It is conventional dietary wisdom — at least among a certain well-informed crowd — that fiber in the diet is supposed to make you feel full. This makes a certain amount of intuitive sense. Both soluble fiber (fiber that can dissolve in water) and insoluble fiber add bulk, but not calories, to the contents of the stomach and intestines. And because insoluble fiber tends to take on a gummy or gel-like consistency when dissolved in water, it can slow the digestion and absorption of other nutrients in the digestive tract.
So it comes as something of a surprise that a study released earlier this month shows no effect from certain forms of fiber on feelings of fullness. Published in the Journal of the Academy of Nutrition and Dietetics, the study’s participants were 22 women who were not on any restricted diet and were not obese. As a Chicago Tribune article on the study notes, participants were each given nutrition bars to eat on five different occasions. They were instructed to eat one bar before bed and another the next morning for breakfast, and then to come in for an evaluation around lunchtime, after which they were served lunch. In the evaluation, researchers asked them to rate their feelings of hunger and fullness on a standard scale. On each occasion, participants received the same “chocolate crisp” nutrition bar to eat at night and in the morning, but five different bars were tested (for a total of 10 bars per participant). Four of these bars contained a form of added fiber: either oligofructose, soluble corn fiber, resistant wheat starch, or inulin (not to be confused with insulin). The fifth bar contained no added fiber.
No nutrition bar led to an overall difference in reported feelings of hunger or fullness. Neither did any bar have a unique effect on how much the participants ate for lunch; researchers measured this at each evaluation. The only overall difference was that the bars containing added fiber, especially the one with oligofructose, led to an increase in bloating and flatulence.
It is worth noting that none of the bars used in the study, according to provider Kellogg’s, is currently on the market. As the company explained, it wished to find out more about what forms of fiber can increase feelings of fullness. Many nutrition bars and other foods on the market, however, contain added forms of fiber including inulin (often listed as chicory root extract), cellulose, psyllium, and guar gum. Even if added fiber in processed food products does not increase feelings of fullness, it still may have other benefits, such as supporting bowel regularity. But as this study indicates, much rawer forms of fiber — in foods such as beans, oatmeal, berries, and artichokes — may be needed to have a substantial effect on fullness.
Do you use a fiber supplement or consume food products that contain added fiber? If so, do you notice any effect from the extra fiber on your hunger level? What foods tend to make you feel full the longest? Does this effect seem to correspond with the calorie content of your meals, or are there “better value” foods, in your experience, that leave you feeling full without contributing too many calories? Leave a comment below!