Obesity is recognised as a disease which takes a toll on the overall health of a person. Dr Shashank R Joshi, department of diabetology and endocrinology, Lilavati Hospital and Research Center, Mumbai, says that obesity is usually defined as abnormal fat accumulation with a body mass index over 25 in Indian adults. Apart from psychological issues, he says, obesity can also affect the cognitive function of a person. Now, some studies suggest that obesity can lead to a reduction in brain size and white matter.
The brain size usually depends on different ethnicities, says Dr Sandeep Vaishya, HOD and executive director, Neurosurgery, Fortis Memorial Research Institute, Gurugram. He adds that the brain weight is generally between 1,300 to 1,500 grams in males and slightly less in females. The recent study, ‘Relations of Metabolic Health and Obesity to Brain Aging in Young to Middle‐Aged Adults’ published in the Journal of the American Heart Association found that people with metabolic syndrome and obesity had lower total cerebral brain volume. They were associated with structural and functional evidence of brain ageing.
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Obesity and brain function
Experts say it is unclear if obesity is an independent factor for effects on the human brain. People with obesity may have decreased memory, attention span and decision-making capabilities. But they may not be directly related to obesity. Owen Carmichael, professor and director of biomedical imaging, Pennington Biomedical Research Center, Louisiana, USA, says, “It is not clear whether obesity per se has its independent effects on the human brain; or whether the other factors that usually accompany obesity, such as high blood pressure, high cholesterol, diabetes are primarily responsible for the brain effects. In fact, the association between obesity and cognitive function is very complex; the data does not suggest a simple situation in which greater body weight is always associated with poorer cognitive function.”
Dr Vaishya adds diabetes affects the blood vessels and any decreased blood supply to the brain will affect its function too.
Dr Joshi, also the president of the Indian Academy of Diabetes, adds that obesity can lead to inflammation in the body too as it causes the release of pro-inflammatory cytokines, which can affect the brain. People with obesity mostly also suffer from sleep apnea. And Dr Vaishya says sleep apnea does affect brain function as it significantly reduces the cognitive function of a person. Dr Vaishya adds that it could affect the frontal lobe probably more because it controls cognitive function.
Obesity and the risk of dementia
The brain grows to about 90 per cent of the adult size by the age of five. After that, as the body grows, the brain size stabilises. The brain starts degenerating (which means it starts shrinking) naturally at the age of 70 or 80 but in some people, in the 60s. Dr Vaishya says, “So when the size of the brain reduces, the weight also decreases proportionately. There are many studies which suggest that the risk of dementia is higher in people with obesity. In the general population, you see dementia in a pretty late age group and in people with obesity, it may start in middle age. With dementia, the brain always shrinks. So, the early reduction in brain size in people with obesity could probably be due to dementia.”
Prof Carmichael adds brain cells are what we use to think. A reduction in brain size is a reflection of the death of brain cells. “So, the real issue is not that the brain is getting smaller per se — it’s that brain cells are dying. And clearly, if the brain cells used to create thought die away, it should not be surprising that our ability to produce thoughts goes downhill,” he says.
Does losing weight improve brain function?
Losing weight may help improve brain health and cognitive function. Dr Vaishya recalls performing a spine surgery on a Kenyan man with obesity, who’s been wheelchair-bound for five years. “He had put on weight due to lack of exercise and was 110 kg. After he became wheelchair-bound, his weight shot up to 165 kg. He was breathless, hypertensive, diabetic and had liver issues and many health complications. We also put a balloon in his stomach, which is a non-operative alternative to bariatric surgery. And since then [in five weeks], his weight has come down to about under 120 kgs,” he says, adding that since then, he has been feeling better, has become more alert and has a better recall of his case history. “Earlier, he would be rambling but now, his memory has improved,” says Dr Vaishya.
Obesity is highly prevalent and there are effective methods both to prevent obesity and to treat it, says Prof Carmichael. He adds, “But we don’t know whether reducing body weight among people with obesity is adequate to reduce brain risks back down to levels, typical of normal-weight adults. We also don’t know if there is a ‘point of no return’, a body size so large that there is effectively little chance of ever reducing risks to brain health via weight loss therapy. Finally, we don’t know if certain individuals are resilient to obesity’s brain effects, or especially vulnerable to them. Because of these unknowns, studying the relationships between obesity and brain size is important.”
- Studies show that obesity can lead to a decrease in brain size and volume.
- However, it is unclear if obesity is an independent factor for effects on the human brain. Other complications due to obesity like diabetes, hypertension and heart and liver issues can also affect the brain.
- Obesity rises the risk of dementia and the brain shrinks in people with dementia.
- Obesity can also lead to sleep apnea, which affects brain function.
- Losing weight may help improve brain health but further research needs to be done to understand the association between obesity and brain size better, say experts.