23 Mar Trial of Current Dietary Guidelines Reduced Waistlines and Cardiovascular Risk Markers
MedicalResearch.com Interview with:
Tom Sanders, PhD DSc
Emeritus Professor of Nutrition & Dietetics, Diabetes and Nutritional Sciences Division,
King’s College London London, UK
Medical Research: What is the background for this study? What are the main findings?
Dr. Sanders: Controversy surrounds the effectiveness of dietary guideline for cardiovascular disease (CVD) prevention in healthy middle-aged and older men and women. These dietary guidelines are similar in UK and other Western countries and focus on modifying the overall dietary pattern so that food and nutrient targets are met. However, surprisingly the overall impact of changing the dietary pattern has never been tested in a trial. We conducted a 12-wk controlled dietary trial in 165 healthy non-smoking men and women (aged 40-70 years) to compare a diet conforming to current dietary guidelines with a traditional nutritionally balance British diet on well established (blood pressure measured by 24-h ambulatory monitoring and blood lipids) and newer predictors of cardiovascular disease risk (measures of blood vessel functioning and stiffness, inflammation and the body’s sensitivity to insulin). The dietary guideline targets were to reduce total and saturated fat intake to provide no more than 35% and 10% of the food energy, to cut salt to below 6g/day, to meet the 5-a-day recommendation for fruit and vegetables, to consume at least 1portions of oily fish a week (i.e. mackerel, salmon, sardines), to obtain half of the cereal intake from wholegrains and to restrict intake of non-milk extrinsic sugar to no more than 10% energy. Subjects were counseled by a dietitian and provided with advice tailored to their individual food preferences and were provided with some foods to assist them following the dietary advice. The control diet was a nutritionally balanced traditional British diet without restriction on salt and sugar intake. It was based around refined cereals (white bread, pasta, breakfast cereals, white rice) and potatoes with meat (red meat, meat products or poultry), but with a limited intake of oily fish (less than once a month) and wholegrain cereals. Participants allocated to control were supplied with a butter-based spread and a liquid unhydrogenated vegetable oil (palm olein) that contained 40 % saturated fatty acids. They were advised to consume three servings of full-fat dairy products (milk, yogurt and cheese), and at least one serving of fruit and two servings of vegetables each day. Both groups were given advice to limit consumption of confectionery, snack foods (chips, cake, cookies) and drink alcohol within safe limits.
Food intake records showed few differences in micronutrient intakes between diets with the exception of vitamin D where the intake and plasma 25-OH-vitamin D levels were greater on the dietary guidelines diet owing to the higher intake of oily fish. The average body weight in the group who followed the modified diet fell by 1.3 kg whilst that in the control group rose by 0.6 kg after 12 weeks, resulting in an overall difference in weight of 1.9 kg between the two groups; the equivalent difference in Body Mass Index (BMI) was 0.7 kg/m2 between the groups. Waist circumference was 1.7 cm lower in the dietary guidelines group compared to the control group.
The drop-out rate was low, with 80 participants completing on the dietary guidelines diet and 82 on the control. Adherence to the dietary advice was confirmed both with dietary records and by measuring specific biomarkers in the participants’ blood and urine. The latter indicated an increase in potassium and fibre intake in the dietary group along with a drop in sodium (salt) and saturated fat and added sugar intake. However, total sugar intake remained unchanged owing to the increase in sugar intake from fruit.
The primary outcomes were changes in day-time systolic blood pressure, endothelial function measured using the flow mediated dilation technique and total cholesterol: HDL cholesterol ratio. All other outcomes were secondary or exploratory outcomes. Significant falls in systolic blood pressure/diastolic blood pressure of 4.2/2.5 mm Hg for daytime and 2.9/1.9 mm Hg for night time were measured in the dietary group compared with the control group; the average heart rate was found to have lowered by 1.8 beats per minute. Causal mediated effects analysis based on urinary sodium excretion indicated that sodium reduction explained 2.4 mm Hg (95% CI 1.0, 3.9) of the fall in blood pressure There were no changes in endothelial dependent or endothelial independent vasodilation but arterial stiffness measured as carotid to femoral pulse wave velocity was 0. 29 m/sec lower on the dietary guidelines diet compared with the control diet. Total cholesterol:HDL cholesterol ratio was 4% lower on the dietary guidelines diet compared to the control low density lipoprotein and triglyceride concentrations were 10% and 9% lower respectively. The reduction in LDL-C (0.30 mmol/L) was greater than that achieved in most community based studies of dietary advice where the average reduction is 0.16 mmol/L but still modest compared with what can be achieved with statins (1.0 mmol/L). Compared with the control diet, the dietary guideline diet decreased low-grade inflammation (C-reactive protein). No significant change was recorded in markers for 24-h insulin secretion or insulin sensitivity, which predicts the risk of developing type 2 diabetes.
Medical Research: What should clinicians and patients take away from your report?
Dr. Sanders: The strength of this study is in it size and the good evidence of compliance to the dietary advice as well as multiple measurements of blood pressure using ambulatory monitoring. Its findings apply to middle-aged and older people without existing health problems. This is important because most heart attacks and strokes occur in those not identified as being at high risk. The study shows that adherence to a dietary patterns consistent with current dietary guidelines, which advocate a change in dietary pattern from the traditional British diet (high in saturated fat, salt and sugar, low in fibre, oily fish and fruit and vegetables) would substantially lower that risk. The control diet was a nutritionally balanced and not a “junk food” diet. Recently, there has been a much controversy in the media regarded the dietary recommendations for saturated fat and salt and much focus has shifted from these to the effects of sugar. Current dietary guidelines recommend replacement of saturated and trans fatty acids with mainly monounsaturated fatty acids and not refined carbohydrates. While the dietary guidelines diet possessed several characteristics of a Mediterranean diet (plenty of fruit and vegetables and a high intake of monounsaturated fatty acids), the latter is not necessarily low in salt and sugar or high in wholegrains and fish. A particularly interesting observation was that the dietary guidelines diet promoted the loss of small amounts of weight especially around the waist compared with those of the control diet, which had the opposite effect. This could be seen could be seen a limitation to the study but may be an unavoidable consequence of conforming to the dietary guidelines. While this diet was well received by participants, it may be a greater challenge to bring about change in groups who are less health conscious. In conclusion, selecting a diet consistent with current dietary guidelines as compared to a traditional UK dietary pattern would be predicted on the basis of the changes in BP and lipids, reduce risk of fatal and non-fatal CVD by 15% and 30% respectively in the general population.
Medical Research: What recommendations do you have for future research as a result of this study?
Dr. Sanders: The main limitation of the study is that risk was estimated using surrogate markers. However, randomized controlled trials with clinical endpoints in healthy participants are unlikely to be conducted due, large numbers of participants required and the practicalities of sustaining differences in dietary intake over several years. Although, this study was able to show that the intake of added sugar was reduced, total sugar intake did not change because of the increase in fruit consumption. In view of recent recommendation to restrict the intake of sugar by WHO, further studies are needed to see if restrictions in total sugar intake have any further benefits on CVD risk factors.
How effective are current dietary guidelines for cardiovascular disease prevention in healthy middle-aged and older men and women? A randomized controlled trial.
Dianne P Reidlinger, Julia Darzi, Wendy L Hall, Paul T Seed, Philip J Chowienczyk, and Thomas AB Sanders on behalf of the Cardiovascular disease risk REduction Study (CRESSIDA) study investigators
Am J Clin Nutr ajcn097352; First published online March 18, 2015. doi:10.3945/ajcn.114.097352
Link to full text available on open access
MedicalResearch.com Interview with: Tom Sanders, PhD DSc (2015). Trial of Current Dietary Guidelines Reduced Waistlines and Cardiovascular Risk Markers