Did scientists find out that pistachios are the most melatonin-rich food ever recorded? No, that's not true: the study in question has only been done once and has questionable methods. Experts would say this is still an open issue and should not be considered settled science.
The claim appeared in a February 17 2020, Facebook post (archived here) where it was published by Time For Natural Health Care, a Facebook page that claims it's "for educating people about healthy food and healthy lifestyle." It opened:
Did you know? Eating just 2 Pistachios before bed...Helps with sleep as they are the most melatonin rich food ever recorded. Eating a whole handful of pistachios is like a high-dose melatonin supplement!
This is what the post looked like on Facebook on April 23, 2021:
(Source: Facebook screenshot taken on Fri Apr 23 15:46:39 2021 UTC)
The study "Dietary Sources and Bioactivities of Melatonin," published in 2017 in the open-access journal Nutrients, found that four types of pistachios had almost 100,000 times more melatonin than other nuts. The results used in this study were taken from another study, "Spectrofluorimetric determination of melatonin in kernels of four different Pistacia varieties after ultrasound-assisted solid-liquid extraction," published in 2014 in the open-access journal Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. The authors of the latter study could not be reached for comment.
Lead Stories asked Dr. Tod Cooperman, an expert on dietary supplements who founded ConsumerLab.com, via phone if he has seen any research confirming that pistachios are the "most melatonin rich food ever recorded."
"That claim was based on a super small study in Iran," he said in an April 24, 2021 phone conversation with Lead Stories. "They said that pistachios have one thousand times more melatonin than a melatonin supplement, which is highly unlikely. We've only seen the study done in 2014, so until we see it repeated again, it's a questionable study with experimental methods that doesn't hold any weight. I would say it's still a pretty open issue. An average melatonin supplement has 0.2 milligrams of melatonin, so to get that same amount from pistachios, you'd have to eat four pistachio nuts. One pistachio has about 25% the amount of melatonin from a supplement."
Reproducibility is a hallmark of sound research. Credible scientists provide their methodology and data for review by peers and a new finding is usually not accepted until independent researchers have reproduced the experiment and found the same outcomes.