Can your weight affect your brain?

It’s not just your waistline that suffers when you pile on excess kilograms. A Mediclinic neurologist weighs in on how obesity can influence your brain functioning too.

A growing body of research suggests that obesity in early or midlife can lead to memory deficits, impaired cognitive function, dementia and even Alzheimer’s disease later in life.

Dr Rudi Renison, a neurologist at Mediclinic Cape Gate, says brain areas that play a role in memory, learning and cognitive functions (including the hippocampus and frontal lobes) are especially affected.

‘The exact ways obesity can lead to brain atrophy (the shrinking of the brain caused by the loss of its cells, called neurons) and impaired cognitive function are complex and may involve multiple factors,’ Dr Renison adds.

These factors include systemic and central chronic low-grade inflammation, insulin resistance, Type 2 diabetes, hypertension, microvascular (small arteries) and macrovascular (large arteries) ischemic brain changes, sleep apnoea and complex genetic factors.

Citing a study by Majid Fouhi and Brooke Lubinski published in the July/August 2013 Practical Neurology, Dr Renison explains that adipocytes (fat cells) produce inflammatory cytokines (proteins such as interleukin 6 and TNF-α) leading to systemic (i.e. initiated outside the nervous system – in the blood system) chronic low-grade inflammation which affects the brain and is associated with a reduction in brain size.

‘In the case of central (in the central nervous system – the brain) chronic low-grade inflammation, there is increased activation of your brain’s innate immune cells called microglial cells that produce inflammatory cytokines in the hippocampal formation,’ Dr Renison adds.

Another mechanism that may lead to brain impairment in obese people is insulin resistance. This happens because of:

Vasoactive effects on cerebral arteries or narrowing of arteries

Neurotoxicity (toxic to the nervous system) caused by diminished clearance of amyloid protein fragments from the brain and stimulation of the formation of neurofibrillary tangles or abnormal protein accumulation (similar pathology as in Alzheimer’s disease)

Dr Renison adds that Type 2 diabetes and hypertension can also contribute to brain atrophy in obese people. ‘Poor glucose control significantly correlates with brain atrophy while obesity-associated diseases like Type 2 diabetes and hypertension are vascular risk factors leading to complications such as ischemic stroke,’ he says.

Interestingly, poor nutrition isn’t just bad for your brain if you’re overweight. The same type of brain atrophy can be found in people who suffer from very low body weight or anorexia nervosa.

Despite this gloomy overview of the impact poor nutrition and obesity can have on your brain, Dr Renison asserts there is hope. ‘Research suggests that these negative effects of obesity on the brain can be reversed by losing weight, eating a healthy, balanced diet, exercising and not smoking,’ he says.