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Part 4: What Happens To Your Body When You Fast? - Healing and Longevity

Posted Aug 23 2008 3:02pm

Here we are at the fourth installment of our look at the physiology of fasting. Thus far, we’ve looked at energy production, hormonal effects, the anti-inflammatory nature of fasting, and changes in blood markers. Today, let’s look at healing, disease, aging, and longevity.


Let’s start with disease. We’ll start with The Big C, cancer, the second-leading cause of death in the United States. All of the studies I found were in rats and mice, but we have to remember that IF is still an emerging science. In our rodent friends, cell proliferation rates are lowered by 25% caloric restriction, but not as much as by Alternate Day Fasting. A report on another study showed that a 5% reduction in calories, but only being fed every other day , also reduced cell proliferation rates.

And if you’re unfortunate enough to have a case of cancer, a 48-hour fast prior to chemotherapy can help normal cells express protective mechanisms, limiting the therapeutic damage to the cancerous cells. In fact, in mice the effect was to make normal cells 5-10 times more resistant than cancerous cells to chemo. Unfortunately, human studies are lacking, but again, we’re dealing with emerging science.

Since we’ve looked at the second-leading cause of death, we might as well take a gander at the leading cause, heart disease, where there is a bit of data on humans. HDL and homocysteine levels improved in healthy 21-35 year old volunteers fasted on a Ramadan-like schedule. Animal research shows other intriguing data. Rats fasted intermittently have shown a propensity to lower a heart rate and blood pressure . Beyond the beneficial cardiovascular effects, the researchers noted that the IF rats had an improved neuroendocine stress response.

A study that I commented on in the last post also has implications here. Three doctors have found that using a protocol of eating 20-50% of their normal caloric intake one day and ad-lib eating the next (Alternate Day Caloric Restriction) resulted in improvements in numerous health problems , such as “asthma, seasonal allergies, infectious diseases of viral, bacterial and fungal origin (viral URI, recurrent bacterial tonsillitis, chronic sinusitis, periodontal disease), autoimmune disorder (rheumatoid arthritis), osteoarthritis”. I’ve noticed similar effects in that fasting seems to help me get over anything that tries to get a hold of me.

And while we’re talking about disease, Intermittent Fasting also has effects on Huntington’s Disease , a genetic condition characterized by lack of coordination and effects on some mental abilities and behaviors. While this was tested in mice, humans and this breed of mice exhibit the same Huntington gene, an interesting fact. These mice saw a delayed onset of the disease symptoms along with improved longevity. There is a fasting-induced increase in brain-derived neurotrophic factor, discussed below, and in a specific heat-shock protein that are hypothesized to be the contributing factors. As you’ll recall from my second post in this series, heat-shock proteins help ensure that proteins maintain their proper form.


Unfortunately, I couldn’t find anything on healing of wounds such as fractures or cuts. But, in my mind, more important than healing from a broken arm faster or reducing muscle soreness to allow for another hard workout, is protecting the brain. Scientists at the University of Kentucky found that “ fasting for 24 hr confers neuroprotection , maintains cognitive function, and improves mitochondrial function after moderate (1.5 mm) TBI [traumatic brain injury].” So fasting does definitely promote a healing effect in the body, though there’s no telling if it carries through to other areas (I’m betting it does). Interestingly, one symptom of a concussion is a decreased appetite. Could the body be telling us something?

Aging and Longevity

One purported benefit of fasting is an increase in longevity. But living longer isn’t all that fun if your body is giving out. You want to age well, not just age. One of the keys to aging well is maintaining your brain function at a high level. As luck would have it, intermittent fasting protects brain neurons from excitotoxic stressors. That means your brain is more resistant to injury. While that abstract doesn’t report what the Intermittent Fasting protocol was, it does specifically say “Intermittent Fasting”.

It also looks like fasting increases levels of brain-derived neurotrophic factor (BDNF) , a substance that increases the growth of brain nerve cells. This stuff is also “neuroprotective against stress and toxic insults to the brain and is somehow–no one yet knows how, exactly–involved in the insulin sensitivity/glucose regulating mechanism.”

Both caloric restriction and Intermittent Fasting have shown promise in protecting the brain from the damages that seem to come with age and contribute to diseases like Alzheimer’s and Parkinson’s . The fasting protocol activates “FoxO transcription factors, sirtuins and peroxisome proliferator-activated receptors [PPARs].” FoxO transcription factors are part of a family of proteins that regulate cell growth and longevity. Sirtuins manage cellular regulation. And PPARs regulate gene expression, growth, and metabolism.

Art DeVany had an interesting post on autophagy , or “self-eating,” some time ago. Essentially, when the cell is depleted of energy, it turns to its own damaged proteins for energy, effectively using old worn out pieces to repair itself. Constant overconsumption down-regulates cellular repair, obviously not good for longevity. But as we saw in the first piece, by forcing the body to find ways other than incoming food to provide for energy needs, fasting depletes cells of energy.

Chris at Conditioning Research had a post titled Intermittent Fasting for Longevity . The key mechanism here is the expression of a hormone called FGF21 (fibroblast growth factor 21) that inhibits the actions of growth hormone, slowing aging. It all pieces together very nice between the body suppressing excessive growth, consuming worn out building blocks, and growing new pieces to replace the old.

Wrapping Up

Well, I think four short books is enough of a look at the science behind Intermittent Fasting. Sorry for getting all technical there at the end with FoxOs and sirtuins, but I’m learning as I go here and find this stuff fascinating. In the next post, I’m going to touch quickly on exercising while fasted, then I’m going to do a Q&A post to close it out. If you have any questions, stick ‘em in the comments!

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