Diets May Matter, but Let’s Not Jump to Conclusions
I notice in the May 2013 Issue of the Townsend Letter you printed a review and commentary on page 45 written by Julie Chen, MD, on the recent study on the Mediterranean diet. I am sorry to say that it appears that Dr. Chen did not actually read the study, or at least not carefully enough.
The paper under discussion was published last February (2013) in the New England Journal of Medicine and was written by Ramón Estruch and colleagues, and is titled, “Primary Prevention of Cardiovascular Disease with a Mediterranean Diet.” Dr. Chen is not alone; many writers are describing these results as evidence that the Mediterranean diet can be used to treat cardiovascular disease. For example, the New York Times writer Gina Kolata described Estruch’s results: “About 30 percent of heart attacks, strokes and deaths from heart disease can be prevented in people at high risk if they switch to a Mediterranean diet rich in olive oil, nuts, beans, fish, fruits and vegetables, and even drink wine with meals. …”1
Unfortunately, both Chen and Kolata are either a bit too optimistic or didn’t take the time to read the details. Let me tell you about this study. Then you may be able to understand my criticism.
This was a large multicenter trial conducted in Spain. About 7500 people who were at high risk of having a heart attack or stroke were divided into three groups. One group, which served as the control group, was instructed to follow a “low-fat diet.” The other two groups were instructed to follow a Mediterranean-style diet and also supplement their diet with either extra virgin olive oil or nuts. In fact these two groups were supplied with either the extra virgin olive oil or nuts for free. Those given the extra-virgin olive oil were told to consume 4 tablespoons per day. Those given nuts were told to eat and average of 30 grams per day (about 1 ounce). That they did so was confirmed via blood tests, hydroxytyrosol to measure olive oil consumption and alpha-linolenic acid to measure nut consumption.
The different groups were encouraged to follow their respective diets through mailings and quarterly counseling sessions with dieticians.
The researcher tracked the occurrence of major cardiovascular events (myocardial infarction, stroke, or death from cardiovascular causes) as the primary end point.
After only 4.8 years
,
a primary end point had occurred in 288 of the participants. Those study participants supplementing with extra virgin olive oil had a 30% lower risk of having a cardiovascular event and those supplementing with nuts had a 28% lower risk than the “low-fat” control group.2
So at first glance, it sounds as if the Mediterranean diet works, but you have to read the fine print. While it won’t hurt and will probably help if we tell our high CVD risk patients to follow a Mediterranean diet, it is not the truth to say that this study proves it.
When you do sort through the data, what is astounding is that all the dietary counseling appears to have done little to change what these people ate. The researchers did everything that they could to enhance adherence to the prescribed diets in what should have been motivated study participants, people at high risk for heart attacks or strokes, most of whom were already on medications for cholesterol, blood pressure, and diabetes. The reality is that the study participants, despite four counseling sessions a year with dieticians, hardly changed what they ate at all.
Over the almost 5 years that the trial lasted, the only significant dietary changes made by those in the two Mediterranean diet groups were slight increases in fish and bean consumption; fish consumption increased by one-third a serving per week and beans by just less than half a serving per week. No other changes were statistically significant, except for extra-virgin olive oil or nut consumption in the respective cohorts. This was Spain, after all. People tend to eat a Mediterranean diet. The low-fat control group’s adherence score to a Mediterranean diet averaged about 9 out of a possible 14 points throughout the course of the trial. This is better than we can probably achieve with most patients.
While dietary counseling made little difference in this current study, earlier, smaller, and shorter-lasting clinical trials using similar dietary cohorts have seen changes in eating patterns, particularly if the trials were shorter, and attention was focused on those individuals whose diets were worse at the start of the study.3,4 It should also be added that these and other earlier trials tell us that similar protocols are associated with significant improvements in various biomarkers of CVD such as reducing levels of c-reactive protein, interleukin-6 (IL6), endothelial and monocytary adhesion molecules, chemokines, and plasma brain-derived neurotrophic factor (BDNF).5–7 It might be more accurate to say that dietary counseling suffers from the law of diminishing returns: It may be useful for the people who make really poor food choices, but the better someone eats to start with, the less impact your advice will have. Back to the current Estruch study, though. …
No one is going to convince me that eating an additional third of a serving of fish or less than a half a serving more of beans per week will make a difference in stroke occurrence. Recall the results of Belin’s 2011 study in which 5 servings of fish per week were required to see a similar 30% decrease in CVD risk.8 Beans may be good for you, but they can’t be so good as to be responsible for these changes. Following the Mediterranean diet isn’t what made a difference. It’s has to be the increase in either nuts or extra-virgin olive oil being eaten.
It wasn’t just olive oil that did the trick, it was clearly the extra-virgin olive oil. This Estruch study was done in Spain. People in Spain already eat olive oil, though how much they consumed surprised me. One year into the study, nearly 92% of those in the “low fat diet” control group reported that olive oil was the primary culinary fat in their diets and nearly 60% of these “low fat diet” control group people reported eating more than 2 ounces of olive oil per day. Thus the difference between the control group and the oil group was only in the type of olive oil; switching to extra-virgin olive oil instead of regular olive oil appears to be what made the difference.
Nuts were a different story. There were big differences in nut consumption between the experimental and control groups. By the end of the trial, nearly 91% of the nut group was eating 3 or more servings of nuts a week, while less than 17% of the control group ate that many. What this study tells us is that switching from regular olive oil to extra-virgin olive oil or eating a lot more nuts does good.
This study did not compare a Mediterranean diet with a low-fat diet.9 In fact, we can’t say anything about a low-fat diet based on this study. The amount of fat consumed by the control group, the so-called low fat diet group, did not change significantly over the course of the study. The percentage of Total Energy in the diet from fat dropped nonsignificantly by just under 2%.10,11 Not enough to be statistically significant and certainly not clinically significant. Thus any commentaries you might read about how the “low fat diet” failed should be ignored.
So if dietary counseling doesn’t do much to change person’s diet, then we should probably focus on the things that do work, in this case getting people to eat extra-virgin olive oil and nuts.
Somewhere along the way we should mention Fraser’s 1992 study, the one that tracked about 31,000 Seventh Day Adventists and which reported that those who “… consumed nuts frequently (more than four times per week) experienced substantially fewer definite fatal CHD events (relative risk, 0.52; ….) and definite nonfatal myocardial infarctions (relative risk, 0.49; ….), when compared with those who consumed nuts less than once per week.” Though these reductions were greater than those Estruch reports, keep in mind that Fraser’s population was healthy and not at high risk for CVD as were those in the current study.12
After considerable rumination on this information, I find myself less inclined to invest patient time trying to get them to follow a Mediterranean diet. Time spent focused on increasing nut and extra-virgin olive oil consumption may yield more measureable benefit.
In recent years, those of us who practice alternative, holistic, and complementary medicine have followed a similar trend of mainstream medicine toward evidence-based medicine. Articles in the Townsend Letter more and more focus on reviewing current publications. When working with patients we are all more inclined to quote the science. If we are going to do this, we have a responsibility to each other and to our patients to do so accurately and honestly.
Notes
1. Kolata G. Mediterranean diet shown to ward off heart attack and stroke. New York Times. February 25, 2013.
2. Estruch R, Ros E, Salas-Salvadó J, et al; the PREDIMED Study Investigators. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med. 2013 Feb 25.
3. Zazpe I, Sanchez-Tainta A, Estruch R, et al. A large randomized individual and group intervention conducted by registered dietitians increased adherence to Mediterranean-type diets: the PREDIMED study. J Am Diet Assoc. 2008 Jul;108(7):1134–44; discussion 1145.
4. Zazpe I, Estruch R, Toledo E, et al. Predictors of adherence to a Mediterranean-type diet in the PREDIMED trial. Eur J Nutr. 2010 Mar;49(2):91–9. doi: 10.1007/s00394-009-0053-7. Epub 2009 Sep 4.
5. Estruch R, Martínez-González MA, Corella D, et al. Effects of a Mediterranean-style diet on cardiovascular risk factors: a randomized trial. Ann Intern Med. 2006 Jul 4;145(1):1–11.
6. Urpi-Sarda M, Casas R, Chiva-Blanch G, et al. Virgin olive oil and nuts as key foods of the Mediterranean diet effects on inflammatory biomarkers related to atherosclerosis. Pharmacol Res. 2012 Jun;65(6):577–583.
7. Sánchez-Villegas A, Galbete C, Martinez-González MA, et al. The effect of the Mediterranean diet on plasma brain-derived neurotrophic factor (BDNF) levels: the PREDIMED-NAVARRA randomized trial. Nutr Neurosci. 2011 Sep;14(5):195–201. doi:10.1179/1476830511Y.0000000011.
8. Belin RJ, Greenland P, Martin L, et al. Fish intake and the risk of incident heart failure: the Women’s Health Initiative. Circ Heart Fail. 2011 Jul;4(4):404–413.
9. Estruch et al: Table S5. Participants with a Positive Answer (%) to each of the 14 Items of the Mediterranean Diet Score by Treatment Arm during Follow-up.
10. Estruch et al: Table S7. Intake of Energy, Nutrients and Supplemental Foods at Baseline and the end of the Trial by Study Group.
11. Estruch et al: Table S8. Mean Baseline Values and Changes in Energy, Nutrient and Supplemental Food Intake by Study Arm.
12. Fraser GE, Sabaté J, Beeson WL, Strahan TM. A possible protective effect of nut consumption on risk of coronary heart disease. The Adventist Health Study. Arch Intern Med. 1992 Jul;152(7):1416–24.
13. Sofrito is a sauce made from tomato, onion and garlic with herbs, which are simmered together in olive oil
Table
1:
Mediterranean Diet Recommendations
Recommended
Olive oil 4+ Tbsp/day
Nuts 3+ servings/day
Fresh fruits 3+ servings per day
Vegetables 2+ servings per day
Fish 3+ servings per week
Legumes 3+ servings per week
Sofrito13 2+ servings/week
Wine with meals (only for those who were habitual drinkers at start of study) 7+ glasses/week
Discouraged
Soda drinks <1/day
Commercial bakery goods <3 servings/week
Spread fats <1 serving/day
Red and processed meats <1 serving/day
Table
2:
Low-Fat Diet Recommendations
Recommended
Low-fat dairy products 3+ servings/day
Bread, potatoes, pasta, rice 3+ servings/day
Fresh fruits 3+ servings/day
Vegetables 2+ servings/day
Lean fish and seafood 3+ servings/week
Discouraged
Vegetable oils (including olive) 2 or less Tbsp/day
Commercial bakery goods 1 or less servings/week
Nuts and fried snacks 1 or less servings/week
Visible fat in meats and soups: Always remove
Fatty fish, seafood canned in oil 1 or less servings per week
Spread fats 1 or less servings/week
Sofrito not more than 2 servings/week
Table
3: Quantitative Score of Compliance with the Mediterranean Diet.
1. Do you use olive oil as main culinary fat? Yes
2. How much olive oil do you consume in a given day (including oil used for frying, salads, out of house meals, etc.)? 4 or more tablespoons
3. How many vegetable servings do you consume per day? (1 serving = 200g – consider side dishes as 1/2 serving) 2 or more (at least 1 portion raw or as salad)
4. How many fruit units (including natural fruit juices) do you consume per day? 3 or more
5. How many servings of red meat, hamburger, or meat products (ham, sausage, etc.) do you consume per day? (1 serving = 100–150 g) Less than 1
6. How many servings of butter, margarine, or cream do you consume per day? (1 serving = 12 g) Less than 1
7. How many sweet/carbonated beverages do you drink per day? Less than 1
8. How much wine do you drink per week? 7 or more glasses
9. How many servings of legumes do you consume per week? (1 serving = 150 g) 3 or more
10. How many servings of fish or shellfish do you consume per week? (1 serving: 100–150 g fish, or 4–5 units or 200 g shellfish) 3 or more
11. How many times per week do you consume commercial sweets or pastries (not homemade), such as cakes, cookies, biscuits, or custard? Less than 3
12. How many servings of nuts (including peanuts) do you consume per week? (1 serving = 30 g) 3 or more
13. Do you preferentially consume chicken, turkey, or rabbit meat instead of veal, pork, hamburger, or sausage? Yes
14. How many times per week do you consume vegetables, pasta, rice, or other dishes seasoned with sofrito? 2 or more
Scoring: 1 point for each answer meeting criteria listed.
* 0 points if these criteria are not met.
Full text: Estruch R, Ros E, Salas-Salvadó J, et al; the PREDIMED Study Investigators. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med. 2013 Feb 25. http://www.nejm.org/doi/full/10.1056/NEJMoa1200303. Supplementary Appendix: http://www.nejm.org/doi/suppl/10.1056/NEJMoa1200303/suppl_file/nejmoa1200303_appendix.pdf.
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