As a vegan, I prefer to avoid fish and fish-oil supplements. Are algae pills that contain some of the same omega-3 fatty acids a good substitute? —H.W., Philadelphia

Probably not. Clinical trials have shown that the omega-3 fatty acids DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) in fish and fish oil reduce heart-attack and stroke risk. But algae supplies only DHA, which alone has not been proved to reduce cardiovascular risk.While your body can manufacture DHA and EPA from alphalinolenic acid—found in flax and certain vegetable oils—researchers haven’t determined whether getting omega-3s from those vegetarian sources is adequate to reduce risk. The best documented way for nonfish eaters to protect against heart attack and stroke through diet is to consume lots of plant foods, including leafy greens, nuts, and whole grains, while limiting intake of trans and saturated fats and cholesterol.