 In my last video, we started to explore what might explain the higher stroke risk in vegetarians found in the Epic Oxford study. A lower risk of heart disease and lower risk of cardiovascular disease overall, but higher risk of stroke. We looked into vitamin D levels as a potential mechanism, but that didn't seem to be the case. What about long-chain omega-3s? The fish fats like EPA and DHA found, not surprisingly, markedly lower levels in vegetarians and vegans. About 30% lower in vegetarians and more like half as low in vegans. But according to the most extensive systematic assessment of effects of omega-3 fats on cardiovascular health to date, there is no benefit for stroke. Combining 28 randomized controlled trials, and in fact, there was evidence that taking fish oil didn't help with heart disease or overall mortality either. This may be because on one hand, the omega-3s may be helping but the mercury in fish may be making things worse. That's the constant challenge among public health professionals balancing the benefits with the contaminant risks. For example, dietary exposure to PCBs may be associated with increased risk of stroke. In this study, for instance, neither fish nor intake of PCBs was related to stroke risk. However, at the same fish intake, dietary PCBs were associated with an increased risk of stroke, so the PCB pollutants may be masking the fish benefit. Thus, if we had a time machine and could go back before the industrial revolution and find that fish in an un-polluted state, it might protect against stroke. But looking at the data, if fish really was protected, then we might expect that the pescaterians, those who eat fish but no other meat, to be down here or something, since they would have the fish benefit without the meat risk, but no. And they're stuck out here, so it doesn't seem to be the omega-3s either. Let's take a closer look at what the vegetarians were actually eating. When it comes to plant-based diets for cardiovascular disease prevention, all plant foods are not created equal. There are basically two types of vegetarians, those that do it for their health and those who do it for ethical reasons, for global warming or animals, and they tend to eat different diets. So for example, health vegans tend to eat more fruit and less sweets. You don't tend to see those doing it for health, chowing down on vegan donuts. In the United States, the primary motivations for meat reduction are health and cost. Middle-class American families four times more likely to reduce meat for health reasons compared to environmental or animal welfare concerns. But in the UK, where the stroke study was done, the number one reason given for becoming a vegetarian or vegan is ethics. We know plant-based diets that emphasize higher intakes of plant foods and lower intakes of animal foods are associated with a lower risk of incident cardiovascular diseases, a lower risk of dying from all causes put together, but that's only for healthy plant foods. Eating lots of wonderbread soda and apple pie isn't going to be doing you many favors. For all types of plant-based diets, it's crucial that the choice of plant foods is given careful consideration. We should be using whole grains over refined grains, whole fruits, avoiding trans fats and added sugars. Could it be that the veggie brits were just eating more chips? We'll find out next.