Did you hear on the radio or read on-line about a new study that found little evidence of any link between higher vegetable intake and reduced risk of major cardiovascular disease? The study was published on February 21, 2022 (1). Its headlines were astonishing to say the least and were understandably the subject of much discussion among scientists and non-scientists alike. Such an outcome is completely unexpected given the wealth of evidence already amassed regarding the benefits of eating more vegetables.
But the devil is in the details, as the old saying goes. This is a perfect example of why it is essential not to simply pay attention to the headlines. Whether intentional or not, the methods used in this study could not possibly provide any new information regarding the effects of consuming vegetables on heart risk.
Here is why.
I settled down to read the actual study and it didn’t take long to pinpoint its weakness. Looking at the methods used, I found a description of how the researchers gathered their data.
Their source was the UK Biobank, a population-based prospective cohort study which collected information from its half-million middle-aged participants between 2006 and 2010. Using a touchscreen questionnaire, participants entered information on their lifestyle, health status, medication use, reproductive history and environmental factors. Physical measurements were also taken along with blood, urine and saliva samples. (1)
Among the many questions asked of the participants were these two (1);
“On average how many heaped tablespoons of salad or raw vegetables would you eat per day? (including lettuce, tomato in sandwiches)”
“On average how many heaped tablespoons of cooked vegetables would you eat per day? (Do not include potatoes)”
Can you see the problem? Their measurement was the number of TABLESPOONS of vegetables eaten. Can you imagine trying to estimate the number of heaped tablespoonsful of spinach in your salad? Besides that challenge, vegetable recommendations from food guides are measured in cups, not tablespoons.
In the study result, four levels of total vegetable intake per day were considered – 0 to 1 heaped tablespoon of vegetables; 2 to 3 heaped tablespoons of vegetables; 4 to 7 heaped tablespoons of vegetables; and 8 or greater heaped tablespoons of vegetables. If you consider that a heaped tablespoon might contain 20 grams of vegetables (1 level tablespoon is 15 grams), the first three intake levels would provide at the most 140 grams of vegetables, equivalent to slightly more than half of a cup. The highest intake would be 160 gm or more, about 2/3 of a cup. These are all very small quantities of food. (1)
Final results of the study reported that the average daily intakes of vegetables in their participants were (1);
- 5 heaped tablespoons (100 grams) of total vegetables
- 2.3 heaped tablespoons (47 grams) of raw vegetables
- 2.8 heaped tablespoons (56 grams) of cooked vegetables
What has the preponderance of evidence already shown us about how to gain the health benefits of eating vegetables?
- Canada’s Food Guide emphasizes the consumption of plant-based foods including fruits and vegetables, whole grains, nuts and seeds due to their positive effects on health. The guide points out that the more plant-based foods consumed, the less room there is on the plate for unhealthy foods like those sourced from animals and processed foods. Canada’s Food Guide suggests that adult men should eat at least 8 servings of fruits and vegetables daily and women should eat at least 7 servings. (2)
- The recommendation from the American Heart Association is that eating five servings of fruits and vegetables daily is associated with the lowest risk of early death. Eating about two servings daily of fruits and three servings daily of vegetables is associated with the greatest longevity. This level of fruit and vegetables in the diet offers a 13% lower risk of death from all causes; a 12% lower risk of death from cardiovascular disease, including heart disease and stroke; a 10% lower risk of death from cancer; and a 35% lower risk of death from respiratory disease, such as chronic obstructive pulmonary disease (COPD). (3)
- In the huge EPIC Study (European Prospective Investigation into Cancer and Nutrition), over 450,000 participants from ten European countries were followed to estimate the proportions of deaths that could be prevented if all participants would increase their fruit and vegetable intake by 25%. Results showed that this small increase in fruit and vegetable consumption would result in a 15% reduction in death from cardiovascular disease. (4)
- Another analysis of the EPIC Study found that those reporting consumption of more than 569 grams per day of fruits and vegetables (about 2.4 cups) had 15% lower risks of death from diseases of the circulatory, respiratory and digestive systems when compared with participants consuming less than 249 grams (about 1 cup) per day. (5)
What constitutes one serving of vegetables? For most vegetables it is 1 cup (240 grams). For raw leafy greens, one serving is 2 cups.
The average total amount of vegetables being consumed per day by participants of the February 2022 UK Biobank study was only 100 grams. The participants would have to eat seven to ten times more vegetables per day to reach the recommended 3 to 4 servings of vegetables a day (720 to 960 grams per day or 3 to 4 cups).
Not surprisingly, even at the very low intake of vegetables consumed in the recent study, benefits were found. Results of this study indicated that eating RAW vegetables in these amounts was associated with lowered risk of developing cardiovascular disease and reduced risk of death from cardiovascular disease. In this analysis, eating COOKED vegetables showed no benefits. (1)
My conclusion? If you want to get the full benefits of eating vegetables, you have to eat the vegetables. A few tablespoonsful a day are not enough. There is no upper limit on vegetable consumption so feel free to eat all the vegetables you can fit into your meals. Choose a wide variety of vegetables because food diversity is the key to a healthy gut microbiome. Most of all, enjoy the dazzling array of flavours, colours and textures that can be yours when you simply “eat your vegetables”.
1 Feng Q, Kim JH, Omiyale W, et al. Raw and cooked vegetable consumption and risk of cardiovascular disease: a study of 400,000 adults in UK Biobank. Front Nutr. Published online February 21, 2022. Ddoi:10.3389/fnut.2022.831470.
3 Wang, D.D., Li, Y., Bhupathiraju, S.N., Rosner, B.A., Sun, Q., Giovannucci, E.L., Rimm, E.B., Manson, J.E., Willett, W.C., Stampfer, M.J., Hu, F.B. Fruit and Vegetable Intake and Mortality: Results From 2 Prospective Cohort Studies of US Men and Women and a Meta-Analysis of 26 Cohort Studies. Circulation, 2021; Doi: 10.1161/CIRCULATIONAHA.120.048996.
4 Leenders, M., Sluijs, I., Ros, M.M., Boshuizen, H.C., Siersema, P.D., Ferrari, P., et al. Fruit and vegetable consumption and mortality: European prospective investigation into cancer and nutrition. Am J Epidemiol. 2013 Aug 15; 178(4): 590-602. Doi: 10.1093/aje/kwt006.PMID: 23599238 DOI: 10.1093/aje/kwt006.
5 Leenders, M., Boshuizen, H., Ferrari, P., Siersema, P., Overvad, K., et al, Fruit and vegetable intake and cause-specific mortality in the EPIC study. European Journal of Epidemiology. 2014; 29(9): Doi:10.1007/s10654-014-9945-9.