There are many reasons to follow a vegan, or the newest trend, “seagan” diet, which includes fish. Many studies have shown significantly lower rates of cancer and heart disease in vegans and pescatarians (vegetarians who eat fish) than in people eating a meat-based diet. And for vegans, it is a choice to avoid harm to animals by eating only plant-based foods.

There’s another benefit to eating a plant-based diet. Because our environment has become contaminated by decades of industrial production, there are no truly pollutant-free places left on the planet, with some places more contaminated than others. Although both plants and animals are exposed to pollutants such as PCBs, mercury, and dioxins, animals like cattle and chickens accumulate these chemicals at up to a million times higher levels than plants and store them in their fatty tissues. Fish also accumulate pollutants at high levels when they’re reared in contaminated environments.

Consequently in addition to what we’re exposed to in our environments, eating animal products that are high in fats like meat, cheese, and butter greatly increase the transfer of these pollutants into our bodies. This is of concern because these toxins are harmful to our neurological and reproductive health.

So why would vegans eat fish? Adding seafood to a plant-based diet can help you overcome nutritional deficits like inadequate levels of the brain-healthy omega-3 fats eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Although plants like walnuts and flax have omega-3 fats, it is primarily alpha-linoleic acid (ALA) instead of EPA and DHA and studies have not shown links between consuming ALA to improved brain health.

If your concern as a vegan is to avoid animal-based products or you want to reduce your exposure to fat-based contaminants, then you can choose to include algal sources of fats in your diet, either through supplements, or eating sea-based veggies like kelp. Because algae are plants, they are often much less contaminated than fish. Just make sure you’re choosing products that have been grown in clean waters.

However, if you want to include fish in your diet, these are the best steps to take to avoid getting a hefty dose of toxic chemicals along with your meal:

1. Eat lower on the food chain. Small fish like sardines and herring tend to have lower levels of toxins than predator fish and, if you like tuna, go for “canned light” over albacore or ahi, which have higher levels of the neurotoxin mercury.
2. Choose wild-caught fish from cleaner waters (I recommend checking one of the great fish consumption guides from the Environmental Defense Fund or the Natural Resources Defense Council).

Bottom line: the more organic, unprocessed, and plant-based foods you include in your diet, the lower your risk of disease and exposure to toxic chemicals so prevalent in our environment. And if you add fish to your vegan diet, make sure you use a guide to choose cleaner options to reduce your exposure to pollutants.