 I've made videos about cannabis, HIV, circumcision, raw food diets, evolution, GMO, and food additives. All very controversial topics. I've become very comfortable with angry criticism and trolls. Yet I know that this topic is very close to religion for some people. It defines who and what they are, and they don't like criticism, in the same way that religious people don't like critical examination of their beliefs. I'm talking about vegetarians. A full review of the topic will have to wait for another day. Ethical vegetarians make their dietary choice on a desire not to harm animals, which is fine with me. It's a personal ethical choice. The science has little to say on the topic. However, I want to just address the health argument. Do western vegetarians live longer, have less cancer, and heart disease. In this slide, I present a systematic review of the only five large studies to compare vegetarian and non-vegetarian matched populations. It's an article in the American Journal of Clinical Nutrition, but the authors are from the UK, Germany, New Zealand, and California. The five studies chosen, shown here, are all large population perspective studies, which means they enrolled people in the study, then followed the course of their lives for some period, and they monitored deaths. Usually this means phone interviews on some schedule. The alternative is retrospective studies, where the death statistics are examined in hindsight. Combining across all these studies gives a pool of more than 76,000 people, almost 28,000 of which were vegetarians. They paired vegetarian and non-vegetarians up on several factors like age, sex, and smoking. They then tested to see if there was a confounding effect, like one of the two diet groups had more drinking or were heavier to begin with. The potential confounders tested were body mass index, alcohol use, education level, and exercise level. Vegetarians were, in general, thinner, drank less alcohol, smoked less, and exercised more, but these differences couldn't statistically be used to explain the results. The end points, the outcomes being monitored for were stomach cancer, colorectal cancer, lung cancer, female breast cancer, prostate cancer, ischemic heart disease, cerebral vascular disease, all other causes and all causes combined. There's a great deal of discussion of statistics, which is typical of this kind of epidemiology, but I'm going to skip it and just say that the authors are applying the best methodology they could to the dataset, which is a cymbal piecemeal from several different study populations. Let's get to the results. After a mean of 10.6 years of follow-up, there were 8,330 deaths before age 90 years, where they set the cut off. If they broke up the population by how long they had been vegetarians, less than five years had some serious increase in risk from almost everything. The authors suggested that this might be people who switched to vegetarian diets as a result of some health problems or to make up for a lifetime of bad dieting, smoking, or previous heavy drinking, although they weren't able to demonstrate this. Longer than five years as a vegetarian is where we see the most obvious benefit. Vegetarians had a 24% lower mortality from ischemic heart disease than non-vegetarians. Ischemia has reduced blood flow in the heart, usually as a result of fatty plaques in the blood vessels. It's linked to high serum cholesterol, diabetes, and genetics, so it makes sense that a high-fiber, low-fat diet, like the standard western vegetarian diet, would reduce risk. If we break the data out a little further and compare strict vegans to lacto-ova vegetarians, or even people who eat fish but not red meat, or people who eat just a little meat like a few times a week, the data gets more interesting. In comparison with regular meat eaters, mortality from ischemic heart disease was 20% lower in occasional meat eaters, 34% lower in people who ate fish but not meat, 34% lower in lacto-ova vegetarians, and 26% lower in vegans. So eating a little dairy and eggs or only fish was more protective for the heart than strict veganism, which actually makes a lot of sense. Cold water fish contain the omega fatty acids that can aid in healthy lipid metabolism, and most vegans have vitamin B deficiencies that can lead to heart problems in the very long term. I don't want to make too much out of these very small differences. I don't think veganism has been forever discredited. It's still much safer for your heart than regular meat eating. But a little meat or some fish plus a diet high in veg and fruit is probably your best choice for heart health. If you are an ethical vegan, make sure you're getting vitamin B supplements. What about cancers and all causes mortality? For the most part, the noise was too large to pick out any differences. There are some really big differences in average risk but the range in the values overlapped one, meaning that if there was an effect it couldn't be determined. What was surprising was the lack of risk reduction in areas like colon cancer, breast cancer, and stomach cancer. These are known to have a dietary component in their etiology. The authors extend a possible explanation that it's not so much the lack of meat as the increased fruit and vegetables that are preventative. I'm not sure I follow their logic there but it's an interesting perspective. This study had some shortcomings, most notably that it combines data from such diverse studies and populations. The populations are large but not large enough to really get to the heart of whether vegetarians really have improved quality and quantity of life. It's still an interesting study and I think of it when I encounter vegetarian propaganda. I'll leave it to the authors to have the final word. In conclusion, vegetarians had a 24% lower mortality from ischemic heart disease than non-vegetarians but no associations of a vegetarian diet with other major causes of death were established. Thanks for watching.