The effects of fasting on the brain
xMark Mattson, a neuroscientist at the National Institute on Aging and a professor at Johns Hopkins University, reveals the surprising brain benefits of fasting……
“The way we as scientists who study fasting define it is not consuming food for a long enough period of time to elevate the levels of compounds called ketones. In the fed state — that is, when you’re not fasting — glucose is the primary fuel used by cells, including neurons. Fasting depletes the liver’s store of glucose, prompting fat cells to release fats. The fats travel to the liver where they’re converted into ketones, which are essentially small pieces of fats that cells can use as an energy source.
This metabolic switch — going from using glucose to using ketones as an energy source — happens after about 10 to 14 hours of not consuming food, depending on how active you are. Exercise will accelerate the onset of the switch.
There are different types of fasting regimens. In lab animals, the main regimen we use is alternate-day fasting where the rats or mice have no food for a 24-hour period, followed by a 24-hour period where they can eat, and so on. Alternatively, you can restrict the amount of time animals have access to food to a four- to six-hour window so that they’re fasting between 18 and 20 hours a day. In people, we’ve studied a fasting regimen called the 5:2 diet, where people eat normally for five days out of the week and then eat only about 500 calories on the other two days.
In an animal in the wild, like a cougar or a wolf that hasn’t killed any prey in a couple of weeks, during that time they’re pretty much running on ketones rather than glucose. Obviously, it’s important that their brain and body are able to function well in that fasted state. And that’s what we’re finding in lab animals — the brain and body actually perform better during fasting. In the case of the brain, cognitive function, learning, memory, and alertness are all increased by fasting. And in the body, we recently found that mice maintained on an alternate-day fasting diet during a month of treadmill training have better endurance than mice fed every day. So intermittent fasting enhanced the mice’s physical performance.
In lab animals, fasting, as well as exercise, stimulates the production of a protein in nerve cells called brain-derived neurotrophic factor, or BDNF. This protein plays critical roles in learning, memory, and the generation of new nerve cells in the hippocampus. BDNF also makes neurons more resistant to stress. Fasting also triggers a process called autophagy, where cells remove damaged molecules and dysfunctional mitochondria, and turns off cell growth. So neurons are in a kind of “resource conservation and stress resistance” mode during fasting. When the animal, and by extrapolation probably the human, eats after fasting, neurons shift to a “growth” mode — they make lots of proteins, grow, and form new synapses. We think these cycles of metabolic challenge, whether it’s exercise or fasting, and then a recovery period may optimize neuroplasticity, learning, memory, and the resistance of the brain to stress.”
This has been known throughout history. In Ancient Greece, the great thinkers would fast for days on end, not because they needed to lose weight, but because they believed (correctly) that fasting would increase their mental agility. Even today, we marvel at the ancient Greek philosophers and mathematicians. In stories of Japanese prisoners of war in World War II (Unbroken by Laura Hillenbrand), many have described the amazing clarity of thought that often accompanies starvation. In this book, the main character describes a prisoner who would read entire books from memory, and another who learned the Norwegian language in a few weeks. Incredibly, these feats were so commonplace that prisoners simply accepted it as a fact of life that starvation increases cognitive ability.
When we say we are ‘hungry’ for something (hungry for power, hungry for attention), does it mean we are slothful and dull? No, it means that we are hyper-vigilant and energetic. So, fasting and hunger clearly activate us towards our goal. People always worry that fasting will dull their senses, but in fact, it has the opposite, energizing effect……
Fasting and neuro-degenerative diseases
There are also very interesting mouse models of neuro-degenerative diseases. Mice maintained on IF, compared to normal mice, showed less age-related deterioration of neurons and less symptoms in models of Alzheimers disease, Parksinon’s and Huntington’s disease…..
Fasting might prevent Alzheimer’s disease
Alzheimer’s disease (AD) is characterized by the abnormal accumulation of proteins. There are two main classes – amyloid plaques and neurofibrillary tangles (tau protein). The symptoms of AD correlate closely with the accumulation of these plaques and tangles. It is believed that these abnormal proteins destroy the synaptic connections in the memory and cognition areas of the brain.
Certain proteins (HSP-70) act to prevent damage and misfolding of the tau and amyloid proteins. In mouse models, alternate daily fasting increased the levels of HSP-70. Autophagy removes these tau and amyloid proteins when they are damaged beyond repair. This process, too, is stimulated by fasting.
There is substantial evidence that risk of AD is related to obesity. A recent population based twin study demonstrated that weight gain in middle age predisposes to AD.
Taken together, this suggests a fascinating possibility in the prevention of Alzheimer’s disease. Over 5 million American have AD and this number will likely increase rapidly due to the aging population. AD creates significant burdens upon families that are forced to care for their afflicted members.
Certainly fasting may have significant benefits in reducing weight, type 2 diabetes along with its complications – eye damage, kidney disease, nerve damage, heart attacks, strokes, cancer. However, the possibility also exists that it may prevent the development of Alzheimer’s disease as well.
The method of protection may also have to do with autophagy – a cellular self cleansing process that may help removed damaged proteins from the body and brain. Since AD may result from the abnormal accumulation of Tau protein or amyloid protein, fasting may provide a unique opportunity to rid the body of these abnormal proteins.
“I fast for greater physical and mental efficiency.” – Plato (428-348 B.C.)
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