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  1. The more I read the more I come to a more conservative position on this topic Most eye opening is the synopsis here ( sorry, no full text available): https://www.ncbi.nlm.nih.gov/pubmed/26374764 In essence, most of the benefits of fasting arise and reach near maximal levels within the first 12-24 hours of fasting: lower average fasting glucose, lower average fasting insulin, increased insulin sensitivity, lower mean CRP / TNF-alpha / IL-6 inflammation as well as near peak levels of autophagy by the end of each day's fasting cycle That being the case, I don't see how regular 5 day water fasts improve upon this unless they carry additional benefits. For the sake of discussion, let's leave out caloric restriction as a benefit as this can be achieved in either or neither regimen). In other words, if 20/4 intermittent fasting is a (mostly) daily ritual, the cumulative influence of daily spurts of of autophagy may not benefit any more from performing an annual or semi-annual or perhaps even monthly 5-day fast. It appears that longer (e.g. 3-5 day+ fasts) do temporarily do several additional and unique things that daily 20/4 intermittent fasting has not been demonstrated to do: For example, a higher level of ketosis/ ketone bodies during the fast, and upregulation of sirtuin pathways that take several days to activate. This won't be achieved by daily shorter fasts by itself in the absence of overall caloric restriction. However, I do not see evidence these unique changes achieved with and specific to prolonged fasts are in any way lasting once completing such fasts. Thus while the impact of autophagy (something both daily 20/4 fasts and 5 day fasts both have in common) is expected to persist --- ie, once a cell undergoes apoptosiis, or autophagy eliminates defective proteins or damaged nucleic acid, etc --- in contrast, the things unique to 5 day prolonged fasts such as upregulation of sirtuin pathways are short-term and transient phenomenon. Since the benefits that are accrued by and unique to 5-day fasts appear to be proportional to the time in these pathways, even a monthly 5 day fast is still ~ 5/30 or a bit longer to the extent the cascade does not shut off right away. Less so for less frequent 5-day fasts. So it is not clear to me that 5-day fasts, unless performed very frequently add anything to a 20/4 daily time restricted feeding. The advice "if you are healthy perform a 5 day fast twice a year or quarterly if you are healthy" ( paraphrasing Valter Longo) may not apply if you are already performing daily intermittent fasting. What do you think? Do 5-day fasts add anything unique AND clinically significant above and beyond the potentially benefits of shorter daily ( "intermittent") fasts? Does anyone here practice or feel that the data is supportive of doing both? Edited 2/16/17am
  2. All, I personally don't do extended fasts except on rare occasions (like my last colonoscopy, when I had to go 5 days without food to clear out my colon for imaging). But I do eat in a limited time window, and fast for most of the day and night, both for convenience, and because I believe it to be healthy for a number of reasons (reduced glucose / insulin exposure, increased autophagy, etc). It looks like we can add 'reducing breast cancer recurrence' to the list of benefits of an extended overnight fast, according to a new study [1] in this month's issue of JAMA (popular press story). In a study of 2400 breast cancer survivors, researchers found that waiting more than 13 hours between her last meal or snack in the evening and her first meal in the morning resulted in a 36% reduction in a woman's risk of breast cancer recurrence relative to fasting for less than 13 hours. The women who fasted longer had better markers of glucose control (HbA1C) and increased sleep duration. The researchers think these benefits may have been at least partly responsible for the reduction in breast cancer recurrence. --Dean ------------ [1] JAMA Oncol. 2016 Mar 31. doi: 10.1001/jamaoncol.2016.0164. [Epub ahead of print] Prolonged Nightly Fasting and Breast Cancer Prognosis. Marinac CR(1), Nelson SH(2), Breen CI(3), Hartman SJ(4), Natarajan L(4), Pierce JP(4), Flatt SW(3), Sears DD(5), Patterson RE(4). Free full text: http://oncology.jamanetwork.com/article.aspx?articleid=2506710 Importance: Rodent studies demonstrate that prolonged fasting during the sleep phase positively influences carcinogenesis and metabolic processes that are putatively associated with risk and prognosis of breast cancer. To our knowledge, no studies in humans have examined nightly fasting duration and cancer outcomes. Objective: To investigate whether duration of nightly fasting predicted recurrence and mortality among women with early-stage breast cancer and, if so, whether it was associated with risk factors for poor outcomes, including glucoregulation (hemoglobin A1c), chronic inflammation (C-reactive protein), obesity, and sleep. Design, Setting, and Participants: Data were collected from 2413 women with breast cancer but without diabetes mellitus who were aged 27 to 70 years at diagnosis and participated in the prospective Women's Healthy Eating and Living study between March 1, 1995, and May 3, 2007. Data analysis was conducted from May 18 to October 5, 2015. Exposures: Nightly fasting duration was estimated from 24-hour dietary recalls collected at baseline, year 1, and year 4. Main Outcomes and Measures: Clinical outcomes were invasive breast cancer recurrence and new primary breast tumors during a mean of 7.3 years of study follow-up as well as death from breast cancer or any cause during a mean of 11.4 years of surveillance. Baseline sleep duration was self-reported, and archived blood samples were used to assess concentrations of hemoglobin A1c and C-reactive protein. Results: The cohort of 2413 women (mean [sD] age, 52.4 [8.9] years) reported a mean (SD) fasting duration of 12.5 (1.7) hours per night. In repeated-measures Cox proportional hazards regression models, fasting less than 13 hours per night (lower 2 tertiles of nightly fasting distribution) was associated with an increase in the risk of breast cancer recurrence compared with fasting 13 or more hours per night (hazard ratio, 1.36; 95% CI, 1.05-1.76). Nightly fasting less than 13 hours was not associated with a statistically significant higher risk of breast cancer mortality (hazard ratio, 1.21; 95% CI, 0.91-1.60) or a statistically significant higher risk of all-cause mortality (hazard ratio, 1.22; 95% CI, 0.95-1.56). In multivariable linear regression models, each 2-hour increase in the nightly fasting duration was associated with significantly lower hemoglobin A1c levels (β = -0.37; 95% CI, -0.72 to -0.01) and a longer duration of nighttime sleep (β = 0.20; 95% CI, 0.14-0.26). Conclusions and Relevance: Prolonging the length of the nightly fasting interval may be a simple, nonpharmacologic strategy for reducing the risk of breast cancer recurrence. Improvements in glucoregulation and sleep may be mechanisms linking nightly fasting with breast cancer prognosis. PMID: 27032109