A new study on whole grains demonstrates how nuanced & complicated nutritional science can be.
Substituting whole grains for refined grains in a 6-wk randomized trial favorably affects energy-balance metrics in healthy men and postmenopausal women (Karl et al., 2017)
Sounds simple enough…
Study design: adequate to address the questions being asked. Isocaloric, weight-maintenance diets. Biggest differences between the two diets were whole grains (0 vs. 200 g/d) and insoluble fibre (15 vs. 30 g/d).
Disclaimer: I’m not a huge fan of cereal fibre, but that’s irrelevant for the point of this post.
The food was provided and the people abided. YAY BIOMARKERS!
Nobody in either group was supposed to lose weight, but those assigned to refined grains lost more weight and fat mass, and gained more muscle than those assigned to whole grains (NS). All of this happened despite a metabolic rate drop in refined grains and increase in whole grains:
All of this is weird. Even weirder that the changes seemed to favor refined grains.
As expected, the whole grains group was pooping a lot more, and with it was losing almost 3 times more calories in their stools.
This should’ve increased the alleged benefits of whole grains, except it didn’t.
Hunger, fullness, diet satisfaction, eating-behavior, and food cravings were the same in both groups. Whatevs.
No differences in glucose and insulin dynamics either.
Refined grains: no change in energy intake (by design), no change in insulin yet fat loss and muscle gain? That’s an exaggeration, but not by much. And as stated before, even in an ad lib context, I don’t think insoluble fibre would do much to curb obesity otherwise Metamucil would’ve done it long ago. Best get your fibre elsewhere. Nutrient-dense plants, even the gristly bits of “animal fibre.” No need to max out on the grains, whole or otherwise. It’s not even about the gluten.