In addition to being healthy for a wide variety of reasons, dietary fiber might also help you get lean. Researchers examined the effects of fiber on hunger and blood sugar in a study published in Nutrition Journal.



Effects of Fiber

Fiber is one of the substances that slows digestion. If you’ve ever mixed a lightly processed fiber source like psyllium into a cup and let it sit for more than a second, you have seen why. Fiber, particularly the soluble kind, expands into a thick gel when combined with water. You may have filled that cup with water, but if you turn it over after letting it sit, that gel isn’t going anywhere.


The slowing of digestion doesn’t just fill you up, it also reduces the glycemic index (the speed at which carbohydrates are absorbed into the blood) of anything consumed either with it or shortly afterward. Lower glycemic values are widely known to be healthier and better for weight loss than high glycemic values.


The dual effects of better blood sugar balance and a filling food make fiber a good candidate for satiety. This means that fiber might make you feel full while not contributing calories. When you look at nutrition labels, calories from fiber are included in the count at the top of the label. However, these calories cannot actually be digested by the body. They simply move through your digestive tract like a sentinel, providing the regularity you get from a high-fiber diet.


Study Details

In the study, two fiber breads were compared to regular bread. The fiber breads were made by the scientists and contained two different kinds of powders. One of the powders was fruit-derived and mainly insoluble, non-viscous fiber, meaning it didn’t flow like a liquid. The other fiber bread contained a brand-name supplement called FiberMax, which had a blend of both insoluble and soluble fibers. These fibers came from various sources like psyllium, oats, and fruit. Each of the fiber breads had a total of about thirteen grams of fiber, whereas the regular bread had only 3.5g. Otherwise, all the breads were pretty similar.


The participants ate two slices of one of the three types of bread and drank 250mL of water. The bread had some margarine on it as well, for all three conditions. The subjects had to eat the bread within fifteen minutes. Three hours after eating the bread, each participant consumed a meal of pasta. The researchers measured blood sugar, feelings of fullness, how much the subjects enjoyed the bread, and how much they ate in the pasta meal.



The participants didn’t like the fruit fiber bread. But it did reduce glycemia (glucose levels) by 35%, making the bread healthier than the non-fiber bread. Regardless, the subjects thought it was gross and it made some of them feel sick.


The FiberMax bread was more palatable and even better at reducing glucose levels, with a 43% reduction rate. Unfortunately, neither of the breads made the participants less hungry for the later meal, and thus the high fiber content didn’t reduce the amount they ate.


So we know that adding fiber to bread makes it healthier. A blend of fibers is even better than insoluble fiber alone, and it's also healthier for the digestive tract and actually edible. If you wait three hours after fiber intake, you will probably be hungry again, but I suspect that if a meal is eaten shortly afterward it may help with portion control.



1. Jannie Yuan, et. al., “The effects of functional fiber on postprandial glycemia, energy intake, satiety, palatability and gastrointestinal wellbeing: a randomized crossover trial,” Nutrition Journal, 2014, 13:76.


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