The findings challenge previous research that suggests eating more vegetables is linked to a lower risk of heart attack, stroke and death.
21 February 2022
Packing your diet full of vegetables does not protect against heart disease, a new study suggests.
The findings challenge previous research that suggests eating more vegetables is linked to a lower risk of cardiovascular disease (CVD) – which can lead to stroke, heart attacks, and death.
Researchers say past studies may not have taken into account lifestyle factors such as smoking, drinking alcohol, and meat intake – and socioeconomic factors such as a person’s education, income and wealth.
They add that evidence from previous studies has been inconsistent.
New results from a large-scale UK study shows that a higher consumption of raw or cooked produce is unlikely to affect the risk of CVD.
But the experts stress that eating a balanced diet and maintaining a healthy weight remains important in reducing the risk of major diseases.
Dr Qi Feng, a researcher at the Nuffield Department of Population Health at the University of Oxford, and the study’s lead author, said: “Our large study did not find evidence for a protective effect of vegetable intake on the occurrence of CVD.
“Instead, our analyses show that the seemingly protective effect of vegetable intake against CVD risk is very likely to be accounted for by bias from residual confounding factors, related to differences in socioeconomic situation and lifestyle.”
The researchers used data from 399,586 people (of whom 4.5% went on to develop CVD) enrolled in the UK Biobank study.
When they signed up to the study in 2006-2010, they were asked about their diet, lifestyle, medical and reproductive history, and other factors.
Responses to questions about how many raw and cooked vegetables they ate on average daily were analysed, together with how likely they were to be admitted to hospital from heart attack, stroke, or major CVD, and the risk of death.
Factors such as socio-economic status, physical activity, and diet were also considered.
The researchers assessed whether unknown additional factors or inaccurate measurement of known factors might lead to a misleading statistical association between CVD risk and vegetable consumption.
In the study, the daily intake of total vegetables, raw vegetables, and cooked vegetables was 5.0, 2.3, and 2.8 heaped tablespoons per person.
The researchers found the risk of dying from CVD was about 15% lower for those with the highest vegetable intake compared to the lowest.
However, this apparent effect was substantially weakened when possible socio-economic, nutritional, and health- and medicine-related factors were taken into account.
When these factors were taken into consideration, the effectiveness of using vegetable intake to predict the risk of CVD fell by more than 80%.
According to the scientists, future studies should further assess whether particular types of vegetables or their method of how they are cooked might affect the risk of CVD.
Last author Dr Ben Lacey, associate professor in the department at the University of Oxford, concluded: “This is an important study with implications for understanding the dietary causes of CVD and the burden of CVD normally attributed to low vegetable intake.
“However, eating a balanced diet and maintaining a healthy weight remains an important part of maintaining good health and reducing risk of major diseases, including some cancers.
“It is widely recommended that at least five portions of a variety of fruits and vegetables should be eaten every day.”
Dr Ian Johnson, nutrition researcher and Emeritus Fellow, Quadram Institute Bioscience, said: “This study raises interesting questions about the relative importance of the many different aspects of healthy diet and lifestyle, but it should not discourage consumers from following public health recommendations to consume diets high in vegetables of all types.”
Prof Naveed Sattar, professor of Metabolic Medicine, University of Glasgow, said: “In short this paper should in no way change advice to eat at least five portions of fruit and vegetables a day.
“Many living in the UK fall well short of this, sadly, and more needs to be done to encourage better intake of vegetables.
“In fact, I suspect we may have underestimated the importance of a healthy diet on health and disease in general.
“We are good at treating with preventative drugs, but the UK needs to up its game in helping people improve lifestyles, including diet and activity – that is the big goal going forward post pandemic.
“How we best do this, though, requires more thought from Government and health agencies.”
– The findings are published in the Frontiers in Nutrition journal.