PREDIMED: Does Eating Nuts Prevent Strokes?

Michael Greger M.D. FACLM · March 2, 2015 · Volume 23

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A randomized controlled trial found that a Mediterranean-type diet can dramatically lower the risk of subsequent heart attacks. How does it compare with plant-based diet data?

Discuss

Transcript

The Lyon Diet Heart Trial showed that a Mediterranean-type diet could significantly reduce the risk of having a second heart attack, but since many first heart attacks are fatal, better to prevent heart attacks in the first place. But no randomized controlled trial had ever been conducted to test the Mediterranean diet for this so-called “primary prevention” until now: the PREDIMED study, from the Spanish PREvención con DIeta MEDiterranea in which a whopping 7,447 patients were randomized into three groups. These were folks at high risk for a heart attack. About half were obese and diabetic. Most had high blood pressure and high cholesterol, but had not yet had their first heart attack or stroke. A third were told to eat a Mediterranean diet and given a free quart of extra virgin olive oil every week. The second group was told to eat a Mediterranean diet and given a half pound of free nuts every week, and the third group was told to follow the American Heart Association guidelines and reduce their fat intake. No portion control or exercise advice was given, and they were followed for about five years. The results were published in the prestigious New England Journal of Medicine.

The first thing you do when you look at a diet intervention trial is see what the groups actually ended up eating, which can be very different from what they were told to eat. For example the so-called low fat group started out at 39% of calories from fat, and ended up getting 37% of calories from fat, which is high fat even compared to the Standard American Diet, which comes in at 33%–something the researchers plainly acknowledged. In fact, the control group didn’t change much at all over the years, so can be thought of as the what-if-you-don’t-do-anything group, which is still an important control group to have, though the two Mediterranean diet groups didn’t get much more Mediterranean.

They were told to eat more fruits and vegetables, for example, less meat and dairy, but didn’t accomplish any of those compared to control. The biggest changes recorded were, not surprisingly, in the consumption of the freebies. The group that got a free jug of extra virgin olive oil delivered to their home every week really did start increasing their consumption, in part by replacing some of the refined olive oil they had been using, but of course would have to pay for. And those who got a half pound of free nuts sent to them every week for four years straight did start eating more nuts (too bad they couldn’t have slipped a little free broccoli in there too).

Basically they designed a study to test two different Mediterranean diets versus a low-fat diet, but ended up studying something very different–in essence, what happens when thousands of people switch from consuming about three tablespoons of olive oil a day, half virgin, to four tablespoons of all virgin, compared to thousands of people who all of a sudden go from eating about half an ounce of nuts a day to a whole ounce, compared to thousands of people who don’t make much of a change at all. It may not have been what they were hoping for, but these are important research questions in and of themselves. Let’s say you’re at high risk for heart disease, eating like this; what would happen if you started to add an extra half-ounce of nuts to your daily diet, or more unrefined olive oil? We didn’t know, until now.

With no significant differences in meat and dairy intake, there were no significant differences in saturated fat or cholesterol intake, so, no surprise, there were no significant differences in their blood cholesterol levels, and their subsequent number of heart attacks. In the five or so years the study ran, there were 37 heart attacks in the olive oil group, 31 in the nut group, and 38 in the neither group. No significant difference. Same with dying from a heart attack or stroke, or dying from any cause—but those in the olive oil, and especially the nut group, had significantly fewer strokes. All three groups were eating stroke-promoting diets; all groups had strokes in them after eating these diets for years. And so, ideally, we’d choose diets that can stop or reverse the disease process, but the diet with added extra virgin olive oil caused about a third fewer strokes. And adding nuts seemed to cut their stroke risk nearly in half. If this worked as well in the general population, in the U.S. alone, that would mean preventing 89,000 strokes a year. That’s would be like ten strokes an hour around the clock, prevented simply by adding half an ounce of nuts to one’s daily diet.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.

Please consider volunteering to help out on the site.

Sources

Acknowledgements

The Lyon Diet Heart Trial showed that a Mediterranean-type diet could significantly reduce the risk of having a second heart attack, but since many first heart attacks are fatal, better to prevent heart attacks in the first place. But no randomized controlled trial had ever been conducted to test the Mediterranean diet for this so-called “primary prevention” until now: the PREDIMED study, from the Spanish PREvención con DIeta MEDiterranea in which a whopping 7,447 patients were randomized into three groups. These were folks at high risk for a heart attack. About half were obese and diabetic. Most had high blood pressure and high cholesterol, but had not yet had their first heart attack or stroke. A third were told to eat a Mediterranean diet and given a free quart of extra virgin olive oil every week. The second group was told to eat a Mediterranean diet and given a half pound of free nuts every week, and the third group was told to follow the American Heart Association guidelines and reduce their fat intake. No portion control or exercise advice was given, and they were followed for about five years. The results were published in the prestigious New England Journal of Medicine.

The first thing you do when you look at a diet intervention trial is see what the groups actually ended up eating, which can be very different from what they were told to eat. For example the so-called low fat group started out at 39% of calories from fat, and ended up getting 37% of calories from fat, which is high fat even compared to the Standard American Diet, which comes in at 33%–something the researchers plainly acknowledged. In fact, the control group didn’t change much at all over the years, so can be thought of as the what-if-you-don’t-do-anything group, which is still an important control group to have, though the two Mediterranean diet groups didn’t get much more Mediterranean.

They were told to eat more fruits and vegetables, for example, less meat and dairy, but didn’t accomplish any of those compared to control. The biggest changes recorded were, not surprisingly, in the consumption of the freebies. The group that got a free jug of extra virgin olive oil delivered to their home every week really did start increasing their consumption, in part by replacing some of the refined olive oil they had been using, but of course would have to pay for. And those who got a half pound of free nuts sent to them every week for four years straight did start eating more nuts (too bad they couldn’t have slipped a little free broccoli in there too).

Basically they designed a study to test two different Mediterranean diets versus a low-fat diet, but ended up studying something very different–in essence, what happens when thousands of people switch from consuming about three tablespoons of olive oil a day, half virgin, to four tablespoons of all virgin, compared to thousands of people who all of a sudden go from eating about half an ounce of nuts a day to a whole ounce, compared to thousands of people who don’t make much of a change at all. It may not have been what they were hoping for, but these are important research questions in and of themselves. Let’s say you’re at high risk for heart disease, eating like this; what would happen if you started to add an extra half-ounce of nuts to your daily diet, or more unrefined olive oil? We didn’t know, until now.

With no significant differences in meat and dairy intake, there were no significant differences in saturated fat or cholesterol intake, so, no surprise, there were no significant differences in their blood cholesterol levels, and their subsequent number of heart attacks. In the five or so years the study ran, there were 37 heart attacks in the olive oil group, 31 in the nut group, and 38 in the neither group. No significant difference. Same with dying from a heart attack or stroke, or dying from any cause—but those in the olive oil, and especially the nut group, had significantly fewer strokes. All three groups were eating stroke-promoting diets; all groups had strokes in them after eating these diets for years. And so, ideally, we’d choose diets that can stop or reverse the disease process, but the diet with added extra virgin olive oil caused about a third fewer strokes. And adding nuts seemed to cut their stroke risk nearly in half. If this worked as well in the general population, in the U.S. alone, that would mean preventing 89,000 strokes a year. That’s would be like ten strokes an hour around the clock, prevented simply by adding half an ounce of nuts to one’s daily diet.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.

Please consider volunteering to help out on the site.

Doctor's Note

This is the third of a six-part video series on the Mediterranean diet. For some historical backdrop, check out out the first two at Why Was Heart Disease Rare in the Mediterranean? and The Mediterranean Diet or a Whole Food Plant-Based Diet? Here are the next three to come:

The PREDIMED study got a bad rap because of how it was reported, but it’s an extraordinary trial that continues to churn out useful results.

More on nuts in:

But what about nuts and weight gain? See Nuts and Obesity: The Weight of Evidence.

I’ve got lots more on olive oil coming up, but I did do one already:
Extra Virgin Olive Oil vs. Nuts

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