Leading medical journal published 10K words on intermittent fasting (IF). Here’s my 3 minute summary.

Within minutes of this paper’s release, my buddy, (and blog contributor) Dr. Jason Valadao texted me the link.  I later replied with a thumbs up, two big hearts, gold trophy, and five eggplants emojis.  This article is a big deal because The New England Journal of Medicine (NEJM) is the most highly respected medical publication in the world, just narrowly beating out JAMA, The Lancet, and DrJimmywestbrook.com.  The NEJM’s recent extensive article on the many benefits of intermittent fasting (IF) marks a turning point in the study of health.  It firmly puts tired statements like, “eat 6 small meals per day,” and “breakfast is the most important meal of the day,” in the same category as those old timey scientific proclamations, “smoking helps us breathe better,” “masturbation will make you go blind,” and “redheads don’t have souls.”  This post is a very brief summary of the NEJM article, but not a how-to guide of IF.  Here’s a link to the full NEJM article and here’s a link to my short guide to easy intermittent fasting.


Defining IF.  The NEJM defines IF as, eating in a 6-8 hour window each day, with 16-18 hours of fasting (18:6 vs 16:8) or eating normally for five days per week and only eating one moderate sized meal per day on the other two non-consecutive days (5:2).

Daily Caloric Restriction (CR).  Animal studies have repeatedly shown that calorie restriction extends the lifespan of animals, ranging from yeasts and worms to dogs, rats, and monkeys.  The life extension can be dramatic, up to 80% in some cases and the restriction does not have to be lifelong.  Even starting CR in older animals shows a huge life extending benefit.

This is the face of daily caloric restriction.

The problem is that daily CR can be miserable.  These animals may live longer but they often seem to be praying for death, and there are side effects like brain shrinkage (seen in monkeys), depression, cold intolerance, decreased energy, and slow metabolism.  Humans subjected to daily CR also start resembling Woody Allen, an unpleasant side effect indeed.

It seems that the benefits of CR may be a result of the restricted feeding time window and not the CR.  In more recent experiments, animals were not calorie restricted, but their feeding was time restricted (IF) which showed the same life-extending benefits of CR, but is much easier for humans to follow and doesn’t have the unwanted side effects.

What Happens when we intermittently fast?  IF obviously helps us lose weight, but so does Jenny Craig. So what’s the big deal? I’ll tell you.  When we fast, our bodies switch fuels, from glucose to fats (in the form of ketones).  This switching to ketones acts as a signal to the body to activate a host of anti-aging processes.  IF allows for old, useless cells to be killed (autophagy), which doesn’t occur when we stay in a “fed” state, here’s a link to my article about it.  Even better, after the old cells die, new young cells take their place.  Studies show that the benefits of IF are independent of the healthy effects of weight loss and therefore IF is a good idea whether we are overweight or normal weight.  Here are some more benefits of IF discussed in the NEJM article:

Weight Loss:  This seems obvious, but the type of weight we lose is also super important.  Studies show that IF causes greater loss of body fat, specifically abdominal fat, resulting in a smaller waist circumference, as compared with caloric restriction.

Maintenance of muscle mass.  Keeping your muscle mass when you’re losing weight is important for metabolism, insulin sensitivity, and increasing your odds of waking up with attractive strangers.  Studies show that IF is great for this as well.

Heart Health.  Decreased inflammation, blood pressure, and LDL (bad) cholesterol are all helpful for keeping your ticker healthy, and are coincidentally all documented benefits of IF.  The subtle theme of this post is that IF is good for you.

Brain Health.  IF research has shown improvements in cognition, balance, coordination, and active memory, both in young people and in older folks with dementia.  IF has shown promise (in animal models) to reduce the risk of stroke, Alzheimer’s, Parkinson’s, and other neurodegenerative diseases.

Type II Diabetes.  IF cures type II diabetes.  That’s all I have to say about that.

Cancer.  As we age our risk of cancer increases exponentially.  IF is shown to prevent cancer through many different mechanisms, but IF also shows promise in improving the survival of those with active cancer, and reducing the side effects of chemotherapy.   Despite this new research, patients with cancer are often told to try to gain weight, and thus are discouraged from fasting, but I expect this will change soon.

Other.  IF has shown early evidence of benefit in rheumatoid arthritis, multiple sclerosis, asthma, traumatic brain injury, spinal cord injury, other inflammatory or autoimmune conditions, and the gum disease gingivitis.  That last one may be bullshit.

Healthchecklist (1)
Bear Avoidance is the most important

Dr. Jimmy’s Editorial Conclusion:  So, why does IF help all these very different health issues?  Here’s my take.  Our single greatest risk factor for all of these diseases is age and IF fights the aging process.  Our bodies don’t have a clock that keeps track of time in hours, days, and hockey seasons.  Instead, our bodies age by detecting things like inflammation, nutrient consumption, cell divisions, and damage to our DNA.

IF reduces our body’s inflammation, strengthens our DNA, lowers insulin, and keeps things tight both at the cellular level and with regards to our midsections.  Many people say that they don’t want to live to be 95 or 100.  What if you feel amazing at 94, with a sharp mind, supple body, an active sex life (gross), and you just inked a sweet deal with a member of the Nigerian Royal family who needs five hundred dollars in order to access his family’s vast fortune which he will share with you?  Cha-ching!  Would you still want to check out at 95?  I didn’t think so.

IF has shown that it can fix what ails us today and delay what is coming down the road tomorrow.  Also IF is pretty easy, as well as being free.  So instead of making the same doomed and clichéd New Year’s resolution to lose 30 pounds by joining a gym, counting calories, or cutting off a limb, start IF to lose the 30 pounds and in the process you may gain 30 years.  Thank you for coming to my Ted Talk.




  1. Dr. Sweet J – sexy article. I laughed so hard I came. Twice.

    Is IF an all or nothing thing? Can I do IF three- four times a week and still see some benefits?

    What is the ideal AM coffee concoction on days when I am doing IF?

    1. Four times a week is still helpful. It’s like medicine and sometimes we only need a low dose but some of us need a bigger dose. Also, coffee is fine, but try to not put any sugar or processed garbage in the coffee. Doing a keto coffee with MCT, grassfed butter, or heavy cream is not ideal because it’s technically not fasting but it’s the next best thing to fasting. We can consider this a modified fast. Our body primarily receives signals of nutrient consumption by insulin and mTOR which are signaled by carbs and protein respectively (actually protein is a weak signaler of insulin as well). Fat doesn’t send these signals so it’s the best thing to eat if you must eat something. Sorry for the wishy washy answer but it’s a bit complicated. I’m glad fasting gets you as excited. It certainly excites me as well.

  2. Thanks Jimmy for distilling it down for us!!! Now quit telling Brian (pilots) that one glass of bourbon is ok….🤪 you know they only hear… “bourbon is ok”!

    1. Liz, thanks for your kind words, but telling pilots like Brian to stop drinking bourbon is like telling fish to stop swimming. I can’t fight nature.

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