More people than ever take fish oil dietary supplements—around 8% of US adults in 2012 compared with around 5% five years earlier, according to the National Center for Health Statistics. But a recent meta-analysis of 10 large clinical trials came to a disappointing conclusion: The popular capsules do little to protect patients with heart disease. The findings are at odds with advice from the American Heart Association (AHA), including a 2017 science advisory recommendation to consider fish oil supplementation for patients with a recent myocardial infarction, or heart attack.