Posted by Dave on April 28, 2010 | 12 Comments
It seems like every few months we hear about some new diet that is supposed to help us melt away the pounds and add years to our lives. But how different are these diets, really? I’ve already discussed studies suggesting that the DASH diet does indeed appear to decrease risk of heart disease and reduce blood pressure.
So I decided to look into another diet that’s gotten a lot of coverage in the media: the Mediterranean diet. The concept of the Mediterranean diet is that people in nations around the Mediterranean typically share similar diets, and also seem to live longer than people in other places. The traditional diet is high in vegetables, legumes, fruits, nuts, cereals, olive oil, and fish, with a moderate consumption of dairy and alcohol. Red meat and poultry, and foods high in saturated fat, are avoided.
The diet has been widely studied; a typical study was led by Antonia Trichopoulou in 2003. The researchers surveyed 22,043 Greek adults about their eating habits and followed them for almost 4 years. Over that time period, 275 died; what Trichopoulou’s team wanted to know if those who did a better job adhering to a Mediterranean diet were less likely to die. So, as in the DASH study I discussed last week, they created a scoring system. Respondents got a point for how much they ate of each of the items in the list, compared to the average. For example, if you ate more vegetables than average, you got 1 point, but if you ate fewer fruits and nuts than average, you didn’t get a point. Scoring was reversed for meats and poultry, as well as for potatoes and eggs.
The higher-scoring survey respondents were significantly less likely to die than lower-scoring respondents. Scoring just 2 points higher on the Mediterranean diet corresponded to a 25 percent reduction in the risk of dying over the course of the study, even after adjusting the results for age, gender, and a number of other factors. Even overweight individuals benefitted from the Mediterranean diet (though, of course, being overweight was an independent risk factor).
But of course any one study could be problematic, so a team led by Francesco Sofi conducted a meta-analysis of a dozen different studies of the Mediterranean diet (including a follow-up to the Trichopoulou et al. study I discuss above). They chose the studies by reviewing every study of the diet and related diets they could find. Then they eliminated studies that duplicated results, or that weren’t comprehensive in their design, which left them with 12 large studies, covering over 1.5 million individuals. How did the results add up? This chart sums up the results:
As you can see, every study found a reduction in risk of death for people on the Mediterranean diet. All these studies used a similar scoring system to Trichopoulou et al, and the graph shows the difference in risk of death for people with a 2-point-higher score. Horizontal lines are 95 percent confidence intervals, so most of these results are statistically significant. Bigger squares represent larger effect sizes (I find this part of the graph a little confusing–to me it makes it appear as if those results are less certain, when in fact they are more reliable). The diamond at the bottom represents the weighted average of all the results, which again shows a significantly reduced mortality rate for following the Mediterranean diet.
So why do both the Mediterranean diet and the DASH diet appear to have similar health effects? I’d submit that they really aren’t very different. Sure, the Mediterranean diet is more restrictive on meats, but both the Mediterranean and DASH diets are low in saturated fat. Yes, DASH is more restrictive on sodium, but the Mediterranean diet probably makes up for that difference by restricting saturated fats even more.
Which diet is “healthiest”? At this point, there’s not a lot of research directly comparing the two. For an individual, the healthiest of the two diets is probably the one that’s easiest to follow.
Trichopoulou, A. (2003). Adherence to a Mediterranean Diet and Survival in a Greek Population New England Journal of Medicine, 348 (26), 2599-2608 DOI: 10.1056/NEJMoa025039
Sofi, F., Cesari, F., Abbate, R., Gensini, G., & Casini, A. (2008). Adherence to Mediterranean diet and health status: meta-analysis BMJ, 337 (sep11 2) DOI: 10.1136/bmj.a1344