The new PREDIMED (Prevención con Dieta Mediterránea) study was big news. Spanish researchers reported that high-risk people on either of two “Mediterranean” diets had a remarkable 30 percent lower risk of cardiovascular events (mostly strokes) than those on a so-called “low-fat” diet.
But the findings got garbled in the media. “I think the results are being misinterpreted,” says Lawrence Appel of Johns Hopkins University. Here’s the scoop.
Mediterranean Diet Checklist
What researchers call a Mediterranean diet may not match what people in the region typically eat, or what they typically ate. The people of Crete— whose low rates of heart disease in the 1940s were documented in the landmark Seven Countries study—got nearly 40 percent of their calories from bread, pasta, and other “cereals” and 30 percent from oils, leaving little room for fish, vegetables, fruit, or much of anything else.1
However, when studies report that people who eat a “Mediterranean diet” have a lower risk of disease, here’s how they typically define the diet.2
☑ High in beans
☑ High in whole grains
☑ High in fruit
☑ High in vegetables
☑ High in fish
☑ High in nuts
☑ Low in red and processed meats
☑ Far less saturated than monounsaturated fat (which is found in foods like olive and canola oils)
☑ Moderate in alcohol
Note: While Mediterranean diet checklists often look for monounsaturated fat, the polyunsaturated fats in nuts and fish should also protect arteries.
1 Am. J. Clin. Nutr. 61 (suppl): 1313S, 1995.
2 Am. J. Clin. Nutr. 92: 1189, 2010.
WHAT GOT GARBLED
The PREDIMED study made headlines for two reasons: First, it was the rare kind of study that can prove cause and effect, because it randomly assigned nearly 7,500 people to one of three diets for nearly five years. Second, it found surprisingly lower disease rates in people on two of the three.
But beyond that, the story got muddled.
“About 30 percent of heart attacks, strokes and deaths from heart disease can be prevented in people at high risk if they switch to a Mediterranean diet rich in olive oil, nuts, beans, fish, fruits and vegetables, and even drink wine with meals, a large and rigorous new study has found,” reported The New York Times in February. Well, not exactly.
1. All three diets were Mediterranean.
The study didn’t pit a diet “rich in olive oil, nuts, beans, fish, fruits and vegetables,” and wine against a non-Mediterranean diet.It pitted two “Mediterranean” diets against a “low-fat control” diet.1
The people in one Mediterranean group got home deliveries of extra-virgin olive oil, and those in the other group got a mix of nuts (almonds, hazelnuts, and walnuts). The low-fat-diet group got no free food.
But despite many news reports, all three diets were Mediterranean. Although the advice varied somewhat, everyone in the study was told to eat fruits, vegetables, and fish and to cut back on commercial pastries and sweets, “spread fats” (like butter and margarine), and fatty red or processed meats.
“If you want to test the Mediterranean diet versus a crappy American diet, I’d say let’s go to Baltimore and feed people either what they usually eat or a Mediterranean diet,” suggests Lawrence Appel, director of the Welch Center for Prevention, Epidemiology and Clinical Research at Johns Hopkins University in Baltimore.In a Mediterranean country like Spain, notes Appel, “everyone is eating a variant of the Mediterranean diet.”
2. The study had no low-fat diet.
The “low-fat” group was supposed to eat “nothing…like, lettuce,” according to a video on The New York Times Web site.
|High risk. Roughly 80 percent of the PREDIMED participants had high blood pressure, 70 percent had high “bad” or low “good” cholesterol, half had diabetes, and the average waist measured nearly 40 inches, even for women.|
Not true. The low-fat group was allowed red meat (if it wasn’t fatty), olive oil (up to two tablespoons a day), and sofrito (a tomato-olive oil sauce), though less often than the other groups.“I was flabbergasted that some reports didn’t point out that the control diet wasn’t low fat,” says Alice H. Lichtenstein, director of the Cardiovascular Nutrition Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston. “We’re talking about people who got 37 percent of their calories from fat.” (That’s more than the 33 percent that the average American gets.)
The researchers are partly at fault. “Low fat was an inappropriate label, and it spawned an immense amount of inaccurate communication to the public,” notes Lichtenstein.
Mediterranean Diet Plan
|Looking for a healthy Mediterranean diet?Try the OmniHeart “Unsaturated Fat” diet (see middle column of chart).It’s close to what people in PREDIMED were eating when they entered the study (as far as we can tell, since PREDIMED reported only “key foods”).
Not much changed during the study, except that one PREDIMED group ate extra nuts and another ate extra olive oil (see the “NUTS” and “OLIVE OIL” rows).
Want more fish or grains or some other food? Add a serving, and drop a tablespoon of OmniHeart’s oil. Think of oil as a “wild card”.
3. Only oil and nuts changed.
“The participants stayed with the Mediterranean diet, the investigators reported,” said The New York Times. “But those assigned to a low-fat diet did not lower their fat intake very much.”
The Los Angeles Times had a similar take: “What this study may have shown us about the difference between Mediterranean and low fat is that the former is easier to follow. There were no big problems getting subjects to ingest olive oil, wine and seafood. Low fat? Not so much.”
In fact, none of the three groups changed much of what they ate, with one key exception: people who got free deliveries of olive oil or nuts ate somewhat more of them.
“The conclusion should be that if you provide foods to people, there’s a good chance that they’ll increase their consumption,” says Rena Wing, professor of psychiatry and human behavior at the Alpert Medical School at Brown University in Providence, Rhode Island.
Other than some extra olive oil and nuts, all three groups ended up eating basically the same diet. (The study also reported a slight increase in fish and beans in the two Mediterranean groups: roughly half a dozen extra beans or an extra teaspoon of fish a day.)
Yet some reports made it sound as though the PREDIMED study tested a traditional Mediterranean diet against a typical junk-food diet.“So the study wound up comparing the usual modern diet, with its regular consumption of red meat, sodas and commercial baked goods, with a diet that shunned all that,” said The New York Times. Wrong.Fruits, vegetables, red meat, pastries, sodas, dairy, whole (or refined) grains, wine—all three groups ate the same amounts, according to the best diet data reported by the study.
(While a short, 14- item questionnaire found other differences, it wasn’t very precise. “I don’t trust the results of that questionnaire,” says Appel.)“Dr. Estruch said he thought the effect of the Mediterranean diet was due to the entire package, not just the olive oil or nuts,” said The New York Times, referring to lead author Ramón Estruch, professor of medicine at the University of Barcelona. (Estruch, along with several other PREDIMED authors, reported ties to a variety of alcohol, food, and drug companies.)
|What a Mediterranean Diet ISN’T
What researchers call a Mediterranean diet isn’t a typical American diet plus extra-virgin olive oil. It’s a diet rich in vegetables, fruit, fish, beans, whole grains, unsaturated fats (mostly from oils), and alcohol (in moderation). The diet is also low in saturated fat (mostly from red meat and cheese), added sugars, and refined flour that we get from foods like these:
|What a Mediterranean Diet IS
Here’s a sampling of dishes that play key roles in a Mediterranean diet, as defined by researchers. (Whether the diet matches what people in the region eat now—or ever ate—is another story.)
Americans may think of pizza as a Mediterranean food. Yet its cheese and (often) red meat are high in saturated fat, and its crust is a load of refined flour.
This salad gets unsaturated fat from nuts, avocado, and dressing. Typical U.S. restaurant salads have more saturated fat from meat and/or cheese.
The (healthy) OmniHeart diet has less than two teaspoons of added sugar a day. Americans average about 22 teaspoons (half of it from sugary drinks). We also get added sugar—plus refined flour and saturated fat—from cakes, cookies, doughnuts, pies, and other sweets.
This pasta primavera is short on pasta and long on vegetables and salmon. Cutting back on pasta leaves more room for the calories in the oil-based sauce. (Whole-grain pasta would be even healthier.
The classic spaghetti, meatballs, and Italian bread dinner has too much white flour, meat, and cheese to be a healthy Mediterranean meal.
Making salad a main dish means more veggies and less bread. This salad includes garbanzo beans, tuna, and dressing made with oil.
But the study itself concluded that “extravirgin olive oil and nuts were probably responsible for most of the observed benefits,” notes Wing, who directs the Weight Control & Diabetes Research Center at The Miriam Hospital in Providence.
“Oil and nuts. That’s where the action was,” says Appel, who wrote an editorial that accompanied the PREDIMED report in the New England Journal of Medicine.2
“A little was related to fish and legumes, but nothing else.”
4. You can’t eat as much olive oil, nuts, and chocolate as you want and not gain weight.
“I was amazed,” said deputy business editor David Gillen to reporter Gina Kolata in a video that The New York Times posted on its Web site.Gillen was surprised that people in the study were told to eat as much olive oil and nuts as they wanted with no worry that they would be “packing on more weight.”
The researchers “said that they looked at studies and people who ate all the nuts they wanted and just poured on the olive oil; they didn’t gain weight,” explained Kolata. “They think it’s because these things are so filling.
And what they called black chocolate—which I think is dark chocolate at least 50 percent cocoa—all you want.”
“Wow! It sounds like a dream diet,” replied Gillen. It may, in fact, be a dream.It’s true that the study’s two Mediterranean diets didn’t limit olive oil, nuts, or dark chocolate and that the Mediterranean groups didn’t gain weight. However, the control group—which had no limits on bread, pasta, rice, and potatoes— didn’t gain weight either.
“None of the three diets did any harm regarding obesity or weight gain,” explained senior author Miguel Angel Martínez-González, who chairs the department of preventive medicine and public health at the University of Navarra Medical School in Spain, in an e-mail.
Why wouldn’t unlimited oil or nuts make the participants put on pounds? Clearly, some of them had a tendency to overeat. More than 90 percent were overweight or obese when the study started, and the average waist was nearly 40 inches in both men and women.
“The authors suggested that people who eat oil and nuts are going to feel more full so they eat less of other foods,” says Lichtenstein, who is vice chair of the National Heart, Lung, and Blood Institute’s Expert Panel on the Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults.
But there’s no good evidence that something about nuts and olive oil kept people from overeating. And in the largest and longest weight-loss studies, which lasted one or two years, people on high-fat diets lost no more weight than those on low-fat diets.3-5
“I don’t know if olive oil would make you feel full,” says Appel. His OmniHeart study pitted a diet high in unsaturated fats—like olive oil—against diets with either more protein or more carbs.
“People didn’t report greater satiety on the diet with more unsaturated fat,” he notes.
So why didn’t the nut and olive oil Mediterranean groups gain weight?
“They had to eat less of something else,” says Wing. But not much less. The participants ate only 120 calories’ worth of extra oil or nuts per day—just one extra tablespoon of oil or an extra sixth of a cup of nuts. And the study’s diet data could easily have missed 120 calories less of something else.
In any case, it’s risky to assume that you’ll compensate for extra calories by eating less of something else.
“If we did a good job at compensating for calories, two-thirds of us wouldn’t be overweight or obese,” says Lichtenstein.
WHAT THE STUDY MEANS
Despite the confusion over what PREDIMED found, its results are important.
“PREDIMED is a landmark study that should encourage Americans to improve their diets to prevent cardiovascular disease,” says Frank Sacks, professor of cardiovascular disease prevention at the Harvard School of Public Health.
But both Sacks and Appel question the researchers’ decision to stop the trial early because the two Mediterranean groups were faring better than the control group. “That tends to inflate benefit,” says Appel.
In a recent analysis of more than 500 trials, researchers estimated that completed trials that found no benefit would, on average, have found a 29 percent lower risk of an outcome (like heart attacks) if the trials had been stopped early.6 That’s because what looks like a benefit could be just a random fluctuation.“I would have preferred that they hadn’t stopped the trial early unless there was a safety issue,” says Sacks. “When you pull the plug because of too much benefit, trials sometimes get a distorted result.
”But PREDIMED’s results still matter.
“I do think the benefit is real, but I don’t know if the reduction in risk is 30 percent,” says Appel. “It’s impressive that the reduction is related to diet, so I find it intriguing. But the message is not totally clear.”
Another uncertainty: How did the olive oil and nuts lower cardiovascular risk?
It’s too early to know, because the paper didn’t include changes in the participants’ blood pressure, cholesterol, triglycerides, blood sugar, or other measurements.
“We are now finishing these manuscripts, and expect to have them published in approximately one year,” wrote Martínez-González in an e-mail.Until then, experts have to speculate.
“The effects occurred very early in the study,” notes Appel. “If they were due to less atherosclerosis— thickening of the arteries—that would take years. Here something happened relatively quickly.”
He points to a preliminary 2006 report on 772 PREDIMED participants after they were in the study for just three months.7
“It looks like the two Mediterranean groups got a substantial blood pressure reduction,” says Appel. Their systolic pressure (the higher number) was 7 to 8 points lower than the control group’s. What’s more, the final PREDIMED study found a 30 percent lower risk in cardiovascular events— heart attacks, strokes, and cardiovascular deaths combined. But when the researchers delved deeper, only strokes were significantly lower.
“If you look at the blood pressure reductions in the 2006 paper and the stroke reductions in the latest report, I’d say it’s a blood pressure effect that’s driving the benefit,” says Appel. “I can’t prove it, but that’s how it looks.”
The bigger question— which PREDIMED alone can’t answer—is whether a Mediterranean diet would reduce the risk of heart disease and stroke compared to a typical American diet. Odds are, it would. The evidence:
■ Observational studies. “There were great observational data that a Mediterranean diet was healthy before PREDIMED,” says Appel. Granted, those studies—which observed a lower risk of disease in people who typically ate what researchers call a Mediterranean diet—can’t prove cause and effect.8
And the studies may have exaggerated the benefit by the way they defined a Mediterranean diet (see “Mediterranean Diet Checklist”).
“It seems that scientists project whatever they think is good about a diet to the Mediterranean diet,” says Lichtenstein.
“It’s amazing how many people have told me that the Mediterranean diet is high in whole grains. I don’t know where those whole grains are coming from. If you’re eating paella, that’s certainly white rice. And what bread or pasta in the Mediterranean region is whole grain?
”Indeed, all three PREDIMED groups averaged just one ounce of whole grains and six ounces of “refined grains and potatoes” a day.
The same goes for nuts. “Besides baklava, I’m not sure which Mediterranean dishes are rich in nuts,” notes Lichtenstein. The PREDIMED participants averaged just one-twelfth of a cup of nuts—that’s five walnut halves or nine almonds—a day when they entered the study.
That’s about how much the average American eats, though it’s mostly peanuts. “And the majority are coated with salt,” says Lichtenstein.
But regardless of what the residents of Mediterranean countries eat, what scientists call a Mediterranean diet is healthy.
■ Feeding studies. “A Mediterranean diet is close to a DASH-style or OmniHeartstyle diet,” notes Appel.The DASH and OmniHeart studies fed people with high blood pressure or pre-hypertension diets that were rich in fruits and vegetables and low in sweets, red meat, butter, and other saturated fats.9,10 (See “A Healthy Mediterranean Diet.”)
In the OmniHeart study, which tested three diets on blood pressure, cholesterol, and triglycerides, the one that was high in unsaturated fat (a third of it from olive oil) was one of the best at lowering blood pressure and triglycerides.
But more unsaturated fat means less of something else. “You’ve got to cut back on some source of calories,” says Appel. “Sugars and saturated fat are a great start.”
And most Americans eat more bread, pasta, rice, cereal, potatoes, muffins, and doughnuts than did people in the Omni- Heart study.
“You have to cut back on carbs, or a diet high in unsaturated fat just doesn’t work,” notes Sacks. He and Appel coauthored both DASH and OmniHeart.
Does the unsaturated fat have to be extra-virgin olive oil? It’s not clear.In PREDIMED, “people who ate extra extra-virgin olive oil had the same reduced risk as those who ate extra nuts,” notes Lichtenstein. “That suggests that extra-virgin olive oil may not be all that unique.”
Until we have more data to settle that and other issues, the good news is that PREDIMED’s results fit with current advice for a healthy diet.
“The evidence supports eating more fruits, vegetables, legumes, and nuts, and less saturated fat, just like the Mediterranean diet,” says Appel. “So we’re back to the same message we’ve been saying for a long time.”
1 N. Engl. J. Med. 368: 1279, 2013.
2 N. Engl. J. Med. 368: 1353, 2013.
3 N. Engl. J. Med. 360: 859, 2009.
4 JAMA 293: 43, 2005.
5 Ann. Intern. Med. 153: 147, 2010.
6 JAMA 303: 1180, 2010.
7 Ann. Intern. Med. 145: 1, 2006.
8 Am. J. Clin. Nutr. 92: 1189, 2010.
9 N. Engl. J. Med. 336: 1117, 1997.
10 JAMA 294: 2455, 2005.