What does the term "evidence-based advice" even mean? How are nutritional guidelines formulated? How come nutritional advice keeps changing, and why the heck can't anyone agree?
"Evidence-based advice". It can be rather reassuring to hear this term, especially when your health is involved.
Would you take the advice of a doctor or nurse who had just read about a cool new treatment on the internet, and wanted to try it on you? Yeah, nah. Qualified health professionals base their advice and treatment options on scientific evidence, not the number of "likes" a post gets on social media (thank goodness).
So how do nutrition professionals get their hands on the evidence they require?
The study of human nutrition, although relatively new, is still a science (and for the nerds, here is a little history of modern nutritional science from the British Medical Journal - you can even download a cool poster graphic!). As such, it employs the scientific method. This is a step-by-step and very ordered way of investigating the world around us, and involves the following 6 steps:
you make an observation about something
you formulate a hypothesis to explain what you've observed
you make some predictions about what will happen, based on this hypothesis
you test those predictions, using an experiment or further observations
you tweak your hypothesis if the results of your experiment or observations deem it necessary
you repeat all of these steps until the hypothesis matches the results of your experiments or observations very closely
Now, your use of the scientific method hasn't proven your hypothesis to be true. What it has done is gradually tweaked and strengthened your hypothesis, and refined your understanding of what you originally observed.
What you are left with after all the testing of your hypothesis, is a theory. A scientific theory is an explanation of what you have observed that has been substantiated by repeated testing - all those exhausting experiments or observations you performed! (click here for a quick run-down of the most common mis-used scientific words from the Scientific American website).
As the great Carl Sagan once said:
"Humans crave absolute certainty...but the history of science teaches that the most we can hope for is successive improvement in our understanding".
...and:
"Science is a self-correcting process".
Nutrition science is no different. The more research is undertaken, the more refined our understanding becomes, but there is no absolute certainty. There will still be some doubt remaining, but as the body of evidence grows, we become more and more confident about certain relationships, and consensus is reached. This means that the "totality of evidence" supports certain food/nutrient and disease relationships, and so dietary guidelines reflect this.
Also, nutrition research (by virtue of needing to test hypotheses) can sometimes focus on a single factor - a specific nutrient, a particular food - in order to learn more about its effect on health. But real people don't live in the sort of controlled conditions required during experiments, neither are they unaffected by a whole host of other factors in observational studies. Therefore, rather than the occasional contradictory result from a single study leading to changes in dietary recommendations, the results add to the body of evidence, and can lead to new research that further investigates those results. If, over time, the totality of evidence points in a different direction, then dietary guidelines will be modified.
An example of such a modification can be seen in the case of eggs. Where it was previously thought that eating foods that contained cholesterol would directly impact the levels of cholesterol in the blood (and therefore everyone should limit egg consumption to a maximum of three per week), further research found that it was the intake of saturated fat that had the most impact on cholesterol. Current advice is that even those at increased risk of heart disease can eat up to six eggs a week as part of a heart-healthy diet.
So, what does all this mean for me?
I'm so glad you asked.
It can be so easy to get excited about some new diet based on a superfood, said to have amazing benefits. It can be hard to resist all those posts in your social media feed from people pushing their new book or product, especially if they include before and after photos, or personal success stories. Personal stories are very powerful, and appeal to our emotions. But, if the advice you are seeing goes against current evidence-based eating guidelines (for example, cutting out all carbohydrates, or giving up dairy and not replacing it with a nutritionally equivalent substitute), then go carefully my friend.
This dude had it right when he said:
"The greatest wealth is health"
Virgil, Roman poet (70BC - 19BC)
When it comes down to it, most of these new diet fads are all about weight loss, and many of them can have a negative impact on your long-term health. For instance, we are discovering more about the importance of maintaining a varied population of gut bacteria for our overall health (not just gut health). If we eliminate almost all of the carbs from our diets, there goes a whole lot of really important food for those little critters, in the form of dietary fibre. Recent evidence shows that low carbohydrate diets can even increase mortality (science-speak for you'll die earlier). Yikes.
My advice would be if you are considering making significant changes to the way you eat, and the changes fly in the face of current guidelines, pause and ask yourself these questions:
What are the qualifications of the person recommending this way of eating?
Are they telling me to cut out a whole food group (or two)?
Is the language they use all about weight loss or appearance?
Are they trying to sell me something?
If the answers to these questions are: "I can't find any information on their qualifications" followed by "yes" three times, and you want some advice on how to eat to support your health, head on over to the HealthEd website and read up on the current dietary guidelines. You can also find yourself a qualified nutrition professional through the Nutrition Society of New Zealand or Dietitians New Zealand.
And if you are interested in following some evidence-based nutrition professionals on social media, check out some of my favourites:
Tara Leong - The Nutrition Guru and the Chef
Dr Timothy Crowe - Thinking Nutrition
Anthony Warner - The Angry Chef (he can get a bit sweary, but loves to take down pseudoscience)
Dr Megan Rossi - The Gut Health Doctor
You can also find links to more evidence-based nutrition goodies on my Resources page, on this very website!