Limits and truths of dietary advice
“As a long-time subscriber, here’s what I think. I love the nutritionist’s column. It’s always interesting, though I know a couple of months later she’ll totally rescind everything she said before. Very funny.”
This feedback, submitted by a loyal reader as part of an itemized report card of the National Post, could be construed as criticism. On the other hand, it could also be thought of as a gateway to some very important dialogue. Why is it that we hear one thing in nutrition research, only to be told something seemingly contradictory a short time later? For example, how is it possible that, after years of intense pressure to reduce our sodium intake, we now have new evidence that cutting too much salt out of our diet could do us harm?
These questions don’t necessarily have simple answers, but if we step back and take a broader perspective of food and nutrition, as well as research and the scientific method, a few important concepts do emerge. So, the next time you read something about nutrition that seems contradictory, keep a few of these points in mind:
1. Nutrition, like all aspects of science and medicine, is an evolving area of study At any given moment, there are thousands of studies being conducted on food and nutrition, all around the world. Most of the results won’t make any headlines, but it all contributes to the fabric of what we now know. The bottom line? It is always possible that tomorrow’s findings will change the way we think of things today.
2. It is difficult to assess the impact of a single nutrient on our health This is one of the great challenges and potential shortcomings of the reductionist method of nutrition that targets individual nutrients. Focusing on fibre, omega-3 fatty acids or vitamin C may keep things straightforward, but it tends to undervalue the interrelation of the dozens and in some cases even hundreds of nutrients in each food.
3. The endpoints of nutrition research can be difficult to define While the aim of research on a drug, by comparison, is to assess its impact on a particular medical condition over a set period of time, it is much more challenging to track all of the possible outcomes — both good and bad — for different nutrients and eating habits that affect every element of our being, especially when considered over years or decades.
4. The findings of one study are exactly that Bias is an inherent risk in all research — it is human nature to see what we want to see, after all — but the best researchers design their studies to reduce its impact. Even so, multiple studies need to be conducted by different research groups to determine whether a single finding is valid, or an anomaly.
5. The findings of a study do not necessarily translate across the entire population This is true whether the experiment is being performed on cell lines, animals or even one part of our population, such as post-menopausal women or African-American men.
In spite of the challenges inherent in conducting and interpreting research, there are some general “truths” that have evolved over time. Among them:
- Food is more complex and more valuable than individual nutrients. And, by extension, diets based on nutrient-dense whole foods are increasingly being shown to be the most healthful. We now have good evidence, for example, that higher carbohydrate plant-based diets, and lower carbohydrate diets that are rich in animal protein, can both be effective for reducing heart disease risk. Despite the obvious differences, one common denominator is they both include little low-quality “junk food.”
- There is a U-shaped curve for many, if not most aspects of nutrition. When it comes to hot-then-not nutrients such as vitamin E, it’s not uncommon that the doses that have caused problems could be considered pharmacological. Put another way, just because something is good for you, doesn’t necessarily mean that more is better.
- There is more to nutrition than nutrition. Sleep, stress, exercise, exposure to pollutants, and mental health — just to name a few — all influence the way our bodies function. These elements need to be considered in nutrition research.
- The placebo effect is strong.
- We tend to create our own narratives about health (and life) that influence the way we interpret things we read, hear and experience. For example, if we believe the caveman diet is the healthiest way to eat, or that vitamin D is (or isn’t), critical to human health, then we will be more likely to believe a story that supports what we already believe. And if the finding refutes what we believe, we will be more likely to find fault or dismiss it.
- If in doubt, remember to eat mostly vegetables. Everything else is controversial.
Jennifer Sygo is a registered dietitian at Cleveland Clinic Canada (clevelandclinic.ca), which offers executive physicals, sports medicine and prevention and wellness counselling in Toronto.
