- The findings of a new observational study support most of the current dietary guidelines on fruits and vegetables.
- The daily intake of 5 servings of fruits and vegetables was associated with a lower risk of death related to cancer, cardiovascular diseases or respiratory diseases.
- Starchy vegetables and fruit juices, however, do not appear to contribute to risk reduction.
For many decades, nutritionists have recommended a balanced diet to provide the body with the proper nutrients to stay healthy. The main components of this diet include vegetables, fruits, grains, proteins and dairy products.
A recent study by researchers at the Harvard TH Chan School of Public Health in Boston, MA, provides more evidence for current dietary guidelines and expands them, finding that consuming at least 2 servings of fruits and 3 vegetables daily can decrease the risk of death related to disease and death from all causes.
The study appears in Circulation, a scientific journal from the American Heart Association (AHA).
“While groups like the American Heart Association recommend 4-5 servings of fruits and vegetables daily, consumers are likely to receive inconsistent messages about […] the recommended amount and what foods to include and avoid, ”said Dr. Dong D. Wang, MD, Sc.D., an epidemiologist and nutritionist at Harvard Medical School and lead author of the study.
The Department of Health and Human Services and the Department of Agriculture published their recommendations in the form of 2020–2025 Dietary Guidelines for Americans.
According to this set of guidelines, half of the plate for each meal must contain fruits and vegetables.
However, the guidelines also note that more than 80% of people in the United States do not meet this recommendation and should aim to increase consumption of nutrient-rich foods.
The researchers collected self-reported dietary information from two large cohort studies: the Nurses ‘Health Study (NHS) and the Health Professionals’ Follow-up Study (HPFS).
The NHS cohort included registered nurses between the ages of 30 and 55, while the HPFS cohort included men aged 40-75 years with occupations in the health profession. These studies included follow-up with participants every 2–4 years to accumulate dietary information over a period of approximately 30 years.
The researchers excluded participants with heart disease, cancer or underlying diabetes, leaving them with data for 66,719 women and 42,016 men.
They also incorporated data from another 26 studies involving a total of 1.9 million participants, which examined the relationship between fruit and vegetable consumption and mortality rates.
The high number of participants and continuous longitudinal assessments provided the team with an extensive collection of data for analysis.
However, it is important to note that the criteria of the two cohorts – occupation and corresponding education – suggest a similar socioeconomic situation among the participants, who may have been more likely than other members of the population to have access to a healthy diet. The study does not address the realities and effects of food insecurity.
The study results showed that increased fruit and vegetable intake is associated with a lower risk of death, including death from cancer, heart or respiratory disease.
In addition, the researchers saw the lowest risk of death within a limit of 5 combined servings, beyond which there was no apparent benefit in the risk.
These results point to the nutritional value of these foods. For example, increased consumption of fruits and vegetables increases potassium intake and antioxidant activity, which are related to lowering blood pressure and improving lung function, respectively.
As the data are fully self-reported, there may be discrepancies between actual and reported intake. Participants with higher intake, in particular, may have tended to overestimate how many servings they consumed.
This margin of error can obscure the defined limit of 5 portions, so the study authors recognize that slightly larger portions (up to 10) can also lead to reduced risk.
This study also goes beyond the current guidelines by differentiating specific groups of fruits and vegetables.
The researchers observed trends with a lower risk of death for vegetables and foods rich in vitamin C and beta-carotene. Fruits and vegetables that fall into these categories include spinach, kale, carrots and citrus fruits.
On the other hand, they have not identified trends for starchy fruit or vegetable juices, such as potatoes and peas. One possible reason for the latter is the highlight of canned foods. The canning process can deprive starchy vegetables of their antioxidant properties.
Compared to whole fruits, the fluid form of the juices can cause a faster rise in blood glucose and insulin levels, which can increase the risk of disease.
In contrast to existing guidelines, which include canned foods and juices among the recommended foods and drinks, this study requires more research on the health effects of these items.
Rather than being an intervention study, in which the researchers directly implement the variables and analyze the effects, this study was observational. Thus, it is not possible to conclude that the trends present in this study indicate a causal relationship.
In spite of everything, there is a lot of evidence that highlights the benefits of a balanced diet containing lots of fruits and vegetables. The present conclusions also correspond to the results of similar observational studies on the associations between fruit and vegetable consumption and diseases.
The results of this study are in line with current general dietary guidelines for eating at least 5 servings of fruits and vegetables a day. In addition, it provides more information about the specifics and benefits of eating fruits and vegetables.