“Eat your almonds,” say some TV ads. “A weapon in wellness,” say others. Don’t get carried away.

Researchers randomly assigned 34 adults with prediabetes and excess weight to eat 50 grams (1¾ oz.) of almonds a day for five months and none for another five months. (The Almond Board of California funded the study and supplied the almonds.)

Contrary to expectations, insulin sensitivity (measured by the gold standard technique), after-meal blood sugar, and fasting insulin levels were worse after the almond-eating period. The participants gained weight and waist size during the almond period, but that didn’t fully explain the drop in insulin sensitivity.

What to do

Eat nuts instead of—not in addition to—other foods.