Today, we begin a four-part series on strokes.
Here’s a fun fact. Did you know that more than 90% of stroke risk is attributable to modifiable risk factors?
Strokes are one of the leading causes of death and disability in the world, the most common cause of seizures in the elderly, and the second most common cause of dementia and a frequent cause of major depression. In short, stroke is a burdensome—but preventable––brain disorder.
According to the Global Burden of Disease Study, the largest study of risk factors for human disease in history, funded by the Bill and Melinda Gates Foundation, more than 90% of the stroke burden is attributable to modiﬁable risk factors, though some are easier to modify than others. For example, about 10% of all healthy years of life lost due to stroke may be due to ambient air pollution. So, yeah, technically that’s a modifiable risk factor; you could just move out of the city to some place with cleaner air. But perhaps easier to just quit smoking, which accounts for 18% of the stroke death and disability––about as much as diets high in sodium. Diets high in salt are as bad as smoking when it comes to stroke burden, but not as bad as inadequate fruit and vegetable consumption. Yes, there’s also other things, like sedentary lifestyles, which is not as bad as not eating enough whole grains, but of the 89% of stroke death and disability that’s attributable to modiﬁable risk factors, fully half appears to be due to just not eating enough fruits and veggies.
Fruit… and vegetable consumption is associated with lower risk of about a dozen different diseases, and stroke is way up there. There appears to be a linear dose-response relationship, a straight-line relationship between more fruits and vegetables and lower stroke risk, suggesting that the risk of stroke decreases by 32% for every 200-gram increase in fruits—that’s just like one apple a day, and 11% lower risk for each equivalent amount of vegetables. Particularly potent: citrus fruits, apples and pears…and dark green leafy vegetables, one of which you can drink: the green leaves of green tea. Drinking three cups of green tea a day is associated with an 18% lower stroke risk.
But association doesn’t necessarily mean causation. Have there ever been any vegetables put to the test in randomized controlled trials? Yes. Garlic is so potent you can stuff garlic powder into a capsule or compress it into a tablet, so you can put it head to head against a sugar pill. And…garlic beat out placebo for the prevention of CIMT progression (meaning the thickening of the major artery walls in the neck going up to the brain, a key predictor of stroke risk), which continued to worsen in the placebo group, but not the garlic group that had been taking just a quarter teaspoon of garlic powder a day. That would cost about a penny a day, and just make your food yummier anyway.
Okay, but has there ever been an interventional trial that actually followed people out to prove that a certain food reduced strokes? Yes, nuts. The PREDIMED study showed that an ounce a day of nuts, which is what I recommend in my Daily Dozen, cut stroke risk nearly in half. But wait, PREDIMED? Wait a second, wasn’t that the study that was retracted? The PREDIMED trial is one of the most influential randomized trials ever, yet in 2018 it was retracted––only to be later republished, after making the necessary corrections, due to irregularities in their randomization procedures. The original paper was withdrawn, but in their reanalysis, they found the same results. The same 46% fall in stroke risk in the added nuts group, dropping the 10-year risk of stroke from about 6% down to 3%.
The good news is that stroke risk can be reduced substantially by an active lifestyle, cessation of smoking, and a healthy diet. All we have to do now is educate and convince people on the beneﬁts that can be expected from healthy lifestyle and nutrition.
In our next story, we look at the relationship between stroke risk and dairy, eggs, meat, and soda.
The large majority of the available evidence is in favor of a protective association between fruit and vegetable consumption and the risk of stroke. The worst foods appear to be meat and soda. Eating, like, a burger for lunch and a pork chop for dinner, two breakfast sausage links, and a typical 20-ounce bottle of soda may increase stroke risk by 60%. Reviewers suggest the meat effect may be the saturated fat or cholesterol, the iron-mediated oxidized fat or the salt, but it could also be the TMAO. The carnitine in meat and the choline in dairy, seafood, and especially eggs is converted by our gut bacteria into trimethylamine, which is oxidized by our liver to TMAO, which may then contribute to heart attacks, stroke, and death.
And indeed, in a 2019 study published in the Journal of the American Medical Association following tens of thousands of Americans for a median of about 17 years, up to a maximum of 31 years, found that “higher consumption of dietary cholesterol or eggs was significantly associated with higher risk of incident cardiovascular disease and all-cause mortality, in a dose-response manner.” Meaning those who ate more eggs or consumed more cholesterol in general appeared to live significantly shorter lives, on average, and the more eggs, the worse it was––and this includes egg consumption and stroke. But that’s not what a meta-analysis funded by the egg industry found.
It turns out such meta-analyses have evidently been flawed by major methodological drawbacks; so, to eat or not to eat? It would seem moderation of egg consumption is called for, along with other sources of dietary cholesterol, given the new study data, which had the advantage of a “longer follow-up than the majority of the previous studies and may [therefore] have provided more power to detect associations.”
Similarly, with meta-analyses of dairy, no apparent link emerged, but evidence of publication bias was found––meaning there appeared to be missing studies, potentially shelved by industry-funded researchers for not showing funder-friendly effects. Researchers studying the relationship between funding sources and conclusions in studies of sugary drinks and milk found that studies funded by the likes of Coca-Cola or the Dairy Council had over seven times the likelihood of coming to funder-friendly conclusions than independent research––which is twice as bad as drug companies. Big Pharma only seems to be able to get away with a three-fold bias. Of particular interest, not a single one of the interventional studies looking at soda or milk ended up with an unfavorable conclusion.
The bottom line is that yes, dairy fat may be better than other animal fats, such as those found in meat, but something like whole grains would be better still––though swapping dairy out for refined grains or added sugar wouldn’t be doing you many favors. When it comes to stroke risk, vegetable fat is better than dairy fat, meat fat is the worst, whole grains are better, and fish fat, added sugars, or refined grains are statistically about the same.
In terms of dietary patterns and stroke, most of the studies on plant-based dietary patterns have found a protective effect against stroke, whereas those looking at Westernized patterns, those based more on animal foods and added sugars and fats, found a detrimental effect of the adherence to Westernized patterns. African-Americans are five times as likely to die from a stroke in middle age, a black/white disparity largely driven by the fact that they’re just having so many more strokes. In this population, a Southern-style diet, characterized by a lot of fried foods and meat, may be playing a role in increasing the risk of stroke, whereas adherence to more plant-based diets may reduce stroke risk.
Yes, wrote the director of the Stroke Prevention & Atherosclerosis Research Centre, “learning to make vegetarian meals every other day is a tall order for most North Americans, but is feasible given tasty recipes and a positive attitude.”
In our final story today, we hear about one of the first studies on the incidence of stroke in vegetarians and vegans.
When ranked in order of importance, among the interventions available to prevent stroke, the three most important are probably diet, smoking cessation, and blood pressure control. Most of us are doing pretty good on smoking these days, less than half of us are exercising enough, but according to the American Heart Association, only one in a thousand Americans are eating a healthy diet, and fewer than one in 10 are even eating a moderately-healthy diet. Why does it matter? Because diet is an important part of stroke prevention. Reducing sodium intake, avoiding egg yolks, limiting the intake of meat, and increasing the intake of whole grains, fruits, vegetables, and lentils. Like the sugar industry, the meat and egg industries spend hundreds of millions of dollars on propaganda––unfortunately, with great success. I was excited to check out box number 1, and was then honored when I did.
The strongest evidence for stroke protection is for increasing fruit and vegetable intake, with more uncertainty regarding the role of whole grains, animal products, and dietary patterns such as vegetarian diets. I mean, one would expect they’d do great. Meta-analyses have found that vegetarian diets lower cholesterol and blood pressure, and enhance weight loss and blood sugar control, and vegan diets may work even better. So, all the key biomarkers are going in the right direction. But, you may be surprised to learn that there hadn’t ever been any studies on the incidence of stroke in vegetarians and vegans…until, now. And, if you think that is surprising, wait until you hear the results.
The risks of heart disease and stroke in meat-eaters, fish-eaters, and vegetarians over 18 years of follow-up. Yes, less heart disease among vegetarians (by which they mean vegetarians and vegans combined); no surprise—been there, done that––but more stroke.
An understandable knee-jerk reaction might be: “Wait a second, who did this study?” But this is EPIC-Oxford, world-class researchers whose conflicts of interest may be more likely to read, “I was a member of the Vegan Society.”
What about overadjustment? If you crunch the numbers over a 10-year-period, they found 15 strokes for every thousand meat-eaters, compared to only nine strokes for every thousand vegetarians and vegans. Wait – so, how can they say there were more strokes in the vegetarians? This was after adjusting for a variety of factors. For example, the vegetarians were less likely to smoke. So, you want to cancel that out by adjusting for smoking, so that you can effectively compare the stroke risk of nonsmoking vegetarians to nonsmoking meat-eaters. If you want to know how a vegetarian diet itself affects stroke rates, you want to cancel out these non-diet-related factors. Sometimes, though, you can overadjust. The sugar industry does it all the time.
This is how it works. Imagine you just got a grant from the soda industry to study the effect of soda on the childhood obesity epidemic. What could you possibly do after putting all the studies together to arrive at the conclusion that there was near zero effect of sugary beverage consumption on body weight? Well, since you know that drinking liquid candy can lead to excess calories that can lead to obesity, if you control for calories, if you control for a factor that’s in the causal chain, effectively only comparing soda drinkers who take in the same number of calories as non-soda-drinkers, then you could undermine the soda-to-obesity effect––and that’s exactly what they did. That introduces overadjustment bias. Instead of just controlling for some unrelated factor, you control for an intermediate variable on the cause-and-effect pathway between exposure and outcome.
Overadjustment is how meat and dairy industry funded researchers have been accused of obscuring the true association between saturated fat and cardiovascular disease. We know that saturated fat increases cholesterol, which increases heart disease risk. Therefore, if you control for cholesterol, effectively only comparing saturated fat eaters with the same cholesterol levels as non-saturated-fat eaters, you see how you could undermine the saturated fat-to-heart disease effect.
So, now let’s get back to this. Since vegetarian eating lowers blood pressure, and a lowered blood pressure leads to less stroke, controlling for blood pressure would be an overadjustment, effectively only comparing vegetarians to meat-eaters with the same low blood pressure. That’s not fair, since that’s one of the benefits of vegetarian eating, not some unrelated factor like smoking. And so, it would undermine the afforded protection. So, did they do that? No. They only adjusted for unrelated factors, like education, and socioeconomic class, and smoking, and exercise, and alcohol. That’s what you want. You want to tease out the effects of a vegetarian diet on stroke risk; you want to try to equalize everything else to tease out the effects of just the dietary choice. And since, for example, meat-eaters in the study were on average 10 years older than the vegetarians, you can totally see how when you adjust for that, vegetarians could come out worse. Since stroke risk can increase exponentially with age, you can see how having nine strokes among a thousand vegetarians in their 40s could be worse than 15 strokes among a thousand meat-eaters in their 50s.
The fact that vegetarians had greater stroke risk despite their lower blood pressure suggests there’s something about meat-free diets that so increases stroke risk it’s enough to cancel out the blood pressure benefits. But, even if that’s true, you still would want to eat that way. Stroke is our fifth leading cause of death, whereas heart disease is #1. So, yes, in this study, there were this many more cases of stroke in vegetarians. But, there were this many fewer cases of heart disease. But, if there is something increasing stroke risk in vegetarians, it would be nice to know what it is, in hopes of figuring out how to get the best of both worlds. This is the question we will turn to, next.