The key to oats’ effect on satiety is in fact the viscous nature the oat fiber develops when fully hydrated. And, according to a new study presented last week, it has to be in oatmeal itself. The oats and oat fiber added to boxed cereals has been changed by the manufacturing processes common to ready-to-eat cereals (RTEC).
“RTEC is [often produced via] an extrusion process, and that changes the molecular weight of the fiber itself. The soluble fiber is the component that influences satiety; it absorbs a lot of water and becomes viscous,” Marianne O’Shea, senior director of nutrition R&D for Pepsico told FoodNavigator-USA.
“If you change or reduce the molecular weight of that fiber it does not reach the same level of viscosity. The thickness is not there any more,” she said.
The study, sponsored by PepisCo on behalf of its Quaker Oats brand and presented at the Experimental Biology 2013 conference in Boston, MA, showed that an oatmeal breakfast enhanced feelings of fullness and helped curb hunger to a significantly greater extent than a leading oat-based ready-to-eat cereal (RTEC).
Candida Rebello, RD, MS, of the Pennington Biomedical Research Center at Louisiana State University in Baton Rouge, LA, presented the research on the impact of eating oatmeal versus a RTEC of equal calories. The statistically significant results show that oatmeal enhances satiety, feelings of fullness and reduces the desire to eat more than RTEC.
“Our research builds on previous studies that show oatmeal can help extend feelings of fullness and suppress the desire to eat for several hours,” Rebello said.
Oatmeal is unique
The research paper did not delve deeply into the reasons why the oat fiber is changed during RTEC processing, O’Shea said. Several factors in the extrusion manufacturing process combine to cause this, and it’s a phenomenon that has been well-known for some years, she said.
“Our interest was on the oatmeal itself. In oatmeal the soluble fiber is intact. Oatmeal is a unique product because you cook it in liquid. That allows the fiber to completely absorb the water and become quite viscous. The heating gelatinizes the starch and the fiber is completely solubilized, so you end up with quite a viscous product,” she said.
And even if in a RTEC the fiber handn’t been altered in the processing, the presentation alone would negatively affect the hydration of the fiber and therefore its satiating effect, O’Shea said.
“Your challenge with ready to eat is that you pour milk on it and you generally eat it quite quickly. People like to eat the cereal when it’s crunchy, so that hydration does not happen in the same way,” she said.
And the satiating effect of the hydrated fiber appears specific to the beta glucan fiber structure found in oats, O’Shea said. The effect can’t be generalized to hot cereals based on other grains.
Forty-seven healthy men and women completed the randomized, controlled crossover investigation. Following an overnight fast, subjects completed two breakfast trials in random order at least a week apart. Each breakfast consisted of either 250 calories of instant oatmeal or 250 calories of a RTEC served with 113 calories of lactose-free skim milk. After eating breakfast, subjects’ satiety measures were assessed at 30, 60, 120, 180 and 240 minutes.
After four hours, subjects were given lunch and were told that they could eat as much or as little as they wanted.
The results showed that when subjects ate oatmeal, they reported increases in overall fullness, as well as stomach fullness, and reductions in hunger and the desire to eat. At lunch, the subjects who had oatmeal consumed significantly less calories (about 85 fewer calories).
In addition, when subjects ate oatmeal for breakfast, they chose low-fat options at lunch, suggesting that enhanced fullness may actually help control the desire for foods that are higher in calories and fat.
Update as of Dec 10, 2013: The results of this study have now been published in the Journal of the American College of Nutrition (Volume 32, Issue 4, 2013).