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The Mediterranean Diet and heart disease

The last week in February (2013) saw headlines all over the world: “Mediterranean diet shown to ward off heart attack and stroke.” The Guardian ran with “Mediterranean diet ‘cuts strokes and heart attacks in at-risk groups‘.”  The Sydney Morning Herald announced “Mediterranean diet cuts risk of first heart attack by 30%”.

The world headlines were all based on this article in the highly respected New England Medical Journal. The researchers’ own headline was “Primary Prevention of Cardiovascular Disease with a Mediterranean Diet”. The study is known as PREDIMED (Prevención con Dieta Mediterránea).

Someone I follow on twitter – Rob Lyons (@robspiked) captured it beautifully when I was having my usual rant about people not knowing what the real Mediterranean diet is. Rob replied: “@zoeharcombe no, that’s the diet Mediterraneans eat. This is the ‘Mediterranean Diet’, a mythological diet invented by US researchers.” How true!

The study

Let’s get the facts on the table first. The study involved 7,447 people. 57% were women. The women were aged 60 to 80 and the men were aged 55 to 80. The Guardian was right that they were at-risk groups, as only people with type 2 diabetes or at least three other “major risk factors” (smoking, obesity, family history of heart disease etc) were included in the study. The Sydney Morning Herald was also right about the first heart attack, as only people with no cardiovascular disease at enrollment were admitted to the study.

The diet

This is where we need Rob in our minds. The real Mediterranean diet is high in meat (if it moves, it is eaten – rabbit, pork, beef, chicken, turkey, game, snails etc); fish; cheese; eggs; cream; vegetables & salads; fruits in season and white grains (white bread, white rice, white pasta). Those who eat more of the real food are slim. Those who eat more of the pasta become “Italian mammas”.

The first reference in the study is thus wrong. It claims “The traditional Mediterranean diet is characterized by a high intake of olive oil, fruit, nuts, vegetables, and cereals; a moderate intake of fish and poultry; a low intake of dairy products, red meat, processed meats, and sweets; and wine in moderation, consumed with meals.”

This is what Americans, who have never been to the Med, fantasise that the Mediterranean diet is. However, the truth is that the French/Italians/Greek etc are eating their body weight in red meat and cheese and “wine in moderation” would have an Italian rolling in the aisles. Here are the top wine drinking countries in the world. The prime Mediterranean countries, France and Italy, are in the top five. But for the staggering consumption of the Vatican City, they would be higher! ;-)

Anyway – allowing for the fact that American researchers don’t know what the real Mediterranean diet is, let’s see what the study diet actually was. The 7,447 people were divided into three groups. The study says that they were randomly assigned so, by luck, they appear to have been fairly equally distributed between groups so that there are no obvious confounding differences where, for example, one group has ended up with more than its share of smokers, older people, obese people etc. For once, we can look at the diet as the primary difference to observe.

Two groups were put on this Fictitious Mediterranean Diet (FMD from now on) and the control group were put on a low-fat diet. The two groups on the FMD were also told to avoid soda drinks, bakery goods, spreads, red and processed meat (apart from the red meat, this is excellent advice). The low-fat diet group was told to have at least three servings a day of bread, pasta, potatoes, rice etc – those nicely fattening products that raise triglyceride levels and damage arteries. The FMD group were told to have oily fish. The low-fat group were told to avoid it.

Group 1 doing the FMD was given additional olive oil and group 2 was given 30g of mixed nuts per person per day. The article details that one litre of extra-virgin olive oil was given to group 1 each week and that they were encouraged to consume 50g or more per day. The nut group were given 15g walnuts, 7.5g hazelnuts and 7.5g almonds daily. That’s at least 440 extra calories with virtually no nutrients for the olive oil group (some vitamin E and K but nothing else). The nut group would get approximately 200 extra calories with far more nutrients. Nuts have virtually every vitamin and mineral – many in good amounts. They have protein (olive oil doesn’t – it’s a pure fat).

The fat content in both oil (100%) and nuts (c. 65%) is huge – way higher than the 7% fat content of sirloin steak or the 4% fat content of pork chops. This was a daft study. Why tell groups to avoid natural fat in real food (meat, dairy, eggs) and to replace it with very high fat interventions? (We’ll see why when we see the funders of the study!)

The results

The objective of the study was to measure “primary end points” defined as a major cardiovascular event – a heart attack, stroke or death.

There were 288 such incidents – 96 in the olive oil group, 83 in the nut group and 109 in the low-fat (current government dietary advice) group.

When the incidents in each group were presented as a percentage of person years (i.e. number of people in each group times the average years of follow-up), the incident rate was 0.81% for the olive oil group; 0.80% for the nut group and 1.12% for the low-fat group. As ever, the headlines are big, the real numbers are small. Barely 1 person in 100, in the highest risk groups for cardiovascular disease, at the worst possible age to have cardiovascular disease, actually had an incident during the 5 year study. For the nut and oil groups it was slightly less than 1 person in 100, for the low-fat group it was slightly more than 1 person in 100.

When the incident rate numbers are weighted so that the control group is 1.00, the oil group is 0.73 and the nut group is 0.72. This is relative risk, not absolute. It’s the oldest trick in the book to play to make numbers seem far more dramatic than they are. This is where the headline nonsense of “30% lower risk” comes from. Plus, we always need to remember that this is association, not causation.

The trial was intended to last 6 years. The researchers stopped at 4.8 years – this is usually positioned as “the differences were just so great that we could not morally continue to disadvantage the control group any longer”. A couple of points on this:

1) look at the graph on p8 of the New England Medical Journal paper. The gap between the intervention and control groups is starting to close at the point the experiment is stopped. I’ve seen this convenient ending of trials before.

2) the disadvantage for the control group is that they are following a low-fat diet – not that they are missing out on nuts and/or olive oil. That’s why the headline of the article should have been: “Low-fat diets are associated with cardiovascular disease” Which the media would have likely reported as: “Low-fat diets cause heart disease”. (Except they wouldn’t because the media just loves a good old eulogy about the Fictitious Mediterranean Diet.)

The bottom line

This could have been a very useful study. It could have been an original study to prove that our current low-fat, high-carb, starchy food, diet advice is doing more harm than good. It was essentially comparing a low-fat diet with a real food diet, but with an unnecessary messing around of natural fat delivery mechanisms (being told to avoid natural fat in meat and dairy and to replace it with unnatural levels of olive oil/nuts). Given the nutrition in nuts vs. olive oil, I was surprised that there was no difference between these two groups. This also reinforces the fact that the difference observed was about the low-fat diet being bad and not olive oil or nuts being good.

So why not just do a straight study comparing real food with its natural fat intact and our fake food/low-fat government dietary advice? Who would fund such a study? The funders of this study included: Hojiblanca and Patrimonio Comunal Olivarero (extra-virgin olive oil); the California Walnut Commission; Borges (almonds) and La Morella Nuts (hazelnuts). In the really, really, small print at the end of the article, we also discover that the author conflicts note: “Dr. Ros serves on the board of ‘his institution’ – the California Walnut Commission”; “Dr. Salas-Salvadó is on the board of and receives grant funding from ‘his institution’ – the International Nut and Dried Fruit Council”; Dr. Lamuela-Raventos receives funding from PepsiCo – their snack division does nuts; and Dr. Serra-Majem reports serving on the boards of the Mediterranean Diet Foundation (I never knew there was such a thing!)

As ever – follow the money and all shall be explained!

10 thoughts on “The Mediterranean Diet and heart disease

  • “The real Mediterranean diet is high in meat (if it moves, it is eaten – rabbit, pork, beef, chicken, turkey, game, snails etc)” – haha! you forgot the frogs!! :)

  • A study done in 2008 reported in NEJM did compare all three ie Mediterranean, low carb (Atkins), and low fat. Mediterranean and low carb both had better CV disease risk marker improvements. Low carb had the best numbers but not yet statistically significant. Too small a study 322 participants. Also Nina Teicholz did a great breakdown of the Mediterranean diet in Big Fat Surprise which of course came out last year, after this post. She too revealed the huge corporate money behind the diet’s promotion.

    Despite all this, most physicians I know now are recommending “Mediterranean” diets based mainly on this study and when I talk about LCHF/Atkins they say it’s not proven safe for long term.

  • Alex, I think the financial links explain the study being poorly designed around the fantasy diet. Surely the paper could have read “we are interested in getting people to eat more nuts and designed a study to see whether this could be made to seem desirable”. That would have been honest, with no need to insult the people of the Mediterranean.

  • If you want to know about the real Med diet, ask someone who grew up there. Me. After WWII, when the island I grew up on was flattened by bombs and there was famine, all they had was bread, pasta, oil and sugar – imported and rationed until the 70s. Those who could went on to their usual meat/rabbit/fish/poultry diet, but those who stayed on the pasta, bread and sugar developed diabetes. Most people who thrived on salami (farm-made), homemade soft cheeses, wine, olives and olive oil stayed well.
    The cheapest foodstuffs to import in bulk stayed carb-rich, which did a generation in.
    The richer you were, the more likely to survive you were.
    Mind you, those who had access to black-market bully beef in tins (remember those key-openers?)and could stomach it, did even better.
    What am I getting at here? That carb-rich diets encourage diseases like diabetes and heart trouble, of which both my parents died – they were adolescents in the war, and ate grains… too many grains, and potatoes. When corn-oil margarine came in they were hoodwinked to think it was healthy. Yeah, right. If they had continued to put butter on steak, they’d still be alive today.

    • The oil was the cause of the diabetes. Dont blame the carbs.

      • To Lou Mario, how can oil cause diabetes? It has no glucose and does not raise insulin. It is the one material that cannot cause your glucose to go up, the definition of diabetes.

        Moreover, it is hard to put on weight drinking oil or eating fat, unless it comes with excess ‘fast’ carbs that trigger insulin, the molecule that helps turn carbs into fat and then prevents you burning it.

        P.S. Zoe is right on about that ‘study’

  • I would like to know more about how to lower LDL. My LDL 188.
    Thank you,

  • This wasn’t a scientific study. This was damn near being a felony. Given the ‘3-score-years-and-ten’ life-span jingo, everyone was heading for the danger zone anyway. Just a nudge, and you’re gone!
    The poor blighters on the low-fat diet were lucky to survive at all. Imagine holding vegetables down to about 2 servings/wk”, but mounds of carbs/sugars (each at least 3 servings/day).

  • Actually, you’re wrong the study is an intervention study not cohort or epidemiological so it shows causation not association in regards to the type of diet. Also, relative risk is needed to be calculate risk reduction including the original risk from the control. You need to brush up on your knowledge of studies and nutritional knowledge. Also, your main criticisms of studies are always that the researchers are associated with food companies, this is the worst kind of critical appraisal ever, no scientist would ever use this as a point as it’s not critically evaluating the study itself. The results are not going to be significantly different just because of the researchers, it would be better to criticism the design of the study which would influence the results.

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