SAN FRANCISCO, June 24 — Moderate alcohol intake may be the single biggest contributor to the Mediterranean diet’s longevity benefit, accounting for 23.5% of the effect in a prospective cohort study.
Surprisingly, the high ratio of monounsaturated-to-saturated fat in the olive oil-rich diet was a more modest contributor to the reduction in all-cause mortality, at 10.6%, according to Dimitrios Trichopoulos, MD, PhD, of Harvard, and colleagues.
Low meat consumption and lots of fruits, vegetables, and nuts were the main contributors to health benefits after alcohol.
Meanwhile, high fish and seafood consumption was actually associated with a nonsignificant increase in mortality risk, they reported online in BMJ.
Despite the surprises, these findings shouldn’t cast any doubt on the overall health benefits of the Mediterranean diet, or encourage us to banish fish and olive oil from the “good foods” list, said David L. Katz, MD, MPH, of the Prevention Research Center at Yale University.
Dr. Katz, who was not involved in the study, said mutual statistical adjustment for various components of the diet was probably responsible for the apparent lack of benefit from foods that nutritionists largely recommend.
“Once a diet is heavily based on vegetables and fruits, it becomes tough to show much additive benefit from anything else,” he said. “They would represent a stronger benefit when used as substitutions in the typical American diet.”
Like prior studies, Dr. Trichopoulos’ analysis of the Greek segment of the larger European Prospective Investigation into Cancer and Nutrition (EPIC) study revealed a link with survival.
All-cause mortality dropped with tighter adherence to the Mediterranean diet, with an adjusted mortality ratio of 0.864 per two-unit increase on the 10-point adherence scale (P<0.001).
While the EPIC study looks at diet, lifestyle, and environment as a factor in chronic disease across 10 European countries, the Greek cohort itself was substantial.
The analysis included 23,349 men and women without a baseline history of cancer, coronary heart disease, or diabetes and complete information on nutritional and other important covariates.
After an average 8.5 years of follow-up, the researchers found that above average fish and seafood intake was the only component of the Mediterranean diet that did not perform as expected. Instead of being beneficial, it trended in the wrong direction (mortality ratio 1.078, P=0.243).
“Maybe fish is not as important as we have expected,” Dr. Trichopoulos acknowledged.
Another possibility: fish eaten in the Mediterranean are not the high omega-3 fatty acid species, such as cod or salmon, which have been repeatedly linked to cardiovascular benefits.
Or, average fish consumption might have been too low in these populations to show a benefit, Dr. Trichopoulos said. (See Moderate Fish Intake Could Drop HF Risk)
With alcohol, previous studies have also shown a dose effect, in that moderate intake appears protective compared with either high or low consumption.
The researchers defined moderate intake as 10 to <50 grams of alcohol per day for men -- the equivalent of one to five drinks. For women, it was half of that.
In the Greek cohort of the EPIC study, moderate alcohol consumption was associated with a significant reduction in mortality compared with higher or lower intake (MR 0.810, 95% CI 0.706 to 0.931).
“My advice to people is drink wine unless you like it too much,” Dr. Trichopoulos said. “Excessive drinking is very hazardous to your health and society.”
He emphasized that alcohol intake in Greece is typically red wine with meals, although the study did not present details for different consumption patterns.
Subtracting alcohol as a component, the Mediterranean diet still appeared to contribute significantly to a long life.
Other components of the diet driving the mortality benefit included:
* Low intake of mean and meat products (16.6% of the effect)
* High vegetable intake (16.2% of the effect)
* High fruit and nut consumption (11.2% of the effect)
* High monounsaturated-to-saturated fat intake (10.6% of the effect)
* High intake of legumes (9.7% of the effect)
High cereal intake and low dairy consumption were minimal contributors to the mortality effect, accounting for 6.1% and 4.5%, respectively.
Alice H. Lichtenstein, DSc, a nutritionist at Tufts University in Boston, noted that the findings were largely consistent with current dietary recommendations for cardiovascular health.
But she cautioned that diet needs to be considered as a whole, particularly with respect to the balance of calories consumed versus expended.
“It is important to remember that each dietary component should not be considered independently, but within the context of the entire diet,” Dr. Lichtenstein said.
The researchers also noted that the study was limited by a dietary assessment that typically occurred years before death and so that diet may have changed over time. The study also lacked the power to assess synergistic effects among foods.
The study was supported by the Europe against Cancer Program of the European Commission, the Greek Ministries of Health and Education, and a grant to the Hellenic Health Foundation by the Stavros Niarchos Foundation.
The researchers reported no conflicts of interest. Drs. Lichtenstein and Katz provided no information on conflicts of interest.
Primary source: BMJ
Trichopoulou A, et al “Anatomy of health effects of Mediterranean diet: Greek EPIC prospective cohort study” BMJ 2009; 338: b2337.