There's a reason why academics no longer use sugar-pills as placebo, because sugar has immediate psychological effects.
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Edit: Just read it, the blog author doesn't understand statistics.
"—Sixteen reports met the inclusion criteria for a total of 23 within-subject design studies. The weighted mean effect size and related statistics for each of the 14 measurement constructs revealed that although the range for these means was from -0.14 for direct observations and up to +0.30 for academic tests, the 95% confidence interval for all 14 mean effect sizes included 0."
So there's a world of difference between "The studies didn't prove X" and "The studies proved X is not true."
To illustrate - I could do a study right now on myself about whether getting hit on the head reduces IQ, and odds are, I wouldn't have enough data to prove anything. Doesn't mean I proved the opposite.
Also, if the article wasn't paywalled I'd be curious how many grams of sugar were given etc, but probably not even worth my time. I also think that a placebo of artificial sweetener is dubious unless we are sure those can't cause behavior changes too.