Our Intelligence Depends on Our Weight

The prevalence of obesity (defined as a Body Mass Index equal to or greater than 30) is increasing around the world. Medical doctors and investigators have long wondered if there is a link between obesity and brain disorders. 

Interesting observations were made regarding the age of obesity onset. Higher fetal and postnatal levels of adiposity contribute to better brain development. However, obesity in mid-life - at ages 40-55 - and during late-life - at age 70+ - increases risk for dementia, independent of education, IQ or other factors.
But what are the mechanisms by which obesity influences the brain and cognitive function? Adipose tissue may contribute to cognitive decline in a variety of ways. This may happen indirectly because obesity can cause diabetes or hypertension, leading to cardio- and cerebrovascular diseases that are able to impair cognitive function.

A more direct link is via adipokines. They can cross the blood-brain barrier and cause structural abnormalities, such as increased amounts of white matter. Leptin, produced mainly by adipose tissue, has remarkable effects on neurogenesis, neuroprotection, and regulation of beta-amyloid levels. Hereby, it is able to improve cognition, delay age changes, and optimize learning and memory processes. However, patients with common obesity can not benefit from elevated leptin levels because they show increased leptin resistance. A number of mechanisms, including the leptin-stimulated phosphorylation of Tyr(985) on LRb and the suppressor of cytokine signaling 3, attenuate leptin signaling and promote a cellular leptin resistance in obesity [1]. Another important multifunctional hormone is ghrelin. It is produced in a wide variety of tissues associated with the progression of obesity and metabolic syndrome. Acyl-ghrelin may modulate specific molecular intermediates involved in memory acquisition and consolidation through promotion of synaptic plasticity. In patients with Alzheimer's disease, the ghrelin autocrine/paracrine loop in the temporal lobe was found to be dramatically disrupted [2].

Furthermore, the brain can be susceptible to higher adiposity due to basic underlying differences in the structure and function of the nervous system. Studies using MRI have identified a number of brain regions potentially related to adult human obesity. These are mostly prefrontal areas which are different in gray matter density in obese and lean individuals. Higher BMI has also been related to a higher rate of brain atrophy using serial MRI [3].
It looks like exercise and maintaining a healthy weight are necessary not only to keep ourselves fit, but also to keep our brains functioning well.

[1] Paz-Filho G, Int J Clin Pract, 2010
[2] Gahete M et al., Peptides, 2011
[3] Enzinger C et al., Neurology, 2005

By Natalia Denisova, MSc Student Medical Neurosciences  

Tis article originally appeared December 2012 in Volume 05, Issue 04, Fat Gut or Fat Brain