Intermittent fasting: What you need to know

Time for a reboot

Has this ever happened to you? You’re at your computer working diligently on an important project that needs to be finished NOW. You try to save your work only to see the “Critical Error” message flash across your screen. Oh no! Your computer’s innards are corrupted. You try every keyboard combination to get it started. No luck. So you do the unthinkable: You reboot, hoping the computer will clear the corruption and fix itself. It’s worked before, right? After a few anxious minutes, the hard drive starts, and phew, you’re up and running.

Have you ever wondered if it were possible to reboot our body’s biology and thereby fix our own “corrupted” innards?

Like that computer error message, autoimmune problems seem to pop up without warning. Causes run the gamut: inappropriate internal cell-signaling, corrupted gene expression, or dietary excesses. So, is it possible to reboot the body’s system back to normal without excessive medical intervention, drugs, or surgery? Indeed, there are examples — with caveats — that show it is possible to return corrupted systems to (nearly) normal for certain autoimmune diseases like rheumatoid arthritis, metabolic syndrome, osteoarthritis, fibromyalgia, hypertension, chronic pain syndromes, migraine headaches, recovery from chemotherapy, and mood-enhancement.

Here’s the scoop.

Intermittent fasting as a reboot

An empty white plate with a criss-crossed knife an fork serves as a visual metaphor for fasting.

(Image: iStock.)

Firm evidence exists that shows intermittent fasting, followed by specific health-promoting dietary changes, can initiate potent changes in metabolic pathways and cellular processes such as stress resistance, use of different energy sources, and autophagy (the process that allows a cell to disassemble its “junk parts” and repurpose the salvageable bits and pieces into new, usable cell parts), resulting in disease reduction, often to the point where medication may no longer be needed.

Since the late 1950s, research into different effects of fasting – starvation being the most extreme – reveals that certain protocols, accompanied by changes in dietary patterns, can change cellular responses to reduce inflammation, optimize energy use, and bolster cellular reorganization and protection. The data suggest specific individuals might be able to ‘reprogram’ metabolic and stress-resistance pathways to help prevent and treat diseases, particularly those resulting from poor/inadequate nutrition.

Types of intermittent fasting

Intermittent fasting represents an eating pattern where the hours during which one eats are restricted rather than the amount of food one ingests. This distinction is important since many intermittent fasting protocols may not (necessarily) result in weight loss or other harmful side effects.

Intermittent Fasting Types Definition Example
Time-restricted feeding (TRFF) Eating during specific hours daily; fasting during other hours. 16/8 method: Fasting 16 consecutive hours; eating during the other 8 hours
Alternate-day fasting (ADF) Fasting every other day or on certain weekdays 5/2 method: Fasting 2 nonconsecutive days per week; eating for the other five days.
Modified alternate-day fasting (MADF) Similar to ADF except allows minimal food during fast (300-500 kCal/d) Modified 5/2 method: Eating 300-500 kCal during 2 nonconsecutive days per week, eating normally for the other five days.
Other types Fasting for religious, spiritual, or other reasons Ramadan fasting from dawn to sunset, typically lasting 11-16 hours.


The table describes intermittent fasting regimens. One form, known as time-restricted feeding (TRE), restricts eating for certain hours in a day such as fasting for 16 hours with an 8-hour feeding window. One can alter the pattern to create a shorter feeding window based on lifestyle preference. Other forms include alternate-day fasting, in which one feeding day is followed by one fasting day. Generally, TRE fasting encompasses fasting from 16-48 hours with little or no energy intake. However, the literature has also reported a daily time-restricted 12- or 14-hour fasting window. Although this fasting method is more prevalent as a weight management regimen, scientists have found different fasting regimens can have more health benefits than weight loss alone.

Brief history and a U-M connection

A black & white formal portrait of Dr. Dewey circa mid-1800s.

Michigan alumnus E.H. Dewey blamed an excess of gastric juices for most diseases afflicting humans. (Image: Wikipedia.)

Fasting can be traced back to the 5th century by the “father of medicine,” Hippocrates. He often prescribed food abstinence (starvation) to people displaying certain health conditions.

In the mid-1800s, E.H. Dewey, M.D., an 1864 graduate of the “College of Medicine and Surgery at the University of Michigan” published the book The True Science of Living: The New Gospel of Health; Practical and Physiological. The text contended that “every disease that afflicts mankind [develops from] more or less habitual eating in excess of the supply of gastric juices.”

His sequel, The No-Breakfast Plan and the Fasting Cure (1900), was a big seller. By 1921, it had gone through three editions with translations in French and German. Dewey argued for people to abstain from breakfast and only consume two meals daily. He attributed all disease and physiological problems to “excessive eating.” He advocated long fasts and believed that abstinence from food could cure insanity and mental disorders.

Dewey was an assistant surgeon in the U.S. Army.

Fasting success

Testimonials and case reports dating back decades suggest the most rapid way to reduce arthritic pain relief and swelling due to rheumatoid arthritis is through intermittent fasting for three months, followed by a plant-based diet (avoiding meat and dairy). The method can be applied to other autoimmune diseases as well. Many reports indicate that when individuals stayed on the plant-based diet following fasting, their arthritis remained in remission. However, these studies represent the weakest evidence type since they often fail to control for the placebo effect (see Health Yourself – “The Mind Drives the Mass”), which is especially important when it comes to relying on self-reported subjective symptoms.

However, there are objective, lab-test inflammation measures that aren’t affected by subjective reporting and that yield the most robust scientific evidence. One comprehensive report pooled data from 31 studies involving intermittent fasting in patients with rheumatoid arthritis and found the results supported the case-study findings. The report included four controlled studies that combined intermittent fasting with subsequent plant-based diets for at least three months. The effects appear to be very robust: Following the three-month fasting/diet protocol, those who remained on the plant-based diet continued to experience reduced pain, stiffness, and tender and swollen joints. The control subjects, in contrast, who continued to eat their regular meat-and-egg diet, continued to suffer symptoms.

An old-fashioned alarm clock sits atop a plate as a metaphor for intermittent fasting.

Research suggests the most rapid way to reduce arthritic pain relief and swelling due to rheumatoid arthritis is through intermittent fasting for three months, followed by a plant-based diet (avoiding meat and dairy). (Image: iStock.)

In the most extensive “observational” fasting study (published in 2019), 1,422 individuals between ages 18 and 99 participated in a supervised modified fast for different periods. The subjects were cleared of any predefined contraindication to fasting (“wasting syndrome”), anorexia nervosa, advanced kidney, liver or cerebrovascular insufficiency, dementia, or other debilitating cognitive disease. Also, prior to and following the fasting period, subjects were put on a vegetarian diet.

During the fasting period, subjects underwent either a five-day fast (659 subjects), a 10-day fast (530 subjects), a 15-day fast (196 subjects), or a 20-day fast (37 subjects). During their fasting periods, subjects were asked to consume three liters of water or non-caloric herbal teas daily with an optional 20 grams of honey. Additionally, an organic, freshly squeezed fruit or vegetable juice (8.5 oz) was served at noon with vegetable soup in the evening. Participants consumed an average of 200–250 kcal and 25–35 grams (0.89–1.1oz) of daily carbohydrates. Researchers also collected much the same data on about 1,000 individuals who were put on a “normal” vegetarian diet without fasting.

The scientists measured weight, abdomen girth, blood pressure, heart rate, well-being, mild symptoms and adverse effects, and major health complaints. They completed laboratory blood tests to assess circulating blood-fat levels, ketone levels (and other autoimmune indices), and kidney and liver complications.

Both the fasting and diet-only groups experienced significant increases in both physical and mental quality of life. Notably, there was no significant difference between the groups regarding 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-type headaches. The fasting group experienced slightly more improvement in most objective measures, but both groups did well, with about 80 percent reporting improvements. About 4 percent of respondents reported feeling worse.

How intermittent fasting works

Understanding how and why different intermittent fasting protocols are successful for so many people is difficult to establish. So many factors are in play at once.

One explanation points to changes in the gut microbiome (see Health Yourself – “Gut Check”). Improvement in symptoms seems to coincide with a significant alteration in the intestinal flora, with subsequent changes to related regions of the brain.

It could be as simple as reductions in eicosanoids, fat-based signaling molecules that play a unique role in the immune response. Multiple eicosanoid types, such as prostaglandins (PGs) and leukotrienes (LTs), permit innate immune cells to respond rapidly to bacterial invaders. They are inflammation mediators formed from arachidonic acid. Arachidonic acid is a long-chain inflammatory omega-6 fatty acid found in highly processed foods and oils like soybean, corn, canola, and cottonseed. The most significant contributors to elevated arachidonic acid levels in humans are chicken and eggs, contributing to nearly half of Americans’ animal-based food intake. Scientists hypothesize that higher eicosanoid (arachidonic acid) intakes may contribute to a neuroinflammation cascade.

That could explain why following an intermittent fasting regimen with a plant-based diet is essential to prevent recurrence of inflammatory activity. Intermittent fasting also can be an effective tool to radically kickstart a change in eating patterns.

Takeaway message

A growing body of literature from animal and human studies supports, in some form, periodic intermittent fasting for adults who are overweight and sedentary to promote optimal health and reduce chronic disease risk. Moreover, experiencing intermittent fasting (with dietary changes) may motivate one to add more fruits and vegetables to the daily diet while diminishing animal-based food intake.

A consensus panel of fasting experts concluded in PubMed: “Nutritional therapy is a vital and integral component of fasting. After the fasting therapy and refeeding period, nutrition should follow the recommendations … of a plant-based whole-food diet.”

  • Abbasi, J. “Can a diet that mimics fasting turn back the clock?” JAMA. 2017;318(3):227-229.
  • Barnosky, R., et al. “Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: A review of human findings.” Translational Research. 2014;164(4):302.
  • Beezhold, B.L., et al. “Vegetarian diets are associated with healthy mood states: A cross-sectional study in Seventh Day Adventist adults.” Nutrition Journal. 2010;9:26.
  • Beezhold, B.L., Johnston C.S. “Restriction of meat, fish, and poultry in omnivores improves mood: A pilot randomized controlled trial.” Nutrition Journal. 2012;11:9.
  • Brandhorst, S. et al. “A periodic diet that mimics fasting promotes multi-system regeneration, enhanced cognitive performance, and healthspan.” Cell Metabolism. 2015;22(1):86-99.
  • Collier, R. “Intermittent fasting: The science of going without.” Canadian Medical Association Journal. 2013;185(9):E363–E364.
  • Finnell, J.S. et al. “Is fasting safe? A chart review of adverse events during medically supervised, water-only fasting.” BMC Complementary and Alternative Medicine. 2018;18(1):67.
  • Fuhrman, J., et al. “Brief case reports of medically supervised, water-only fasting associated with remission of autoimmune disease.” Alternative Therapies in Health and Medicine. 2002;8(4):112, 110-1.
  • Goldhamer, A., et al. “Chapter 37 Fasting. In: Pizzorno J, Murray M, eds. Textbook of Natural Medicine.” (4th ed.) Churchill Livingstone; 2013.
  • Gustafson, C., et al. “Water fasting — The clinical effectiveness of rebooting your body.” Journal of Integrated Medicine (Encinitas). 2014;13(3):52-7.
  • Johnstone, A.M. “Fasting: The ultimate diet?” Obesity Reviews. 2007;8(3):211-222.
  • Kjeldsen-Kragh, J., et al. “Vegetarian diet for patients with rheumatoid arthritis — Status: Two years after introduction of the diet.” Clinical Rheumatology. 1994;13(3):475-82.
  • Longo, V.D., Mattson, M.P. “Fasting: Molecular mechanisms and clinical applications.” Cell Metabolism. 2014 Feb 4;19(2):181-92.
  • Mattson, M.P., et al. “Impact of intermittent fasting on health and disease processes.” Ageing Research Reviews. 2017;39:46-58.
  • Michalsen, A., et al. “In-patient treatment of fibromyalgia: A controlled nonrandomized comparison of conventional medicine versus integrative medicine including fasting therapy.” Evidence-Based Complementary and Alternative Medicine. 2013;2013:908610.
  • Michalsen, A., et al. “Incorporation of fasting therapy in an integrative medicine ward: Evaluation of outcome, safety, and effects on lifestyle adherence in a large prospective cohort study.” The Journal of Alternative and Complementary Medicine. 2005 Aug;11(4):601-7.
  • Michalsen, A., Li, C. “Fasting therapy for treating and preventing disease: Current state of evidence.” Forsch Komplementarmed. 2013;20(6):444-453.
  • Müller, H., et al. “Fasting followed by vegetarian diet in patients with rheumatoid arthritis: A systematic review.” Scandinavian Journal of Rheumatology. 2001;30(1):1-10.
  • Wang, Y., Wu, R. “The effect of fasting on human metabolism and psychological health.” Disease Markers. 2022 ;2022:5653739.
  • Wilhelmi De Toledo, F., et al. “Fasting therapy: An expert panel update of the 2002 consensus guidelines.” Forsch Komplementarmed. 2013;20(6):434-443.
  • Wilhelmi de Toledo, F., et al. “Safety, health improvement, and well-being during a 4- to 21-day fasting period in an observational study including 1422 subjects.” PLoS One. 2019 Jan 2;14(1):e0209353.
  • Zhou, J., et al. “Dynamical alterations of brain function and gut microbiome in weight loss.” Frontiers in Cellular and Infection Microbiology. 2023;13:1269548


  1. Craig Tillman - 1983 Physical Therapy 1986 Kinesiology

    Thanks Dr. Katch for the very informative and insightful article. As you are aware, this topic is particularly impactful during this time of the proliferation of weight loss medications seen by some as viable options for weight loss and wellness. I remain intrigued as well by the concept of Autophagy with respect to cellular changes and repair, augmentation of the immune response, life extension and longevity. I greatly enjoyed your Advanced Exercise Physiology, F-604 class in 1986. The discussions regarding “The Scaling of Metabolic Variables” were quite interesting. I am also grateful to have served as a representative of Michigan Kinesiology for the Vic Tanny educational initiative.

    Be Well


  2. David Brown

    Excerpt from the article: “Arachidonic acid is a long-chain inflammatory omega-6 fatty acid found in highly processed foods and oils like soybean, corn, canola, and cottonseed.”
    That’s incorrect. Seed oils contain linoleic acid but not arachidonic acid.

    Another excerpt: “The most significant contributors to elevated arachidonic acid levels in humans are chicken and eggs, contributing to nearly half of Americans’ animal-based food intake. Scientists hypothesize that higher eicosanoid (arachidonic acid) intakes may contribute to a neuroinflammation cascade.”
    That statement is correct. Current average intakes of grain-fed poultry products are problematic for humans.
    (web searches – Dietary arachidonic acid as a risk factor 2016, Kevin Harvatine omega-3 poultry, Poultry Consumption and Human Cardiometabolic Health, Anna Haug Individual Variation.


Leave a comment: