New research questions on a healthy diet for the heart

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Yet another study that seems to contradict much of what we thought we knew about the best way to eat for heart health was published this week. The study suggests that there is a lack of evidence to support taking vitamin supplements or adopting a healthy diet to help prevent heart disease.

But does that mean you can go ahead and stuff yourself with fries and sodas? Not so fast.

The paper, published in the Annals of Internal Medicine, was not a new study, but a meta-analysis, which means that it was based on previous research. In this case, researchers looked at 277 studies involving nearly a million people to determine whether vitamin supplements or diets reduced the risk of death, heart attack, or stroke. They only looked at randomized clinical trials, in which people are assigned to some intervention (in this case, a diet or vitamins) and compared to a control group.

The researchers concluded that, with few exceptions, neither diet nor vitamin supplements seemed to help.

While the study has some strengths, the nutrition researchers CR spoke to unanimously agreed that there is nothing in this study to suggest that we should reject current recommendations to follow a heart-healthy diet. .

"Studies like this help to give the impression that the science of nutrition is still shifting," says Charlotte Vallaeys, MS, Consumer Reports Senior Policy Analyst for Food and Nutrition, "but is essential to health. "

So why has this study not found evidence that taking vitamins and eating a healthy diet is important? And why new studies like this often seem to demystify what we knew before? The answer has a lot to do with how the study was designed and what the researchers were looking for.

Here's what you need to understand about what we've learned from this research and why current recommendations for healthy eating, such as incorporating many vegetables into your diet, are still valid.

That found the study?

Researchers have found little evidence that a low-sodium diet, taking omega-3 supplements and folic acid supplements could reduce the risk of heart attack and stroke. Stroke in the adult. They also discovered that taking calcium and vitamin D could actually increase the risk of stroke.

The analysis did not reveal any benefit in taking other vitamin supplements or following seven different diets analyzed, including a Mediterranean diet, a low-fat diet and others touting it. 39, improving the health of the heart.

Is it true that there is little evidence to support a healthy diet for the heart?

No. There is ample evidence that a diet including fruits and vegetables, whole grains, low-fat dairy products and heart-healthy fats, such as olive oil and canola oil, protects against heart disease. All nutrition experts with whom CR has been maintained are in agreement.

If there is so much evidence, why did not this study find them?

This meta-analysis examined how different diets and vitamin supplements affect the risk of heart attack, stroke and death. The problem is that the longest studies included in the analysis lasted five years and that it can run out for decades before the effects of a bad diet lead to a seizure cardiac or that the protective benefits of a good diet become obvious.

Dr. Edgar R. Pete Miller, MD, Ph.D., professor of medicine at Johns Hopkins University School of Education, says, "You will not see the impact of a diet on a result such as death in a few years" . Drug.

The other major problem was the quality and consistency of the studies evaluating the diet. As each diet is not clearly defined, it is possible that the definition of the "Mediterranean" diet of a study is very different from that of a Mediterranean diet in another study. "And that could explain why they did not see the benefits of a Mediterranean diet," says Penny Kris-Etherton, Ph.D., R.D., a distinguished professor of nutrition at Pennsylvania State University.

Researchers also did not explain how well the study participants followed the diets assigned to them – a common problem in food studies, says Eric Topol, MD, a cardiologist. and director of the Scripps Research Translational Institute, which wrote an editorial accompanying the new article. . Sometimes, he says, participants "will eat what they want to eat".

The researchers may have failed to take into account the possibility of non-compliance, as well as other variables, experts said at CR. "This meta-analysis has unconsciously thrown all studies into a single container regardless of compliance, duration, or basic diet, which may not have important benefits that would could exist, "says Walter Willett, MD, professor, epidemiology and nutrition at Harvard TH Chan School of Public Health.

Finally, Miller and Kris-Etherton claim that some of the diet studies included in the meta-analysis might have had poor design problems and that one of the studies was suspected of fraud.

Safi U. Khan, M.D., lead author of the meta-analysis, did not respond to a request for comment.

Should you stop taking vitamins?

Probably – unless your doctor specifically recommends it (if you are pregnant, for example).

While a study like this has some limitations, CR experts said the meta-analysis of randomized controlled trials made more sense to draw conclusions about vitamins than about diets. Indeed, with other types of research that are not well controlled, it can be very difficult to grasp the effects of vitamin supplements.

People who take vitamins tend to be more concerned with their overall health, which means that they can also adopt other healthy behaviors (such as eating well, exercising, and sleeping enough). By including only randomized controlled trials in the study, the researchers were able to separate the effects of the vitamin from the type of person who took it.

This is where this type of methodology can be most useful. By combining studies, researchers have been able to demonstrate "that supplements are essential [largely] inefficient and can put you at risk in the short term, "says Miller.

Some researchers, however, told CR that the analysis may have also masked the benefits of vitamins in some cases.

The analysis generally did not take into account the nutritional status of the person who was taking vitamins and if the people were already well nourished, they would not get any benefit from the vitamin, says Kris-Etherton . The different doses of vitamins have not been taken into account, so even people who have vitamin deficiency may not have received enough supplement to make a profit.

Even findings showing a benefit of some vitamin supplements can be misleading for some audiences. Research has shown a benefit of folic acid supplementation, for example, but the data comes from China, where the food is not fortified with folic acid, says Topol in its editorial. People living in the United States, where many foods are fortified with folic acid, would probably not benefit from taking a folic acid supplement as well.

What can you learn about healthy eating through this study?

Meta-analyzes can be useful for discovering effects that you would not normally be able to see in small studies, but that have limitations. Willett described a meta-analysis like this as "looking at the world through a narrow, dirty window." It can give you an idea of ​​the effect of interventions, but when you mix so much, you do not have the full story.

The meta-analysis corroborated what previous studies had identified as a general lack of evidence supporting the benefits of most vitamin supplements. It was not possible to demonstrate the cardiovascular benefits of a healthy diet, but this was probably due to the short duration of the included studies as well as to other problems related to the consistency and quality of data.

And some of the findings of the new study are directly contradicted by other robust research. Willet evoked, for example, the 400-page review of evidence produced by the latest Advisory Committee on Dietary Guidelines.

Although there are disagreements in nutrition research, studies have consistently shown that a holistic approach to nutrition rather than simply looking at macronutrients or close interventions improves health.

"Due to the severe limitations of the randomized trials available, especially for dietary interventions, it is important to consider all the evidence," says Willett. For example, "a large body of evidence – including controlled diet studies with risk factors as outcomes, long-term cohort studies, and several randomized trials with good adherence – support the benefits of". a Mediterranean type of diet ".

Evidence of the benefits of eating healthy foods like fruits and vegetables is well established. "It's just a mistake and a bad service to say that we do not know the consequences of eating," says Willett. "In reality, we know a lot about diets and health, and our dietary choices make a major difference in our long-term well-being."

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