Eating a small handful of walnuts every day for six months might slightly increase your BMI, but doesn’t seem to change other aspects of your body like muscle or fat in a noticeable way.

What we've found so far suggests that eating about 35g of walnuts daily for six months may be linked to a slight increase in BMI in adults [1]. However, the evidence does not indicate noticeable changes in body composition, such as muscle or fat levels, over that time [1]. Our analysis of the available research shows that consistent walnut consumption at this amount does not appear to lead to meaningful shifts in body fat or muscle, even if BMI goes up slightly [1]. BMI is a measure of body weight relative to height, so an increase could come from added weight that isn’t necessarily fat—such as water, muscle, or even digestive content. Since the evidence does not report changes in actual body fat or lean mass, we can’t conclude that the BMI change reflects fat gain [1]. The data we’ve reviewed leans toward a small rise in BMI with daily walnut intake over half a year, but without clear evidence of how or why that change happens [1]. It’s also worth noting that only one assertion was analyzed, based on 51.0 supporting inputs and none that refute it—though we don’t have details on the quality or design of those inputs [1]. Because our current analysis is limited and focuses only on BMI without deeper measures like body fat percentage, waist circumference, or metabolic health, we can’t say what this small BMI shift means for overall health or body composition. Practical takeaway: Eating a small handful of walnuts every day for six months might nudging your BMI up a little, but it doesn’t seem to change how your body looks or feels in terms of fat or muscle.