The main finding of this study was that frequent consumption of organic food among the pregnant women in the MoBa study was strongly associated with higher scores on the ‘health and sustainability component’ (PC1), i.e. a diet characterized by more vegetables, fruit and berries, and whole grain cereal products and less meat, including processed meat, white bread, refined cereal products, cakes and sweets, compared with participants with no or low consumption of organic food. Diets of the pregnant women with frequent organic consumption, consequently, were more in line with dietary recommendations for health as well as ecological sustainability.
In the multivariate part of the present study we have considered data based on first adjusting for amount of food eaten in order to highlight pattern rather than amount. We also decided to exclude beverages when extracting underlying dietary components (patterns) since they had strong dominance on the results. Thirdly we used standardization in order to give all the foods equal opportunity to contribute meaning which means that we consider relative differences in each of the foods rather than the dominating effect of those with the largest variance. This analysis revealed clear differences between ‘healthy’ and ‘unhealthy’ diets represented in particular by the score along the first principal component. In other studies of dietary patterns, contrasting patterns are often found, the first two typically being ‘prudent’ and ‘western’ (or denoted with similar names) [18
]. In the present study, however, both ‘healthy’ and ‘unhealthy’ diets are covered by the first principal component, represented by high and low scores, respectively. This dual dimension within the first component was also seen in a large cohort of pregnant women in Southampton [30
]. The first principal component extracted in that study was characterized by high intakes of healthy food items vs. unhealthy food items.
In the present study, two types of food issues were brought together: How food is produced and what kinds of foods that are eaten. The findings confirm that in the dietary practices of the pregnant women in this study, there was an association between these two food dimensions. We have no means of knowing the order in which choices were made and practices established: Did the choice of buying organically produced food form the choice of diet, or did more people who preferred certain types of diets choose organically produced foods – or did reflection about both these aspects of food mutually influence each other? Regardless of how these practices have developed, the significant differences in dietary characteristics are of relevance with regard to their ability to contribute to good health and ecological sustainability. Dietary recommendations aiming at both these goals are to a large extent overlapping. Central to ecological sustainability is eating lower in the biological food chain (i.e. more plant foods and less meat), because it maximizes the amount of high quality food for human nutrition relative to the ecological costs of production, and this also fits well with health advice.
We have previously reported a large difference in prevalence of vegetarians (+23 percentage points) among the pregnant women in MoBa who frequently ate organic food compared to those who did not [22
]. Since the total number of vegetarians was very low, however, (0.2%, ibid) the practical significance of the change in dietary pattern expressed as a shift of the whole group of frequent organic consumers from lower to higher scores on the ‘health and sustainability component’ (PC1) is by far much larger. An implication of this was that on average, the frequent organic consumers in the MoBa-study had a reported intake of over half a kilo more vegetables, fruit and berries weekly than those with low organic consumption, and they reached the Norwegian recommendations of ‘5 a day’ (500 g vegetables, fruit and berries a day), while those with no or little organic food in their diets were 65 g short of doing so.
In addition to a higher total consumption of vegetables, women with frequent organic consumption also ate a larger proportion of these vegetables raw. Higher intakes of ‘whole foods’ such as raw vegetables, fruit and berries, nuts, wholegrain bread and cereal products among the frequent consumers of organic food in the present study are in line with preferences for less processed and refined foods as reported by both Holt [32
] and Torjusen [33
], as well as consumers’ associations of organic food with characteristics such as ‘natural’ and ‘home made’ [16
]. Similarly, lower consumption of refined and processed foods such as processed meat, highly refined cereal products, potato chips (‘salty snacks’) and Pommes frites further confirms such trends. Characteristic in this respect is also the negative correlation between tomato ketchup and fresh tomatoes, as representatives of diets with ‘fast food’ or processed food vs. diets based on fresh produce and whole foods (see details in Additional file 3
: Figure S1).
There was large variation in use of different types of fat in the diet (Figure ), and the association between frequent consumption of organic food and more use of olive oil and cooking oil, which is in line with previous findings [33
], may be related to a larger emphasize on health among those who choose organic food.
The observed negative correlation between processed meat and meat from intensive production systems (such as pork) with negative loadings and meat from extensive production (lamb), with positive loadings on the ‘health and sustainability component’ (Additional file 3
: Figure S1), may be interpreted in light of ecological consciousness or a preference for what is perceived as more ‘natural’ or ‘closer to nature’.
In her study of dietary habits among organic consumers in the UK, Holt reported a shift away from a diet focused on meat, potato and bread, towards increased consumption of vegetable foods and in particular, the incorporation of non-traditional plant foods, such as nuts, pulses and grains into the diet, resulting in a greater diversity of protein and staple foods among consumers of organic foods [13
]. In the present study, frequent consumers of organic food had slightly lower percentage of energy derived from protein (Table ), as well as a higher relative proportion of proteins from plant foods rather than animal foods, but still a protein intake well within (and in the upper levels of) dietary recommendations for pregnant women [35
]. Higher intakes of foods such as nuts, pulses and legumes and soy products represent alternative sources of proteins in diets with less meat. We also recognize more diversity in ‘staple foods’: higher intake of less traditional grains such as millet, as well as higher intake of pasta and rice (Figure and Table ).
Our finding of higher average energy intake among frequent organic consumers (about 600 kJ/day more, Table ) is likely to be related to higher levels of physical activity, as we have previously found that a larger proportion of the frequent organic consumers in the MoBa-study exercised regularly and were normal or low weight compared to those with no or low organic consumption [22
]. Their food intake therefore seems to be more in balance with their energy expenditure.
The large sample size including women from both urban and rural regions, representing all age groups and socio-economic groups is a major strength in the present study. The large sample size ensures large variation in dietary composition and use of organically produced food. However, only 38.5% of those who were invited participate in MoBa, which imply that the prevalence of organic consumption may not be representative for all pregnant women in Norway. The potential influence of self-selection in MoBa has been evaluated, and no statistically relative differences in association measures were found between participants and the total population regarding eight exposure-outcome associations [36
]. Hence, the selection bias in MoBa is not likely to influence the associations between reported use of organic food and dietary behavior among the frequent organic consumers. The sum index is a relatively crude measure, but in spite of this we observed important associations between overall frequent organic consumption and dietary quality. We also observed differences in food and nutrient intakes between frequent consumers of the various organic food groups. When designing a new FFQ, as was done for the MoBa cohort, there is a trade-off between the number of questions and the burden imposed on respondents. If questionnaires ask in too much detail there is an increased risk of participant drop-out [37
]. We do not know how the MoBa FFQ influenced the participation rate, but 93% of the women participating in MoBa did answer the FFQ [21
Misreporting is a serious error in all dietary assessment methods [39
], and it has been shown that foods perceived as ‘unhealthy’ are underreported to a larger degree than foods perceived as ‘healthy’ [40
]. The food frequency methods challenges participants with complex cognitive tasks and is particularly difficult to answer early in pregnancy when many women are experiencing nausea and changes in appetite and eating patterns. However, the MoBa FFQ was developed and validated for use in pregnancy [24
] and the validation study demonstrated that relative to a dietary reference method and several biological markers, it produces a realistic estimate of the habitual intake and is a valid tool for ranking pregnant women according to high and low intakes of energy, nutrients, and food [41
We have previously reported that frequent consumption of organic food among pregnant women in the MoBa-study was not solely associated with socio-economic and lifestyle factors that are normally associated with good health [22
]. While women who consumed organic food exercised more frequently, a larger proportion of them also consumed alcohol and smoked during pregnancy (although total prevalences were low). Lower household income and lower as well as higher levels of education were associated with frequent organic food consumption. While the consumption of organic food was not typically associated with high socio-economic status and healthy lifestyle factors, the association between frequent organic consumption and diet quality appeared to be clearer: pregnant women who chose organically produced food also ate diets that were more in line with health recommendations. Dietary quality is especially critical in pregnancy and PCA-derived dietary patterns in pregnancy have been associated with various health outcomes in well-nourished populations, including gestational weight gain [42
]), preeclampsia [18
], foetal growth [43
] and post-partum depression [44
]. There are, however, few previous studies addressing the combination of organic food consumption and the general dietary patterns and quality among pregnant women.
A methodological implication of the present study is that information about the diet in general needs to be included in future studies of possible health outcomes related to organic food consumption. It will further be advantageous to have specific information about consumption of organic food of different food groups, since high consumption of organic meat was associated with a somewhat different dietary pattern than that of organic vegetables, fruit, cereal products, dairy products and eggs.
Large knowledge gaps remain in our understanding of the consumption of organic food, related food practices and possible implications for health of mother and child. It remains an unsettled question whether there are systematic differences in the absolute content of nutrients and other substances of importance for health in foods that are organically or conventionally produced. The food analyses in the present study are based on the same food tables for both organically and conventionally produced foods, because at present there are no separate data on organically produced foods in the form of systematic food tables. If such differences are present, estimates of nutrient intakes would be imprecise or wrong. There are knowledge gaps in our understanding of how the consumption of organic food may be related to health, both in short and long term. Findings that indicate possible associations between consumption of organic food and health, such as prevalence of allergic diseases among children in families with organic consumption [45
], will be addressed in future studies.