Being overweight is known to increase the risk of many serious health conditions, including strokes, cancer, diabetes and hypertension. In addition, there is a less well known link between being overweight or obese, and developing brain diseases, such as dementia. Obesity puts severe strain on the cardiovascular system and can damage blood vessels, including those that supply the brain cells.
New research, led by neuroscientists from the University of South Australia, has established a clear link between mice fed a high-fat diet over 30 weeks, resulting in diabetes, and a subsequent deterioration in their cognitive abilities. UniSA neuroscientist and biochemist Associate Professor Larisa Bobrovskaya says the research adds to the growing body of evidence linking chronic obesity and diabetes with Alzheimer’s disease, which is predicted to reach 100 million cases by 2050.
“Obesity and diabetes impair the central nervous system, exacerbating psychiatric disorders and cognitive decline. We demonstrated this in our study with mice,” explained Professor Bobrovskaya.
In the study, scientists from Australia and China used genetically modified mice that expressed a mutated form of tau protein in their brains. Tau proteins are essential in the normal functioning of the brain, but the accumulation of abnormal tau in the brain cells is associated with cognitive decline and diseases such as Alzheimer’s.
The researchers randomly assigned these mice to a standard diet or a high-fat diet for a period of 30 weeks. They began on the diet at the age of eight weeks and were monitored for various physiological, metabolic and behavioral attributes. Their food intake was measured weekly, body weight and fasting glucose levels were measured fortnightly, and a comprehensive behavioral test battery was performed to assess anxiety, depression and cognitive dysfunction.
Glucose and insulin tolerance tests were performed on the mice after 30 weeks and, at the conclusion of the dietary experiment, the researchers also investigated the differences in tau proteins in the brains of the mice.
The findings, published in the journal Metabolic Brain Disease, showed that the genetically modified Alzheimer’s mice on the high-fat diet gained a lot of weight, developed insulin resistance and exhibited abnormal behavior, such anxiety and depression. They also showed significant deterioration in their cognitive abilities. Mice with impaired cognitive function were also more likely to gain excessive weight due to poor metabolism caused by brain changes.
“Obese individuals have about a 55 percent increased risk of developing depression, and diabetes will double that risk,” said Professor Bobrovskaya.
More than 50 million people are thought to be living with Alzheimer’s disease but, despite decades of ground breaking studies and a huge global research effort, there is still no cure for this debilitating disease. What is clear is that being overweight or obese may place an additional burden on brain health and may well exacerbate the disease.
“Our findings underline the importance of addressing the global obesity epidemic. A combination of obesity, age and diabetes is very likely to lead to a decline in cognitive abilities, Alzheimer’s disease and other mental health disorders,” said Professor Bobrovskaya.