Observational study finds that a diet of seaweeds, vegetables, soy products, and mushrooms is associated with health benefits. Should we reconsider the one-size-fits-all Mediterranean diet?
Osonoi Y, Mita T, Osonoi T, et al. Relationship between dietary patterns and risk factors for cardiovascular disease in patients with type 2 diabetes mellitus: a cross-sectional study. Nutr J. 2016;15(1):1-11.
Cross-sectional, observational study to assess associations between dietary/lifestyle patterns and cardiovascular risk factors in Japanese patients with type 2 diabetes
There were 726 participants eligible for analysis at study end. Of these, 85.5 % (n=620) were taking diabetes medication, 47.7% (n=346) were taking antihypertensive medication, and 61% (n=442) were taking lipid-lowering medication. All participants were between 25 and 70 years of age (mean 57.8±8.6), and 62.9% were male. Average glycohemoglobin level was 7.0%±1.0%.
Exclusion criteria included history of any cardiovascular event, chronic renal failure, type I or secondary diabetes, liver cirrhosis, moderate or severe heart failure, active cancer, and pregnancy/lactation/intent to become pregnant.
The Brief Diet History Questionnaire, querying the past month of dietary choices, was used. This questionnaire has 56 food and beverage items specific to the Japanese population. Data derived from this questionnaire was used in a factor analysis that resulted in 6 divergent dietary patterns, named for the dominance of the foods consumed: 1) Seaweeds, Vegetables, Soy Products and Mushrooms, 2) Fish and Meat, 3) Noodle and Soup, 4) Meats, Fats, Oils, Seasonings and Eggs, 5) Fruit, Dairy and Sweets, and 6) Rice and Miso.
The Pittsburgh Sleep Quality Index was used to assess sleep quality (eg, duration, disturbances, efficiency).
A Morning/Evening Questionnaire was given to determine whether the participant is a morning or evening person.
Mood was measured through the Beck Depression Inventory II, a 21-item questionnaire that assesses depressive traits such as hopelessness, irritability, weight loss, and cognitive difficulty.
Physical activity was assessed with the International Physical Activity Questionnaire. This validated questionnaire queries activities of daily living as part of overall physical activities over the prior week; the result is measured in metabolic equivalent scores (METs-hour-week).
Blood samples were obtained after an overnight fast and included:
- Aspartate aminotransferase (AST)
- Alanine aminotransferase (ALT)
- Gamma-glutamyl transferase (GGT)
- Uric acid
- Estimated glomerular filtration rate (eGFR)
- Total cholesterol
- High-density lipoprotein cholesterol (HDL-C)
- Glycohemoglobin (HbA1C).
Body mass index (BMI) was also measured, along with blood pressure (BP) and brachial ankle pulse wave velocity (baPWV), a noninvasive marker for arterial stiffness.
Of the 6 dietary patterns, the “Seaweeds, Vegetables, Soy Products and Mushrooms” pattern was associated with lower prevalence of diabetes medication and overall better health (more morning type, less depressive symptoms, and higher physical activity despite this group being older on average). Conversely, the “Noodle and Soup” pattern was associated with higher BMI, higher liver enzymes, and higher triglyceride levels. The “Fruit, Dairy and Sweets” pattern was associated with lower GGT, BP, and baPWV. Participants with this pattern also consumed less alcohol and tended to be female nonsmokers. None of the other 3 dietary patterns were associated with risk factors for cardiovascular disease (CVD), positively or negatively, with the exception of high uric acid levels in the “Meats, Fats, Oils, Seasonings and Eggs” pattern.
The above study, which took place in Japan, suggested that the most cardioprotective dietary pattern was “Seaweeds, Vegetables, Soy Products and Mushrooms.” Certainly, few American practitioners steeped in evidence-based medicine, even those of Japanese descent, would think of such a diet for patients. While these may be obscure findings, and observational studies are not considered strong evidence, they do bring up a relevant question. Given our current desire for “personalized medicine,” to what extent should race or ethnicity guide our dietary recommendations for a given patient?
Using evidence-based medicine, the healthiest diet with the broadest applicability for cardiovascular risk reduction is the Mediterranean diet (MedDiet). Numerous studies have examined lessening cardiovascular risk with a MedDiet.1-3 The large, prospective PREDIMED study published in 2013 in the New England Journal of Medicine corroborated prior studies.4 The conclusion stated, “Among persons at high cardiovascular risk, a Mediterranean diet supplemented with extra-virgin olive oil or nuts reduced the incidence of major cardiovascular events.” I believe this conclusion is missing a qualifier. It should read, “Among Spanish people at high cardiovascular risk...” since all participants were Spaniards. In fact, the vast majority of studies on the MedDiet have been done on Mediterranean country cohorts, with some studies also on northern Europeans and/or European descendants in the United States or Australia.1,5
There is growing recognition that the MedDiet needs to be better proven in non-Mediterranean populations. Recently, a study of a Polish cohort (N=8,821) found that those who adhered more closely to a MedDiet were at less risk of metabolic syndrome.6 This is the same conclusion found in a 2014 publication on 780 male firefighters in the midwestern United States.7 In addition, the firefighter study found that better adherence to the MedDiet over the previous 5 years was associated with less weight gain. Conversely, those who ate fast food and sugary beverages were most likely to be obese. A study in Spokane, Washington found that a low-fat diet was as effective as the MedDiet for reducing cardiovascular risk in those with a history of myocardial infarction.8
There is growing recognition that the MedDiet needs to be better proven in non-Mediterranean populations.
Adherence to any diet that is high in plant-based, whole foods, as the MedDiet is, should have some therapeutic benefit when compared to processed food diets. The replacement of sugary beverages and packaged foods with whole, fresh sources alone seems a plausible means of achieving cardiovascular risk reduction. Using this logic, any study that compares a Western diet to a MedDiet, regardless of the participants’ ethnicity, should show benefit. Given the evidence to date, the MedDiet serves us well in the general sense of improving nutritional intake.
If looked at from a purely biological perspective, however, where we are simply the progeny of many generations, our bodies are adapted to expect what our forbearers ate. A striking example of physiology by inheritance is lactose intolerance. The rate of lactose intolerance is 5% to 17% across the United Kingdom/Europe. The rate of lactose intolerance in South America, Africa, and Asia is over 50%, and is nearly 100% in some Asian countries.9 Milk products were not traditionally consumed on these continents until recently, so there was little biological need to continue producing the enzyme past cessation of breastfeeding. In fact, lactase nonpersistence is the more precise term for what is commonly called lactose intolerance, since it is usually attributable to a loss of lactase production after weaning.
In an attempt to individualize treatments, many progressive clinicians now test single nucleotide polymorphisms (SNPs) involved in the metabolism or activation of nutrients (eg, MTHFR) to optimize diet and supplements. We give inordinate attention (in both research and clinical settings) to small genetic variations, many times without taking into consideration race or ethnicity. We can use current research regarding SNPs to inform treatment. However, is testing for singular enzymes really where we should be putting our effort? I am reminded of the classic tale of the man who searched for his lost keys under the streetlight, not because he lost them there, but because that’s where he could see better.
Returning to the current study under review, the “Seaweeds, Vegetables, Soy Products and Mushrooms” pattern was associated with more favorable cardiovascular risk factor profiles and less need for diabetic medication. While the authors did not assess phytochemical patterns, one can assume those with the highest vegetable intake had the highest phytochemical intake. This is the most likely reason for the benefit seen in those favoring that pattern. Neither of the meat-consuming patterns—the “Fish and Meat” and the “Meats, Fats, Oils, Seasonings and Eggs”—had detrimental effects on lipid parameters, liver enzymes, or BMI. The authors speculate that although consumption of meats/fishes was high with these patterns, Japanese subjects are culturally prone to eat more vegetables than their Western counterparts. This high vegetable intake may offset the otherwise detrimental affects of high-meat diets on cardiovascular parameters. They also added that fish is likely a larger portion of the “Fish and Meat” pattern in Japan.
In keeping with what we would expect from a diet high in refined carbohydrates, subjects in the “Noodles and Soup” pattern had higher BMI, higher liver enzymes, and higher triglycerides. In summary, the food patterns fit exactly what we might expect when considering the macronutrients and micronutrients ingested with each pattern. Namely, the diet with the highest consumption of vegetables is associated with the greatest cardioprotection.
That there may be different dietary ideals for different races or ethnicities is not a novel concept. The Nordic Diet, which is similar to the MedDiet nutrient profile with the exception of using locally sourced, traditional Nordic foods, also has evidence of cardioprotection in those with a history of heart disease.10-11 It is a daunting task for a clinician to keep up with such nutritional research. One resource that can be useful is the nonprofit Oldways that has made “Health through Heritage” its mission. Founded in 1990 as an alternative to the official party line of “low-fat” diets being healthful, it is now an international consortium of nutritionists, doctors, and academics combining the commonalities of healthful diets with the unique culture and traditions associated with regional foods. So far, Oldways has created unique food pyramids for those of African heritage, Latino heritage, and Asian heritage. These food pyramids are a good starting point for us as clinicians to guide our patients to an evidence-based dietary approach that may be more suitable than the one-size-fits-all MedDiet recommendation. In addition, such guidelines may be easier to integrate due to familiarity and offer a welcome sense of connection to one’s own heritage. These psychosocial benefits should not be underestimated.