With pharmacy teams’ focus having been very much on Covid-19, it is easy to forget about health promotion. One aspect of health promotion is heathy eating, and, of course, we are all encouraged to eat our ‘five-a-day’.
A recent review concluded that increasing intake of fruits and vegetables reduced the risk of developing cardiovascular disease and cancer. The reduction in risk was nonlinear and steeper at the lower rather than the higher range of intake. In other words, there was much to be gained by eating additional portions of fruit and vegetables, but the benefits for some conditions levelled off at higher intakes.
For example, the maximum reduction in cancer risk occurred at an intake of between 500-600g/day (i.e. further increases didn’t make any difference). In contrast, increasing intake further and up to 800g/day had the greatest effect (biggest reduction in risk) of coronary heart disease, stroke, cardiovascular disease (CVD) and all-cause mortality.
However, given that one ‘portion’ is defined as 80g, that’s a large amount of fruit and vegetables to swallow each day to achieve these benefits.
Nevertheless, in recent years, rather than specifically focusing on individual foods, there has been a shift towards the health benefits that accrue from eating a balanced diet. This can be seen in the NHS Eat well campaign, which advocates not only fruits and vegetables but some dairy, fish, eggs and starchy foods like pasta and rice. As an example, there is good evidence to show that reductions in CVD can be achieved by eating the broad range of foods contained in the Mediterranean diet.
In order to better understand the influence of a particular diet, rather than individual foods, on health outcomes, several dietary indices have been developed. These are designed primarily to assess the extent to which an individual’s eating habits conform to nationally recognised healthy eating recommendations.
By examining the results of a food-frequency questionnaire, i.e. what someone eats and drinks over a period of time, it is possible to derive a scoring metric (or index) to determine the quality of that person’s diet. One such index is the healthy eating index (HEI). Higher HEI scores represent a greater degree of adherence to a healthy eating regime.
Several other indices have been developed and validated, including the alternative Mediterranean diet score (AMED), the healthful plant-based diet index (HPDI), the alternate healthy eating index (AHEI). By using these tools, researchers can not only evaluate the healthiness of an individuals’ diet but potentially use these metrics to predict an individual’s risk of developing chronic diseases.
However, to date, few studies have examined the association between dietary indices and the risk of adverse health outcomes such as cardiovascular disease, so in a recently published study in JAMA Internal Medicine, a group of researchers from Harvard University examined the link between dietary index scores and health outcomes.
They used the US 2015-2020 dietary guidelines for Americans (DGAs) which defines healthy dietary eating patterns, e.g. wholegrain foods, fruits and vegetables, low fact dairy, lean meats etc. The team hypothesised that following these healthy eating guidelines would lead to a reduction in the incidence of CVD.
The study used data from three prospective cohort studies: The Nurses’ health study; Nurses’ health study II and the health professional’s follow-up study. These massive studies followed a combined total of nearly 280,000 individuals over a 32-year period, with follow-rates in each of the studies exceeding 90%.
None of the participants had CVD at the start of the studies and dietary information (using food frequency questionnaires) was collected from participants every two to four years, allowing researchers to see how often, on average, people consumed a standard portion of particular foods in the past year.
Using this information, they calculated an individual’s HEI, AMED, HPDI and AHEI scores which provided an assessment of the extent to which an individuals’ diet conformed to the DGAs. In the final analysis, data were available for a total of 209,133 individuals who were followed for an average of 32 years, during which time there were 23,366 cases of CVD. The researchers calculated hazard ratios (HRs) to assesses the relationship between the dietary index (e.g. HEI etc) and the outcome of interest, in this case the development of CVD. As an example, a HR of 1.25, means there is a 25% increased risk of developing CVD based on the dietary index score and conversely, HRs less than 1 are associated with a lower risk.
The results showed that the difference between the highest and lowest dietary index scores was associated with a 22% to 14% reduction (depending on which dietary index was used) in risk. In other words, for someone eating a healthy diet (and hence having a higher dietary index score), their risk of developing CVD was reduced by between 21% and 14%, compared to someone with the lowest dietary index score.
In summary, this new JAMA study provides further evidence that adopting a healthy eating pattern appears to be an effective strategy to reduce the risk of cardiovascular disease.