There is scientific debate on what the ideal diet is for a healthy lifestyle and what nutrients are important in mitigating disease. An interesting article just came out in Nature about how confusing vitamin supplementation recommendations are. The writer basically summed it up nicely: “After decades of study, researchers still can’t agree on whether nutritional supplements actually improve health.”
There is so much debate out there about what is a healthy and nutritious diet. Debates include: whole food diets versus nutrient-targeted diets (reductionism), types of diets (paleo, Mediterranean, low fat, high protein, gluten free etc.), and the worth of calories (a calorie in = a calorie out versus not all calories are created equal for weight loss). The pursuit of science is founded on debate, but when science must engage public policy and consumer choices, things get sticky. Not providing the “right” information related to people’s health can have detrimental impacts that last decades in the nutrition field.
Take the United States Dietary Guidelines that are updated and released once every five years. In the 1990s, it was thought that all fats were bad for heart health, so dietary guidelines shifted their recommendations to promote the consumption of low-fat foods. Following these guidelines, food marketers promoted fat-free products that were high in starch and sugars. During this same time in the 1990s, the obesity epidemic in America surged. Was this a coincidence? It was thought that examining individual fats and other nutrient groups in isolation could be misleading, because when people cut down on fats they tend to eat refined carbohydrates that can also be detrimental for heart health.
Now, the science is suggesting the opposite. Fat is once again good and a recent meta-analysis found that total saturated fats are not necessarily bad for heart health (Ravnskov 2014). As Mark Bittman, a NYT food journalist exclaimed, “Butter is back!” Some disagree and say that the type of fat does matter, with mono and polyunsaturated fats being the healthy fats. This flip-flopping of the evidence creates great confusion and mistrust amongst the public, particularly when it becomes “policy” in government driven dietary guidelines.
Reductive understanding of nutrients as the key indicators of healthy food has been termed “nutritionism” and has dominated much of the science of nutrition, which then informs dietary advice and food marketing. What has resulted is less appreciation for overall whole diets and more so on foods being touted to be “super” or “functional” depending on the nutrient contents (often added through food industry processing).
In his book Nutritionism, Scrinis discusses the era of quantification within nutritional sciences, which focused more on nutrients and caloric isolation, and curative approaches to non-communicable complex diseases. What is lost in this scrutiny of the specific is the importance of nutrition and dietary advice in shaping our relationship to food and our bodies and the cultural traditional knowledge of foods. Consumers have heightened nutritional anxieties more than a clear understanding of the healthfulness of foods and whole diets.
The “science” of nutrition is not an easy one. Gary Taubes, co-Founder of the Nutrition Science Initiative, explained: “In nutrition, the hypotheses are speculations about what foods or dietary patterns help or hinder our pursuit of a long and healthy life. The ingenious and severe attempts to refute the hypotheses are the experimental tests — the clinical trials and, to be specific, randomized controlled trials. Because the hypotheses are ultimately about what happens to us over decades, meaningful trials are prohibitively expensive and exceedingly difficult. It means convincing thousands of people to change what they eat for years to decades. Eventually enough heart attacks, cancers and deaths have to happen among the subjects so it can be established whether the dietary intervention was beneficial or detrimental.”
The political mantra on public-health advice is clear: don’t send mixed messages. The media and those who get their information from the media prefer things in black and white: red wine is good for you; trans fats are bad for you. But, of course, science does not deal in black and white, hence the common criticism that scientists cannot make up their minds. Katz and Meller summarized the public health implications of scientific debates in nutrition well. They wrote: “The clutter of competing claims likely obscures the established body of knowledge and forestalls progress, much like the proverbial trees and forest. We need less debate about what diet is good for health, and much more attention directed at how best to move our cultures/societies in the direction of the well-established theme of optimal eating, for we remain mired a long way from it.”