December 11, 2018
Past research suggests that one of the best things you can do for your ticker is eat lots of plants, fish, nuts, and seeds, and not very much red meat or processed food. Now a December 2018 study in JAMA Network Open sheds light on why this style of eating, called the Mediterranean diet, may benefit the heart.
“We didn’t know the potential mechanisms of how a Mediterranean diet reduced risk of cardiovascular disease. It was like a black box,” says the lead study author, Shafqut Ahmad, PhD, a research fellow at Brigham and Women’s Hospital and the Harvard T.H. Chan School of Public Health, both in Boston. “Through this study, we know that a Mediterranean diet reduces or improves a lot of risk factors for cardiovascular disease, which are very important in terms of prevention.”
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In a large, long-term study, more than 25,000 women answered food intake questionnaires and provided blood samples. Researchers from Dr. Ahmad’s institutions and Harvard Medical School followed them for up to 12 years.
Authors found a link between people who followed the Mediterranean diet and a 25 percent reduced risk of heart disease, compared with those who followed the diet the least closely. To look at the mechanisms behind this reduced risk, researchers used blood samples to measure previously established and new biomarkers of heart disease and found changes in inflammation, glucose metabolism, and insulin resistance.
“The finding shows that a Mediterranean diet improves inflammation, which is quite a big risk factor for cardiovascular disease,” Ahmad says. “We now also know that a major pathway through which a Mediterranean diet improves cardiovascular disease risk is through improved glucose metabolism, insulin resistance, and body adiposity [fat].”
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How Researchers Studied the Heart Benefits of the Mediterranean Diet
Researchers put the participants in three categories according to their Mediterranean diet intake: low, middle, upper. Over the course of the study, they observed that 428 women in the low group, 356 women in the middle group, and 246 women in the upper group had the highest risk for heart disease. From that, they determined that women in the middle and upper group, respectively, had a 23 and 28 percent reduced risk of a cardiovascular event compared with the lowest group.
That average reduced risk of 25 percent is similar to the preventative effects of medication.
“Statins and aspirin are routinely used medications for cardiovascular disease prevention,” Ahmad says. “Through diet, you can reduce your risk as comparably as through medications.”
The study data came from the Women’s Health Study, which includes only female health professionals and may limit the effect of the results, as these individuals may be more health conscious than the general public. But Ahmad says he believes the findings could be generalized and also apply to men, as previous smaller studies reported the effects of a Mediterranean diet are similar among men and women.
“It’s very clear, for the first time in a large-scale, epidemiological study, that we showed that Mediterranean diet improves cardiovascular disease risk by 25 percent, but also improves underlying biomarkers, which is really great,” Ahmad says.
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The Numbers Behind Why the Mediterranean Diet Is Heart Healthy
The new study’s findings align with those of previous research, including an April 2013 New England Journal of Medicine study (it was later retracted and republished, but is still significant, experts say) and a March 2015 review in the American Journal of Medicine that tout the cardiovascular benefits of a Mediterranean style diet, while showing how this may happen.
Researchers compared the blood biomarkers of the middle and upper groups with the low group of Mediterranean diet intake and measured changes that indicated a reduced risk of cardiovascular disease. The biggest biomarker changes were inflammation (29 percent reduced risk), glucose metabolism and insulin resistance (27.9 percent reduced risk), and body mass index (27.3 percent reduced risk).
Martha McKittrick, RDN, CDE, a nutritionist in private practice in New York City, says the study findings weren’t surprising, but they may be useful in helping motivate people to adopt this way of eating.
“We hear ‘This is good for you, do this,’ but this study explains how you actually know why,” McKittrick says. “It’s important for people to know that there are real medical reasons why this diet helps to decrease the risk of heart disease.”
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According to the American Heart Association, heart disease is the number one killer of both men and women. But McKittrick notes that her clients tend to focus their diet on other health concerns.
“What I see with a lot of my patients, whether they want to lower cholesterol or lose weight, they come in and they’re cutting down — eating less carbs and calories — not looking at quality,” she says. That’s especially true among women looking to lose weight, McKittrick adds. “Women in their quest to lose weight might skip on whole grains, avoid eating nuts and use less olive oil because they’re ‘fattening,’ and they aren’t thinking about the big picture and quality of what they’re eating.”
The Mediterranean diet is rich in vegetables, fruit, whole grains, legumes, nuts, seeds, healthy fats (olive oil and avocado), and fish, which experts recommend eating one to two times per week. This style of eating allows limited red meat, sweets, sugary foods, refined carbohydrates, and dairy. Moderate amounts of wine are allowed; for women, it’s one glass (5 ounces) or less a day; for men, no more than two glasses per day.
“A Mediterranean diet is sustainable because it includes all the food groups; healthy, whole, plant-based foods; and no real restrictions,” McKittrick says. “Following this style of diet means you’re not just looking at weight and macronutrients; it’s all the other little things.”
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