Podcast: Our Fasting Fascination

Welcome to the Nutrition Facts Podcast.
I’m your host Dr. Michael Greger. The coronavirus pandemic
has made many of us very aware of the importance of maintaining
and improving our health. Make that your silver living. Because the more positive change we can
make to our diet and lifestyle, the better. There have been a lot of studies that
have come out recently about fasting. In fact – I did a whole 
series on fasting recently. And here are two more studies – to add to our understanding. We start off today with a study on
the origins of therapeutic fasting. The story of life on earth
is a story of starvation. Ash from massive volcanoes and
asteroids block out the sun, killing the plants, which then
killed most everything else. As Darwin pointed out though,
from this “war of nature, from famine and death,
the most exalted object that we are capable of conceiving”
arose—namely us. We are “particularly well
adapted to prolonged fasting.” Evolving in a context of
scarcity is believed to have shaped our exceptional ability to store large amounts of calories
when food is available. Of course, now our ability
to easily pack on the pounds is leading to modern diseases
like obesity and type 2 diabetes, but without the ability
to store so much body fat we may not have made
it to tell the tale. And it’s not just asteroids
millions of years ago. “All of Upper Egypt was dying
of hunger,” reads an inscription on an Egyptian tomb
from about 4,000 years ago, “to such a degree that everyone
had come to eating his children…” Or, just hundreds of years ago – parents killed their children
and children killed their parents and ate them; “the
bodies of executed criminals were eagerly snatched from the gallows.” Wiping out as many as two-thirds
of the population of Italy, one-third of the population of Paris. So, we don’t have to go
back to ancient history. Even the most secure and
affluent populations of today need only trace their history
back a short distance. For example, nearly 200 famines in Britain over the last 2,000 years. Now, we tend to be
suffering from too much food, which carries its own problems,
but might there be any negative consequences
to not ever starving? This was a question
raised 50 years ago. I mean, if our physiology is
so well-tuned to periodic starvation, maybe by eliminating that we may be
doing harm to our overall well-being? We just didn’t know. The lack of research in the area
of starvation was attributed to the “difficulty of securing
willing human subjects.” So, what little we had
came from unwilling subjects. Physicians within the Warsaw
Ghetto made detailed accounts before they themselves succumbed;
or Irish Republican prisoners starving themselves to death after
up to 73 days on hunger strike. But starvation isn’t
necessarily the same as fasting, an issue raised in medical
journals over a century ago. Starvation is normally a
forced, mentally stressful, and chronic condition, whereas
therapeutic fasting is voluntary, limited in duration, and
usually practiced by people who start out with adequate nutrition.” Therapeutic fasting? Where did we get this idea
of fasting therapy, fasting for medical purposes? It may have originally
arose out of the observation that when people get acutely ill
they tend to lose their appetite; so, maybe there’s something in
the body’s wisdom to stopping eating. That’s presumably where the whole
“starve a fever” folklore came from. There was this sense that fasting
affords physiological rest for the body, not just the digestive
tract, but throughout, allowing the body to
concentrate on healing. It was evidently an open
secret that veterinarians used to hospitalize dogs only
to fast them back to health; and so maybe, the theory went,
it might work for people too. Beyond just freeing up all the
resources that would normally be used for nutrient
digestion and storage, there’s this concept that
during fasting our cells switch over to some
sort of protection mode. Why would fasting reduce
free radical damage and inflammation and bolster
cellular protection? It’s the that-which-doesn’t-kill-
us-makes-us-stronger concept known as hormesis. So, that’s kind of the opposite of
the let-the-body-rest theory. It’s more like let-the-body-stress. The stress of fasting may
steel the body against other stresses coming your way. This was demonstrated perhaps most
starkly in a set of cringe-worthy experiments in which mice were
blasted with Hiroshima-level gamma radiation sufficient
to kill 50% within two weeks, but of the mice who had first
been intermittently fasted for six weeks before,
not a single one died. It’s this kind of dramatic data
that led to extraordinary claims, like therapeutic fasting could drive
half of all doctors out of business. But you don’t know, until you put it
to the test, which we’ll explore next. A century ago, fasting—starvation
as a therapeutic measure— was described as the ideal
measure for obesity. As you can see, fat shaming is not a
new invention in the medical literature. I’ve extensively covered fasting for
weight loss in a nine-video series starting with this one, but what about
all the other purported benefits? I do have a video series on fasting for
hypertension, but what about psoriasis, eczema, type 2 diabetes, lupus,
metabolic disorder, rheumatoid arthritis and other autoimmune disorders,
depression, anxiety? Why hasn’t it been tested more? One difficulty with fasting research
is what do you mean by fasting? When I think fasting, I think of
water-only fasting, but in Europe they tend to practice so-called
modified fasting, or Buchinger fasting, which is more like very low-calorie
juice fasting with some vegetable broth. Some forms of fasting may
not even cut calories at all. Ramadan fasting is when devout
Muslims abstain from food and drink from sunrise to sunset,
yet interestingly, they end up eating the same amount,
or even more food, overall. The largest study on fasting
to date was published in 2019. More than a thousand individuals
were put through a modified fast, cutting intake down to about 10
cups of water, a cup of fruit juice, and a cup of vegetable soup a day. They reported very few side effects,
which is in contrast to the latest water-only fasting data, which only
involved half as many people but reported nearly
6,000 adverse effects. Now the modified fasting study did seem
to try to undercount adverse effects, only counting reported symptoms
if they were repeated three times, but still only reporting single cases
of things like nausea, feeling faint, upset stomach, vomiting, or palpitations,
whereas the water-only fasting study reported about one to two hundred of
each. What about the benefits though? In the modified fasting study,
participants self-reported improvements in physical and emotional well-being,
along with a surprising lack of hunger. And the vast majority of those who came
in with a pre-existing health complaint reported feeling better,
with less than 10% reporting their condition worsening
or remaining unchanged. They weren’t just fasted though,
but engaged in a lifestyle program, which included being placed before
and after on a plant-based diet. Too bad they didn’t have some
people just do the healthier diet without the fast to tease out the
fasting effects. Oh, but they did! About a thousand folks fasted
for a week on the same juice and vegetable soup regimen
versus those put on normocaloric, meaning normal calorie,
vegetarian diet the whole time. Both experienced significant
increases in both physical and mental quality of life,
and interestingly there was no significant difference
between the groups. In terms of their major health
complaints—rheumatoid arthritis, chronic pain syndromes like
osteoarthritis, fibromyalgia, and back pain, inflammatory and
irritable bowel disease, chronic pulmonary diseases,
and migraine and chronic tension headaches—the fasting group
appeared to have an edge, but both groups did good,
with about 80% reporting improvements in their condition,
with only about 4% feeling worse. Now, this was not
a randomized study; people chose which
treatment they wanted. So maybe, for example, those choosing
fasting were sicker or something. The improvements in quality of
life and disease status were also all subjective self-report, which
is ripe for placebo effects, no do-nothing control group, and
the response rates to the follow-up quality of life surveys
were only about 60 or 70%, which also could have biased the
results. But extended benefits are certainly possible, given they
all tended to improve their diets. More fruits and vegetables,
less meats and sweets, and therein may lie the secret.
Principally, the experience of fasting may support motivation for
lifestyle change. Most fasters experience clarity of mind and a feeling
of letting go of past actions and experiences, and thus may develop a
more positive attitude towards the future. As a consensus panel of
fasting experts concluded: nutritional therapy is a vital and
integral component of any fasting. After the fasting therapy and
refeeding period, nutrition should follow the recommendations of
a plant-based whole-food diet. We would love it if you could
share with us your stories about reinventing your health
through evidence-based nutrition. Go to We may share it on our social media
to help inspire others. To see any graphs charts, graphics,
images or studies mentioned here, please go to the Nutrition Facts Podcast
landing page. There you’ll find all the
detailed information you need – plus links to all of the sources
we cite for each of these topics. For a vital, timely text on the
pathogens that cause pandemics – you can order the e-book, audio book, or now hard copy of my latest book
“How to Survive a Pandemic.” For recipes, preorder my “How Not to Diet
Cookbook” out this December. It’s beautifully designed, with more than 100
recipes for delicious and nutritious meals. And all proceeds I receive from
the sales of my books go to charity. is a nonprofit,
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via bite-sized videos and articles. Everything on the website is free. There’s no ads, no corporate sponsorship. It’s strictly non-commercial.
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as a labor of love – as a tribute to my grandmother – whose own life was saved
with evidence-based nutrition.
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