SEARCH

SEARCH BY CITATION

Keywords:

  • Dietary intervention;
  • glycaemic index;
  • protein;
  • weight-loss maintenance

Summary

  1. Top of page
  2. Summary
  3. Background
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Conflict of Interest Statement
  9. Acknowledgements
  10. References

The aim of this study was to describe the development and implementation of a multifaceted, low-fat, weight-loss strategy for a Pan-European randomized controlled dietary intervention study, Diogenes. There were 891 families with at least one overweight/obese parent who underwent screening. Eligible, overweight/obese adults followed an 8-week weight-loss phase with a fixed low-energy diet (800 kcal). On attaining weight loss of ≥8%, families were randomized to a 6- or 12-month low-fat (25–30%E) diet either based on national dietary guidelines or one of four interventions: low protein (LP)/low glycaemic index (LGI), LP/high GI (HGI), high protein (HP)/LGI and HP/HGI. The impact of each diet in preventing weight (re)gain was tested. A points-based system was used to manipulate dietary protein and carbohydrate. Manipulating carbohydrate composition involved substituting foods with a relatively high or low GI. A questionnaire was designed and completed by study investigators, providing feedback on the dietary intervention methods used to inform future interventions. The points system allowed macronutrient manipulations without compromising dietary flexibility or enforcing energy restrictions. Reported centre/participant differences in the ease of implementing the intervention may reflect dietary diversity and personal preferences for specific weight-management strategies. The points system provides a useful starting point for designing improved experimental paradigms for the manipulation of dietary intake in future trials.


Background

  1. Top of page
  2. Summary
  3. Background
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Conflict of Interest Statement
  9. Acknowledgements
  10. References

Overweight and obesity are increasing in both sexes, and at all ages, across the majority of European countries (1). In a recent WHO report, overweight was estimated to affect between 30% and 80% of adults and up to one-third of children in Europe (2), with rates of obesity increasing. The health consequences of these trends present a bleak outlook and is accentuated by the increasing numbers of children developing health problems, until recently, associated with adult life. Addressing the imbalance between energy intake and energy expenditure presents a huge challenge, and there is a pressing need to develop strategies to facilitate reduced energy intake and increased levels of physical activity.

A large body of evidence has demonstrated that a reduction in dietary fat content under ad libitum conditions can produce modest but clinically important weight loss in 6–12 months (3). For weight maintenance, decreases in fat intake must be offset by increases in energy consumed from carbohydrate (CHO) and/or protein, and there is growing interest in the impact of the amount and composition of other macronutrients on weight management (4).

The type of CHO in the diet has recently received much interest in relation to weight management. The glycaemic index (GI) is a system for the classification of CHOs based on the relative effect on postprandial blood glucose levels (5). It is hypothesized that by attenuating postprandial glucose peaks and so delaying or eliminating reactive late postprandial hypoglycaemia, low-GI foods may delay the return of hunger in comparison with high-GI foods (6). Such an effect on appetite control may reduce subsequent energy intake and so have a beneficial effect in weight control. Stabilization of glucose levels may also improve metabolic disease risk. Dietary GI has therefore been subject to much recent investigation in relation to body-weight management and disease risk, and a recent systematic review suggests positive effects on weight loss (7). However, findings have been mixed, and many studies have changed aspects of the diet other than solely the GI (e.g. fibre content). Thus there remains much debate on the role of GI per se. There is also some doubt about the practical utility of the GI concept in the context of dietary advice public health recommendations.

High-protein diets offer an alternative strategy to low-fat, high-CHO diets and have the potential to enhance satiety (8,9) and increase thermogenesis (10). The effectiveness of low-CHO, high-protein diets on weight loss (relative to low-fat diets) had, until recently, only been studied in the short term (11–14). However in a recent study it was shown that a low-CHO/high-protein diet led to greater weight loss than a low-fat diet over a 2-year period with a more favourable impact on some metabolic outcomes (15).

This paper describes the methods used to design and implement an extensive and complex ad libitum dietary intervention, in free-living individuals, involving the manipulation of total intakes of major dietary macronutrients (protein, CHO and fat) while simultaneously manipulating the GI of the diet. The strategy for the macronutrient intervention involved the development of a points-based system that allowed dietary flexibility both in terms of the amounts of food eaten and the types of food included at different eating occasions. The GI intervention was based on substitution of high- and low-GI foods by using country-specific food exchange lists reflecting the main sources of dietary CHO and availability of GI measures.

Developing and implementing multifaceted experimental dietary regimens are time-consuming and require careful consideration. Furthermore, additional challenges are faced in designing protocols for use across more than one country with differences in habitual intake and food composition data. A description of methods used and qualitative feedback from study researchers on the ease with which the Diogenes dietary intervention strategy was understood and implemented will provide a scientific and practical insight, for other researchers facing a similar challenge.

Methods

  1. Top of page
  2. Summary
  3. Background
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Conflict of Interest Statement
  9. Acknowledgements
  10. References

Experimental design

Diogenes (Diet, Obesity and Genes) is a Pan-European Programme consisting of five thematic blocks or Research and Technological Development Lines (RTDs). This paper, together with the paper by (16), describes the methodological aspects of the work conducted in RTD1 that involved a large-scale randomized, controlled, dietary intervention study conducted in obese/overweight families (adults and children) across eight European centres: Maastricht (the Netherlands), Copenhagen (Denmark), Cambridge (UK), Heraklion (Greece), Potsdam (Germany), Pamplona (Spain), Sofia (Bulgaria) and Prague (the Czech Republic). The aim of the intervention was to test the impact of low-fat diets differing in the proportion of protein and CHO and reductions in the GI on weight regain.

The study was approved by the local ethics committees in the respective countries. The protocol was in accordance with the Helsinki II and the UN Convention on the Rights of the Child. All study participants (including children where possible) signed an informed consent document after verbal and written instructions, and according to local legislation.

Participants

Families eligible for inclusion consisted of at least one overweight (body mass index > 27 kg m−2), but otherwise healthy parent aged less than 65 years with at least one healthy child between 5 and 18 years of age. The weight status of the children was defined according to gender – and age-adjusted iso-body mass index > 25 limits suggested by the International Obesity Task Force (17). Families where no biological relationship existed between parents and children (e.g. children were adopted) were included. Larsen et al. provide further details on the study exclusion criteria and study recruitment (16).

Low-calorie diet

A total of 772 families were recruited to the study. All eligible adults (= 932), but not children, followed an 8-week low-calorie diet (LCD) (Modifast®, Nutrition et Sante, France) consisting of 800 kcal d−1, 14%E fat, 42%E protein and 44%E CHO. In addition, 200 g lettuce, cucumber or tomatoes per day was allowed as a supplement to the LCD.

Families, in which at least one of the overweight/obese parents achieved the target weight loss (≥8% of initial body weight) during the LCD period were cluster-randomized according to the protocol described in (16). Participants were assigned to a 6-month low-fat (25–30%E) diet based on either current country-specific official dietary guidelines (Control) or one of four interventions: low protein (LP)/low GI (LGI), LP/high GI (HGI), high protein (HP)/LGI and HP/HGI. Target intakes in the LP diets were 10–15%E protein and 57–62%E CHO and in the HP diets 23–28%E protein and 45–50%E CHO. The aim was to achieve a reduction of 15 GI points in the LGI diets, compared with the high-GI diets. During the intervention period subjects were instructed to maintain their weight loss, and there were no restrictions on further weight loss.

Overall dietary intervention strategy

Specific strategies were developed to attain the four dietary intervention plans with the desired dietary protein : CHO ratio and GI. In designing the intervention strategy it was necessary to consider dietary manipulations that were in general agreement with healthy eating principles and which avoided inadvertent changes in dietary composition.

At six centres (UK, Greece, Germany, Spain, Bulgaria and the Czech Republic) participants received 6-month dietary instruction only and were followed up after a further 6 months (see Fig. 1). During the 6-month intervention period, participants purchased their food from ordinary supermarkets. In the remaining two centres (the Netherlands and Denmark) participants participated in an initial 6-month ‘shop model’. This involved provision of most foods, free of charge, from a specially established trial shop, together with dietary instruction. On completion of the shop protocol, families purchased foods in their usual environment according to their dietary instruction for a further 6-month period and were then followed up after another 12 months (see Fig. 1). The ‘shop model’ allowed control and monitoring of food purchases, and compliance was therefore likely to be higher than in the instruction centres.

image

Figure 1. Time line for dietary instruction centres only (grey) and shop model centres (black). CID, clinical investigation days; LCD, low-calorie diet.

Download figure to PowerPoint

Families assigned to one of the intervention diets were given careful, intensive and regular dietary and behavioural guidance during the intervention period i.e. 6 months for the ‘instruction’ and 12 months for the ‘shop’ model both individually and in groups. In contrast to the intervention groups, the control group did not receive advice regarding the macronutrient composition (protein : CHO) or GI of their diet, but healthy eating recommendations only.

During the intervention period, families attended nine dietitian visits at the ‘instruction-only’ centres and 16 visits in the ‘shop’ centres. The visits took place every 2 weeks up to week 6 and once a month thereafter. Most visits were individual family sessions, but group sessions were encouraged at week 14, 18 and 22. Weight, adverse events and dietary compliance (using a compliance questionnaire specifically developed for the study) were assessed at each visit. In addition to focusing on the specific dietary intervention and general healthy eating advice, the dieticians also covered other aspects related to food intake including eating patterns and eating behaviour together with physical activity and general health issues. The centre dieticians were provided with a guideline on the topics to cover, which they were encouraged to follow. However they were allowed to change or omit topics in order to individualize the treatment according to individual family's needs. No standardized material for the behavioural arm of the dietary intervention was provided, and the different centres were encouraged to use and develop their own material.

During the intervention period adherence to the macronutrient composition of the diet was emphasized while allowing ad libitum energy intake. Therefore, the diets' ability to satisfy and control appetite is the key focus of the intervention and will be tested by measuring the impact on body weight.

Recommendations for healthy eating

The dietary intervention targets were positioned within the context of national healthy eating recommendations as far as possible. These were broadly similar in each of the participating countries and included lowering both total and saturated fat intake, emphasizing a minimum intake of fruit and vegetables per day, consuming two portions of fish per week and restricting sugary foods/drinks and alcohol.

Strategy for macronutrient (protein : CHO) intervention

A points-based system was chosen as the primary tool to attain the desired proportion of dietary protein and CHO in the prescribed diets in order to facilitate ad libitum eating and give flexibility in terms of the types of foods included at different eating occasions.

The points system was based on the following rationale. In the HP diet, the target energy from dietary CHO was approximately twice that from protein and in the LP diet approximately five times i.e. Protein : CHO (%E) ratios of 1 : 2 and 1 : 5 respectively. Given that each gram of protein and CHO contributes a similar amount to energy intake the points system was devised so that for every gram of protein eaten, participants would eat either 2 g of CHO on the HP diet or 5 g of CHO on the LP diet when used correctly. So that participants would not have to calculate ratios, tables of commonly eaten foods were developed, in each study centre, and units of protein and CHO were calculated for specific servings for both the HP and LP intervention groups (see Fig. 2 for example of calculations). In this way participants were instructed to eat the same amount of protein and CHO units.

image

Figure 2. Example of calculation of protein and CHO units for a 90 g banana on the HP and LP intervention groups. CHO, carbohydrate; HP, high protein; LP, low protein; PRO : CHO, protein : CHO.

Download figure to PowerPoint

Foods included in the tables were those regarded by centre-specific researchers to be commonly eaten foods within their country and consistent with ‘healthy eating’ principles. The quantities of food described in the tables were based on individual units or small quantities that could easily be multiplied to smaller or larger portions. ‘Appropriate’ servings of foods were not imposed to ensure ad libitum intake was uninhibited. Participants were asked, where possible, to eat the foods listed in the tables. However if more diverse foods were eaten, participants were instructed to seek the advice of the centre dietitian/research assistant on the protein and CHO units of that food. Individuals were offered an electronic spreadsheet as a tool for calculating their protein and CHO units and were asked to aim for a protein : CHO of 1:1. As a guide, a discrepancy of ±3 units was considered acceptable if total intake (protein + CHO) was less than 50 units or ±5 units if total intakes were above 50 units.

Strategy for glycaemic index intervention

The Diogenes GI intervention was based on substitution of high- and low-GI foods by using country-specific food exchange lists reflecting the main sources of dietary CHO and availability of GI measures. The tables of foods used to check protein and CHO intakes were adapted to include either high- or low-GI CHO foods for the respective dietary regimens.

Across each of the countries, cereal products (including bread, breakfast cereals, rice and pasta) contribute a large proportion to CHO intakes compared with other dietary CHO sources, therefore emphasis was placed on appropriate substitutions within this food group to achieve the biggest GI differences between the high and low groups. For other sources of dietary CHO (including fruit/fruit juice, vegetables, legumes and dairy foods) further guidance was given to participants on choosing and avoiding certain products within these food categories. Cultural differences in dietary intake meant that centre-specific approaches were taken in respect to the GI manipulation, and Table 1 highlights some of the considerations underlying the different strategies undertaken.

Table 1.  Counter-arguments for different strategies to manipulate GI
  1. CHO, carbohydrate; GI, glycaemic index.

Discussion point 1: Potatoes should be avoided on the low-GI intervention
Argument forArgument against
‘In order to achieve bigger differences in GI, potatoes should be replaced by pasta or a low GI rice.’‘. . . this is [not] a realistic strategy, at least not in a potato loving country. . . . . . . . . Due to cultural differences every DiOGenes partner should make his own approach on this topic, either by replacing pasta by potatoes and vice versa or by guidance to different types of potatoes (cooked, baked, mashed, cold).’
Discussion point 2: Advice on fruit intake should be included in the GI manipulation
Argument forArgument against
‘. . . we very strongly believe that fruit has to be controlled in some way . . . . . . We agree that fruit seldom is a main CHO contributor and the GI differences are rather low, but  . . . , even small changes have influence on the overall result.’ ‘. . . we do not see any conflicts with public health guidelines by “discriminating” some fruit as long as we emphasize intake of 2–300 grams a day and support the intake of a wide range.’‘. . . we strongly believe that [advice on] fruit should be excluded. The contribution from fruit to CHO intake is generally low. . . .’ ‘The GI difference between the suggested low and high GI groups is small. Taken the effects of ripeness into account the real difference might even be smaller.’ ‘Discriminating against some fruits undermine the broader well established public health guidelines on fruit intake.’

Questionnaire

A questionnaire was designed to obtain feedback on the intervention strategy from investigators at each of the intervention centres. It also sought to identify centre-specific approaches to the standard protocol to reflect national dietary intakes and availability of data on the composition of foods. The questionnaire was designed to obtain data on the types and numbers of foods included in the tables of protein and CHO units, more information on centre-specific strategies to manipulate GI, feedback on the ease of implementation, understanding and perceived usefulness of the protein : CHO points system, further information on additional tools used to help compliance to each of the dietary prescriptions and any general comments regarding the dietary intervention protocol.

Results

  1. Top of page
  2. Summary
  3. Background
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Conflict of Interest Statement
  9. Acknowledgements
  10. References

At least one dietitian, nutritionist or research assistant from each of the centres completed the Evaluation Questionnaire on behalf of their respective lecture (for Greece, UK and Germany two individuals gave their combined responses). Most had been involved in the study throughout its duration.

Food tables of protein and carbohydrate units

The types of foods included in the protein : CHO tables were country-specific but generally included fruit and dried fruit, vegetables, legumes, cereal products (e.g. bread, rice, pasta, potatoes, breakfast cereals, couscous, bulgur, buckwheat); dairy products, meat and poultry, lean and oily fish, eggs, vegetable protein (e.g. soy products), savoury snack foods, sweet snack foods, soups and beverages, convenience foods and cooked mixed products e.g. moussaka, pizza and lasagna.

Figure 3 shows the total number of foods contained in the tables for each dietary prescription at each of the centres. The average number of foods for each of the dietary prescriptions was similar across all centres (HP/LGI 211 ± 104; HP/HGI 204 ± 121; LP/LGI 214 ± 102; LP/HGI 210 ± 120), but the total number of foods varied between the different countries being highest in Denmark and Germany. In Bulgaria information on protein and CHO units was available for fewer foods on the high- compared with the low-GI intervention (see Fig. 2).

image

Figure 3. Number of foods included in the protein : CHO tables for each dietary prescription at each study centre. B, Bulgaria; CHO, carbohydrate; CR, the Czech Republic; D, Germany; DI, dietary instruction centres; DK, Denmark; ESP, Spain; G, Greece; HP, high protein; LGI, low glycaemic index; LP, low protein; NL, the Netherlands.

Download figure to PowerPoint

Centre-specific strategies to manipulate glycaemic index

Centres differed in terms of the number of food groups included in the strategy to manipulate GI (see Fig. 4). The UK and the Netherlands who had the lowest number also had the greatest number of foods with ‘in-house’ measurements of GI and therefore could be more confident of making true high- and low-GI substitutions and achieving target GI differences with a smaller range of foods. In the UK ‘in-house’ GI measurements were available for breakfast cereals (= 13 types), breads (8), pasta (2), rice (2) and potatoes (7 types and/or preparation) (18); in the Netherlands breads (5), sweet snacks (2) and rice (2) and in Denmark breads (7), breakfast cereals (1) and rice (3). Other centres relied principally on published values. All centres gave advice on bread/rice/pasta and breakfast cereals reflecting their large contribution to CHO intake in each of the countries. Further country-specific staple foods were also included e.g. in Greece and the Czech Republic advice was given to choose whole-grain foods on the low-GI diet. The predominant advice for pasta and potatoes was their avoidance or substitution depending on the GI prescription and/or the method of cooking (with shorter cooking times prescribed for the LGI diets). Basmati and/or long grain rice were in general prescribed on the low-GI diets; however, there was greater diversity across the centres on HGI choices for rice (i.e. basmati rice, short grain rice, sticky or jasmine rice, easy cook rice and white rice). Similarly the advice on selection of breads and breakfast cereals in the HGI and LGI groups showed substantial inter-centre variation and reflects the wide range of products eaten across the different countries and the extent to which GI values were available. For centres without in-house GI measures of these foods, a common element to the advice given for LGI bread was to include products containing whole grains (e.g. multi-grain bread, wholemeal bread with kernels and granary bread), and for breakfast cereals there was a tendency to prescribe oat-based and whole-grain cereals to the LGI interventions.

image

Figure 4. Food groups included in dietary instruction intervention strategy at each study centre. Grey shading indicates advice given. 1Shop centres. B/fast cereals, breakfast cereals; veg, vegetables.

Download figure to PowerPoint

Usefulness of system to implement dietary strategy

Researchers were asked a series of questions relating to the ease of understanding and implementation of the points system both by the research team and by participants. Responses were rated from on a 5-point scale [5 = strongly agree to 1 = strongly disagree]. The results are shown in Table 2. All centres agreed or strongly agreed that they understood the rationale of the protein/CHO points system, and this reflects the extensive training sessions given to the centre dietitians/research staff prior to the start of the study. The majority of centres agreed or strongly agreed that the points system was easy to explain (five out of eight) and was an easy or useful tool to help participants achieve their dietary targets (six out of eight) and for monitoring their compliance to the intervention (seven out of eight). Six out of the eight centres agreed that they would consider using a similar tool to manipulate intake in further dietary intervention studies. For the two remaining centres (UK and Greece), general comments given at the end of the questionnaire indicate less enthusiasm for this approach, with both centres indicating that participants would have preferred more prescriptive menus to work from (UK: ‘. . . . . . . . . participants thought it would be better if they had received at least a week's worth of . . . menus to work from’. Greece: ‘Subjects. . . . wanted to see a specific regimen, updated regularly, on what they are allowed to eat’.). The researchers' perceptions of how useful or easy participants found the points system to follow their dietary prescription were mixed. Researchers obtained feedback from participants on the points system, but only three centres agreed/strongly agreed that this feedback was positive. This may not be surprising given the extent of the dietary changes that participants were being asked to make and the likely impact on their usual lifestyle and may reflect the challenge of dietary change and not just the specific points system employed. The majority of respondents (= 5) to the questionnaire reported that once the points system had been explained, participants indicated that it was easy to use and half of the respondents thought participants found it a helpful tool in reaching their target intakes of protein and CHO. Most of the respondents (five out of eight) indicated that it took ≥1 h to explain the points system to participants with four centres indicating that >50% of participants needed further guidance after their initial dietary instruction visit. Six out of eight centres agreed that the participants tended to calculate their points in the first few weeks of the study, but only intermittently later in the intervention.

Table 2.  Number of centres responding to each category of agreement for statements on understanding and implementation of the points system
StatementStrongly agreeAgreeNeitherDisagreeStrongly disagree
 1. I fully understood the rationale behind the points system62   
 2. The points system was easy to explain to participants 512 
 3. The points system was an easy tool to help participants reach their dietary targets 6 2 
 4. The points system was a useful tool for monitoring participants' compliance to the dietary intervention25  1
 5. I would consider using a similar system in further studies to manipulate macronutrient intakes 6 11
 6. Most participants indicated that they found the points system difficult to understand1241 
 7. Once the points system had been explained, participants indicated it was easy to use14 3 
 8. Participants thought that the points system was a helpful tool in reaching target intakes of protein & carbohydrate 431 
 9. Generally there was positive feedback from participants on using the points system1232 
10. There was no feedback from participants on the use of the points system  332
11. Participants tended to calculate their points in the first few weeks of the study25 1 
12. Participants tended to calculate their points intermittently during the intervention161  
13. Participants did not calculate their points throughout the whole intervention period24 2 

Use of other tools to implement the dietary strategy

All centres used example full-day menus and/or meal and snack suggestions either as a supplementary method to implement the protein : CHO manipulation, or as a ‘teaching’ tool, to describe the proportions of foods that should be included in each meal to achieve the correct balance of macronutrients. The approach taken and the number of menu examples and meal/snack suggestions provided differed between the centres. Both the Netherlands and Denmark worked out menu examples and/or made meal and snack suggestions on an individual basis at the counselling sessions. Greece provided a relatively large number of menus and meal suggestions (for each diet: menu plans [60], meals [50] and snacks [10]), reflecting the comments, described earlier, regarding the preference of participants in this country for more prescriptive dietary regimens. For four of the remaining five centres (UK, Germany, Bulgaria and the Czech Republic) a similar number of example menus and meal/snack suggestions were provided for each of the diet groups (average number across centres: menu plans [2], meals [8] and snacks [3]). However, in Spain, a greater number were provided for the LP diets, which reflects the dieticians' comments that these diets were ‘very complicated to develop’.

Discussion

  1. Top of page
  2. Summary
  3. Background
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Conflict of Interest Statement
  9. Acknowledgements
  10. References

A fundamental tenet of the Diogenes project was to allow ad libitum energy intake in order to imitate real life. This presents a particular challenge for dietary prescriptions to achieve a particular macronutrient profile. In general, the centres viewed the points system as an appropriate tool to achieve the macronutrient manipulation. In addition it was designed to allow dietary flexibility without enforcing energy restrictions. While some research centres reported that their participants' had expectations of a more structured dietary regimen with individualized meal plans this was not consistent with the ad libitum study design. These expectations may have been influenced by participants' previous experiences of dieting. In addition, taking part in the initial LCD may have strengthened the participants' desire for a more structured approach; a dietician from one centre indicated that ‘the volunteers after following the LCD (very controlled) found difficulties to eat ad libitum’.

While the general principles of the dietary intervention were agreed among the consortium and standard operating procedures were developed, the between-centre dietary diversity and differences in access to nutrient composition data warranted a degree of local planning to implement the dietary interventions. In particular, it became evident during the training sessions, that there were population differences in the awareness of GI. For example, in the UK GI is an increasingly familiar nutritional concept with articles appearing regularly in popular media and supermarkets and some labelling of low- or medium-GI foods. In this centre there was a greater availability of GI data on commonly consumed foods. Furthermore it was possible for participants, if informed of the specific intervention to which they had been assigned, to implement more extensive changes to their diet that were consistent with either a high- or low-GI regimen. However these potential advantages were balanced against the potential drawback of participants perceiving the high-GI intervention as ‘less healthy’, reducing their enthusiasm to cooperate in the trial. These factors combined with differences in food intakes led to centre-specific food exchange lists and approaches to the GI intervention. It is interesting that those centres with the greatest access to in-house measures of GI implemented this intervention in fewer food groups while in other centres broader changes to the diet were prescribed. Further analysis of the data to compare the GI differential between the high and low groups by using each of these approaches may give some insight into the effectiveness of each strategy.

Comments from study researchers indicated that some subjects found the points system ‘time-consuming’, ‘too difficult’ and not always an effective educational tool e.g. ‘They [the participants] . . . would snack at the end of the day to even out their intake’. However others ‘. . . did not struggle with the counting system and found it an easy way to keep track of their dietary intake’. There is evidence to suggest that different strategies for dietary manipulation (in particular weight loss) are more or less acceptable to different people (19) and finding a strategy to suit all individuals represents a real challenge. For example it is possible that, in this study, those with less numeric ability found the points system difficult to work with and for these subjects the provision of alternative methods e.g. menu plans and meal/snack suggestions may have been preferable. The degree of family involvement may also have been an influential factor, e.g. study involvement may have been driven by one individual on whom the responsibility fell for the whole family's compliance to the dietary prescription. In the questionnaire one centre reported that ‘There was a tendency that the women had to do the job for the whole family’.

The questionnaire gives some insight into how workable and useful researchers and participants found the intervention strategy in achieving the dietary targets. However the responses were taken from only one or two members of the research team at each of the study centres and may not reflect wider views. It also relies on the recall of past experiences, the questionnaire having being administered only on completion of the study. In addition there is potential for bias in the responses with researchers likely to have received more feedback from those participants who found difficulties in following the intervention protocols and hence to have focused more attention on negative comments.

Conclusions

  1. Top of page
  2. Summary
  3. Background
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Conflict of Interest Statement
  9. Acknowledgements
  10. References

For EU projects the desire for a controlled dietary intervention needs to be set against the flexibility required to meet the needs of a heterogeneous population, with significant differences in food habits, in diverse countries across Europe. The points system used in Diogenes provides a useful starting point for designing improved experimental paradigms for the manipulation of dietary intake in future trials; however, there is scope for further methodological development that may be informed by the feedback from study investigators and participants on the implementation of intervention tools in the Diogenes study.

Acknowledgements

  1. Top of page
  2. Summary
  3. Background
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Conflict of Interest Statement
  9. Acknowledgements
  10. References

The authors would like acknowledge the following investigators at each of the sites for contributing feedback to the questionnaire on the design and implementation ofthe dietary intervention study: Sandy Monsheimer, Pia Håkansson, Dorle Schreiber, Danielle Jackson, Angeliki Papadaki, Anna Viskadourou, Angela Koh, Daniela Hoffmann, Maria Hernández Ruiz de Eguilaz, Teodora Handjieva-Darlenska, Vaclava Kunova.

References

  1. Top of page
  2. Summary
  3. Background
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Conflict of Interest Statement
  9. Acknowledgements
  10. References
  • 1
    Silventoinen K, Sans S, Tolonen H, Monterde D, Kuulasmaa K, Kesteloot H, Tuomilehto J. Trends in obesity and energy supply in the WHO MONICA project. Int J Obes Relat Metab Disord 2004; 28: 710718.
  • 2
    WHO. WHO European Charter on counteracting obesity. W. Organisation, Editor. Istanbul, Turkey. 2006. [WWW document]. URL http://www.euro.who.int/document/E89567.pdf (accessed 1 October 2008).
  • 3
    Astrup A, Grunwald GK, Melanson EL, Saris WH, Hill JO. The role of low-fat diets in body weight control: a meta-analysis of ad libitum dietary intervention studies. Int J Obes Relat Metab Disord 2000; 24: 15451552.
  • 4
    Saris WH, Tarnopolsky MA. Controlling food intake and energy balance: which macronutrient should we select? Curr Opin Clin Nutr Metab Care 2003; 6: 609613.
  • 5
    Jenkins DJ, Wolever TM, Taylor RH, Barker H, Fielden H, Baldwin JM, Bowling AC, Newman HC, Jenkins AL, Goff DV. Glycemic index of foods: a physiological basis for carbohydrate exchange. Am J Clin Nutr 1981; 34: 362366.
  • 6
    Ludwig DS. Dietary glycemic index and obesity. J Nutr 2000; 130(Suppl.): 280S283S.
  • 7
    Thomas DE, Elliott EJ, Baur L. Low glycaemic index or low glycaemic load diets for overweight and obesity. Cochrane Database Syst Rev 2007 (3): CD005105.
  • 8
    Porrini M, Santangelo A, Crovetti R, Riso P, Testolin G, Blundell JE. Weight, protein, fat, and timing of preloads affect food intake. Physiol Behav 1997; 62: 563570.
  • 9
    Rolls BJ, Hetherington M, Burley VJ. The specificity of satiety: the influence of foods of different macronutrient content on the development of satiety. Physiol Behav 1988; 43: 145153.
  • 10
    Mikkelsen PB, Toubro S, Astrup A. Effect of fat-reduced diets on 24-h energy expenditure: comparisons between animal protein, vegetable protein, and carbohydrate. Am J Clin Nutr 2000; 72: 11351141.
  • 11
    Westerterp-Plantenga MS, Rolland V, Wilson SA, Westerterp KR. Satiety related to 24 h diet-induced thermogenesis during high protein/carbohydrate vs high fat diets measured in a respiration chamber. Eur J Clin Nutr 1999; 53: 495502.
  • 12
    Skov AR, Toubro S, Ronn B, Holm L, Astrup A. Randomized trial on protein vs carbohydrate in ad libitum fat reduced diet for the treatment of obesity. Int J Obes Relat Metab Disord 1999; 23: 528536.
  • 13
    Nordmann AJ, Nordmann A, Briel M, Keller U, Yancy WS Jr, Brehm BJ, Bucher HC. Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials. Arch Intern Med 2006; 166: 285293.
  • 14
    Gardner CD, Kiazand A, Alhassan S, Kim S, Stafford RS, Balise RR, Kraemer HC, King AC. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA 2007; 297: 969977.
  • 15
    Shai I, Schwarzfuchs D, Henkin Y, Shahar DR, Witkow S, Greenberg I, Golan R, Fraser D, Bolotin A, Vardi H, Tangi-Rozental O, Zuk-Ramot R, Sarusi B, Brickner D, Schwartz Z, Sheiner E, Marko R, Katorza E, Thiery J, Fiedler GM, Bluher M, Stumvoll M, Stampfer MJ. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. N Engl J Med 2008; 359: 229241.
  • 16
    Larsen TM, Dalskov S, Van Baak M, Jebb SA, Kafatos A, Pfeiffer A, Martinez JA, Handjieva-Darlenska T, Kunesova M, Holst C, Saris WHM, Astrup A. The Diet, Obesity and Genes (Diogenes) Dietary Study in 8 European countries – a comprehensive design for long term intervention. Obes Rev 2009; doi: 10.1111/j.1467-789X.2009.00603.x.
  • 17
    Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. Establishing a standard definition for child overweight and obesity worldwide: international survey. BMJ 2000; 320: 12401243.
  • 18
    Aston LM, Gambell JM, Lee DM, Bryant SP, Jebb SA. Determination of the glycaemic index of various staple carbohydrate-rich foods in the UK diet. Eur J Clin Nutr 2008; 62: 279285.
  • 19
    Truby H, Baic S, DeLooy A, Fox KR, Livingstone MB, Logan CM, Macdonald IA, Morgan LM, Taylor MA, Millward DJ. Randomised controlled trial of four commercial weight loss programmes in the UK: initial findings from the BBC ‘diet trials’. BMJ 2006; 332: 13091314.