Candis M. Morello, PharmD, CDE, FCSHPD
and Sarah A. Bijorek, Second Year Student Pharmacist at UCSD
TCOYD Newsletter, Vol. 28, 2009

What comes to mind when you think of the warmth of hot oatmeal, the sweetness of fresh strawberries or the crunch of crisp celery? If you didn’t think about your glucose or cholesterol levels, you may want to think again. Healthy foods such as fresh fruits, vegetables, legumes and whole-grains that are high in soluble fiber have been shown to decrease post-prandial (after meal) glucose concentrations and cholesterol levels. So grab a crunchy carrot and read on to see how you too can lower your levels!

What is Fiber?

Dietary fiber refers to parts of plant foods that your body cannot digest and absorb into your bloodstream. These parts move through the digestive tract absorbing water and adding bulk to your stool, so-called “roughage.” There are two categories of fiber, soluble and insoluble, and their names describe how they work. Soluble fiber dissolves in the stomach to form a gel-like substance while insoluble fiber does not. Rather, it remains relatively intact throughout the digestive system. Both add bulk to the stool and promote regular bowel movements. Both types are found in everyday foods, such as fruits and vegetables. To get the most fiber out of fruits and veggies, try to eat them with the skin on since that is where the insoluble fiber is. Also, be careful not to overcook vegetables since heat can destroy some of the fiber. Fiber supplements are available in many varieties, such as capsules and dissolvable powders, and can be used daily to boost fiber intake.

How Does Fiber Help Diabetes?

Foods rich in soluble fiber are digested more slowly than refined foods such as white bread, cookies, cake or processed foods. Therefore, nutrients, such as glucose, are absorbed at a slower rate. This means blood glucose concentrations rise more slowly and peak at a lower level after eating, resulting in decreased post-prandial glucose concentrations. Adding more fiber to the diet is even being recommended by the American Diabetes Association for people with pre-diabetes, to help prevent them from developing diabetes.

Most foods high in soluble fiber have a low-glycemic index. The glycemic index ranks foods based on how much they raise blood glucose concentrations. Eating foods with a low-glycemic index can cause blood glucose concentrations to rise more gradually, while foods with a high-glycemic index produce a rapid spike. Therefore, low-glycemic foods are better for controlling post-prandial glucose concentrations because they slow the digestion and absorption of carbohydrates. Foods rich in soluble fiber with a low-glycemic index include oats, nuts, beans, lentils, and fruits such as apples, pears, oranges and berries.

How Does Fiber Help Control Cholesterol?

Soluble fiber also plays an important role in reducing cholesterol levels. Cholesterol comes from two sources: our body makes it and it is in the food we eat. Cholesterol has many important roles in our body, including the break down of fats. However, when we have more cholesterol than needed, it is absorbed into our bloodstream where it can cause clogged arteries. Soluble fiber decreases cholesterol levels because the gel-like substance that forms binds to and “traps” extra cholesterol in the intestine. The cholesterol is excreted when you have a bowel movement instead of being absorbed into your bloodstream. Insoluble fiber has not been shown to decrease postprandial glucose concentrations or cholesterol levels; however, it is still important in promoting regular bowel movements.

When selecting a fiber supplement, it is important to look at the ingredients since the fiber source varies between brands. The only ingredient that has been shown to decrease both blood glucose and cholesterol is psyllium, found in Metamucil®. Psyllium is very high in soluble fiber. Regardless of the source, increasing your soluble fiber will not only help control glucose levels but also help reduce cholesterol levels.

Recommendations

The recommended daily amount of fiber for both people with type 2 diabetes and pre-diabetes is 14 grams/1000 kcal (about 21 grams per day for a 1,500 calorie diet). The average daily fiber consumed by most Americans is approximately half of the recommended amount. Most food products list the fiber content on labels (see food label), so become a label-reader. To have the biggest impact on blood glucose and cholesterol levels, increase soluble fiber intake (see fiber table). If you are not near 20 grams per day, start adding fiber in gradually, about 3-5 grams every few days. This is as easy as having an apple with skin for a snack or a cup of broccoli for dinner. Gradually increasing your fiber intake will help decrease the side effects. It is very important to drink lots of water, as this will help dissolve the soluble fiber and form the gel-like substance.

What Can You Expect?

If you don’t drink enough water, fiber may cause constipation. Be sure to drink 6-8 cups of water each day. Initially, added fiber may also cause gas and/or bloating, but increasing fiber intake gradually will prevent these symptoms. Since fiber is not absorbed, it adds bulk to the stool, resulting in improved and more regular bowel movements, especially if constipation is an issue. Also, if you take a fiber supplement (like a psyllium product), separate oral medications from the fiber supplement by two hours. People with certain gastrointestinal conditions like bowel obstruction should avoid taking fiber supplements.

Is Fiber Right for You?

If you are having difficulty controlling your blood glucose and/or cholesterol levels, or just want an excuse to eat more fruits and vegetables, then increasing soluble fiber intake is for you! As always, be sure to talk to your physician before making any changes to your diabetes or cholesterol therapies.

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