This seems pretty likely to be placebo effect, at least in the human trials which are the only parts of the paper I read. The paper cited [0] pre-registered on clinicaltrials.gov [1] -- which is great and everyone in the field should do so. However, looking at what they pre-registered, we have:

- Two different diet treatment regimes: fasting-like for 3 months followed by Mediterranean diet (FMD), and ketogenic diet (KD).

- Control diet was simply telling people to eat the same way as usual. So there's no real accounting for how well a placebo would do here.

- Measurements included a 54-question survey, adverse event counts, and various lab measurements. These measurements were taken at start, 1-month, 3-month, and 6-month intervals.

The problem then is that what was report was:

- Results of the first half of the first treatment (fasting-like for 3 months) for a subset of the measurements. What if things only worked in the second half? Or if things worked only for KD? So many implicit comparisons here.

- Comparison against the control group at 3 months, with reported p-values. Even though one of the reported measurements was the overall survey results, all of the values reported are p-values without any mention, that I can find, of multiple hypothesis testing across all measurements. This comes despite the fact that for all of the mouse results, they explicitly state they used Bonferroni correction.

- Baseline performance which involved no placebo. How many people would have improved if simply given some bullshit diet? Or if they had simply been given a diet that was vegetarian, or something that gave them the impression it was a treatment? Especially in surveys, placebo effect is a huge thing to look out for. Their more hard metrics like lab results show a more mixed bag with WBC dropping for fasting subjects. Sure, it returns once the 3 months is over, but then the supposed quality of life scores drop; so you can't have it both ways, though their writing makes it sound that way.

I'm not saying it isn't a great result from a bio standpoint. I'm sure the Cell reviewers found the mouse model results compelling. I just don't see any way to conclude the broad sweeping title of the article from the actual content of the paper, and it's unethical to do so without strong evidence.

[0] http://www.cell.com/cell-reports/pdfExtended/S2211-1247(16)3...

[1] https://clinicaltrials.gov/ct2/show/NCT01538355?term=NCT0153...