Health activists are constantly touting the newest study as the basis for claims against the latest food, beverage or ingredient they have targeted. So it was nice to see one of the most vocal activists admit that nutrition research is often based more on a researcher’s personal views rather than rock-solid science.

“It never seems to get better, I think because there are so many interests vested in one viewpoint or another,” said Marion Nestle when asked about the state of nutrition advice during an interview.

Nestle says that nutrition research is hard to do because it’s just not feasible to study and control the diets of a sizable population of people over the considerable length of time needed to get reliable results.

“For reasons of practicality, cost and ethics, you can’t do that. Anything short of that is flawed. Flawed science is uncertain and requires interpretation. Interpretation draws on the minds of interpreters, which gets us into matters of bias,” she says.

Yet that has not stopped many researchers from presenting incomplete studies as evidence for action against foods and beverages they do not like.

As Nestle points out, when science is missing, viewpoints are substituted.

“People working in the field develop a ’feel,’ a sixth sense if you will, for interpretation, and hold views based on their experience,” Nestle said.

No wonder dietary advice is always changing. Claims you read on nutrition are often not based on fact or solid science but on conjecture as has happened with bad advice on cholesterol, saturated fats, eggs, whole milk and caffeine.

What’s the lesson from all of this? Proceed with caution when it comes to dietary advice.