By Rylee Price, Samantha Schilling, and Laura Wild; edited by Tara Talebi-Talghian
You may know people who are vegetarians and, at one time or another, have tried to convince you to try it out. They talk about ethical reasons and the environmental benefits of vegetarianism—but what about the health benefits? Is it actually a better option for a long and healthy life? Well, it turns out that the evidence is a bit unclear. Let us explain:
The benefits of eating more fruits and vegetables may be obvious, but because a vegetarian diet excludes protein from animal meat, some worry that certain nutrients (like protein) may be lacking. But vegetarian diets are high in plant-based proteins and low in fats, and this may compensate for the lack of animal protein and be quite healthy (if done properly). Still, it’s unclear how such diets may affect health in the long run, partly because it’s impossible for researchers to follow people over their entire lives. One way that scientists approach this problem is to follow a group of people over a shorter time (10 years for example), record what happens to people during that time, and see if those eating a vegetarian diet are more or less likely to develop any diseases (or even die). The technical term for this is calculating the “mortality risk” associated with a diet or behavior over time. So, one good question might be: Does eating a vegetarian diet actually decrease mortality risk?
First, What Is Vegetarianism?
Before we start talking about science and mortality risk, let’s review the basics of vegetarianism. There are different kinds of vegetarianism (summarized in the figure below). The most restrictive type is veganism, which excludes all animal products. Less restrictive types of vegetarianism are lacto-ovo, lacto-, and ovo-vegetarianism. These diets all exclude animal meat, but they differ in their inclusion of eggs and dairy. Lacto-ovo includes both eggs and dairy, ovo- includes eggs but excludes dairy, and lacto- includes dairy but excludes eggs. From here on out, we’ll use the term “vegetarianism” to refer to lacto-ovo vegetarianism unless otherwise specified, as this type of vegetarianism is most commonly studied.
A Look at the Evidence
To see what the evidence says about vegetarianism and mortality risk, we systematically looked through scientific studies on the topic (for more details, see “Research Methods” at the end of this article). We found nine studies on the topic, and as you can see from the Table below, most of these found mixed results. All of the studies we looked at were cohort studies, which followed groups of people (vegetarians and nonvegetarians) for a specific amount of time. (Remember, it’s impossible to really follow people over their entire lifespan.)
Of these nine studies, two found that vegetarianism reduced all-cause mortality (risk of dying from any cause) (1, 2), whereas the other seven showed no relationship (3-9). However, even among the studies that showed no impact on all-cause mortality, two studies showed that vegetarianism reduced the risk of dying from specific causes (a.k.a. “cause-specific mortality”), such as cardiovascular disease, respiratory disease, or cancer. Strangely, one study actually found that vegetarianism increased cause-specific mortality (3), but not by much.
Mixed Evidence—What Does it Mean?
To zero in on the impacts of a vegetarian diet on mortality, we took a closer look at the individual studies listed above. Remember, some showed that a vegetarian diet reduced the risk of all-cause and cause-specific mortality (1, 2), whereas others showed no change. Here are a few key examples:
Yay to Vegetarianism?
Scientists in California conducted an observational cohort study on 73,308 Seventh-day Adventists and classified these people as either nonvegetarian, semi-vegetarian, pesco-vegetarian, lacto-ovo vegetarian, or vegan (1). The researchers followed this cohort for six years and found that the vegetarian groups had 9% lower all-cause mortality risk and suffered less frequently from cause-specific mortality compared to nonvegetarian group. Interestingly, this study found that a vegetarian-style diet had a larger benefit for men than women, so it’s not clear that this would apply to everyone.
Another similar study showed that a vegetarian diet reduces risk factors for ischemic heart disease and all-cancers (2). Here, researchers in the UK followed 6115 non-meat eaters (most of whom were lacto-ovo vegetarians, but some of whom ate fish) and a group of 5015 meat eaters for 12 years. They found that non-meat eaters had a 20% lower all-cause mortality rate. However, when researchers accounted for smoking and lifestyle habits, this advantage was less common. Still, non-meat eaters had a 39% lower risk of mortality from cancer and 45% lower cardiovascular disease risk.
Nay to Vegetarianism?
In contrast to the examples above, some studies have shown that a vegetarian diet has no impact on all-cause or cause-specific mortality (4-6, 8, 9). In one such study, a group of German researchers followed 1904 health-conscious people over the course of 21 years (4). At the end of the study, they found no differences between the mortality risks of the vegetarian and non-vegetarian groups. Instead, the greatest predictor of mortality was smoking at the beginning of the study, which doubled mortality risk. This suggests that it’s not diet, but instead other lifestyle factors that influence your longevity (risk of dying, really). However, these researchers did find that among non-vegetarians, eating meat more than three times per week vs. just once per month was associated with almost five times greater risk of developing heart disease. This suggests that limiting the amount of meat you eat may protect against heart disease, even if it doesn’t reduce overall mortality risk.
So, Yay or Nay to Vegetarianism?
Some of the evidence suggests that a healthy vegetarian lifestyle may reduce your risk of heart disease, cancer and all-cause mortality combined. However, the individual studies also show that vegetarian diets can have different impacts on different people. And overall, research on whether or not vegetarianism decreases mortality is fairly mixed. Seven out of nine studies suggest that vegetarianism does not affect all-cause mortality, but two suggest it reduces all-cause mortality by an average of 22.5% (1, 2). Additionally, separate studies show that a vegetarian diet reduces the risk of death from cardiovascular disease by 45% (2), respiratory disease by 63% (7), and cancer by 39% (2). On the other hand, another study suggests vegetarian diets may increase cardiovascular and respiratory mortality by 10% and 9%, respectively (3).
That’s a lot of numbers, so to make things clearer, we calculated the average change in all-cause and cause-specific mortality risk for vegetarians compared to meat eaters for each study, and we summarized this in the figure below. A negative percent change indicates that there is a decreased mortality risk, whereas a positive percent change indicates increased risk.
As you can see above, the data on vegetarian diets and long-term health really are mixed. It also seems likely that vegetarianism may not be the only factor contributing to reduced mortality risk. Instead, the benefits may be a result of the fact that people who adopt vegetarian-type diets simply pay closer attention to what they eat in general. Vegetarians are often more health-conscious than non-vegetarians (2). For example, they may smoke less than the overall population (7), which could reduce their risk of respiratory disease related mortality (7), and effects like this make it hard to say if a vegetarian diet itself is extra protective. Vegetarians’ increased health-consciousness could also contribute to the net decrease in cardiovascular and cancer mortality shown in the data (2), and it’s hard to sort this out, as some of the studies we reviewed did not ensure that people remained on the same diet for the whole time (4, 5, 9). On the other hand, the studies we reviewed were large cohort studies, and this is a good way to look at the long-term effects of health behaviors over time.
Overall, a vegetarian diet may be an effective way to increase your longevity by making you more aware of what you are putting into your body, which can lower your risk for numerous diseases, especially if you combine it with other healthy behaviors. To be clear, it’s not the fountain of youth, but any healthy diet could help you stay healthier longer. And if you are just looking for a new diet in general, you should know that you don’t have to be a vegetarian. There are several other diets such as the Mediterranean or DASH diets that have known health and longevity benefits (and contain lots of vegetables!).
ABOUT THE AUTHORS
Rylee Price, Samantha Schilling, and Laura Wild are students in the Integrative Physiology Department at the University of Colorado Boulder. This paper was reviewed by scientists at CU Boulder.
The authors conducted a systematic review, by searching PubMed using the search terms: “(vegetarian OR plant-based) AND (longevity OR mortality OR lifespan OR healthspan)”. They limited their search to human only studies and to studies written in the English language. Then, they scanned through 183 abstracts looking for relevant articles that included vegetarianism and measured mortality directly. After excluding duplicate studies, they found 9 scientific studies that fit their criteria.
- Orlich, M. J. et al.Vegetarian dietary patterns and mortality in adventist health study 2. JAMA Intern. Med.173,1230–1238 (2013).
- Thorogood, M., Mann, J., Appleby, P. & Mcpherson, K. Risk of death from cancer and ischaemic heart disease in meat and non-meat eaters. Bmj308,1667 (1994).
- Appleby, P. N., Crowe, F. L., Bradbury, K. E., Travis, R. C. & Key, T. J. Mortality in vegetarians and comparable nonvegetarians in the United Kingdom. Am. J. Clin. Nutr.103,218–230 (2016).
- Chang-Claude, J., Hermann, S., Eilber, U. & Steindorf, K. Lifestyle Determinants and Mortality in German Vegetarians and Health-Conscious Persons: Results of a 21-Year Follow-up. (2005).
- Key, T. J. A., Appleby, P. N., Thorogood, M. & Burr, M. L. Dietary habits and mortality in 11 000 vegetarians and health conscious people: Results of a 17 year follow up. Bmj313,775–779 (1996).
- Key, T. et al.Mortality in British vegetarians: results from the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford). Am J Clin Nutr89,1613S–9S (2009).
- Kinlen, L. J., Hermon, C. & Smith, P. G. A proportionate study of cancer mortality among members of a vegetarian society. Br. J. Cancer48,355–361 (1983).
- Li, S. et al.Low carbohydrate diet from plant or animal sources and mortality among myocardial infarction survivors. J. Am. Heart Assoc.3,1–12 (2014).
- Mihrshahi, S. et al.Vegetarian diet and all-cause mortality: Evidence from a large population-based Australian cohort – the 45 and Up Study. Prev. Med. (Baltim).97,1–7 (2016).