Conclusion: Although Probably Healthy, Chris Kresser has important caveats here.
Intermittent Fasting (IF) is an umbrella term for various diets that cycle between a period of fasting and non-fasting. I have compiled some comments and links from the best known, research-focused IF practitioners and included some research papers at the bottom. Let me know what I have missed.
Brad Pilon “Fasting is the simplest method our body has for maintaining its caloric balance. Store a little energy when we eat in excess, burn a little energy when we don’t eat. It’s a very simple approach to getting and staying lean that revolves around the idea that it’s OK to take the occasional break from eating every now and again.”
Mark Sisson – The health benefits of Intermittent Fasting -“fasting once in a while seems to offer many of the same benefits of calorie restriction – you know, stuff like increased longevity, neuroprotection, increased insulin sensitivity, stronger resistance to stress, some cool effects on endogenous hormone production, increased mental clarity, plus more ”
Peter Attia – On trying IF “My performance, especially in light of my reduced training volume (or maybe because of it!) has not deteriorated. In fact, this week I had 3 best times in 3 of the activities I do weekly”.
Dr Rhonda Patrick – “Diet mimicking fasting for 5 days/month boosted stem cells & lowered inflammation, heart disease, & cancer biomarkers. ”
James B Johnson “..recent studies have shown that calorie restriction is only necessary every other day in order to impart the same, and perhaps even greater, health benefits(than calorie restriction).”
Rob Wolf – IF is something that can definitely be beneficial but sleep, performance markers, and stress levels all need to be well taken care of or IF can have some negative results on body composition, performance, and mood.
Christ Masterjohn – “I don’t think practicing intermittent fasting is necessary to be healthy, but I do think it has the potential to lengthen life, prevent cancer and other forms of degeneration, expand dietary flexibility in a practical way, and offer the opportunity for spiritual growth for those interested.”
Martin Berkhan – The Leangains Guide – Arguably the most comprehensively researched public resource on IF, although primarily focused on how to become as lean and strong as possible. “In summary, maintaining blood sugar within a healthy range is very important for individuals with poor glucose tolerance and insulin sensitivity (“prediabetes”)”
Chris Kresser – There’s definitely some research that suggests that it is beneficial for weight loss and also, more particularly, the improvement of metabolic markers, blood sugar, lipids, and things like that. But I think the confusion arises for the same reason that it arises on a number of different subjects — individual circumstances vary.
Saudrine Thuret – IF creates New Brain Cells.
Ray Cronise, NASA Scientist – Cold exposure and fasting book yet to be released. Advocates longer fasts.
Genome Network News – “The first theory says that calorie restriction reduces the amount of glucose that comes into cells over time, curtailing production of free radicals in the mitochondria —organelles that contain many enzymes important for metabolism.
The second theory says that dietary restriction increases life span because it imposes mild stress on the organism. The mouse or rat—or human—who learns to exist on a curtailed diet is better able to cope with more severe stress at the cellular level and to resist diseases that are associated with certain types of stress.”
Scientific American “Occasional fasting increases the levels of “chaperone proteins,” which prevent the incorrect assembly of other molecules in the cell.”….”Fasting also ramps up autophagy, a kind of garbage-disposal system in cells that gets rid of damaged molecules, including ones that have been previously tied to Alzheimer’s, Parkinson’s and other neurological diseases.”
- Research cardiologists at the Intermountain Medical Center Heart Institute are reporting that fasting not only lowers one’s risk of coronary artery disease and diabetes, but also causes significant changes in a person’s blood cholesterol levels.
- “These preliminary findings show promise for the use of IF and ADF as alternatives to CR for weight loss and type 2 diabetes risk reduction in overweight and obese populations”.
- “The hypothesis is that if the body is intermittently exposed to low levels of oxidative stress, it can build a better response to it,” Wegman said
- “We conclude that CR and IF dietary regimens can ameliorate age-related deficits in cognitive function”
- “A Periodic Diet that Mimics Fasting Promotes Multi-System Regeneration, Enhanced Cognitive Performance, and Healthspan.”
- Protect cells, slow tumor growth and reduce side effects of chemotherapy treatment in cancer patients.
Potential Negative Effects
- In rats, it can cause a switch to survival mode and affect reproductive capacity. This study looks like fairly extreme dietary restriction though. It caused 34% loss of body weight in 3-4 months which would be in excess of most of the main IF regimes practiced today.
- Chris Kresser – “Circumstances in which I would be cautious to recommend intermittent fasting include some of the things that Codi mentioned in the question, which is if there is hormone imbalance, if a woman is trying to maximize fertility, unless that woman is really overweight and has blood sugar issues, in which case intermittent fasting may actually move the needle in the positive direction. But if that’s not the case, if weight and insulin and leptin resistance aren’t standing in the way and the woman is just generally trying to maximize fertility, I probably wouldn’t recommend it. If someone has pretty significant HPA axis dysregulation or adrenal fatigue — so that would manifest as feeling tired when you wake up in the morning even if you get enough sleep, having afternoon energy crashes, not being able to fall asleep or stay asleep, your quality of sleep is poor, you have poor stress tolerance, poor exercise recovery or exercise tolerance, these kind of classic signs of — I’m doing air quotes here — adrenal fatigue, in my experience, intermittent fasting usually makes those patients worse.”