Mediterranean Diet and Metabolic Syndrome: 50 Studies
Greek and Italian researchers have pooled 50 studies covering 534,906 people and found that sticking to a Mediterranean pattern of eating goes with a lower risk of metabolic syndrome, the cluster of blood pressure, blood sugar, waist and blood fat problems that leads toward diabetes and heart disease. The review appears in the Journal of the American College of Cardiology. Here is what it pooled, how big the effects actually are, and what it says about olive oil in particular, which is less than the press release suggests.
What was pooled
The team, led from Harokopio University in Athens with colleagues in Ioannina and Naples, took every English language study they could find up to April 2010 that measured Mediterranean diet adherence against metabolic syndrome or its parts. That gave them 35 clinical trials, 2 prospective studies and 13 cross sectional ones.
Mediterranean adherence in this literature is a score, not a menu. Points are given for vegetables, fruit, legumes, cereals, fish, a moderate amount of wine and a high ratio of monounsaturated to saturated fat, which in practice means olive oil in place of butter and lard, and points are lost for red meat and dairy. Two people can reach the same score eating quite different dinners.
How big the effect is
Pooling the prospective studies and the trials, higher adherence was associated with a reduced risk of having the syndrome. The clinical trials also showed improvements in each of its components, and this is where it pays to look at the actual numbers rather than the adjectives.
| Component | Average difference with a Mediterranean diet |
|---|---|
| Waist circumference | 0.42 cm smaller |
| HDL cholesterol | 1.17 mg/dl higher |
| Triglycerides | 6.14 mg/dl lower |
| Systolic blood pressure | 2.35 mm Hg lower |
| Diastolic blood pressure | 1.58 mm Hg lower |
| Blood glucose | 3.89 mg/dl lower |
None of those numbers would impress a drug company. Taken together across a whole population they are worth a great deal, which is the authors’ point: this is a cheap pattern of eating that shifts several risk factors a little in the right direction at once, and it can be adopted by people who are not ill.
What it says about olive oil
Not much on its own, and that is not a criticism of the paper. The diet score treats olive oil as the fat that carries the rest of the pattern, and the studies pooled here did not set out to isolate it. Anyone selling you oil on the strength of this review is borrowing credit from vegetables, fish and legumes as well.
What can be said honestly is narrower and still useful. Replacing butter, lard and hardened vegetable fats with olive oil is the single change that moves a person’s score most, it is the change Mediterranean populations actually made and kept, and the fat itself performs well in the trials that have looked at blood lipids.
Lead author Demosthenes Panagiotakos makes the public health case in the paper’s conclusion: this is a pattern any culture can adopt and it is cheap enough to serve for prevention rather than treatment. I would add the trade view, which is that a diet pattern sells a way of cooking, not a premium bottle, and the premium bottle still has to earn its price on flavor.
This is general information, not medical advice. If you are being treated for blood pressure, cholesterol or blood sugar, talk to your doctor before changing how you eat.
Watch for the word diet doing the work of the word oil. Almost every headline health claim made for olive oil rests on studies of a whole eating pattern, and the pattern includes the vegetables that the oil is poured over. That does not make olive oil useless, it makes it the reason people eat the vegetables. Sellers quote the study; they rarely quote the score sheet.
Sources
- Kastorini et al., The effect of Mediterranean diet on metabolic syndrome and its components, Journal of the American College of Cardiology, March 15, 2011
- Olive Oil Times, Diet with Olive Oil Can Reduce Heart Risks, and Weight, Research Shows