When you eat a high-fat food, such as butter, ice cream, whipped cream, or, say, fried chicken, the contents of your digestive tract become “smoother” and more viscous. Sensitive cells lining your intestine detect a change in the fluidity of the food in your gut. They release a hormone called cholecystokinin. This hormone tells your brain that you have eaten a filling, satisfying food.
Bran does the same thing. The fibers in bran swell up with water and make the contents in your digestive tract “smoother.” The cells lining your intestine sense a change in the fluidity of the food being digested and release cholecystokinin, just as if you had eaten fat. Even though you have consumed relatively few calories, you feel full. Cholecystokinin also tells the nerves lining your stomach to “hold” the food longer so fats can be digested completely—even if there is little fat in the food because you have been eating bran.
This keeps your digestive tract from dumping a load of sugar into your bloodstream causing the sugar highs and sugar lows. Men and women, however, differ in their responses to cholecystokinin. Women are more sensitive to the hormone, and more likely to feel full after eating bran. Men are less sensitive to the hormone, and more likely to continue to want any food that is in sight.
You get this effect from eating bran, not from taking an oat bran powder supplement or a wheat bran powder supplement. And as you will read in a moment, oat bran powder supplements have benefits for lowering cholesterol that wheat bran powder supplements do not.
You have to be careful about combining bran and high-fat foods. Fat “revs up” the liver to make a chemical called triacylglycerol. This chemical stores fat. Eating bacon and eggs tells the liver to make triacylglycerol to store any excess fat that may come along. (Of course, if you are, say, on Atkins and all you eat is one strip of bacon and one egg, there may not be any energy left over to store.) Eating a bran bagel also tells the liver to “rev up” to store fat.
If you eat the bran bagel with butter and cream cheese, and also have bacon and eggs, your fat storage system is going to especially primed to soak up those calories, more than if you ate just the bacon and eggs and cream cheese, and more than if you ate just the bran bagel. If you eat fiber, save the fatty foods for another time.
If bran stimulates the storage of fat, how can it lower cholesterol? The answer is, it doesn’t, if you are eating a high-fat diet. If you limit your consumption of fats, however, every time you eat bran your liver is a little less likely to “rev up” to store fat. After about six weeks of including oat or rice bran in a daily diet including five to nine servings of fruits and vegetables will raise your protective HDL cholesterol and lower the potentially destructive LDL cholesterol, usually in the range of 10 to 20 “points (mg/dl).
Wheat bran does not lower cholesterol. It raises it. The best bran for cardiovascular health is oat bran, which not only improves cholesterol but lowers blood pressure. If you eat an ounce and a half (45 g) of oats every day and you follow a low-fat diet, you can expect your upper number (systolic) pressure to fall up to 7 “points” (mm/Hg) and your lower number (diastolic) pressure to fall up to 10 points.
Reduction in blood pressure when you eat oats every day is greater than if you lose weight or take medication without eating oats. Scientists do not know why oat bran lowers blood pressure and other kinds of bran do not, but there seems to be something in the soluble fiber of oats that stops the production of insulin, which helps the kidneys eliminate salt without losing other minerals, which lowers blood pressure. A word of caution on eating oat bran: Don’t eat oat bran if you have gallstones. Eating oat bran stimulates the release of bile, and can make your gallbladder painful.
Recent reader questions:
Q. What can I do about eating fiber & bloat?
A. Eat your fiber earlier in the day, when it does not have to compete with as much other food to be digested.