Effects of targeted substitution dietary guidelines on dietary intake and ischaemic heart disease risk factors in an adult Danish population: The DIPI randomised controlled trial

Background and aim: Ischaemic heart disease (IHD) is the leading cause of morbidity and mortality worldwide with an estimated 7.4 million deaths due to IHD in 2015. Addressing modifiable risk-factors such as diet can help prevent IHD. The overall aim of this thesis was to study the effects of targeted substitution dietary guidelines on dietary intake and IHD risk factors in an adult Danish population.

The specific research objectives were: i) to investigate the associations between adherence to the current Danish official dietary guidelines assessed by a diet quality index (DQI) and selected cardio-metabolic risk factors (paper I); and ii) to examine the short- and long term effects of applying targeted substitution dietary guidelines on dietary intake (paper II) and IHD risk factors (Paper III).

Methods: A 6-month single-blinded parallel randomised controlled trial (RCT) with a 6-month follow-up was conducted in a real-life setting including an adult Danish population with a minimum of one self-reported risk factor of IHD. At baseline participants were assigned to either a control group advised to follow their habitual diet or one of two intervention groups receiving either targeted substitution dietary guidelines or the Danish official dietary guidelines.

At baseline and after 6 and 12 months, information on dietary intake of the participants was obtained by a 7-day web-based dietary record, and a DQI score was calculated as a marker for adherence to the two sets of dietary guidelines. Fasting blood samples were analysed for lipid- and glyceamic biomarkers and alkylresorcinols, and blood pressure, heart rate, anthropometric measurements, and background questionnaires were collected.

Linear regression analyses were applied. Results: A total of 222 participants were enrolled with a median age of 51 years, 59% were women, and 73 % were overweight or obese. In the cross-sectional study (paper I) based on the baseline data of the RCT, the DQI score was significantly inversely associated with low-density lipoprotein cholesterol/high-density lipoprotein cholestreol (HDL-c) -ratio and triglycerides and positively associated with HDL-c.

For men, DQI was inversely associated with body mass index, trunk fat, high-sensitivity C-reactive protein, haemoglobin A1c, insulin, and insulin resistance. In women, DQI was positively associated with systolic blood pressure. The overall results of the RCT (paper II and paper III) showed that compared with the habitual diet group, the group following the targeted substitution dietary guidelines statistically significantly increased their intake of whole grains, dietary fibre, and fine vegetables, and statistically significantly decreased their percentage of energy (E%) intake from saturated fat (SFA) from baseline to 6 months.

In the same period the group following the Danish official dietary guidelines statistically significantly decreased their E% intake from SFA compared with the habitual diet group. From baseline to 12 months, both intervention groups statistically significantly increased their intake of whole grains and fish, and the group receiving the Danish official dietary guidelines still showed a statistically significantly decrease in E% intake from SFA compared with the habitual diet group.

Additional analysis showed that from baseline to 6 and 12 months the DQI score statistically significantly increased in both intervention groups compared to the habitual diet group. No overall statistically significantly differences in change in cardio-metabolic risk factors were found in either of the two intervention groups compared to the habitual diet group.

In addition, selfreported whole grain intake was associated with plasma alkylresorcinol concentrations at baseline. Conclusion: Closer adherence to the current Danish official dietary guidelines, assessed by a DQI, was associated with a more beneficial cardio-metabolic risk profile in a Danish adult population with at least one self-reported risk factor for IHD (paper I).

In the short-term the targeted substitution dietary guidelines were more effective than the Danish official dietary guidelines in changing the diet, resulting in a dietary composition of the overall diet being more cardio-protective compared with the habitual diet. The long-term effectiveness of the two sets of dietary guidelines was similar (paper II).

This was supported by the observed short and long term increase in DQI score, indicating increased adherence to both sets of dietary guidelines. However, neither the targeted substitution dietary guidelines nor the Danish official dietary guidelines showed any overall beneficial effects on IHD risk factors compared with the habitual diet (paper III).

The findings of the three papers included in this thesis will add to the understanding of the impact of applying dietary guidelines on dietary intake and IHD risk factors and will be of importance in future revisions of dietary guidelines.