Body mass index, BMI is the ratio of weight to height. To determine it, it is necessary to divide the body mass of a person by the square of height in meters. A BMI above 30 speaks of obesity. The ratio of waist and hips is measured by dividing the waist circumference by the circumference of the hips.

Fatness is usually affected by men with a ratio of more than 0.9 and women with a ratio of more than 0.85.

“Existing research has linked the decrease in brain volume with memory impairment and a higher risk of dementia, but the effect of excess fat on the brain has not yet been studied,” said Dr. Mark Hamer, lead author of the study. “We studied a large group of people and found that obesity, especially excess fat in the middle of the body, can be associated with a decrease in brain volume.”

The survey participants were 9,652 people, the average age of 55 years. 19% suffered from obesity. Using MRI, the researchers examined the participants' brains, drawing attention to its volume and the ratio of white to gray matter.

The gray matter contains the main part of the nerve cells of the brain; it consists of areas involved in self-control, muscle control, and sensory perception. White matter contains bundles of nerve fibers that connect different areas of the brain.

The researchers took into account other factors affecting the brain volume - age, physical activity, smoking, high blood pressure. Even corrected for them, increased BMI was associated with a reduced brain volume.

However, the most noticeable decrease in volume was observed in those participants who had an excess of fat on the abdomen.

In particular, in 1 291 people with the highest BMI and the most pronounced fat deposits in the abdomen, the average volume of gray matter in the brain was 786 cubic meters. While in the 3025 most healthy participants - 798. In 514 people with high BMI, but without pronounced excess fat on the abdomen, the volume of gray matter was 793 cubic meters. So no significant difference in white matter was observed.

In addition, obesity was associated with a reduction in certain regions of the brain. Thus, the ratio of the waist and hips was associated with the size of the caudate nucleus - the area involved in the regulation of muscle tone and food-producing behavior, as well as in the formation of conditioned reflexes. The more body fat was at the waist of the participant, the smaller was the caudate nucleus.

BMI has been associated with the pallium, controlling movement and regulating the production of dopamine and other neurotransmitters - the more the BMI was, the more the cortex decreased.

With the growth of fat mass, the pale ball lowered - a structure associated with behavioral complexes, information exchange between the hemispheres, and information storage during brain damage. The contiguous nucleus, which is involved in the reward system, the formation of pleasure, laughter, dependence, aggression, fear and the placebo effect, also decreased.

But the hypothalamus, the atrophy of which is associated with Alzheimer's disease, was not affected - there was no noticeable difference between overweight people and without it in the volumes of this brain area.

“Although our study showed that obesity, especially body fat in the middle of the body, is associated with a smaller amount of gray matter, it is unclear whether abnormalities in the brain structure lead to obesity or obesity leads to a change in brain volumes,” Hamer concludes. - We also found a link between obesity and a decrease in certain areas of the brain. This will require further research, but perhaps in the future, measuring BMI and the ratio of waist and hips will help determine brain health. ”

The relationship between obesity and health status is rather controversial, the authors note that it increases the risk of some diseases and reduces the risk of others. However, the connection between obesity and a decrease in the volume of gray matter should alert the doctors, they say. In addition, a decrease in the volume of areas related to the reward system and nutritional behavior can lead to a violation of these functions, introducing a person with obesity in a vicious circle, so you need to find out what is the root cause - obesity or changes in the brain.