I recently came across a great article interviewing 8 researchers, regarding nutritional research and the complexity behind nutritional science. They highlight several key complications that display we don't know as much as we think we do. Many of these have to do with the sheer difficulty in gathering meaningful information. In spite of these difficulties, there are great recommendations agreed upon by a broad group of nutritional researchers at the end of this article.
Here is the summarized version of the article. I highly recommend reading the full article yourself when you get a chance. (See the link posted at the end of this article.)
1. It's not practical to run randomized trials for most big nutrition questions - Questions regarding long term effects are almost impossible to test with the variability in lifestyles, errors in self reporting and an inability to have true "control" groups, at least of any meaningful size. This means studies, such as "feeding" studies, are done where participants are kept in a lab for days or weeks with control over everything they eat. While changes are observed based on these short duration experiments, researchers have to infer what long-term health effects might result.
2. Instead researchers rely on observation studies - which are rife with uncertainty - These involve researchers tracking a large number of people eating a particular way. While also valuable, "noise" from an overwhelming number of variables can blur cause-and-effect observations. Consider the effects of lifestyle outside of strictly nutrition components, with the inability to control an individual’s free will or an individuals flawed understanding, this can leave observational research lacking.
3. Additionally, most nutrition studies rely on (wildly imprecise) food surveys - Both due to genuine forgetfulness as well as the fact that people lie about what they eat; Researchers who study self reporting stated that they were "fundamentally and fatally flawed."Over the 39-year history of the National Health and Nutrition Examination Survey — which is a national study based on self-reported food intake — the researchers found that the alleged number of calories consumed by 67 percent of the women in the study was not "physiologically plausible" given their body mass index.
4. More complications: food and people are complex - As if difficulty in tracking accuracy wasn't complex enough, individuals respond to the same food very differently. In a large 800 person study, tracking the food over the span of a week in relation to blood sugar, researchers found individuals responded wildly differently. This varied response was in spite of individuals consuming the same meals, meaning "universal" nutrition guidelines ultimately have a limited utility. This was also compounded by the variability in food source and nutritional qualities, meaning the farm fresh carrot has different nutritional properties than the mass-produced baby carrots found in most stores.
5. Conflict of interest is a huge problem in nutrition research - Nutritional research has not caught up to medical research in regards to safeguarding against conflict of interest in sponsored or funded research. This can be seen in the consumer confidence in nutritional findings, and for good reason. Between March and October of last year, Nestle identified 76 industry funded studies, and of those, 70% were favorable towards the industry sponsor. A great example of this is that "independent studies find a correlation between sugary drinks and poor health, whereas those studies supported by the soda industry do not."
6. Even with all those faults, nutritional science is not futile - In spite of these challenges, there are a number of things that we have learned. "Without nutritional research," said Frank B. Hu, a professor of public health and nutrition at Harvard, "we would not know that folate deficiency among pregnant women causes birth defects; we would not know trans fat is bad for heart disease; and we would not know drinking too much soda increases risk of diabetes and fatty liver disease."
Recommendations for reviewing quality research studies include looking for meta analysis instead of individual studies to see if trends can be observed in a variety of settings and populations to determine who or how the research can be applied. Consider the source of funding for the study, as independent government agencies or foundations tend to be more reliable than industry funded research. Recently a broad group of nutritional researchers gathered to discuss what they could all agree on.
Here's what they came up with:
A healthy dietary pattern is higher in vegetables, fruits, whole grains, low- or non-fat dairy, seafood, legumes, and nuts; moderate in alcohol (among adults); lower in red and processed meats; and low in sugar-sweetened foods and drinks and refined grains.
Additional strong evidence shows that it is not necessary to eliminate food groups or conform to a single dietary pattern to achieve healthy dietary patterns. Rather, individuals can combine foods in a variety of flexible ways to achieve healthy dietary patterns, and these strategies should be tailored to meet the individual’s health needs, dietary preferences and cultural traditions.
So, someone telling you it is more complicated than that, such as certain foods like kale or gluten, are killing people, probably isn't speaking from science. As you can see, there is not yet a scientific way to make that determination.
Original Article - http://www.vox.com/2016/1/14/10760622/nutrition-science-complicated