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| The Mediterranean Sea from Cap Bon in Tunisia. Image from Wikimedia |
Today's article comes from CNN; it is about the findings of a new study published in the British Medical Journal. In this study researchers investigated the association between telomere length and adherence to a "Mediterranean" diet. They found that middle age women who ate diets more similar to the Mediterranean diet had longer telomeres than women the same age who ate a more standard American diet.
The news piece and the research article both state that this pattern was only seen when the diet as a whole was considered, no single component of the diet (such as moderate wine intake) was statistically correlated with longer telomeres. These telomeres, it's important to note, are considered to be markers of cellular/metabolic age; shorter telomeres are associated with several diseases of aging. But does the data really show that we can protect our telomeres, and thus our youthful health, by eating more like the Greeks?
Let's start by defining what exactly the "Mediterranean diet" is. In modern context the diet is defined as one that is proportionally high in olive oil, legumes, whole grains, and vegetables; fish is also consumed, but little other meat. A "Mediterranean diet" will also involve moderate alcohol consumption (generally red wine). This definition is not an accurate description of the diets of all people living in the Mediterranean region; for example, people from Northern Italy like to cook with butter, while people from North Africa and the Middle Eastern part of the region use both butter and rendered sheep fat. Also, the lack of non-fish meat is only traditionally associated with poorer people from the region; affluent individuals enjoyed lamb, veal, beef, pork, and poultry. Truly there is no "Mediterranean diet", but rather many different traditional cuisines of the many people living in that region. That being said, the term Mediterranean diet came to be defined as the diet I described above in the 1940s by Ancel Keys. This use of the term, and the diet itself, gained wide recognition in the US in the 1990s along with the "French Paradox" as American researchers tried to reconcile why, in spite of removing fat from their diets per the American Heart Associations recommendations in the 1980s, Americans continued to have high rates of heart disease. And why, inspite of their high fat diets, the French and Mediterranean peoples had low rates of heart disease.
On of the things that researchers have found is associated with heart disease is telomere length. Short telomeres are associated with heart disease, and with other disease of age including cancer, and Parkinson's. Telomeres are the "caps" on the ends of each of your 46 chromosomes. They are made of repetitive stretches of DNA that can be looped back onto themselves. These caps are important because every time a cell with linear chromosomes divides a small amount of DNA is lost from the ends. Without telomeres this loss would result in the loss of biologically important information. The looping nature of telomeres is also important. The loops and their genetic sequence attract proteins that function to protect and maintain the telomeres. Specifically, the loops help the cell's DNA repair mechanisms recognize that these are the proper legitimate ends of the chromosome. Without such an indicator the chromosomes could be randomly fused together by the non-homologous end-joining repair mechanism, an important mechanism that repairs broken chromosomes. Inappropriate random chromosomal fusion could lead to cancer or other genetic disorders (such as Down's syndrome).
What did the authors of the British Medical Journal article find out about the telomeres of women who ate a Mediterranean diet?
For this study the researchers used data from the Nurses' Health Study. This is a large study that started in 1976 with 121,700 female nurses from 11 states all aged 30-55 at enrollment. These nurses have been surveyed biannually ever since '76 and their children are also part of a related study (Growing Up Today Study). The biannual surveys have changed over the years but primarily focus on diet, exercise, and overall heath. Here is the 2010 survey sent to the nurses, if you're interested.
Specifically, researchers used data from the expanded food questionnaire the nurses did in 1990 and a blood draw done in 1989 or 1990. The blood saved from '89/'90 was used to determine the average length of each nurse's telomeres. The food questionnaire data was used to calculate each nurse's Alternate Mediterranean Diet Score. This score included nine components: vegetables (excluding potatoes), fruits, nuts, whole grains, legumes, fish, monounsaturated:saturated fatty acid ratio, red and processed meats, and moderate alcohol intake. The possible score range is 0-9, with a higher score representing a closer resemblance to the Mediterranean diet. Scores were based on how each nurse's intake compared to the overall median. They gave nurses with intake above the median 1 point each for vegetables, fruits, nuts, whole grains, legumes, fish, and monounsaturated:saturated fatty acid ratio; intake equal to or below the median earned 0 points. Red and processed meat consumption below the median earned a nurse 1 point, and nurses received 1 point for alcohol intake between 5 and 15 g/day.
The researchers also took note of each nurses smoking habits, BMI, exercise, and total caloric intake as co-variant controls. This helps the researchers show that it really is the Mediterranean diet affecting the telomeres and not one of these other factors.
When the researchers considered each component individually they found that age was statistically significantly associated with telomere length (P-value < 0.001), as was number of cigarettes smoked (among smokers; P-value = 0.024). On the other hand, BMI (P-value = 0.13); exercise (P-value = 0.87); total caloric intake (P-value = 0.72); daily vegetable (P-value = 0.51), fruit (P-value = 0.81), whole grain (P-value = 0.77), fish (P-value = 0.68), red meat (P-value = 0.54), legume (P-value = 0.72), nut (P-value = 0.91), and alcohol consumption (P-value = 0.90); total daily fat (P-value = 0.76), saturated fat (P-value = 0.95), and monounsaturated fat intake (P-value = 0.78) were all not statistically significantly associated with telomere length.
When researchers looked at the over all Alternate Mediterranean Diet score, they found a statistically significant trend (P-value 0.016 for age adjusted; P-value 0.004 for multivariable adjusted), with a higher score associated with longer telomeres. The multivariable adjustment included age, BMI, smoking, exercise, and total caloric intake. These statistical controls are important because the researchers found that a higher Alternate Mediterranean Diet score was statistically significantly (all P-values < 0.001) associated with older age, lower BMI, less smoking, more exercise, and higher caloric intake.
When the researchers compared telomere length to other diet scores they found a statistically significant association with the Healthy Eating index (p-value = 0.02), but no statistically significant associations between telomere length and the Prudent Diet index (p-value = 0.09) or Western diet index (p-value = 0.32). The Healthy Eating index is based on the (now defunct) USDA food pyramid; the prudent index is a hybrid between the food pyramid and the Mediterranean diet based on limited added sugar and taking in about 30% of daily calories from fat. The Western diet is the average American diet.
Based on their findings the researchers conclude that a diet more similar to the Mediterranean diet is significantly associated with longer telomore length. This contributes to the broader conclusion that there are many health benefits to eating a Mediterranean diet. They do acknowledge that their use of a single time point is a limitation of the study, there is no way to know how the diet affects telomere length change over time. Another limitation is the self-reported nature of the dietary data; the nurses are supposed to report how many servings of food they consume per day/week/month on average, but data is only collected bianually. This could introduce bias if many nurses are in denial about how often they enjoy a "rare treat". There is also a potential limitation in that the nurses in the study are all women and almost all of European ancestry, the interaction between diet and telomere maintenance could be different in people with different genetic backgrounds or men.
What are my conclusions?
I wonder if the issue of ethnic ancestry is more important than these researchers realize. Other research has shown that young people living in different parts of Europe have different telomere lengths. And it isn't hard to imagine that people with Mediterranean ancestry would eat a diet that scores higher on the diet score these researchers used. Particularly since the scoring system was based on the average eating habits of all the nurses and not a specific cut off intake value (except for alcohol). That being said, this research does corroborate other research that has shown 1) the length of telomeres is associated with diseases of aging, particularly heart disease, and 2) that a Mediterranean diet is good for heart health.
Of course, that still leaves us with the French Paradox. How can research show that heart disease is associated with dietary fat AND that French and Mediterranean diets, both high in fat, are associated with better heart health? The real answer is still something of a mystery, a source of debate among researchers, and beyond the scope of this work. However, I'd like to share an idea about it. I wonder--this is speculation by a scientist, not a rigorously tested scientific theory--if the difference is as much or more about culture than carbs. I know people--smart, thoughtful people--who've decided the Standard American Diet is terrible and that they will eat differently. I've seen them choose to eat vegan/vegetarian/Ornish (high carb, low fat) and Paleo/Atkins/Modified Keto (high fat, low carb), and both groups seem to see improvements in how they feel. Could it be that the real "magic" isn't the ratio of fats and carbs, but in becoming more thoughtful about what we eat? Sounds kind of "woo", doesn't it? And as a scientist I hate "woo". At the same time I think many Americans valorize the idea that "I eat to live" (not the other way around), while other cultures do not (see coq au vin, baklava, and other delicious time consuming dishes). I think this may turn around and bite us Americans in the butt. If we think it's wrong to care too much about food, we're at risk of caring too little and just eating whatever will make our tummy stop growling instead of eating what will really satisfy us. I think the drive to fuss about food is integral to what makes us a successful species--there's 7 billion of us! From an evolutionary perspective the goal is to survive and reproduce; eating is integral to survival. In a sense we do "live to eat" (and get "lucky"). That drive to fuss over food could once have inspired us to hunt woolly mammoths, dig up tubers, tame fire, and eventually invent agriculture; now we still have that drive but food is easy to get. Well, once you have the money, anyway. Maybe that's the core of the problem and the answer to the paradox: maybe, just like well fed pet cats still hunt, the human drive to eat is more complex and not satiated by simply chugging soylent.
More specific to these findings about the Mediterranean diet, learning to cook new things is surely good for us in many ways. As is eating a larger variety of foods. With beef prices having risen to where even cheap ground beef is $4 or more per pound I see no reason not to eat more fish. And I think "more veggies" might be the only piece of nutrition advice that every one can agree on! I also noticed a little side finding of this study was that women who ate more Mediterranean-like ate more calories but weighed less, that might be the real selling point! As for the news article, I give it a B+. It's actually a quite good summary of the research and it's findings, with nothing overly dramatic. But, as is often the case, it did not cite the research article well.
References
Bou-Crous, M., et al. "Mediterranean diet and telmere length in Nurses' Health Study: population based cohort study." Brittish Medical Journal (2014)349.
Nilsson, Peter M. "Mediterranean diet and telomere length." Brittish Medical Journal (2014)349.
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