Total fruits and vegetables showed a small non-significant inverse association among men and women with low carbohydrate intake; there was no association among the moderate and high carbohydrate groups. There was a smaller inverse association for total vegetables (but not for total fruits) with increasing carbohydrate intake. Similar trends were seen for green leafy vegetables and carotene-rich fruits and vegetables. The analyses controlled for the major cardiovascular risk factors. However, we cannot exclude the possibility that the associations may reflect residual confounding by additional factors related to dietary selection.
The association between total fruits and citrus fruit intake and ischaemic CVD is modest in the present study. Our previous publications from the same populations with shorter follow-up showed significant inverse associations between total fruit, citrus fruit and citrus fruit juice with ischaemic stroke(2
), but less with CHD(3
). In the present study, we combined CHD and ischaemic stroke and we found a weaker association, because the majority of cases were CHD. Since fruit and vegetable intake is self-reported, there is an inherent limitation in the accuracy of these data. We have found the validity of our FFQ to be good for both fruits and vegetables(11
). However, some misclassification of diet is unavoidable, and the non-differential misclassification would likely bias the associations towards the null. Because of the prospective design where diet was assessed prior to the occurrence of CVD, the ascertainment of diet was unlikely to be biased with respect to cardiovascular outcomes. Also, given our high socio-economic population, fruit and vegetable intake is on average higher in our cohort than in the general population. Hence, stronger effects seen at lower thresholds of intake could be missed.
The lack of association between total carbohydrate intake and CVD is consistent with our previous publications, which suggest that it is the form of carbohydrate rather than total carbohydrate intake which is important(20
). In a recent publication, a lower risk of CHD was seen only among women with low carbohydrate intake who consumed vegetable sources of fat and protein, but not among those consuming animal sources of fat and protein(22
). Although low-carbohydrate diets have been gaining popularity in recent years(23
), we were not able to capture the very low carbohydrate group in the present analysis. In our populations, energy-adjusted carbohydrate intake in fact showed a small increase over time in both cohorts. There were no consistent trends over time in intake of fruits, vegetables, green leafy vegetables, citrus fruit and energy-adjusted vitamin C. Fruit intake was strongly associated, but vegetables showed a very small correlation with carbohydrate intake over time. As expected, with increasing carbohydrate intake, there was an increase in whole grains but a much smaller increase in dietary and cereal fibre. The data for the present study spanned from 1984 to 2000, which was prior to the escalation in popularity of low-carbohydrate diets. Also, our population included health professionals, who may be less likely to adopt radically low carbohydrate diets. We still saw a lower intake of fruits and vegetables in the low carbohydrate intake group, which might probably be due to a low-carbohydrate high-fat diet being the less ‘healthy’ diet of the 1990s, as most behavioural risk factors were worse in the low carbohydrate group. In other words, because of the widespread recommendations about low-fat diets, people who consumed such diets tended to be more health-conscious and adapted a healthier lifestyle.
In conclusion, total fruit and vegetable intake was inversely associated with ischaemic CVD among persons with low carbohydrate intake. The inverse association was due primarily to vegetable intake. As consumption of fruits and vegetables also tended to be lower among those choosing low-carbohydrate diets, maintaining a daily consumption of at least 5 servings in this group would be important.