Friday April 4 2014
Around 1 in 50 people in the UK are vegetarian
“Vegetarians are 'less healthy and have a lower quality of life than meat-eaters’,'' The Independent reports. A study from Austria suggests there is an association between a vegetarian diet and an increased risk of certain chronic diseases.
But before any meat eating readers start feeling smug, the study provides no proof that vegetarians are in poorer health than meat eaters.
This was an Austrian survey which simply took a group of 330 people put into a general “vegetarian” category (some in this category were not exclusively vegetarian). They were matched with groups of people from three “carnivorous” categories; ranked in terms of total meat consumption.
The groups were then compared on a range of different health and lifestyle measures to see if any differences were observed.
The researchers found various differences; both good and bad.
The “vegetarians” had lower body mass index (BMI) and alcohol intake, but they also had increased prevalence of three chronic diseases: “allergies”, “cancer” and “mental illness”.
The study has numerous limitations, including the cross sectional survey design, where data is taken at a single point in time, so it cannot prove cause and effect.
It could be the case, for example, that people with certain cancers could chose to adopt a vegetarian diet to try and improve their health, rather than a vegetarian diet increasing the risk of developing cancer.
However, as the research included a relatively small sample of only 330 vegetarians, the prevalence of the 18 diseases questioned in this group could differ from another group, meaning these associations with the three diseases could purely be due to chance.
Overall the decision to follow a vegetarian diet or one containing meat remains a personal lifestyle choice, often based on ethical as well as health reasons.
Where did the story come from?
The study was carried out by researchers from Medical University Graz, Graz, Austria. No sources of funding were reported.
The study was published in the peer reviewed, open access medical journal PLOS one and can be read online for free (PDF, 158kb).
Most of the UK media’s reporting on the study does not mention its numerous limitations and that it cannot prove cause and effect.
There were also inaccuracies in reports that vegetarians were 50% more likely to have a heart attack. There was no significant difference between the vegetarian and three carnivorous groups for any cardiovascular diseases questioned – history of heart attack, high blood pressure, stroke or diabetes.
What kind of research was this?
This was a cross sectional study using Austrian survey data collected in 2006/7. It aimed to see whether there was any difference in various health-related variables between people following different dietary habits.
The researchers say that previous research has associated vegetarian and Mediterranean diets with various health benefits and reduced risk of certain diseases.
Meanwhile increased red meat consumption has often been associated with detrimental health effects.
Therefore the researchers aimed to investigate health differences between different dietary habit groups among Austrian adults. The main limitation with this study is that it is only cross sectional and looking at a specific population. It can note associations, but it can’t prove cause and effect. It is possible that the associations seen might be in fact be due to ‘reverse causality’.
Any associations seen could be due to people with health problems switching to diets that are perceived to be healthier, rather than their diet causing health problems.
What did the research involve?
The researchers analysed the diet, health and lifestyle of 15,474 Austrian people aged over 15 years (55% female) who took part in the Austrian Health Interview Survey (AT-HIS) which ran from March 2006 to February 2007. The surveys are carried out every eight years and include a representative sample of the Austrian population (response rate for this survey 63%).
In face-to-face interviews people were asked about socio-demographic characteristics, health related behaviours (including smoking, alcohol and physical activity), BMI, diseases and medical treatments, and also psychological health.
Without a clear definition of the categories being given, people were asked whether they considered their diet to be:
- vegetarian including milk and/or eggs
- vegetarian including fish and/or milk/eggs
- carnivorous but rich in fruits and vegetables
- carnivorous but less rich in meat
- carnivorous rich in meat.
Few people reported that their diet corresponded to one of the vegetarian diets, and therefore all three of these were grouped together. The 330 “vegetarians” were then age- sex- and socioeconomically-matched to one individual from each of three “carnivorous” groups, resulting in a total sample size of 1,320 people.
Assessments of health and diseases included questioning self-perceived health (ranging from 1 very good, to 5, very bad) and functional impairment (1 very to 3 not impaired). They assessed 18 specific diseases (including heart attack, high blood pressure, stroke, cancer, arthritis and mental illness), which were classed as being “present” or “absent”. “Medical treatments” was classed as having consulted a GP or one of seven different specialists in the past 12 months (“consulted” or “not consulted”).
The number of vaccinations was also coded, in addition to looking at preventative care measures such as attending for “preventive check-ups”, “prostate gland check-up”, mammography and smear tests.
They also measured quality of life using the short version of an established questionnaire assessing four domains of physical, psychological health, social relationships and environment.
They then looked at differences between the “vegetarians” and the matched individuals in the three different “carnivorous” groups and their various lifestyle habits and diseases.
In some of the analyses the researchers adjusted for BMI, physical activity, smoking behaviour and alcohol consumption.
What were the basic results?
The researchers found that the “vegetarians” had lower BMI (22.9kg/m2) compared to the three other carnivore groups (23.4 in those with less rich meat, 23.5 in those rich in fruit and veg, and 24.9 in those rich in meat). Looking at lifestyle behaviour, vegetarians drank less alcohol, drinking on 2.6 days of the week in the past month than those in the three carnivore groups who drank on 3 to 4.8 days. They didn’t differ on smoking or physical activity.
Looking at health and disease they found that “vegetarians” tended to self-report poorer health and higher levels of functional impairment. They also reported more chronic diseases overall. Looking at specific diseases, those significantly more common among the vegetarians were:
- “allergies” (31% prevalence compared to between 17 and 20% in the different carnivorous groups)
- “cancer” (5% prevalence compared to 1 to 3%)
- “mental illness” (anxiety and depression only: 9% prevalence compared to 4 to 5%)
“Urinary incontinence” was significantly less common in “vegetarians” (2% vs. 3 to 6% in the different carnivorous groups).
Vegetarians consulted doctors more than those eating a carnivorous diet less rich in meat, but were vaccinated less than all the other carnivore groups. They also made less use of preventative check-ups than those eating a carnivorous diet rich in fruit and vegetables.
They also found that “vegetarians” had a lower quality of life in the domains of “physical health” and “environment” than those consuming a carnivorous diet less rich in meat.
Lower quality of life regarding “social relationships” were also reported in “vegetarians”.
How did the researchers interpret the results?
The researchers conclude that their results show that “a vegetarian diet is associated with poorer health (higher incidences of cancer, allergies, and mental health disorders), a higher need for health care, and poorer quality of life.” They suggest that “public health programs are needed in order to reduce the health risk due to nutritional factors”.
Despite the media headlines, the results from this Austrian cross sectional survey provide no proof that vegetarians are in poorer health than meat eaters.
The study has simply compared a group of people with a “vegetarian” diet with three different groups of people following “carnivorous” diets on a range of different health and lifestyle measures to see if any differences are observed.
The study has numerous limitations:
- The cross sectional study cannot prove cause and effect and that the dietary pattern is responsible for any of these self-reported differences. In fact it is possible the associations seen could be due to ‘reverse causality’: people with existing health problems might have switched to a vegetarian diet that may be perceived to be more healthy.
- Very general categories of “vegetarian” and three “carnivorous” groups were used. As the person’s dietary pattern was self-reported, and the categories were not defined, people grouped into these categories could in reality have had widely different dietary intake patterns, and some people could be incorrectly categorised.
- Very general categories of diseases were used. The researchers questioned the presence of 18 specific diseases, but these do not appear to have been medically verified and seem to have just been classed as being “present” or “absent” without having any idea of what this means (for example whether the person actually met diagnostic criteria for this condition, how long they’d had it, how severe it was, whether it was being treated). They found links with three of these 18 diseases, but considering this study includes a relatively small sample of only 330 vegetarians; it is possible these may be chance observations. A sample of another 330 could have found different disease prevalence.
- Similar to diseases and dietary groups, very crude measures of all health habits and health variables were also used.
- The study includes only an Austrian sample who may have different dietary, health and lifestyle habits from other countries.
Of note, the study found associations between a vegetarian diet and increased risk of “allergies”, “cancer” and “mental illness”, but not cardiovascular diseases.
Overall the decision to follow a vegetarian diet or one containing meat remains a personal lifestyle choice.
For a healthy lifestyle, all people should aim to eat a diet high in fruit and vegetables and low in saturated fats, salt and sugars, moderate alcohol intake, avoid smoking and take exercise in line with current recommendations.
Read more about healthy eating.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.