The prevalence of overweight and obesity among adults worldwide is high with an increasing trend. Therefore, effective strategies in relation to body weight management, targeting to maintain normal body weight and prevent excessive weight gain, are warranted. Reducing the energy density of the diet may aid to achieve these goals. Energy density of the diet can be reduced by substituting energy-dense food items with less energy-dense food items such as fruit and vegetables. Fruit and vegetables are considered as relatively low energy-dense food groups due to their high content of water and dietary fibre. Most research, currently available, including intervention and observational studies, has investigated the combined role of fruit and vegetables in relation to body weight. However, a separation between these two food groups seems important as they differ in terms of nutrient composition and culinary use.
The overall aim of the present thesis was to examine the potential role of fruit intake in relation to body weight management among adults. The specific objectives were to investigate the association between fruit intake and body weight and aspects of other dietary intake and further to investigate the effectiveness of available and accessible fruit on body weight, fruit intake and certain other dietary intake among free-living individuals. These objectives were attempted achieved by conducting four studies (paper I-IV) upon which the present thesis is based.
The state of the art on the role of fruit intake in body weight management, including the association between fruit intake and body weight and the effect of fruit intake on body weight, among adults was assessed by carrying out a review (paper I) encompassing all human prospective observational, cross-sectional and intervention studies that could be identified and that met the eligibility criteria. The eligibility criteria included that the studies presented separate analyses for fruit and had body weight as a primary aim.
The association between fruit intake and body weight was further investigated in a cross-sectional study (paper II) among 9,758 normal- and overweight subjects, nationally representative of the general adult population in Denmark, France, Hungary, Italy and the UK, representing the East, West, North and South of Europe.
The effectiveness of increased fruit intake on body weight change was examined in an 18-week cluster-randomised, controlled intervention study (paper IV) in UK, including 409 slightly overweight adults allocated into an intervention group, who had access to two pieces of free available fruit per person per day at the workplace and a control group who were not subject to any kind of intervention. As a precursor to the cluster-randomised controlled intervention study, a 5- month controlled feasibility intervention study (paper III) was conducted in order to investigate the possibility to increase fruit intake of the employees simply by increasing the availability and accessibility of fruit at the workplace. The study enrolled 124 mainly normal weight adults from eight Danish workplaces, divided into an intervention group with free access to at least one piece of fruit per person per day at the workplace and a control group who did not.
Only eight prospective observational and five cross-sectional studies and three RCTs could be identified that met the eligibility criteria and were hence included in the review. The majority of the cross-sectional and prospective observational studies showed a suggestive inverse association between fruit intake and body weight or long-term excess increase in body weight. In addition, the majority of the few RCTs showed that fruit intake reduced body weight. This was not supported by the cross-sectional study in paper II, which showed no significant association between fruit intake and body weight. However, there was a direct association between fruit intake and relatively nutrient-dense foods and beverages such as vegetables, fruit juice and processed fruit and an inverse association between fruit intake and relatively nutrient-dilute foods and beverages such as soft drinks and snack foods as well as energy density and E% from fat.
The feasibility study showed a significant increase of approximately 1½ portion of fruit per person per day at the end of the study in the intervention group which was significantly higher than the intake in the control group. Moreover, intake of dietary fibre increased significantly whereas intake of added sugar decreased significantly only within the intervention group not differing significantly than the intakes in the control group at the end of the study. Similarly, in the main intervention study, both groups increased their fruit intake significantly but the increase of approximately 0.7 portions of fruit per person per day at the end of the study was by 0.4 portions significantly higher in the intervention group than the control group. No significant between-group difference in body weight was seen at the end of the study, although those within the intervention group showed a tendency toward a borderline-significant reduction in BMI at the end of the study compared with baseline. Likewise, no significant between-group differences were seen in adiposity or blood pressure measurements at the end of the study but within the intervention group, a significant reduction in adiposity and diastolic blood pressure was seen at the end of the study compared with baseline. In terms of dietary changes, consumption of dietary fibre increased significantly in the intervention group at the end of the study, leading to a significant difference between the two groups. Additional interesting findings included a significant decrease in the consumption of sweets and snacks and E% from fat within the intervention group and significant increase in the consumption of soft drinks within the control group. No significant between-group differences were seen in the three latter dietary changes.
The present PhD thesis suggests that fruit may play a role in prevention of overweight and obesity over time, as the prospective observational studies in the review indicated an inverse association between fruit intake and long-term excessive increase in body weight. Whether fruit, per se, causes the inverse association or it is a marker of a lifestyle and dietary pattern that promote body weight maintenance and prevent overweight and obesity is unclear, as inference making on a causal relationship is precluded, among other things due to the observational nature of the underlying studies. The cross-sectional study in paper II further supports the indication that fruit intake may be positively associated with a dietary pattern adopted by relatively health conscious individuals.
Moreover, according to the present thesis, a simple intervention, comprising free available fruit at the workplace seems ineffective in terms of body weight change. However, such relatively simple interventions may be effective in increasing the consumption of fruit and may in addition enhance the overall quality of the diet.