MOST diet trials in the best journals fail even the most basic of quality control measures. That's the finding of the study by the authors published recently in JAMA Network Open.

THE quality-control problem of diet trials in comparison to ones on pharmaceuticals leads to a bigger issue : underinvestment in nutrition research and how we tackle the mysteries of a healthy diet.

EPIDEMICS of diet-related disease will shorten life expectancy and impose huge economic costs on the world in the coming years.

We continue to lack effective dietary prevention, in part because clinical trials have been too poorly designed and conducted to reach definitive conclusions.

We're still debating questions that have raged for decades : Should we focus on reducing carbs or fat? Is red meat harmful? Is sugar toxic? What about artificially sweetened beverages or moderate amount of alcohol?

High-quality trials are hard to do because diets, and the behavior of humans who consume them, are so complicated. A single meal might have dozens of nutrients and hundreds of other bioactive substances that interact in unknown ways.

Furthermore, if the diet being studied increases intake from one food category, people may eat less from other food categories, making it difficult to attribute results to any specific dietary component.

Diet trials require subjects to change their eating habits, a far greater challenge than taking a pill.

Consider a trial for a promising cancer treatment in which participants assigned to receive the drug didn't take it as intended.

If the drug group showed no benefit over the placebo group, we wouldn't automatically assume the drug lacked promise.

We would conclude that the study failed and that stronger methods [medication organizer trays and daily text message reminders, say] are needed to make sure the drug is properly used so that we can see if it works.

Yet the illogical assumption that a diet didn't work is commonly made when volunteers in weak trials do not follow the assigned diets.

Short diet trials, the great majority of those done, raise special concerns. Many people can lose weight by restricting calories at first, but few can maintain substantial weight loss that way.

After a few days or weeks, the body begins to resist calorie deprivation, with rising hunger and slowing metabolism.

Making matters more complicated, it takes several weeks to adapt to major changes in nutrients. For those reasons, short-term trials may have little relevance to understanding how diet affects health over the long term.

The honor and serving of the latest operational research on diets, trials and students, continues.

The World Students Society thanks authors : David S Ludwig, a professor of pediatrics at Harvard Medical School, and Steven B Heymsfield is a professor and director of the Metabolism and Body Composition, at Louisiana State University.


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