Amidst the world's sorrow watching Hurricane Dorian pound the Bahamas, headlines started appearing in the media with almost the same force reporting that vegetarian and vegan diets may increase stroke risk.
Some of the headlines were more responsible than others in reflecting the actual published data, but the debate for steak or sprouts was fueled once again. What was the reason for this turmoil and what were some of the nuances headlines do not reveal?
1. The Study
The study was summarized in the British Medical Journal below:
“The EPIC-Oxford study, a cohort in the United Kingdom with a large proportion of non-meat eaters, recruited across the country between 1993 and 2001.
"Participants 48 188 participants with no history of ischaemic heart disease, stroke, or angina (or cardiovascular disease) were classified into three distinct diet groups: meat-eaters (participants who consumed meat, regardless of whether they consumed fish, dairy, or eggs; n=24 428), fish eaters (consumed fish but no meat; n=7506), and vegetarians including vegans (n=16 254), based on dietary information collected at baseline, and subsequently around 2010 (n=28 364).
"Main outcome measures Incident cases of ischaemic heart disease and stroke (including ischaemic and hemorrhagic types) identified through record linkage until 2016.
"Results Over 18.1 years of follow-up, 2820 cases of ischaemic heart disease and 1072 cases of total stroke (519 ischaemic strokes and 300 hemorrhagic strokes) were recorded. After adjusting for sociodemographic and lifestyle confounders, fish eaters and vegetarians had 13 percent (hazard ratio 0.87, 95 percent confidence interval 0.77 to 0.99) and 22 percent (0.78, 0.70 to 0.87) lower rates of ischaemic heart disease than meat-eaters, respectively (P<0.001 for heterogeneity). This difference was equivalent to 10 fewer cases of ischaemic heart disease (95 percent confidence interval 6.7 to 13.1 fewer) in vegetarians than in meat-eaters per 1000 population over 10 years. The associations for ischaemic heart disease were partly attenuated after adjustment for self-reported high blood cholesterol, high blood pressure, diabetes, and body mass index (hazard ratio 0.90, 95 percent confidence interval 0.81 to 1.00 in vegetarians with all adjustments). By contrast, vegetarians had 20 percent higher rates of total stroke (hazard ratio 1.20, 95 percent confidence interval 1.02 to 1.40) than meat-eaters, equivalent to three more cases of total stroke (95 percent confidence interval 0.8 to 5.4 more) per 1000 population over 10 years, mostly due to a higher rate of haemorrhagic stroke. The associations for stroke did not attenuate after further adjustment of disease risk factors.
"Conclusions In this prospective cohort in the UK, fish eaters and vegetarians had lower rates of ischaemic heart disease than meat-eaters, although vegetarians had higher rates of hemorrhagic and total stroke.”
As can be seen, a combined group of vegetarian and vegans experienced a drop in heart attacks and other manifestations of ischemic heart disease compared with meat-eaters that was offset by a smaller rise in a particular type of stroke, hemorrhagic or bleeding, that still favored the health benefits of the vegetarian and vegan diet group.
2. The Data Acquisition
The participants filled out a 130-question survey on their diet on entry between 1993 and 2001 and again repeated the same survey in 2010. An interesting finding reported in the study was that only 28.364 of the original 48.188 filled out both surveys 14 years apart on average. Of those respondents, 96 percent of the meat-eaters remained meat eaters but only 57 percent of fish eaters remained fish eaters and 73 percent of vegetarians remained vegetarians. It was not reported which group they moved to.
3. Where Vegan and Vegetarian Diets Similar?
One has to go to Supplement attached by the link to the article to identify how many vegetarians and vegans were lumped together in the 16,254 members of that group. There were 1,832 vegans and 14, 422 vegetarians. Their diet was very different as shown below with a much higher saturated fat intake as a percentage of calories in the vegetarians and surprisingly low fiber intake in both of the plant groups that as not much higher than the meat-eaters.
4. How Many Hemorrhagic Strokes vs. Heart Attacks Actually Occurred in Vegans?
The Supplement to the study also holds the fact that there were only eight hemorrhagic strokes in the vegans. While always tragic, this is the number that is generating the headlines but not being reported. If there were seven would it reach statistical significance? Or six? And this is compared to the thousands of cases overall of heart attacks and ischemic heart disease events that were significantly less frequent in the vegans.
5. What Did the Authors Conclude?
What is already known on this topic
· Vegetarian and vegan diets have become increasingly popular in recent years, but the potential benefits and hazards of these diets are not fully understood.
· Previous studies of two diet groups have reported that vegetarians have lower risks of ischaemic heart disease than non-vegetarians.
· However, no evidence has been reported of a difference in the risk of mortality from stroke, possibly because of limited available data and lack of available evidence on stroke subtypes.
What this study adds
· This study showed that fish eaters and vegetarians (including vegans) had lower risks of ischaemic heart disease than meat-eaters.
· Vegetarians (including vegans) had higher risks of hemorrhagic and total stroke than meat-eaters.
· Further research is needed to replicate these results in other populations and to identify mediators that might contribute to the observed associations.
Nutrition science is difficult, and the EPIC-Oxford Research Study is a respected group of scientists. However, headlines and even more complete media articles generally provide superficial understanding of the data and even promote inflammatory responses by irresponsible headlines (e.g. ignoring the cardiac benefits of the plant diets). My recommendation is to continue to load your plate with fresh fruits, vegetables, legumes, and whole grains for your health and the health of the planet. The diet should be very high in fiber and naturally very low in calories from saturated fats.
This article was originally published on Medium by Dr. Joel Kahn