Harvard study reveals how Mediterranean-style diets help hearts
Following the fattening holiday season, many folks resolve to lose a few pounds in the New Year.
As recent studies show, you can lose weight fast on calorie-restricted diets, whether they’re low-carb or low-fat — but neither diet is easy to follow or much better at keeping the pounds off.
That’s probably why, in a recent NPR interview, anti-sugar crusader David Ludwig, M. D., stressed that balanced diets featuring whole foods are the way to go.
As author and UC Berkeley professor Michael Pollan famously wrote in his book Food Rules, “Eat food, not too much, mostly plants” — and by “food”, Pollan says he means real, whole, unprocessed food.
Pollan and renowned nutrition professor Marion Nestlé define real food as what your great-grandmother would've served — although margarine dates back to 1869, and some highly processed and synthetic foods appeared in the early 1900s.
There’s ample evidence for the healthfulness of the traditional “Mediterranean” diet — a term that describes the way that people in that area ate before World War II, which persists in some Aegean islands and rural Mediterranean regions.
While many studies link Mediterranean-style diets to reduced risks for cardiovascular disease and diabetes, questions about the exact reasons for its health and weight benefits have remained.
That’s why the American and Swedish authors of a new study decided to probe the reasons why this classic, easy-to-adopt diet appears to help safeguard cardiovascular health.
Before we get to those results, let’s quickly review what researchers really mean by “Mediterranean diet”.
What is the Mediterranean diet?
The term “Mediterranean diet” refers to the eating pattern followed by people on the Aegean islands and in rural areas of Spain, Italy, and Greece.
While it includes its share of animal foods — cheese, yogurt, poultry, eggs, and seafood, with limited amounts of red meat — it famously features more plant foods than the standard American diet, in the form of fruits, vegetables, herbs, beans, whole grains, extra-virgin olive oil, and nuts.
Unlike heart-health diet plans popular in the 1970s and 1980s — such as Dr. Dean Ornish’s super-low-carb plan — the Mediterranean diet is not low in fat.
But instead of butter, margarine — or cheap, omega-6-rich vegetable oils such as corn, soy, safflower, and sunflower — the Mediterranean diet features extra-virgin olive oil, plus omega-3 fats from fish, leafy greens, grass-fed poultry and their eggs, and walnuts.
Note: Only extra-virgin olive oil (EVOO) is rich in antioxidants — especially an uncommon and unusually potent type called tryosols — and is clinically shown to improve artery function and reduce inflammation. Other grades — those labeled “pure”, “olive oil” or “virgin”, contain either no antioxidants or low levels.
For more on EVOO’s special health benefits, see Olive Oil Benefits Linked to EV Grade's Key Antioxidant, Extra Virgin Olive Oil Confirmed as Best Cardiac Prevention Choice, Olive Oil Antioxidants Douse Inflammation Genes, and Olive Oil Earns More Cardiovascular and Anti-Cancer Kudos.
And unlike the standard American diet’s heavy reliance on red meats, the Mediterranean diet features much more fish and other seafood, eaten more than once a week.
Wonder how the Mediterranean diet looks in real life? Here’s a typical daily meal menu:
- Breakfast – Whole-grain bread (thin slice) with smoked fish or a soft-boiled egg and a piece of fruit
- Snack – Small handful of almonds with a few bites of fresh cheese
- Lunch – Tuna on salad greens with tomatoes, avocado, nuts, and a light extra-virgin olive oil vinaigrette
- Snack – Hummus with fresh veggies
- Dinner – Grilled salmon on a bed of quinoa and sautéed greens
American-Swedish team probed Mediterranean diet’s heart effects
Scientists at Sweden’s Uppsala University and Boston-based researchers from Harvard University and Brigham and Women’s Hospital attempted to pinpoint the reasons behind the Mediterranean diets clear heart, brain, and metabolic benefits (Ahmad S et al. 2018).
Here’s how the American-Swedish team described their goal: “Higher Mediterranean diet (MED) intake has been associated with lower risk of cardiovascular disease (CVD), but limited data are available about the underlying molecular mechanisms ...”.
To help reveal the reasons for the Mediterranean diet's heart benefits, they analyzed data from 25,994 women who’d participated in a 1993-2004 clinical trial called the Women’s Health Study — which tested the effects of aspirin and vitamin E versus cardiovascular disease and cancer.
At the beginning of the trial and periodically during it, the participants answered diet surveys and provided blood samples.
The American-Swedish team used that data to compare the volunteers’ cardiovascular outcomes to their self-reported diets and to various “biomarkers” for risk of cardiovascular and metabolic disease — such as blood levels of fats, cholesterol and molecular markers for inflammation, sugar metabolism, insulin resistance, and more.
The researchers looked for links between the participants’ diets and their risk of developing cardiovascular disease, suffering a heart attack or stroke, undergoing coronary bypass surgery, or dying from heart disease.
Each participant was categorized into one of three groups, based on how much their self-reported eating pattern adhered to the Mediterranean diet: — low, middle, or high adherence.
Their analysis revealed that more than 4% of the women in the low-adherence group suffered an adverse cardiovascular event, compared to 3.8% of women in the middle- and high-adherence groups.
That difference equates to a 28% percent drop in the risk for cardiovascular disease or adverse cardiovascular events — a reduction comparable to the risk-reductions seen with use of statins and certain other cardiovascular drugs.
They also found that the middle-and high-adherence groups enjoyed other benefits:
- Lower body mass index — calculated to yield a 27.3% lower heart risk
- Lower levels of inflammation — calculated to yield a 29% lower heart risk
- Better sugar metabolism and less insulin resistance — calculated to yield a 27.9% lower diabetes risk
The researchers also calculated a 25% reduction in the risk of heart disease among women who consumed a diet rich in plants and olive oil and low in meats and sweets — in other words, diets resembling the Mediterranean pattern.
The study’s lead author, Shafqat Ahmad, Ph.D., expressed the implications of their findings: “… modest changes in known cardiovascular disease risk factors, particularly those relating to inflammation, glucose metabolism and insulin resistance, contribute to the long-term benefit of a Mediterranean diet on cardiovascular disease risk.”
And study co-author Samia Mora, MD, MHS highlighted the importance of their findings: “In this large study, we found that modest differences in biomarkers [resulting from greater adherence to the Mediterranean diet] contributed in a multi-factorial way to this cardiovascular benefit ...”.
Harvard review highlights other benefits uncovered in existing research
The Harvard School of Public Health has been publishing a series of “Diet Reviews” that probe the weight-control effects of various eating plans, including Paleo diets, the low-sodium DASH diet, ketogenic diets, gluten-free diets, and the Mediterranean diet.
As their review said, evidence consistently links the Mediterranean diet to reduced risks for heart disease and related deaths — and to long-term success at weight control.
The review highlighted that the health and weight-control attributes of the Mediterranean diet dispel the myth that you need to eat a low-fat diet to enjoy those benefits.
And the reviewers noted that the benefits of the Mediterranean diet show that while the type of fat you eat is crucial, the percentage of calories you get from fat is less of an issue.
Compared with the standard American diet, the Mediterranean diet is low in in omega-6 fats from cheap vegetable oils — or the processed and restaurant foods made with them — and has considerably lower levels of animal-source saturated fats.
The Harvard review article points to recent results from a controlled clinical trial called PREDIMED (Primary Prevention of Cardiovascular Diseases with a Mediterranean Diet), which tested the effects of adding more extra-virgin olive oil or nuts to the diets of 7,447 Spaniards with diabetes or other risk factors for heart disease — without setting any upper limit on total fat intake (Estruch R et al. 2018).
Encouragingly, the PREDIMED trial found that adding either more extra-virgin olive oil or more nuts to the Mediterranean diet reduced the rates of death from stroke by roughly 30%. Previous findings from the PREDIMED trial also found a 43% lower risk of type-2 diabetes from the Mediterranean diet, among people at high risk for cardiovascular disease.
While the average fat levels consumed by participants in the PREDIMED trial were fairly high (39 to 42% of total daily calories), the dietary fat came largely from fatty fish (such as salmon or sardines), extra-virgin olive oil, and nuts.
While the average fat levels consumed by participants in the PREDIMED trial were quite high (39 to 42% of total daily calories), the dietary fat came largely from fatty fish (such as salmon or sardines), extra-virgin olive oil, and nuts.
The Mediterranean diet is also rich in antioxidants, which probably explain many of its disease-preventive and anti-aging effects — see our note about the unique antioxidant content of extra-virgin grade olive oil, under "What is the Mediterranean diet?", above.
In fact, one Harvard team’s analysis of data from the famed Nurses’ Health Study — which involved 10,670 women aged 57-61 and lasted 15 years — found that the women who most closely followed a Mediterranean-style diet were 46% more likely to age healthfully (Samieri C et al. 2013).
The authors defined healthy aging as the relative absence of chronic diseases (e.g., heart disease, diabetes, kidney disease) or major declines in mental health or cognition and physical function.
- Ahmad S, Moorthy MV, Demler OV, et al. Assessment of Risk Factors and Biomarkers Associated With Risk of Cardiovascular Disease Among Women Consuming a Mediterranean Diet. JAMA Netw Open. 2018; 1(8): e185708. doi:10.1001/jamanetworkopen.2018.5708
- Diet Review: Mediterranean Diet. Harvard T.H. Chan School of Public Health. Harvard University. 12 Dec. 2018.
- Estruch R, Ros E, Salas-Salvadó J, Covas MI, Corella D, Arós F, Gómez-Gracia E, Ruiz-Gutiérrez V, Fiol M, Lapetra J, Lamuela-Raventos RM. Primary prevention of cardiovascular disease with a mediterranean diet supplemented with extra-virgin olive oil or nuts. New England Journal of Medicine. 2018 Jun 13.
- Fung TT, Rexrode KM, Mantzoros CS, Manson JE, Willett WC, Hu FB. Mediterranean diet and incidence of and mortality from coronary heart disease and stroke in women. Circulation. 2009 Mar 3;119(8):1093-100.
- Lopez-Garcia E, Rodriguez-Artalejo F, Li TY, Fung TT, Li S, Willett WC, Rimm EB, Hu FB. The Mediterranean-style dietary pattern and mortality among men and women with cardiovascular disease. AJCN. 2013 Oct 30;99(1):172-80.
- Samieri C, Sun Q, Townsend MK, Chiuve SE, Okereke OI, Willett WC, Stampfer M, Grodstein F. The Association Between Dietary Patterns at Midlife and Health in Aging: An Observational Study. Annals of Internal Medicine. 2013 Nov 5;159(9):584-91.