HEALTHY USER BIAS IN NUTRITIONAL RESEARCH
We recently began our “Kickback Science Diet Series” where we will be exploring the research related to common dietary approaches. Each “matchup” will showcase 2 different diets going head-to-head in a science showdown. We will pick a winner based on the amount of available evidence supporting the diet, and the potential impacts it may have on various health outcomes. The first matchup features the Vegan and Carnivore diets (those episodes are available now, so go check them out!).
The unfortunate part about nutritional research is that there is so much anger, aggression, politics, and debate involved. This makes it very hard to have a productive conversation, and more importantly, hinders the quality of research that is conducted within the field. The limited research that we do have is often “observational” and involves survey based assessments to determine the health impacts of various diets. Although observational studies are important, they are difficult to utilize when we are trying to determine “causality”.
For example, when you look into the research surrounding a vegan diet, you will see studies suggesting a variety of health benefits (improved mood, decreased risk of cancer, heart disease, etc.). The problem, however, is that the participants of these studies are subjected to “healthy-user bias”, which essentially means that the restrictive diet is not the only aspect of their health that they are focused on. Moreover, individuals that undergo a highly restrictive diet (such as the vegan or carnivore diet) are often more likely to exercise, focus on sleep, drink less alcohol, use less tobacco, etc. Each of these factors alone could have an impact on the outcomes being measured. This makes it difficult to suggest that It’s the diet ALONE causing the benefits, as opposed to the multitude of other healthy lifestyle interventions.
Healthy-user bias is one (of many) reasons we can find positive results in any diet that has ever been studied (paleo, Mediterranean, low-fat, etc.). Does this mean that every single diet is beneficial for our health? Probably not.. But the media doesn’t care. Instead, we see news headlines saying “Could Bacon Be One of the Keys to Living Longer?”, “Can Guzzling Cup After Cup of Coffee Make You Hear Things That Aren't There?”, or “Does Nutella Cause Cancer?”, you get the point… These false interpretations and misleading headlines have made it so difficult for the general public to determine what they should/shouldn’t be eating. Not only that, but it has created so much unhealthy debate that is based on incomplete evidence.
So what do we do with this information?
When it comes to nutrition, it is clear that there is no “one size fits all” approach. Everyone will respond differently to any given diet/food. The best piece of advice I can provide to help you navigate the crazy world of nutrition is: STOP SPENDING SO MUCH TIME ON WHAT YOU SHOULD AND SHOULDN’T EAT! Instead, spend that time and energy exercising. Unlike nutrition, exercise is an area of research that is not complicated at all.. No matter where you look, you will find that exercise improves all aspects of health, and does so in a much greater fashion than nutrition. I hope someday soon there will be less political influence within the nutrition industry. This will allow funding for the proper research to be conducted, so that we can have a better understanding of our diet, and a more productive conversation about how to approach nutrition. But until then…
GET MOVING AND LIFT HEAVY STUFF,
Dr. Luke
