What Are The Benefits And Risks Of A Vegetarian Diet?
Vegetarian diets are thought to be very healthy. Clinical studies show that vegetarian diets are associated with decreased risk of heart disease, diabetes, cancer, Alzheimer’s disease, and much more. What’s not to like?
That’s why the recent headlines claiming that vegetarian diets may increase the risk of stroke were so surprising. Advocates of meat-heavy diets like the Paleo and Keto diets were overjoyed. These results fit in with their view that we should be eating more meat protein and less plant protein. Nutrition experts, on the other hand, were asking: “What’s going on?” “How can this be?”
Those of you who are regular readers of “Health Tips From the Professor” know that I am an advocate of primarily plant-based diets. Thus, I felt a responsibility to analyze the study (TYN Tong et al, British Medical Journal, 366: 14897, 2019) behind the headlines impartially and give you, my readers, clear guidelines for the healthiest possible diet.
How Was The Study Done?
Let’s start with some background:
· A major study called the “European Prospective Investigation Into Cancer and Nutrition” (EPIC) has been underway since the early 90’s.
· The British component of this study is known as the EPIC-Oxford study.
· While the study has “cancer” in it’s title, it was designed to measure the impact of nutrition on many diseases. In this case, the study focused on heart disease and stroke.
· Finally, enrollment in the EPIC-Oxford study was designed to give a high proportion of vegetarians in the study population.
The EPIC-Oxford study enrolled 48,188 participants with no previous history of heart disease, stroke, or angina between 1993 and 2001. A detailed diet analysis was performed upon enrollment and again in 2010. Based on these data, the participants were divided into three groups:
1) Meat eaters (24,428 participants).
2) Fish eaters (7,506 participants). This group consumed fish but no other meats. People with this eating style are often called pescatarians.
3) Vegetarians (16, 254 participants). This group consumed dairy and eggs, but no meat. People with this eating style are often called lacto-ovo vegetarians.
4) The diet analysis also identified participants who were vegans (no animal foods). However, this group was too small to obtain statistically significant comparisons, so they were included with the lacto-ovo vegetarians in the vegetarian group.
Data on heart disease and stroke were obtained from the UK’s health service records through March 31st, 2016. The average time of follow-up for participants in the study was 18.1 years.
Without going into greater detail, this was a very large, well-designed study.
How Did The Diets Of The Three Groups Compare?
The first step in analyzing this study is to ask how the diets of the three groups compared.
Compared to meat eaters, the fish eaters consumed:
· No meat other than fish.
· Slightly less milk and significantly more cheese.
· Slightly more fruits & vegetables.
· Significantly more legumes & soy foods, nuts & nut butter.
· Slightly more carbohydrate and slightly less protein.
· Slightly less saturated fat and slightly more polyunsaturated fat.
· Around 260 fewer calories per day.
Compared to fish eaters, the vegetarians consumed:
· No meat.
· Slightly less milk & cheese.
· About the same amount of fruits & vegetables.
· Significantly more legumes & soy foods, nuts & nut butter.
· Slightly more carbohydrate and slightly less protein.
· About the same saturated and polyunsaturated fat.
· Around 125 fewer calories per day.
On average, the vegetarians consumed about 1 cup of milk and one ounce of cheese per day. The fish eaters consumed 1.4 ounces of fish per day.
In terms of comparisons:
· The biggest differences were between the fish eaters and the meat eaters. It would be fair to say that the fish eaters consumed a primarily plant-based diet with added fish and dairy.
· The biggest differences between the vegetarians and fish eaters was that the fish eaters got a significant percentage of their protein from fish, while the vegetarians got a significant amount of their protein from plant sources. Otherwise, their diets were fairly comparable.
Finally, the 10-year follow-up diet analysis showed that most participants stuck with their initial diet.
Do Vegetarians Have A Higher Risk Of Stroke?
Now, for the study results:
· Compared to meat eaters, fish eaters had 13% lower risk of heart disease, and vegetarians had a 22% lower risk of heart disease.
o For vegetarians this corresponds to 10 fewer cases of heart disease per 1,000 people over 10 years.
· Compared to meat eaters, vegetarians had a 20% higher risk of stroke, mostly due to an increased risk for hemorrhagic stroke.
o For vegetarians this corresponds to 3 additional cases of stroke per 1,000 people over 10 years.
· The risk of stroke was essentially identical for fish eaters and meat eaters.
In many other aspects, vegetarians were healthier than meat-eaters. For example, they:
· Weighed less.
· Had lower blood pressure.
· Had lower total and LDL cholesterol.
· Were less likely to have developed diabetes during the study.
· Were less likely to have required long-term treatment for other illnesses.
What Are The Strengths And Weaknesses Of The Study?
The strength of this study is obvious. It was a very large, well-designed study. The study also lasted a long time. Participants in the study were followed for almost 20 years.
There are two clear weaknesses, however:
1) Numerous previous studies have confirmed that vegetarian diets decrease heart disease risk by about 20%. However, none of those previous studies have reported an increase in stroke risk. This study is an outlier.
2) There is no clear mechanism that explains why a vegetarian diet might increase stroke risk. Based on previous observations that statin drugs increase the risk of hemorrhagic stroke, the authors suggested the increased stroke risk might be due to lowered LDL cholesterol levels.
This mechanism is speculative at present. Furthermore, if true, it would suggest that any intervention (drug or nutritional) that lowers LDL cholesterol would increase stroke risk.
In the words of the authors:
· “The present study has shown that British adults who were fish eaters or vegetarians had lower risks of heart disease than meat eaters, but that vegetarians had higher risks of stroke.
· Future work should include further measurements…to identify which factors may cause the observed associations. [In plain English: We need to understand how vegetarian diets might increase stroke risk before we put too much weight on the results of this study.]
· Additional studies in other large-scale cohorts with a high proportion of non-meat eaters are needed to confirm the generalizability of these results and assess their relevance for clinical practice and general health.” [In plain English: More studies are needed to confirm this observation before we start changing our recommendations about what constitutes a healthy diet.]
What Are The Benefits And Risks Of A Vegetarian Diet?
Let’s assume for a minute that the results of this study are accurate and take a closer look at the benefits and risks of a vegetarian diet. Here is my assessment:
1) This report is troubling, but it may not be correct. The association of vegetarian diets with a slight increase in stroke risk has only been seen in a single study. This study needs to be confirmed before we become too concerned about vegetarianism increasing stroke risk.
2) On the balance, vegetarian diets should still be considered very healthy. They lower the risk of heart disease, high blood pressure, diabetes, some cancers, inflammatory diseases and possibly even Alzheimer’s disease.
3) However, I have often said that we have 5 food groups for a reason, and it is not a good idea to eliminate whole food groups. In the past, I have used that statement to critique diets that leave out important plant food groups like fruit, whole grains, and legumes.
If the data on stroke risk in this study are true, it suggests it might also not be a good idea to leave out meat. However, you don’t need a lot of meat. The fish eaters in this study were consuming 1.4 ounces of fish per day. That was enough to eliminate the increased risk of stroke.
4) In addition, you don’t have to be a vegan purist to enjoy the health benefits of a primarily plant-based diet. As I describe in my book, “Slaying The Food Myths”, primarily plant-based diets ranging from vegan through pescatarian and semi-vegetarian to Mediterranean and DASH are all incredibly healthy.
I personally follow a semi-vegetarian diet but often recommend Mediterranean and DASH diets to others because they are the easiest primarily plant-based diets for the average American to follow.
5) Finally, if you have a family history, or are at high risk, of stroke, I recommend prudence until we know more. You may wish to adopt a version of primarily plant-based diets that incorporates some meat (That would be in the pescatarian to DASH range of primarily plant-based diets). Your heart will thank you, and you won’t increase your risk of stroke.
The Bottom Line
A recent study enrolled 48,188 British adults; divided them into meat eaters, fish eaters, and vegetarians; followed them for 18.1 years; and looked at their risk for heart disease and stroke. The results were:
· Compared to meat eaters, fish eaters had 13% lower risk of heart disease, and vegetarians had a 22% lower risk of heart disease.
o For vegetarians this corresponds to 10 fewer cases of heart disease per 1,000 people over 10 years.
· Compared to meat eaters, vegetarians had a 20% higher risk of stroke, mostly due to an increased risk for hemorrhagic stroke.
o For vegetarians this corresponds to 3 additional cases of stroke per 1,000 people over 10 years.
· The risk of stroke was essentially identical for fish eaters and meat eaters.
Here is my perspective:
1) This report is troubling, but it may not be correct. The association of vegetarian diets with a slight increase in stroke risk has only been seen in a single study. This study needs to be confirmed before we become too concerned about vegetarianism increasing stroke risk.
2) On the balance, vegetarian diets should still be considered very healthy. They lower the risk of heart disease, high blood pressure, diabetes, some cancers, inflammatory diseases and possibly even Alzheimer’s disease.
3) However, I have often said that we have 5 food groups for a reason, and it is not a good idea to eliminate whole food groups. In the past, I have used that statement to critique diets that leave out important plant food groups like fruit, whole grains, and legumes.
If the data on stroke risk in this study are true, it suggests it might also not be a good idea to leave out meat. However, you don’t need a lot of meat. The fish eaters in this study were consuming 1.4 ounces of fish per day. That was enough to eliminate the increased risk of stroke.
4) In addition, you don’t have to be a vegan purist to enjoy the health benefits of a primarily plant-based diet. As I describe in my book, “Slaying The Food Myths” (https://slayingthefoodmyths.com), primarily plant-based diets ranging from vegan through pescatarian (the fish eaters in this study) and semi-vegetarian to Mediterranean and DASH are all incredibly healthy.
I personally follow a semi-vegetarian diet but often recommend Mediterranean and DASH diets to others because they are the easiest primarily plant-based diets for the average American to follow.
5) Finally, if you have a family history, or are at high risk, of stroke, I recommend prudence until we know more. You may wish to adopt a version of primarily plant-based diets that incorporates some meat (That would be in the pescatarian to DASH range of primarily plant-based diets). Your heart will thank you, and you won’t increase your risk of stroke.
For more details on the study and what it means for you, read the article above.
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.