By Martin S. Lipsky, MD
Adjunct Professor, Institute on Aging, School of Community Health, Portland State University;
Dean Emeritus, University of Illinois College of Medicine, Rockford
Dr. Lipsky is a retained consultant for Health Solutions & Strategies.
SYNOPSIS: Following a diet consistent with current United Kingdom dietary guidelines lowers blood pressure and lipid levels. Based on the observed changes, the study authors estimate a risk reduction of cardiovascular disease by one-third in healthy middle-aged and older men and women.
SOURCE: Reidlinger DP, et. al. How effective are current guidelines for cardiovascular disease prevention in healthy middle-aged and older men and women? A randomized controlled trial. Am J Clin Nutr 2015: doi: 10.3945/ajcn.114.097352 accessed March 31.
Recent controversy surrounds diet and its impact on cardiovascular disease (CVD). In this study, Reidlinger and her colleagues sought to assess diet by comparing the effects on vascular and lipid CVD risk factors of adhering to a diet consistent with United Kingdom (UK) dietary guidelines (DG group) to a traditional British diet (control group).
Using a randomized trial of 165 healthy, non-smoking middle-aged men and women (age 40-70), the researchers measured baseline blood pressure, vascular function, and other CVD risk factors. Treatment was allocated by minimization for age, sex, ethnicity, and body mass index (BMI) using a custom-designed computer database. If two participants cohabited, both were allocated to the same treatment group (17 couples).
The dietary guideline (DG) group were counseled about a heart-healthy diet, including eating oily fish once a week, increasing fruit and vegetable intake, replacing refined with whole grain cereal, swapping high-fat dairy products and meat for low-fat alternatives, and restriction of both salt and simple sugars. The control diet was a nutritionally balanced British diet without salt or sugar restriction and included unrefined cereals (e.g., white bread, pasta), potatoes with meat, a limited intake of both oily fish ( < 1x/per month), and whole grain cereals. The control group was also advised to eat three servings of full-fat dairy products and at least one serving of fruit and two servings of vegetables each day. Both groups were asked to limit their consumption of confectionary and snack foods and to drink alcohol within safe limits. Compliance to guidelines was confirmed using both dietary records and by measuring biomarkers. These markers included measurements such as urine sodium and potassium, sucrose and fructose excretion, eicosapentoic and docosahexaenoic acid in erythrocyte lipids, and plasma alkyrescorcinol concentration.
Outcome measurements included height, weight, blood pressure (BP), lipids, glucose, insulin, high-sensitivity C-reactive protein (hsCRP), arterial stiffness using pulse wave velocity, and vasodilation using a flow-mediated dilation technique. These were measured at the beginning of the trial and after 12 weeks.
The DG groups experienced a 1.3 kg weight loss while the control group gained 0.6 kg. Waist circumference was 1.7 cm lower in the DG group. The DG group also experienced a significant drop in blood pressure: 4.2/2.5 mmHg for daytime readings and 2.9/1.9 mmHG for night-time readings. Cholesterol levels fell by 8%, although changes in the total cholesterol:high-density lipoprotein (TC:HDL) ratio were modest. The C-reactive protein dropped by 36%, and pulse wave velocity also fell. Changes in insulin sensitivity and flow-mediated dilation were not significant.
The authors concluded that following dietary guidelines lowers BP and cholesterol. They estimated a CVD risk reduction of up to one-third for healthy men and women aged 40 and older who adapt a heart healthy diet.
COMMENTARY
Changes in dietary recommendations and recent publications make it difficult for the primary care physician to know exactly how to advise patients. The American Heart Association (AHA) recommends a dietary pattern that emphasizes fruits, vegetables, whole grains, low-fat dairy products, poultry, fish, and nuts, while limiting red meat and sugary foods and beverages.1 As the study authors note, the AHA guidelines are similar to the UK recommendations. Despite the similarity in guidelines and the long-held belief that limiting saturated fats reduces risk, recent publications have cast doubt on these traditional opinions. Notably, a meta-analysis by Chowdhury et al2 in the Annals of Internal Medicine concluded that the current evidence does not clearly support cardiovascular guideless that encourage consumption of polyunsaturated fatty acids and lower consumption of saturated fats.
In light of this recent meta-analysis, it is reassuring to see that what has long been viewed as a healthy dietary lifestyle does seem to work. For primary care physicians who recommend that patients follow AHA guidelines, it should be gratifying to see evidence that this diet does improve risk factors such as BP and lipid levels. As the authors note, study strength is that it evaluates the impact of changing a whole dietary pattern which mimics the clinical world where providers typically provide whole diet counseling rather than advice limited to individual dietary components. One limitation is that the study measured surrogate markers rather than clinical outcomes such as reduced mortality. However, both BP and lipid levels are well accepted as modifiable risk factors that favorably impact CV outcomes.
REFERENCES
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http://www.heart.org/HEARTORG/GettingHealthy/NutritionCenter/HealthyEating/The-American-Heart-Associations-Diet-and-Lifestyle-Recommendations_UCM_305855_Article.jsp accessed March 31, 2015.
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Chowdhury R, et. al. Association of dietary, circulation and supplemental fatty acids with coronary risk: A systematic review and meta-analysis. Ann Int Med 2014;160:398-406.
