Nutrition Science and Everyday Application - beta v 0.1

HEALTHY SKEPTICISM IN NUTRITION SCIENCE 101
Returning to the question of processed foods, all three of these challenges impact how
we interpret observational studies that show a correlation between processed food
consumption and weight gain. It doesn’t mean that these studies are useless, but we want
to be aware of their limitations and consider other ways to test the hypothesis. One way to
overcome these challenges is to conduct a randomized controlled trial (RCT), the study
design that gives us the highest quality evidence. RCTs are time and funding-intensive
experiments, so they’re usually only conducted after consistent evidence from observational
and laboratory studies has accumulated.
It turns out that there has been a randomized controlled trial of processed foods and
weight gain. It was funded by the National Institutes of Health and published in 2019 in the
journal Cell Metabolism. 4 In this study, 20 participants lived in the NIH’s Clinical Center for one
month, where they consumed only processed foods for two weeks and only unprocessed
foods for another two weeks, and they could eat as much or as little as they liked during each
of these periods. The diets were carefully designed by dietitians so that they were matched
in calories, sugar, fat, fiber, and macronutrients, and the exact amounts consumed by the
participants were measured every day (solving the problem of measuring diet complexity
and accurately describing what and how much people eat every day).
The study found that people ate about 500 kilocalories more and gained about a pound
per week when they were eating processed foods. This study design could show
causation, not just correlation, because the other nutritional factors like calories, sugar,
fat, fiber, and macronutrients were held constant, and the diets were tested in the same
people, so other factors such as genetics, sleep, stress, and exercise were constant between
the two types of diets. (This was an example of a crossover randomized controlled trial,