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This is not the only study to look at the arterial walls of those eating plant-based diets. This new study from China, for example, found that compared to omnivores, those that ate egg-free and meat-free diets had all the typical benefits of eating more plant-based: lower body mass index, blood pressure, triglycerides, total cholesterol, bad cholesterol; fewer free radicals; maybe better kidney function, better blood sugar control, etc. But, does all that translate to actual differences in their arteries? Yes. Indeed, the omnivores had comparatively thickened arterial linings—all of which suggests about a tripling in the probability of developing cardiovascular disease. They therefore “recommend that more vegetables should be eaten instead of meat,” and it’s “never too late” to improve one’s diet.

Having said that, if those on plant-based diets don’t get enough vitamin B12, levels of an artery-damaging compound called homocysteine can start to rise in the bloodstream, and may counteract some of the benefits of eating healthy. In this study from Taiwan, the arteries of vegetarians were just as stiff as those of the omnivores, and they had the same level of thickening in their carotid arteries—perhaps because of the elevated homocysteine levels in their blood.

“The negative findings of these studies should not be considered as evidence of neutral cardiovascular effects of vegetarianism, but do indicate an urgent need for modification of vegan diets through vitamin B12 fortification or supplements.” “[V]itamin B12 deficiency is a very serious problem, leading ultimately to anemia, neuropsychiatric disorders, irreversible nerve damage,” and these high levels of artery-damaging homocysteine in the blood. “Prudent vegans should include sources of vitamin B12 in their diets.”

One study of vegetarians whose B12 levels were really hurting even had thicker, more dysfunctional arteries than the omnivores. How do we know B12 was to blame? Well, when they were given B12 supplements, they got better. Their arterial lining started to shrink back, and the proper functioning of their arteries returned.

Without B12-fortified foods or B12 supplements, when omnivores are switched to a vegan diet, they develop vitamin B12 deficiency. Yes, it may take dropping down to around 150 picomoles per liter to develop classic signs of B12 deficiency—like the anemia, and our spinal cord rotting from the inside out. But, way before that, we may start getting increased risk of cognitive deficits and brain shrinkage, stroke, depression, and nerve and bone damage, as well as having our homocysteine shoot through the roof. And, that may “attenuate the beneficial effects of a vegetarian diet on cardiovascular health.” “The beneficial effects of vegetarian diets on [cholesterol and blood sugars] need to be advocated,” but, at the same time, “efforts to correct vitamin B12 deficiency in vegetarian diets can never be overestimated.”

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