What happens in your brain when you don't eat?
When you don't eat enough to keep your body fuelled, your brain flicks into survival mode – essentially switching off the parts of our brain responsible for conscious, intellectual, logical reasoning. Leaving you with your more basic “survival brain” in the driver's seat.
The proper nutrition found in a healthy diet can improve many brain functions, while a poor diet can have a negative effect on our cognitive functions [1].
Under normal conditions, humans can live for roughly five minutes without oxygen, five days without water, and five weeks without food (magician David Blaine held his breath underwater for 17 minutes, and, in 1920, Irish hunger striker Terence MacSwiney lived without food for 74 days, protesting British occupation).
Conversely, an inadequate diet can lead to fatigue, impaired decision-making, and can slow down reaction time. In fact, a poor diet can actually aggravate, and may even lead to, stress and depression. One of the biggest health impairments is society's reliance on processed foods.
If a person continues not to eat, they can have slurred speech, confusion, syncope (fainting), or seizures. Prolonged lack of nutrition can lead to severe weight loss, fatigue, depression, and stomach issues.
As a result of discontinuing eating, patients can die in as early as a few days. For most people, this period without food usually lasts about 10 days, but in rare instances, it can last several weeks.
In the first two years of life, 70% of the brain develops. If a child experiences significant malnourishment, hunger and stress during that time frame, it's likely their brain will be permanently damaged.
Not eating enough can increase the risk of nutritional deficiencies, some of which may cause brain fog. It could also contribute to anxiety and depression, both of which can negatively affect brain function.
Diet can also play a role in brain fog. Vitamin B12 supports healthy brain function, and a vitamin B12 deficiency can bring about brain fog, according to a 2021 research review .
Fasting improves cognition, stalls age-related cognitive decline, usually slows neurodegeneration, reduces brain damage and enhances functional recovery after stroke, and mitigates the pathological and clinical features of epilepsy and multiple sclerosis in animal models.
How often does your brain need food?
Your brain is always "on." It takes care of your thoughts and movements, your breathing and heartbeat, your senses — it works hard 24/7, even while you're asleep. This means your brain requires a constant supply of fuel.
Animal studies suggest that fasting protects brain cells by providing ketones for fuel instead of glucose. Ketones appear to help the brain produce brain-derived neurotrophic factor (BDNF), a compound that promotes the growth of new brain cells and new connections between them.
Now a new Yale study suggests that dieting might also keep you mentally sharper. Blood levels of a gut hormone called ghrelin (rhymes with “melon”) rise when the stomach is empty, flooding the brain's eating control center and stimulating neurons that govern appetite.
Ghrelin activates receptors in a part of your brain involved in hunger called the hypothalamus — more on this brain region later. As ghrelin levels rise, so do your hunger pangs. Although best known as the hunger hormone, ghrelin also plays a role in sleep, glucose metabolism, anxiety, and much more.
Researchers recently found that not getting enough sleep consistently could cause the brain to clear a significant amount of neurons and synaptic connections, while adding that making up for the lost sleep may not be able to undo the damage. In essence, not getting sleep may be causing our brain to start eating itself!