Quantifying the Effects of a Five Day Fast for Comparison with Fasting Mimicking and Calorie Restriction

One of the more interesting developments of recent years in work on the beneficial effects of calorie restriction in humans is the establishment of an optimal boundary of reduced calorie intake. Can one obtain near all the benefits of fasting by eating a little, and how much is "a little" in this context? That question led to the fasting mimicking diet, supported by evidence for "a little" to be something like 750 calories per day for an averagely sized human, when considering a five day fast or low-calorie diet. As researchers note here, improvements in many metabolic parameters are not very different when considering fasting versus a fasting mimicking low calorie intake on this time frame. A range of other topics are also under exploration, such as how long the benefits to metabolism last following a fast, how long one has to fast to obtain those lasting benefits, how frequently to fast, and so forth. But it is always good to see an accumulation of more data and more robust data on these topics.

Fasting is known to have many health benefits such as prolonging lifespan and suppression of tumorigenesis. In the present study, we systematically evaluated the effects of water-only fasting on metabolic-syndrome and age-related risk markers in 45 normal-weight individuals. As shown, a 4.59 kg reduction in body weight, 9.85 cm reduction in waist circumference, and 1.64 kg/m2 reduction in body mass index (BMI) were observed during a 5-day water-only fast. After refeeding for 1 month (day 38), body weight, waist circumference, and BMI were still lower than the baseline level.

Blood pressure (BP) significantly declined during water-only fasting with diastolic BP declining more than systolic BP and gradually both increased to the baseline level by 98 days. Considering many fasting studies showed diastolic BP reduction did not exceed systolic BP reduction, future studies are needed on water-only fasting and BP reduction. Insulin dropped approximately 2.8-fold lower than the baseline level during water-only fasting. Insulin-like growth factor 1 (IGF-1) decreased by a total of 26% during water-only fasting and decreased more in females than males.

The number of pan T cells, CD4+T cells, CD8+T cells, and B cells decreased during water-only fasting. In contrast, the frequency of Treg cells significantly increased during fasting and still exceeded the baseline level 3 months after refeeding. This is an important benefit, since Treg cells have anti-inflammation effects. With regard to thyroid hormones, T4 increased rapidly during fasting, whereas T3 and TSH decreased. The decreased level of T3 during water-only fasting is of particularly importance since a low T3 level, without impairing thyroid function, is strongly associated with longevity.

The present study suggested that water-only fasting for many parameters was similar to calorie restriction and a fasting-mimic diet.The results of the present study are very promising as 5-day water-only fasting has many critical beneficial effects without toxicity.

Link: https://doi.org/10.1002/ctm2.502


I'm not a believer that every calorie is the same.

If you just ate 750 cals of fructose I'd expect very different (and more harmful) effects!

Posted by: Robert Read at September 9th, 2021 12:51 PM

Thanks for posting this great work! I don't know why, but my fasting has been harder these days (maybe house full of delicious cooking smells?) . I needed this motivation.

Posted by: Thomas Mark Schaefer at September 9th, 2021 12:55 PM

So the number of T cells, CD4+T cells, CD8+T cells, and B cells decreased. I can't say I really understand the diagrams in the paper. From a laymen's perspective, it looks like they never got back to baseline by day 98. If I am reading this correctly, is this a good or bad thing? I think fasting dropped my wbc count by one third and below reference ranges at one point.

Posted by: Brad at September 10th, 2021 2:33 PM
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