Today on the podcast, Part 2 of our Strokes and Diet series.
In our first story, we start out with a story on vegetarians and stroke risk.
The risks of heart disease and stroke in meat eaters versus vegetarians over 18 years of follow-up. Not surprisingly, vegetarian diets were associated with less heart disease––10 fewer cases per 1,000 people per decade compared to meat-eaters––but vegetarian diets were associated with three more cases of stroke. So, eating vegetarian appears to lower the risk of cardiovascular disease by seven overall. But, why the extra stroke risk? Could it just be reverse causation?
For example, when studies have shown higher mortality among those who quit smoking compared to continuing smokers, we suspect reverse causality. When we see a link between quitting smoking and dying, instead of quitting smoking leading to people dying, more likely dying led people to quit smoking. It’s the same reason why non-drinkers can appear to have more liver cirrhosis, because it was their failing liver that led them to stop drinking. This is the so-called “sick-quitter effect.” And, you can see it when people quit meat too.
See how new vegetarians can appear to have more heart disease than non-vegetarians? Well, why would some older person all of a sudden start eating vegetarian? Maybe it’s because they’ve just been diagnosed with heart disease; so, that may be why there appears to be higher rates at first: the sick quitter effect. To control for that, you can throw out the first five years of data to make sure the diet has a chance to start working, and indeed, when you do that, the true effect comes clear: a significant drop in heart disease risk.
So, does that likely explain the apparent increased stroke risk? No, because they still found higher stroke risk, even after the first five years. Huh, okay; then, what’s going on? Let’s dive deeper into the data to look for clues.
There are two main types of strokes: ischemic strokes and hemorrhagic stroke. Most are ischemic strokes, or clotting strokes, where an artery in the brain gets clogged off, as opposed to hemorrhagic strokes, or bleeding strokes, where a blood vessel in the brain ruptures. In the United States, it’s about 90:10; 9 out of 10 strokes are clotting, one out of 10 the bleeding type. And, that’s what the vegetarians appeared to have significantly more of. Now, the vegans didn’t, in fact, statistically have significantly higher risk of any kind of stroke. But, that’s terrible news for vegans—vegans have the same stroke risk as meat-eaters? What’s going on? What’s so increasing their stroke risk that it’s offsetting all their natural advantages? And, the same could be asked of vegetarians.
Even though this was the first study of vegetarian stroke incidence, there have been about a half dozen studies on stroke mortality, and the various meta-analyses have consistently found significantly lower heart disease risk, but the lower stroke mortality was not statistically significant. Now, with this new study, vegetarians can take comfort in the fact that at least they don’t have a higher risk of dying from stroke. But that’s terrible news for vegetarians—statistically vegetarians have the same stroke death rate as meat-eaters? What’s going on? What’s so increasing their stroke rate that it’s offsetting all their natural advantages?
Let’s run through a couple possibilities. If you look at the vitamin D levels of vegetarians and vegans, they do tend to run consistently lower than meat-eaters, and lower vitamin D status is associated with an increased risk of stroke. But who has higher levels of the sunshine vitamin? Those who are outside running around and exercising, and maybe that’s why their stroke risk is better. What we need are randomized studies, and when you look at people who have been effectively randomized at birth to have lifelong lower vitamin D levels just genetically, you do not see a clear indicator of increased stroke risk; so, the link between vitamin D and stroke is probably not cause-and-effect.
And so, in terms of an answer to our question, vitamin D doesn’t seem to fit. We’ll explore some other possibilities, next.
In our next story, we ask – does eating fish or taking fish oil supplements reduce stroke risk?
In my last video, we started to explore what might explain the higher stroke risk in vegetarians found in the EPIC-Oxford study. 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, in markedly lower levels in vegetarians and vegans? About 30% lower in vegetarians, and more than 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. 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., 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 that do it for ethical reasons, like global warming or animals. And, they tend to eat different diets. 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 doughnuts.
In the United States, the primary motivations for meat reduction are health and cost. A middle-class American family is four times more likely to reduce meat for health reasons compared to environmental or animal welfare concerns. But, in the UK, where this stroke study was done, the #1 reason given for becoming 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 disease, a lower risk of dying from all causes put together––but that’s only for healthy plant foods. Eating lots of Wonder Bread, soda, and apple pie isn’t going to do 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 choosing 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.
Finally today, just because you’re eating vegetarian or vegan doesn’t mean you’re eating healthy.
Plant-based diets are associated with a lower risk of cardiovascular disease, mortality, and dying from all causes put together. This study of a diverse sample of 12,000 Americans found that “progressively increasing the intake of plant foods by reducing the intake of animal foods may be associated with beneﬁts on cardiovascular health and mortality…”, but when it comes to plant-based diets for cardiovascular disease prevention, all plant foods are not created equal. Were the vegetarians in the British study that found the higher stroke risk just eating a lot of vegan junk food?
Any diet devoid of certain animal food sources can be claimed to be a vegetarian or vegan diet; so, it’s important to see what they’re actually eating. One of the first things I look at when I’m trying to see how serious a population is about healthy eating is look at something undeniably, uncontroversially bad: soda, liquid candy. Anyone drinking straight sugar water obviously doesn’t have health top of mind. In the big study of plant-based eaters in America, where people tend to cut down on meat for health reasons far more than ethics… flexitarians drink fewer sugary beverages than regular meat-eaters, as do pescatarians, vegetarians, and vegans.
In the UK study, though, where the increased stroke risk was found, where folks are more likely to go veg or vegan for ethical reasons, the pescatarians are drinking less soda, but the vegetarians and vegans are drinking more. I’m not saying that’s why they had more strokes; it just might give us an idea of how healthy the people were eating. In the UK study, the vegetarian and vegan men and women were eating about the same amount of desserts, cookies and chocolate, and about the same total sugar. In the U.S. study, the average nonvegetarian is nearly obese, even the vegetarians are a little overweight, and the vegans were the only ideal weight group. In this analysis of the UK study, though, everyone was about the same weight—in fact, the meat-eaters were skinnier than the vegans. The EPIC-Oxford study seems to have attracted a particularly health conscious group of meat-eaters weighing substantially less than the general population.
Let’s look at some particular stroke-related nutrients. Dietary fiber appears beneficial for the prevention of cardiovascular disease including stroke, and it appears the more the better. Based on studies of nearly a half a million men and women there doesn’t seem to be any upper threshold of benefit; so, the more, the better. More than 25 grams of soluble fiber, 47 grams of insoluble dietary fiber, and you can really start seeing a significant drop in associated stroke risk; so, one could consider these as the minimal recommendable daily intakes to prevent stroke at a population level. That’s what you see in people eating diets centered around minimally processed plant foods. Dean Ornish got up around there with his whole food plant-based diet. Maybe not as much as we were designed to eat, based on the analyses of fossilized feces, but that’s the kind of neighborhood where we might expect significantly lower stroke risk. How much were the UK vegetarians getting? 22.1. Now, in the UK, they measure fiber a little differently; so, that may actually be closer to 30 grams, but not the optimal level for stroke prevention. So little fiber that the vegetarians and vegans only beat out the meat-eaters by about 1 or 2 bowel movements a week, suggesting they were eating lots of processed foods.
The vegetarians were only eating about a half serving more of fruits and vegetables, thought to reduce stroke risk in part because of their potassium content; yet, the UK vegetarians at higher stroke risk were evidently eating so few greens and beans they couldn’t even match the meat-eaters, not even reaching the recommended minimum daily potassium intake of 4700 mg a day.
And what about sodium? The vast majority of the available evidence indicates that elevated salt intake is associated with higher stroke risk. There’s like a straight-line increase in the risk of dying from a stroke the more salt you eat. Even just lowering sodium intake by a tiny fraction every year could prevent tens of thousands of fatal strokes. Reducing sodium intake to prevent stroke: time for action, not hesitation. But, the UK vegetarians and vegans appeared to be hesitating, as did the other dietary groups. All groups exceeded the advised less than 2400 mg daily sodium intake—and that doesn’t even account for salt added at the table, and the American Heart Association recommends under just 1500 a day; so, they were all eating lots of processed foods. So, no wonder the vegetarian blood pressures were only 1 or 2 points lower. And, high blood pressure is perhaps the single most important modifiable risk factor for stroke.
What evidence do I have that if the vegetarians and vegans ate better, their stroke risk would go down? Well, in rural Africa where they were able to nail the fiber intake that our bodies were designed to get by eating so many whole healthy plant foods— fruits, vegetables, grains, greens and beans, their protein almost entirely from plant sources, not only was heart disease, our #1 killer, almost non-existent, so apparently, was stroke, surging up from out of nowhere with the introduction of salt and refined foods to their diet.
Stroke also appears to be virtually absent in Kitava, a quasi-vegan island culture near Australia, where diet was very low in salt and very rich in potassium, because it was a vegetable-based diet. They ate fish a few times a week, but the other 95% or so of their diet was lots of vegetables, fruits, corn, and beans, and they had an apparent absence of stroke, even despite their ridiculous rates of smoking. After all, we evolved eating as little as like less than an 8th of a teaspoon a day of salt and our daily potassium consumption is thought to have been as high as like 10,000 mg. We went from an unsalted, whole-food diet to salty processed foods depleted of potassium whether we eat meat or not.
Caldwell Esselstyn at the Cleveland Clinic tried putting about 200 patients with established cardiovascular disease on a whole food plant-based diet. Of the 177 that stuck with the diet only one went on to have a stroke in the subsequent few years compared to a hundred-fold greater rate of adverse events—including multiple strokes and deaths in those that strayed from the diet. “This is not vegetarianism,” Esselstyn explains. Vegetarians can eat a lot of less-than-ideal foods. This new paradigm is exclusively whole food, plant-based nutrition.
Now, this entire train of thought, that the reason typical vegetarians don’t have better stroke statistics is because they’re not eating particularly stellar diets, may explain why they don’t have significantly lower strokes rates, but that still doesn’t explain why they might have higher stroke rates. Even if they’re eating similarly crappy, salty, processed diets at least they’re not eating meat, which we know increases stroke risk; so, there must be something about vegetarian diets that so increases stroke risk that it offsets their inherent advantages?