Eating 45 grams of walnuts every day for a month doesn’t seem to change blood sugar levels in middle-aged white adults who are at risk for metabolic problems, though there was a slight hint of blood sugar going up — but not enough to be sure.

What we've found so far is that eating 45 grams of walnuts daily for four weeks does not appear to meaningfully change blood sugar levels in middle-aged Caucasian adults at risk for metabolic syndrome [1]. Our analysis of the available research shows no clear effect on blood sugar, though there was a slight suggestion of an increase — but not enough for us to say it’s real or consistent [1]. We looked at one assertion from the evidence, drawn from 46 supporting studies, with none that refute it [1]. While the number of supporting studies seems high, we note that they all point to a lack of significant change in blood sugar after four weeks of daily walnut intake [1]. There was no data provided on HbA1c, so we cannot say what effect, if any, walnuts have on longer-term blood sugar markers. The evidence we’ve reviewed focuses only on short-term blood sugar changes. The current analysis suggests that adding walnuts to the diet at this amount and duration doesn’t lower or raise blood sugar in a clear way for this group. However, the slight uptick seen in some measures means we can’t rule out a small effect — it just hasn’t been confirmed with confidence. Our takeaway: For middle-aged white adults at risk for metabolic issues, eating a handful of walnuts every day for a month likely won’t change blood sugar in a noticeable way. It doesn’t seem to hurt, but it also doesn’t seem to help blood sugar control based on what we’ve seen so far.