Large-scale study finds that eating vegetables does not protect against cardiovascular disease.
Previous positive studies may not have sufficiently corrected for confounding socioeconomic and lifestyle factors, suggests new analysis.
A sufficient intake of vegetables is important for maintaining a balanced diet and avoiding a wide range of diseases. But might a diet rich in vegetables also lower the risk of cardiovascular disease (CVD)? Unfortunately, researchers from the Nuffield Department of Population Health at the University of Oxford, the Chinese University of Hong Kong, and the University of Bristol found no evidence for this.
That the consumption of vegetables might lower the risk of CVD might at first sight seem plausible, as their ingredients such as carotenoids and alpha-tocopherol have properties that could protect against CVD. But so far, the evidence from previous studies for an overall effect of vegetable consumption on CVD has been inconsistent.
A Large-Scale Study from the UK Biobank
Now, new results from a powerful, large-scale study in Frontiers in Nutrition shows that a higher consumption of cooked or uncooked vegetables is unlikely to affect the risk of CVD. They also explain how confounding factors might have explained previous spurious, positive findings.
“The UK Biobank is a large-scale prospective study on how genetics and environment contribute to the development of the most common and life-threatening diseases. Here we make use of the UK Biobank’s large sample size, long-term follow-up, and detailed information on social and lifestyle factors, to assess reliably the association of vegetable intake with the risk of subsequent CVD,” said Prof Naomi Allen, UK Biobank’s chief scientist and co-author on the study.
The UK Biobank follows the health of half a million adults in the UK by linking to their healthcare records. Upon their enrollment in 2006-2010, these volunteers were interviewed about their diet, lifestyle, medical and reproductive history, and other factors.
The researchers used the responses at enrollment of 399,586 participants (of whom 4.5% went on to develop CVD) to questions about their daily average consumption of uncooked versus cooked vegetables. They analyzed the association with the risk of hospitalization or death from myocardial infarction, stroke, or major CVD. They controlled for a wide range of possible confounding factors, including socioeconomic status, physical activity, and other dietary factors.
Crucially, the researchers also assessed the potential role of ‘residual confounding’, that is, whether unknown additional factors or inaccurate measurement of known factors might lead to a spurious statistical association between CVD risk and vegetable consumption.
The mean daily intake of total vegetables, raw vegetables, and cooked vegetables was 5.0, 2.3, and 2.8 heaped tablespoons per person. The risk of dying from CVD was about 15% lower for those with the highest intake compared to the lowest vegetable intake. However, this apparent effect was substantially weakened when possible socio-economic, nutritional, and health- and medicine-related confounding factors were taken into account. Controlling for these factors reduced the predictive statistical power of vegetable intake on CVD by over 80%, suggesting that more precise measures of these confounders would have completely explained any residual effect of vegetable intake.
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.”
Feng et al. suggest that future studies should further assess whether particular types of vegetables or their method of preparation might affect the risk of CVD.
Implications for Diet and Cardiovascular Health
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.”
Reference: “Raw and cooked vegetable consumption and risk of cardiovascular disease: a study of 400,000 adults in UK Biobank” by Qi Feng, Jean H. Kim, Wemimo Omiyale, Jelena Beševic, Megan Conroy, Margaret May, Zuyao Yang, Samuel Yeung-shan Wong, Kelvin Kam-fai Tsoi, Naomi Allen and Ben Lacey, 21 February 2022, Frontiers in Nutrition.
DOI: 10.3389/fnut.2022.831470
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7 Comments
well, it is a well-known fact that ppl are not always (read: never) tell the whole truth about their dietry habits, so how did they manage to counter that?
Right. go back to your sugar added, and fried grease food. Then try to get sympathy from healthy people because you’re afraid of coronovirus.
Rejecting meat does.
I think that the study’s attention grabbing headline is misleading. The quote “Previous positive studies may not have sufficiently corrected for confounding socioeconomic and lifestyle factors, suggests new analysis”, from this article, is a more accurate description and better title line. Note this article states “may” and “suggests.” There is a consensus that certain components of vegetables, like fiber and some phytonutrients, likely have health benefits including for the heart. While no amount of association, and correlation can prove causation, the majority of evidence including this study, confirms that vegetables are either protective or neutral. Also, Dean Ornish reversed atherosclerosis with diet? A single study reversing a consensus with a single data set that proves the hypothesis but retracts it because of confounding factors is nonsensical. The latest data is not always the best and the latest analysis is not always right. I’m afraid this article just reinforces a recent trend to confuse lay people about science, health especially, and diet specifically, that gives people the impression that health professionals don’t know what they are talking about and shouldn’t be listened to.
… then, what is left not eating at all?… I guess that will do!
I call BS , they won’t make money if your healthy , so Eat your Veggies, and anything else not veggie in moderation
This is an attention grabbing, misleading, and detrimental article. Shame on you. It says nothing about weather or not participants included meat or animal products in their diet. And 5 tablespoons of vegetables a day is a very small amount of vegetables. I would expect the difference between eating 2.3, 2.8, and 5.0 tablespoons of vegetables to be negligible especially if the other 5 or 6 cups of food you’re eating is meat and dairy. Way to misinform!