For the first time in the history of the Earth, there are more overweight than underweight human beings. While being overweight can cause a multitude of health problems, it’s especially bad for your brain. Numerous studies show that as a person’s weight and BMI (body mass index) increases, their brain shrinks in size. Excess weight often leads to obesity and diabetes. These conditions destroy synapses, wither blood vessels in your brain, batter neural pathways, and kill neurons. The result is a smaller brain.

In Your Brain Shrinks As Your Waist Expands, 

One study found that the brains of obese people looked 16 years older than their healthy counterparts while the brains of overweight people looked 8 years older. Researchers classified this as  ‘severe’ brain degeneration with serious implications for aging, including a heightened risk of Alzheimer’s.

Obesity also increases inflammation caused by excess fatty tissue. This can lead to difficulty in blood flow and an increased risk of blockage, both of which can cause strokes.