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Can We Say What Diet Is Best For Our Health?

Shannon Harvey

When I was first diagnosed with an autoimmune disease for which doctors could offer no cure, naturally the first thing I looked at was my diet. Rightly so.  Diet has well and truly been established as being among the most important influences on our health. Having a bad diet is among the leading causes of premature death and chronic disease. Having a good diet on the other hand is associated with increased life expectancy, dramatic reduction in lifetime risk of all chronic disease, and even improving gene expression.  And while it’s all very well for experts to tell us to eat a healthy diet,  the major problem with this advice is that researchers are still divided on what a healthy diet looks like. In fact, the subject of nutrition is a minefield. As I’ve written about before, not even leading researchers agree on the findings. So where should we turn and who should we believe?  

In 2014 the non-profit organization Annual Reviews, which is dedicated to helping scientists cope with the ever-increasing volume of research and data by providing robust and systematic reviews of published literature, decided it was time to shine the spotlight on diet. The editors selected two researchers from Yale University to perform an analysis of all the available data. David Katz and Stephanie Meller poured over the scientific literature published on the most popular diets including low carb, low fat/vegetarian, low GI, Mediterranean, mixed/balanced diets (which conform to dietary guidelines), paleo and vegan. Katz and Meller were selected because they had no agenda with any one particular diet, but were both experts on nutrition science. As Katz told a reporter for The Atlantic “I don't have a dog in the fight, and I don’t care which diet is best. I care about the truth.”  He and Meller published their findings in a paper titled, "Can We Say What Diet Is Best for Health?” and their conclusions were fascinating:  

"There have been no rigorous, long-term studies comparing contenders for best diet laurels using methodology that precludes bias and confounding, and for many reasons such studies are unlikely. In the absence of such direct comparisons, claims for the established superiority of any one specific diet over others are exaggerated."  

In other words there's no one diet to rule them all, and nor will there likely be one in the future. This is disappointing news for those of us wanting to know what to eat. Nutrition science is fraught with difficulties including the fact that it's impossible to lock 20,000 people of a variety of ages and genders in a lab and feed them particular diets, keeping every other variable the same for 50 years.  

With emerging new evidence indicating that it's likely that dietary advice of the future will need to be different for different people depending on genes it would be easy to give up on the search for the right diet and just eat whatever you want. After all, for every study showing [insert ingredient here regardless of whether it's a fruit, vegetable, sweet treat, caffeinated or alcoholic beverage] is bad for you, you'll surely find a study to show that [certain ingredient] is good. What's the point? Life's short. We may as well eat whatever we want. Right?  

Well... let's not be so hasty. When you take a second look at Katz and Meller's paper, there are actually some very concrete findings. While they did conclude that no one diet is best, they also found a very clear universal thread across them all:  

"A diet of minimally processed foods close to nature, predominantly plants, is decisively associated with health promotion and disease prevention."

In the below table Katz and Meller demonstrate that all these seemingly conflicting diets actually have many things in common. They limit refined starches, added sugars and processed foods. They also emphasize whole plant foods (with or without lean meats, fish, poultry and seafood). In all the noise about what we should not eat, the fundamental message about what we should eat is being lost. Katz and Meller finally conclude:  

"The case that we should, indeed, eat true food, mostly plants, is all but incontrovertible."

Writing this blog post may well open up some heated discussion among readers. There are some very compelling arguments to be made in the diet debate and I would like to know your thoughts in the comments below. If you're following a particular diet and it's working for you, then that is great news. But the main point I'm making here is that if you look at a typically western diet, many of us are eating excessive amounts of cheap, low-quality calories. Rather than engaging in epic debates about which is the villainous or virtuous macro or micro nutrient of the moment, we need to consider the overall quality of what we are eating. We need to take a moment to pause and zoom out to see the big picture.  

Katz and Meller's review paper echoed the famous words of journalist Michael Pollen who, in his 2007 piece for the New York Times, concluded that the short answer to the supposedly incredibly complicated and confusing question of what we humans should eat in order to be maximally healthy is - "Eat food. Not too much. Mostly plants."  Although not quite as eloquent as the original words of multi-award winning journalist, when you consider the literature on the microbiome (which includes Pollen's 2013 feature piece for the New York Times), the takeaway message could be updated to say:

"Eat real food. Not too much. Mostly a variety of plants."


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