14% higher odds of temporal lobe atrophy per one unit of increased) BMI. Women who were heavier were more likely to have temporal lobe atrophy."

However, she adds, the amount of atrophy was not related to increasing levels of BMI. "In other words, those women with more severe temporal lobe atrophy did not have a higher BMI compared to women with mild atrophy."

Theories

Gustafson speculates that the connection between BMI and loss of brain tissue may be due to fat causing more oxidative stress, which increases the amount of free radicals in the body.

Another theory is that fat leads to atherosclerosis, which can limit oxygen flow to the brain.

Still another possibility is that fat causes the release of hormones and growth factors that are harmful to brain tissue.

Implications

Gustafson says it is not known whether these results apply to men or how losing weight affects atrophy. "However," she says, "maintaining a healthy body weight over the course of one's life may decrease the odds of temporal lobe atrophy and subsequent dementia."

"This finding fits logically with a previous paper that showed that people with high BMI at middle age have more Alzheimer's disease," says William Thies, vice president for medical and scientific affairs at the Alzheimer's Association.