This Biome podcast accompanies the Forum article in BMC Medicine on ‘What is the Mediterranean diet and how can we study the benefits?’.
Welcome to this podcast covering the BMC Medicine Forum article on the Mediterranean diet and its health benefits. I’m Claire Barnard, Senior Editor for BMC Medicine. The Mediterranean diet has long been held up as a path to good health and well-being. Studies have attributed reduced mortality risk and a lower incidence of cardiovascular disease to this dietary regime. But what exactly is the Mediterranean diet? How does it differ from other healthy diets across the globe? And how can we study its benefits? Clinicians and researchers with an interest in the effect of diet on health tackle these very questions in the BMC Medicine Forum article. Here we spoke to three of the authors to get their opinions on what the key elements to this diet are, what health benefits it provides, and how we can reap its advantages.
Kicking off the discussion, Miguel Martinez-Gonzalez, Professor and Chair of the Department of Preventive Medicine and Public Health at the University of Navarra in Spain, reveals how the definition of what makes a Mediterranean diet still isn’t entirely clear…..
MMG: The disparity of definitions for the Mediterranean diet does not have an easy explanation; the reasons are complicated and not completely understood. I think the opinions differ in several aspects. First, the total amount of fat, second the specific culinary fat to be used, third the role of low fat dairy and fourth whether to include refined cereals or only wholegrains. The total amount of fat is not the same in all Mediterranean countries. I think that any definition of Mediterranean diet needs to allow for the abundant intake of total intake of fat, provided that this high lipid intake comes from virgin olive oil or tree nuts or fatty fish. The second point is the culinary use of olive oil. For me it is the hallmark of the Mediterranean diet, I mean in my view this specific role of olive oil should be present in any definition of the Mediterranean diet.
Other disparities are related to the potential inclusion of low fat dairy; traditionally there were rarely no fat or low fat dairy products in Mediterranean countries, and they were mainly in the form of yoghurt or cheese, always in small amounts. And the fourth point is that most definitions of Mediterranean diet include cereals, but nowadays we have highly refined cereals and we know that these highly refined cereals can be detrimental for diabetes and cardiovascular health, especially when persons are already overweight or obese.
CB: Although there are many subtleties to consider when defining the Mediterranean diet – from how much fat is acceptable to whether low fat dairy should be included – is it clear that the potential health benefits are numerous, as Antonia Trichopoulou, Professor and Director of the World Health Organization Collaborating Centre for Nutrition at the University of Athens in Greece, explains…
AT: There is overwhelming evidence that the Mediterranean diet conveys protection against coronary heart disease and the thrombotic type of stroke, and compelling, though not concluding, evidence that it conveys protection against some forms of cancer, including the very common colorectal and breast cancer. There have also been reports that the Mediterranean diet slows down cognitive decline and osteoporosis, that are associated with aging. In any case, several studies have shown that adherence to the Mediterranean diet is associated with longer life expectancy. It is not known which components of the Mediterranean diet drive its beneficial effects, or whether the same components of the diet are involved in different disease entities. Moderate consumption of wine during meals in the formation of nitro fatty acids as a result of simultaneous consumption of olive oil and vegetables have been cited. But it is also possible that the health influences of the components of the Mediterranean diet, including high consumption of vegetables, legumes, fruits and nuts, and low consumption of meat products, contribute in an additive way.
CB: Whether it’s reducing risk for cardiovascular disease and cancer or mitigating the effects of cognitive decline, the Mediterranean diet ranks highly for its beneficial influence. However it isn’t the only dietary regime noted for its health benefits. Dariush Mozaffarian, Dean of the Friedman School of Nutrition Science & Policy at Tufts University in the US, takes note of the other global dietary trends that have received similar attention…
DM: The other dietary patterns that people are most interested in and talk most about related to health include the vegetarian diet, or vegan diet, the DASH diet, which is an American diet and stands for Dietary Approaches to Stop Hypertension, and then a traditional diet in Japan, from the island of Okinawa. So among these diets I would say by far the strongest evidence for health benefits is from the Mediterranean diet.
CB: Although evidence for the advantages of the Mediterranean diet continues to grow, quantifying the contribution of this diet to positive health outcomes remains a challenge. Martinez-Gonzalez explains how employing scoring systems can help, picking up on work by Trichoupoulou from an epidemiological standpoint, and noting the interventional study for the prevention of cardiovascular disease, PREDIMED…
MMG: I think that two different settings should be considered. First, an epidemiological study and second, an interventional study. In my view, for the first setting the ideal approach would be the index developed and proposed by Professor Antonia Trichopoulou, she did an extraordinary contribution to the science of nutrition in proposing this operational definition from 0 to 9, taking into account specific medians of the sample, consumption of six beneficial components: the lipid ratio, fruit and nuts, vegetables, legumes, cereals and fish. Whereas one point is given when the consumption is low for detrimental products; for meat and their products and for alcohol, one point is given for moderate consumption. All this is in the context and in the setting of an epidemiological study. This process is time-consuming because it requires processing the full-length food frequency questionnaire and a comparison with sample medians. Another easier approach would be needed in the context of an interventional study because in an interventional study you need a fast, immediate feedback to the participant. In this context I would recommend a 14 point score developed by the PREDIMED trial, in which we have questions in terms of servings per day or servings per week and if you achieve that number of servings you achieve one point for the beneficial components and if you are under the servings you achieve one point for detrimental components. So I would recommend this shorter, easier method for an interventional study.
CB: The use of scoring systems to measure adherence to a Mediterranean diet allows data on its health benefits to be amassed more objectively. The next, equally challenging, step is to translate these findings into dietary policies and guidance. Mozaffarian shares his thoughts on what key messages for policy have emerged from the research so far…
DM: I think one of the most important things we’ve learnt about diets and health, especially obesity, diabetes, heart disease and stroke, is that we can’t make decisions about helpfulness of diets based on looking at isolated nutrients, like just looking at fat, or just looking at saturated fat, or just looking at nutrient X or Y or Z. And we can’t actually make decisions on the healthfulness of foods based on calories, just say this food is higher in calories and that food is lower in calories, so I should just choose the food lower in calories. Those lead to really wrong decisions. What we have learned is that it is the foods that are important, not the single nutrients. And we have to actually focus on foods. So that is the first lesson that we need to translate into policy.
And the second thing that we have learned, which I think is also emphasised by the Mediterranean diet, is that we need to focus what is missing from the diet, the good foods that should be consumed, the positive message, just as much or even more than the bad things in the diet. That’s actually a pretty big change. Most of our dietary focus in terms of policy has been on reducing the bad stuff, initially focusing on lowering fat, on lowering saturated fat and not enough on increasing the good stuff.
CB: Dietary recommendations should therefore focus on the foods rather than the individual nutrients, and should also encompass positive dietary recommendations. However, as Mozaffarian explains, this is only part of the puzzle, and a more holistic approach is needed to tackle poor diets…
DM: In terms of specific policies, I think we need to move beyond just dietary guidelines, recommendations, food labeling. We need to target the whole food system. We need to have policies that change the prices of foods, that make fruits and vegetables and fish and wholegrains and nuts much less expensive and make other foods more expensive, we need to change the availability of foods, we need to have changes in agricultural policies. A lot of things can and should be done to focus on making healthier diets for not only people in wealthy countries, but people around the world.
CB: For those in wealthy countries, where a greater choice of diets is available, there is still often a sense that a healthy diet costs more. So how about the cost of the Mediterranean diet?
DM: We did a meta-analysis where we looked at all the scientific evidence on costs of foods purchased in supermarkets, healthy versus less healthy options. We found the healthiest diets most like a Mediterranean diet actually did cost more on average than the least healthy, worst diets, but it was about US $1.50 a day, which is less than £1 a day difference. That’s not zero, $1.50 a day is something, but on the other hand it’s about the price of a cup of coffee. So for the poorest people in various countries and in the world, $1.50 a day is important, and we need to change our food pricing at the government level to get rid of that difference, or even reverse that difference. But for most people, middle class people in wealthy countries, $1.50 per day is nothing. So I think people should really understand that you can have a healthy diet without much expense.
CB: We’ve heard about what constitutes a Mediterranean diet, how it compares with different diets around the world, and we’ve addressed how we can assess its benefits to extract the key public health messages. But what does it all come down to for the individual? Mozaffarian highlights what you can do to gain some of the benefits of the Mediterranean diet…
DM: One of the first things is to take a near-term, very specific goal. So rather than say I am going to change my whole diet over some undefined period and become more like a traditional Mediterranean diet, that’s a very hard goal. Have a specific goal. Say, “hey how much fruit do I eat right now?”, I am going to increase my fruit intake to three servings a day within four weeks. So that’s as an example. So pick a very specific goal that you are going to change in a specific amount of time, related to one component, whatever component you like, of the Mediterranean diet. And then, the second thing that is needed is to keep track of that goal. So record what you eat every day towards following that goal and give yourself feedback based on what you’re recording. And if you can have somebody to do it with, to give you feedback, some group support, either a family member or a friend to do it with you, that’s even better. One step at a time, one can change their diet from the traditional western, highly processed and packaged food diet toward a healthier Mediterranean diet.
CB: That was Mozaffarian on how making the leap towards a Mediterranean diet starts with just a few small steps, which ultimately may allow us all to reap the long term health benefits. You can find out more about the Mediterranean diet online in BMC Medicine; our recent forum article has more from all of the contributors to this podcast, and is available at biomedcentral.com/bmcmed.
Our thanks to Miguel Martinez-Gonzalez, Dariush Mozaffarian and Antonia Trichopoulou.