is an apple a day really good for you?

prioritizing a healthy lifestyle can become a struggle when we don’t know where to get our information. and this is information that is particularly significant – historically, cardiovascular disease has been the  costliest disease in canada  while obesity is estimated to have an  economic burden of $4.6 to $7.1 billion  annually.

coronary artery disease refers to blockages in the blood vessels of the heart that can lead to heart attacks. it is the  number one cause of death  worldwide. risk factors include high cholesterol, high blood pressure, diabetes, obesity and smoking, all of which are considered modifiable risk factors, with the first four modifiable by diet.

data from the organization for economic cooperation and development tell us that almost 60 per cent of the population of member countries are overweight, with 40 per cent of these individuals classified as obese. morbid obesity, in particular, is on the rise, with morbid obesity accounting for more than 70 per cent of total obesity growth in the united states. the  heavy burden of obesity , an oecd study, says the increasing number of people who are overweight will curb gross domestic product by an estimated 3.3 per cent on average and that for every dollar spent on preventing obesity, the economic return is up to six dollars. these factors are what make having good data on diet and nutrition so important.

but even with the mighty “randomized controlled trial,” we need to be careful. as doctor, epidemiologist and writer amitha kalaichandran  puts it , “one study is just one study… if findings from one study were enough to change medical practices and public policies, doctors would be practicing yo-yo medicine where recommendations would change from day to day.” she warns that we must be wary of headlines that state “a study found” (often what we see in headlines about nutrition), as one study alone often is not enough evidence to change behaviours – study results should be replicable. red meat illustrates the “yo-yo,” garnering a bad reputation over the years, linked to health risks like heart disease and various cancers.

a study published in annals of internal medicine in 2019 , however, led to news headlines on variations of the general idea that red meat is not so bad. since then, a number of researchers  have questioned the methodology and accuracy of these results, once again pushing us to believe red meats may in fact be bad for us.

additionally, these trials often follow subjects for short time periods, making it difficult to extrapolate to long-term outcomes since the sustainability of these diets is called into question. these points are nicely illustrated in a study published in jama network open indicating that 86 per cent of diet trials had a significant discrepancy from the initial registration with clinicaltrials.gov while this rang true for only 22 per cent of drug trials.

also important to recognize are the stakeholders involved in making recommendations. for example, the accuracy of recommendations put forward in the latest  canada food guide , published in january 2019, was questioned by organizations like the dairy farmers of canada and alberta beef producers. unsurprisingly, the new guide deemphasizes dairy and pushes plant-based protein for a healthy diet.

in direct contradiction to the greater challenges we face with diet trials compared to drug trials, diet trials receive much less funding. david ludwig, co-director of the new balance foundation obesity prevention centre at boston children’s hospital and a professor of pediatrics at harvard medical school, and steven heymsfeld, professor and director of the metabolism and body composition laboratory at pennington biomedical research centre, louisiana state university, put it eloquently in their new york times article : issues with quality control in diet trials lead to “underinvestment in nutrition research and in how we tackle the mysteries of a healthy diet.” they argue that “nutrition research to  prevent  disease must have the same quality and rigor as pharmaceutical research to  treat  disease.”

despite these challenges, a select few diets have been proven to be beneficial. for example, a study published in the new england journal of medicine , effectively showed that a mediterranean diet, high in extra-virgin olive oil or nuts, is associated with a lower risk of major cardiovascular events, specifically heart attack, stroke or death from a cardiovascular cause, than a reduced-fat diet. this study, overall, is felt to be a high-quality study based on metrics such as the number of participants enrolled (7447 participants) and the long follow-up period (median 4.8 years).

another example is the portfolio diet , a plant-based diet that encourages cholesterol-lowering foods including nuts, plant proteins, soluble fibre and plant sterols. while the randomized controlled trial is considered the highest form of primary evidence, the meta-analysis takes it a step further by pooling the results of multiple studies to find trends and draw conclusions based on all available data. the portfolio diet emphasizes a pattern of eating as opposed to a strict regimen to make it practical and to encourage uptake. a meta-analysis on this diet and cardiovascular disease found that following its recommendations leads to improvements in lowering “bad” cholesterol, blood pressure and 10-year coronary artery disease risk.