Improved compliance with the Norwegian food-based dietary guidelines lead to increased HDL in young females

Abstract

Background: The Norwegian food-based dietary guidelines (NFBDG) target the general population, and aims to promote public health and prevent chronic diseases. In order to prevent disease, the guidelines must be achievable and applicable also for a young, healthy population. Thus, the objective of this study was to investigate the ability of a multi-faceted intervention to increase compliance with the NFBDG and to affect biomarkers of chronic diseases in a healthy population.

Methods: A two-weeks, single-arm study was conducted with 14 healthy women. The multi-faceted intervention included measures to increase awareness, reminders and economic incentives (free foods and meals). Using biomarkers of food intake, we monitored compliance with selected NFBDG. Furthermore, we monitored blood lipids, blood glucose, and blood pressure.

Results: The intervention resulted in significant increases in biomarkers of fruit and vegetable intake: beta-carotene (19.4 %, p= 0.01), lycopene (28.0 %, p= 0.01), total carotenoids (15.8 %, p= 0.01), and Total Antioxidant Status (8.7 %, p=0.001). Also, red blood cell levels of polyunsaturated fatty acids increased. Furthermore, HDL-cholesterol significantly increased by 8.2 % (p=0.04) during the intervention.

Conclusions: Our study is a «proof-of-principle» that the NFBDG are relevant and achievable, and can affect biomarkers of chronic disease in a healthy young population.

Background

Dietary guidelines traditionally use micro- and macronutrients as the basis for their advice aiming at securing adequate intake of all essential nutrients, however over the last decade there has been a shift towards food-based dietary guidelines as part of public nutrition strategies and policies. In 2011, the Norwegian Directorate of Health published the Norwegian Food-Based Dietary Guidelines (NFBDG) (1), and currently over 100 countries worldwide have developed food-based dietary guidelines adapted to their food and nutrition situation (2).

The NFBDG are summarized into 13 specific advice, including advice on the intake of fruits and vegetables, fish, meats, whole grain, and dairy products, and also include advice on energy balance and physical activity. The target for the NFBDG is the general population, and the main aims of the NFBDG are to promote public health and prevent chronic degenerative diseases (1).

Previous studies have shown that interventions may increase compliance with recommendations for a healthy diet and exercise (3 – 6). Most dietary intervention studies are performed in populations already at high risk of developing chronic diseases, however an important aim for the NFBDG is to prevent disease in the general population. Thus, reaching the young, healthy population is also crucial as estimations show that less than 10 % of the general population in Norway comply with the different advice for each of the NFBDG, and 25 – 67 % comply with the advice for each of the individual food groups (7).

Behavioral or educational interventions to improve nutrition most often target obese or overweight populations, children and their families, or patients with established chronic diseases such as diabetes mellitus II and cardiovascular disease. However, since the focus of the NFBDG is prevention of disease and promotion of public health, the recommendations need to be applicable to the healthy population. The general population in Norway has a high education level. Thus, in order to have a public health interest in Norway, the NFBDG should be applicable and achievable in a healthy population with a high education level.

The primary aim of this study was to investigate the «proof-of-principle» that a multi-faceted dietary intervention could increase compliance with the NFBDG in a presumably healthy, young population with a high education level. In addition, we monitored biomarkers of chronic diseases (blood lipids and fasting blood glucose), since the main aim of the NFBDG is to prevent chronic degenerative diseases.

Methods

Study design and subjects

The study was a single-arm two week intervention study including 14 female master students in clinical nutrition (22 – 28 years). All 14 participants were enrolled in the course «ERN4120» at the Department of Nutrition, University of Oslo. The planning, implementation and conduction of the present study was part of the curriculum for the course. Participation in the trial was voluntary. The study was conducted with a special approval for student trials from the Regional Ethical Committee of the South-Eastern Norway Regional Health Authority, and performed in accordance with the Helsinki Declaration. Written, informed consent was obtained from all the participants. The trial is registered within ClinicalTrials.gov with the identifier NCT02416284.

The Norwegian food-based dietary guidelines

The NFBDG (1) were presented to the participants. However, the focus of our intervention was to increase the compliance with the following recommendations:

  • Eat at least 5 daily portions of vegetables, fruits and berries (equivalent to 500 g/day)

  • Eat 2 – 3 servings of fish weekly (equivalent to 300 – 450 g/week)

  • Daily intake of low fat dairy products

  • Choose lean meat and lean meat products, in place of red and processed meats

  • Include at least 30 minutes of daily physical activity

Intervention

The intervention lasted for two weeks, and focused on three types of measures to increase compliance: increased knowledge and awareness, repeated reminders, and economic incentives (Table 1). The participation rate for both the group meals and exercise sessions was 92 %, as measured by recorded attendance.

Table 1 The measures of the intervention

Measure

Intervention consisted of:

Increased knowledge and awareness

A 45 minute lecture presenting the NFBDG

Printed booklet containing the NFBDG

Suggested meal plan for a week

Suggested recipes

Access to a restricted website with further information on the NFBDG

Reminders

A Facebook-group where «Vegetable of the day» was presented with a suggested recipe

One text-message with encouragement to follow the guidelines

One follow-up phone-call

One group exercise session

One group (~2 hours) hike in the local hillside

Economic incentives

Free group meals (1 breakfast, 2 lunches, 1 dinner)

Free foods (low-fat dairy products, fruits and a juice containing grapes, blueberries, chokeberries and cherries)

Food frequency questionnaire (FFQ)

The habitual intake of fruits, vegetables, fish, fatty fish and red meat prior to the start of the intervention, was recorded by use of a simplified FFQ (manuscript currently under review, Henriksen HB et al.). The current FFQ was based on questions from a formerly validated FFQ (8). The selected foods represent foods from the NFBDG, for which we have corresponding biomarkers (carotenoids for fruits and vegetables; EPA (C20:5 n-3), DHA (C22:6 n-3) and DPA (C22:5 n-3) for fatty fish; and C15:0 and C17:0 for dairy fat). The FFQ captures the average weekly diet, as the NFBDG are based on weekly or daily intakes.

Serum sample collection and analyses

Fasting blood samples were taken by the finger-prick method (lancets and 500 ml serum microvette tubes, Sarstedt, Nümbrecht, Germany), in the morning of day 1 (pre-intervention) and on day 15 (post-intervention). Samples were allowed to coagulate for 30 min, centrifuged at 1500 g for 10 minutes, and serum was stored at -20 °C until analysis. Capillary blood was also drawn directly onto «dried blood spot» (DBS) – cards (Protein Saver™ 903R Cards, Whatman, Sanford, USA). The samples were dried for 2 hours in room temperature before storage at -20 °C. Maximum storage of frozen samples was 21 days.

Triglycerides, cholesterol, total antioxidant status (TAS), fasting glucose and High-Density Lipoprotein (HDL)-cholesterol were measured on a MaxMat platform (MaxMat SA, Montpellier, France) as to manufacturer’s instructions. The following kits were used: cholesterol (Assay no. RMCHOL0400V), direct HDL cholesterol (Assay no. RMHDLC0120V), triglycerides (Assay no.RMTRIG0400V), glucose (Assay no. RMGLUP0400V) (all MaxMat SA, Montpellier, France), and total antioxidant status (NX 2332, Randox Laboratories, United Kingdom). Fatty acids in blood from DBS were measured as described in (9), and carotenoids in plasma were measured as described in (10). LDL cholesterol was calculated using Friedwalds equation (11) (LDL cholesterol = Total cholesterol – HDL cholesterol – 0.45*triglycerides).

Weight and height

Both weight and height were measured prior to the start of the intervention. Weight was determined by using a bioelectrical impedance analyzer (Tanita TBF 300, Tokyo, Japan), subtracting 0.5 kg to correct for clothing. Height was measured using mechanical height rod (Kern MSF- 200).

Statistical analyses

Measurements before and after the intervention were compared using non-parametric paired samples Wilcoxon Signed Ranks Test. Correlations were calculated using the Spearman’s Rank Correlation Coefficient. Statistical analyses were performed by use of IBM SPSS Statistics 20 (Armonk, NY, USA).

Results

The participants were within healthy ranges for cholesterol levels, fasting glucose, BMI, and BP prior to the start of the study (Table 2).

Table 2 Baseline characteristics of the study population

Parameter

Mean ± SD/ Median (min-max)

Age (years)

24.4 ± 1.7

BMI (kg/m2)

20.6 ± 1.6

Systolic blood pressure (mmHg)

105 ± 7

Diastolic blood pressure (mmHg)

66 ± 5

Cholesterol (mmol/L)

3.94 (2.9 – 6.0)

LDL (mmol/L)

2.11 (1.1 – 3.17)

HDL (mmol/L)

1.51 (1.0 – 2.6)

Triglycerides (mmol/L)

1.05 (0.4 – 2.2)

Glucose (mmol/L)

4.82 (4.0 – 6.0)

Furthermore, the participants reported intakes in compliance with the NFBDG for fish, fatty fish, and red meat (Table 3). The median daily intake of fruits was 65 grams short of fulfilling the recommendations, while the intake of vegetables was 106 grams less than recommended per day. In total, the median intake of fruits and vegetables was 132 grams below the recommended daily intake of 5 portions (500 grams) per day. During the intervention the participants reported mean intakes of fruits (301 (181 – 469) g/day), and fruits and vegetables combined 507 (313 – 815) g/day) above the recommendations, and the intake of fruits was significantly higher than at baseline (Table 3).

Table 3 Baseline intake and change during the intervention period for intake of fruits, vegetables, fish and red meat

Intake of:

Median before (min-max)

Median during intervention (min-max)

Change (min-max)

p-value for change a

NFBDG

Fruits (grams per day)

235 (100 – 481)

301 (181 – 469)

73 (-128 – 195)

0.048*

Minimum 250

Vegetables (grams per day)

144 (7 – 475)

235 (78 – 355)

68 (-120 – 162)

0.286

Minimum 250

Fruits and vegetables (grams per day)

368 (231 – 898)

507 (313 – 815)

145 (-243 – 289)

0.079

Minimum 500

Fish in total (grams per week)

375 (0 – 800)

388 (0 – 575)

0 (-275 – 200)

0.666

300 – 450

Fatty fish (grams per week)

282 (0 – 725)

288 (0 – 575)

0 (-200 – 275)

0.455

Minimum 200

Red meat (grams per week)

310 (0 – 915)

178 (0 – 465)

-75 (-650 – 300)

0.294

Maximum 500

a Wilcoxon Signed Ranks Test, * Statistically significant change

Using biomarkers of food intake, we monitored compliance with selected NFBDG. Measurements of carotenoids and TAS in serum were used as biomarkers of fruit and vegetable intake. During the two-week intervention period, ?-carotene (19.4 %; p=0.01), lycopene (28.0 %; p=0.01) and total carotenoids (15.8 %; p=0.01) increased significantly (Fig. 1A), whereas no changes were detected for lutein, zeaxanthin, ?-crytoxanthin, and ?-carotene. Also, TAS significantly increased as a result of the intervention, with a mean change from 1.46 to 1.59 mmol/L (p=0.001) (Fig. 1B).

Figure 1 Serum carotenoids and Total Antioxidant Status before and after the dietary intervention Carotenoids and Total Antioxidant Status (TAS) before and after a 2 weeks intervention designed to increase compliance with the Norwegian food-based dietary guidelines. *p<0.05. Open circles indicate statistical outliers.

Fatty acid profiles in whole blood reflect the dietary intake of fatty acids. Long-chain n-3 fatty acids EPA (C20:5 n-3), DHA (C22:6 n-3) and DPA (C22:5 n-3) are biomarkers for intake of fatty fish, and the saturated fatty acids C15:0 and C17:0 are biomarkers for dairy fat. We found significantly increased levels of EPA (36.2 %, p=0.01), DPA (7.8 %, p=0.001), and DHA (9.3 %, p=0.002), indicating an increased intake of fatty fish (Fig. 2A). The serum levels of both C15:0 (p=0.06) and C17:0 (p=0.001) decreased during the intervention (Fig 2C), indicating a lower intake of dairy fat, while the levels of the saturated fatty acids C14:0 (p=0.048) (Fig. 2B) and C20:0 (p=0.02) (Fig. 2D) were lower post intervention, further underscoring a shift in the dietary fat intake.

Figure 2 Fatty acid profiles in DBS before and after the dietary intervention Fatty acids in «Dried Blood Spots» from whole blood was measured before and after a 2 week intervention designed to increase compliance with the Norwegian food-based dietary guidelines. *p<0.05. Open circles indicate statistical outliers.

Since the main aim of the NFBDG is to promote public health and prevent chronic degenerative diseases, we investigated whether blood lipids, blood pressure, fasting blood glucose or body composition could be affected by the intervention even in a young healthy population. Surprisingly, HDL-cholesterol significantly increased during the intervention (8.2 % increase; p=0.04) (Fig. 3). No significant changes were observed for total cholesterol (0.20 ± 0.47 mmol/L, p=0.10), LDL-cholesterol (0.16 ± 0.52 mmol/L, p=0.30) triglycerides (-0.18 ± 0.47 mmol/L, p=0.20), or fasting blood glucose (-0.05 ± 0.50mmol/L, p=0.57). There were no statistically significant correlations between the changes in HDL and triglycerides, or between the changes in the omega-3 fatty acids and triglycerides, HDL-, LDL- or total cholesterol (data not shown).

Figure 3 HDL in serum before and after the dietary intervention Serum HDL was measured before and after a 2 weeks intervention designed to increase compliance with the Norwegian food-based dietary guidelines. *p=0.038. Open circle indicates a statistical outlier.

Discussion

In this single-arm, two-week dietary intervention study, 14 young females increased their compliance with the NFBDG, as measured by biomarkers of fruit- and vegetable-, fatty fish- and dairy intake, showing achievability of the NFBDG in a young healthy population. Furthermore, HDL-levels significantly increased during the intervention period, indicating effects even on common biomarkers of disease risk in this healthy population. Most importantly, the current study shows a «proof-of-principle» that increased compliance with the NFBDG may introduce positive effects even in a highly educated, young healthy population.

Several previous studies have found associations between compliance with FBDG and reduced all-cause mortality or risk of cardiovascular disease (12 – 15), however these studies almost exclusively focus on high-risk populations. In the PREDIMED study, compliance with a Mediterranean-like diet increased during a 12-month intervention mainly based on motivational interviews in a population at increased risk of cardiovascular disease (16). We demonstrate that compliance with the NFBDG can be increased and achieved in a young healthy population, and that this might be important for the prevention of chronic disease.

Compared to average intakes in Norway, the plasma levels of carotenoids were high in the study population at baseline (10), confirming a healthy profile of the participants prior to the study. This was further underscored by the compliance with the NFBDG for fish, fatty fish and red meat prior to the intervention. Also, the study population was well above the average Norwegian population in terms of the total intake of fruits and vegetables (7). Based on the high level of compliance with the NFBDG prior to the study, and the level of nutrition literary, our study population should have had solid prerequisites to fulfill the NFBDG. On the other hand, a young, healthy population might lack the personal motivation to change towards an even more healthy diet, and this might in part explain why our population does not fulfill all the NFBDG. Thus, even a presumably healthy population with high nutrition literacy could benefit from increased compliance with the NFBDG.

The increases in plasma carotenoids and TAS indicates increased fruit and vegetable intake (17, 18), comparable to changes found by increasing from 300 g to 750 g of fruits and vegetables per week (19). Furthermore, the increase in omega-3 fatty acids in blood is most likely due to an increased intake of fatty fish (20), which may also be linked to increases in HDL also seen in other studies with increased fish intake (5, 21, 22). Even though the biomarkers indicate increased fish intake, the self-reported intake showed no significant differences. We speculate that the biomarkers are more sensitive to small changes in intake than the FFQ.

Our intervention also included physical activity, which may have contributed to the increases in HDL-cholesterol (23, 24). This increase in HDL-cholesterol is encouraging in terms of prevention of disease, since it indicates health effects even in healthy populations.

The NFBDG aims to promote health and prevent chronic disease in the general population. Estimations from the national Norkost 3 survey in Norway indicates that less than 10 % of the population fully comply to all NFBDG, while about 1/4th of the population comply to the NFBDG for whole grains and fruits and vegetables; about 1/3rd comply to the advice on fish intake, and 45 % of men and 67 % of women eat within the recommendations for red meat (7). The current study population consist of master levels students in clinical nutrition with previous knowledge of the NFBDG. Therefore, our population presumably has a high compliance with the current advice on diet and lifestyle. The significant increases in carotenoids, TAS and PUFA, and decreases in dairy-related saturated fatty acids, are thus somewhat surprising and indicate substantial changes in the dietary intakes. Even in a population with high prior knowledge of the advice and the health effects of the NFBDG, compliance can be increased by relatively simple measures such as small economic incentives and repeated reminders. Our findings might imply that it would be of public health interest to target the young population (such as students) to a greater extent, in order to lower the future burden of disease.

The single-arm, non-blinded design with the study group as participants introduces an obvious risk of performance bias and possibly pleasing bias in the current study (25). These possible biases could interfere with the FFQ results; however, the results from the biomarkers should not be affected even if such biases are present. Also, to reduce the risk of bias, biomarker analyses, data analyses and data interpretation were performed by researchers outside the study group.

Conclusions

Our study is «proof-of-principle» that the NFBDG are applicable and achievable for a young, healthy population. Also, our results indicate that increased compliance with the NFBDG can improve biomarkers of chronic disease even in a presumably healthy population.

Competing interests

The following authors declare no competing interest; IP, ETA, HA, MB, ME, IH, KaH, KrH, KSH, JL, HW, ESN, SLS, KT, AROV, HBH.

RB has interests in Vitas AS which was established by Oslo Innovation Center.

The study was financed by the Department of Nutrition, University of Oslo, Norway. Furthermore, the study was supported by products from BAMA (Oslo, Norway) (fruits), Q-meieriene (Bergen, Norway) (Skyr (a low fat dairy product)), and CopyCat (Oslo, Norway) (printing of brochures).

Author’s contributions

ETA, HA, MB, ME, IH, KaH, KrH, KSH, JL, HW, ESN, SLS, KT, AROV (The ERN4120 Study group), IP, and RB designed the study. The ERN4120 study group conducted the blood sampling under supervision of IP, and HBH. HBH provided the FFQ and prepared FFQ-data. IP analyzed data, and wrote the paper with contributions from the ERN4120 study group. All authors read and approved the final manuscript.

Acknowledgements

Nasser Bastani performed carotenoid analyses; Siv Å. Wiik performed MaxMat analyses. Siv K. Bøhn, Hanna Ræder and Torunn E. Tjelle contributed valuable advice and technical help.

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