I have to say that I have learned a HUGE number of things in the last 12 hours or so, as I frantically interviewed scientists and trainees about their work. Sure, Sci knows her own fair bit about things like neuroscience, but blogging Experimental Biology gives me the opportunity to get WAY outside of my field and learn new things, sometimes on topics which I haven’t studied since high school.
Take, for example, nutrition. I’m sure we’ve all heard that high fiber diets are good for you. Eat more fiber, you’ll be fuller longer, you’ll eat less, you’ll lose weight, and the next thing you know you’ll be modeling (side effects include farting and pooping a lot).
(Yeah, I made a nutritional LOLcat. Only Sci is THIS geeky)
But today I learned something that completely shocked me: ALL FIBERS ARE NOT CREATED EQUAL. In fact, all things that are “high fiber” are not created equal! And while fiber may impact how full you feel…does your gut agree? How does fiber impact your gut hormones?
Klosterbuer, Sanders, Thomas, and Slavin. “Addition of fiber to a meal does not consistently alter gut hormone levels in humans” University of Minnesota, presented at Experimental Biology, 2011.
We do know that people who intake more fiber tend to be lower in body weight than those who eat less fiber in their diet. And scientists do think that foods high in fiber increase satiety. The question is HOW this increase in satiety happens. Is it through a change in gut hormones? And does it depend on the kind of fiber?
To answer this question, Klosterbauer et al got 20 volunteers and gave them 5 free breakfasts. The participants always got what looked like the same breakfast: an oatmeal-type dish, a muffin, and a fruit flavored drink. But the amount of fiber varied. The control was a low fiber breakfast, and there were four experimental breakfasts: one high in soluble corn fiber (fiber derived chemically from corn, and an additive in things like cereal bars), one high in resistant starch (which occurs in beans and whole grain bread), one high in soluble cornfiber and pullulan (a fiber produced by a fungus!), and a final one high in resistant starch and pullulan. The total fiber count in the four test meals was 25 g each, a full 100{9f43b4361d9a125bc126dd2a2d1949be02545ec69880430bc4fed2272fd72da3} of the daily fiber.
After each breakfast, they asked the participants how full they felt and took some blood. The blood was analyzed for glucagon-like peptide 1 (GLP-1) and ghrelin. GLP-1 is released when you eat a meal, while ghrelin is a feeding-triggering hormone that is released when you’re hungry and suppressed when you eat. So you’d expect that, after a meal, ghrelin would go down and GLP-1 would go up. But do these measures differ depending on the fiber you’ve had?
Partially, it turns out. Ghrelin went down regardless, with no differences detected when people were given different kinds of fiber. GLP-1 went up, but it went up the LEAST for those who had the resistant starch and pullulan condition, while it didn’t differ in the others. The odd thing about this is that all the participants reported feeling more sated when they had the high fiber breakfasts, and the MOST full after the resistant starch and pullulan combination. So you’d have thought that GLP-1 would go up MOST in that condition.
What this may mean is that fiber may not change satiety feelings via changes in gut hormone (though issues with measuring the hormone in the blood need to be considered). There are other gut hormones to look at, such as cholesystokinin and peptide YY, but then again it could be something else. In the meantime, no one is telling you to stop the high fiber diet, but remember, not all fibers are created equal.
References:
Maskarinec et al “Trends and dietary determinants of overweight and obesity in a multiethnic population.” Obesity (Silver Spring). 2006
Howarth NC, Saltzman E, Roberts SB. “Dietary fiber and weight regulation.” Nutr Rev. 2001
Howarth NC, Saltzman E, & Roberts SB (2001). Dietary fiber and weight regulation. Nutrition reviews, 59 (5), 129-39 PMID: 11396693
Maskarinec, G., Takata, Y., Pagano, I., Carlin, L., Goodman, M., Le Marchand, L., Nomura, A., Wilkens, L., & Kolonel, L. (2006). Trends and Dietary Determinants of Overweight and Obesity in a Multiethnic Population* Obesity, 14 (4), 717-726 DOI: 10.1038/oby.2006.82
