Can change in diet or restricted eating / fasting effect human brain plasticity?

About a year and a half ago, I fasted every other day for a month in an effor to duplicate in myself an effect found in an experiment on rats. The experiment put rats blinded in one eye on a food restricted diet for a month. Vision in their blinded eye was restored. At first this sounds crazy but the experiment is very convincing and interesting.

I have amblyopia, a similar condition to the artificially created blindness the rats in the experiment have. (The rats probably have a worse version of it, in fact.) Naturally I found the study intriguing.

These rats had been prevented from developing vision by blocking light reaching their eyes starting when they were born. When this happens, the visual cortex – the part of the brain that processes information from the eyes – doesn’t develop.

In a classic experiment in the 1960s, kittens had one eye sewn shut until the animal reached adulthood, then the eye was opened; the cat could not see out of the previously shut eye and vision was never recovered in the affected eye, establishing the idea of a “Critical Period” during which the visual system rapidly develops and after which it cannot.

The experiments (both the classic cat experiment, and the rat experiment I’m discussing here) were carried out to investigate brain plasticity, not vision specifically. Illiciting growth in the visual cortex of adults – normally not possible – is just a standard way to test for brain plasticity. Paper full text It seems like a very thorough investigation, but I’m no expert.

By restoring vision in the adult rats, the authors showed that they had re-opened the “critical period” for brain development. The “critical period” is the time in childhood when rapid brain growth occurs; once closed, (around age eight or so in humans,) parts of the brain like the visual cortex normally don’t undergo much growth and can’t recover from serious damage.

Temporary Food Restricted Diet Increases Brain Plasticity

The food restriction appeared to change the inhibitory / exitory balance in the cerebral cortex of the rats. This balance is believed to be important to the critical period. The food restricted rats, all of which developed vision in their blinded eye during the experiment, showed increased disinhibition levels in their visual cortexes.

To demonstrate that decreased inhibition allowed for the CP to reopen the researchers artificially blocked the disinhibition in another group of rats subjected to FR. These rats did not develop any vision in their blinded eyes unlike the first group.

The food restriction was done by denying food every other day. Toward the end of each fasting period high levels of corticosterone were measured in the rats. To test if the corticosterone was connected to the brain plasticity observed in the rats the researchers gave it to one group of rats every other day in their water, bypassing the fasting.

Brain researchers often use vision as a way to experiment on brain plasticity, so results that aren’t intended to directly lead to improving vision but use it as a model are of interest to me nevertheless. Here’s a great overview, “re-opening the windows of brain plasticity.” Indeed the food restriction experiment has some results showing that other parts of the brain in addition to the visual cortex experienced growth.

Fasting has a variety of beneficial effects on the body and there may be a number of reasons why it reopened the critical period for the rat: For instance, After refeeding begins, IGF-1 levels return to normal triggering other growth factors including ones driving neuronal growth. For humans to get that same response requires four or five days of fasting. Here’s a good summary of the effects from fasting.

My Experiment

The rat study of every other day fasting was simple enough so I thought I’d see what subjecting myself to the same thing did to my vision. The fasting every other day lasted a month. It did have an effect (more later.)

The fast was unpleasant at first, but not as difficult as I’d expected. One strategy that ended up helping a lot was to switch to a very low carbohydrate diet on the days I was eating. Once I did so, the “no food” days were quite a bit easier to get through and I never felt terribly hungry, just bored.

I had made the switch to endure the experiment but it turned out to have other benifits: I lost about twenty pounds and kept it off and generally had more energy and slept better. The experience was so good I ended up researching the low-carb diet phenomenon and putting together some notes which I’ll post soon.

Later while researching brain plasticity – which is why I did this at all in the first place – I found studies showing that cutting total calories helps increase brain plasticity, in addition to the fasting approach.

The best way to cut calories without counting them seems to be with the low carb type diet. There’s some evidence this type of diet can be good for brain plasticity independently of the calorie reduction. ( abstract)and full text.

The month on/off fast did seem to produce results, about a 15% improvement. This is a rough estimate, but there were measurable changes. I tracked changes every day in a journal.

  • After the first week and a half, I developed slightly better geometry perception – lines, corners, perspective “gelled” better.
  • After a few weeks I could read particular clocks and signs in my officewhere before I could not
  • After three weeks I could read text on a TV screen (like movie titles, credits etc) I couldn’t before. This seems to be mostly because of higher contrast.
  • After a week or so I could better track moving points on a screen playing a basic video game, going from not being able to play at all to staying alive for ten minutes or so. The games were Galaga, Galaxian, Pac-Man and a few other classics.
  • Also, peripheral vision at the top and bottom of my visual field expanded.

Two years later I’m left with slightly better ability to read large text on a TV screen and better perception of geometric shapes. The rest fluctuates but has more or less returned to where it was before.

What I should have done was to devise a more objective test like a random letter chart on a computer screen. Flash random letters or numbers, sometimes with background patterns (“Gabor Patches”.) This way I can’t train on a particular sequence but the size and difficulty is consistent. Then record how many I correctly identify.

This type of vision is only one way vision might improve. There’s also peripheral vision, tracking movement, contrast sensitivity.

Just because I didn’t greatly improve my vision doesn’t necessarily mean some brain plasticity wasn’t gained; I have other problems (no lens, possible retinal damage.) Even a small change is pretty interesting.

There are two extremely important points to note when thinking about why the rat results are so different from mine:

  1. Rat metabolism is different from human. Besides being faster, the rat day/night cycle is much more regular and powerful than human’s. Coordinating a fasting cycle with waking and sleeping might have pretty different effects on rats than on humans. So my choice of a single day fast was rather arbitrary. After more research a four or five day fast would probably be the next length to try out.
  2. The sheer difference in scale between rat and human visual cortex is so big that it seems possible that the mechanism that causes big changes to a rat would either have little effect in humans or take much longer.

To reasonably expect any more results, I’d need to retry this with different fasting periods appropriate to a human, and perhaps over a longer total time period. Even then I wouldn’t expect large results.

One final question to ponder: What other areas of the brain might be rejuvenated with fasting, calorie restriction or dietary changes? The visual cortex is just one of the most testable and obvious brain areas, but surely other areas should benefit too?

Other than small changes in vision, what I noticed most was better sleep and slight improvements in hearing.