For years, fiber has been the “butt” of jokes due to its ability to keep you “regular.” But now, strong research shows that fiber has benefits well beyond the bathroom. In fact, studies indicate that fiber may be one of the most powerful protectors against type 2 diabetes, weight gain and obesity, and our #1 killer: cardiovascular disease.
Let me bring you up to speed on this humble but complex nutrient.
What is fiber?
Believe it or not, fiber is a carbohydrate. But, unlike the starches and simple sugars we might ordinarily think of when we think “carb,” fiber is a structural carbohydrate. It’s the rigid, supportive scaffolding of plants’ edible parts. It’s what makes kale and Swiss chard stand up in the garden. It’s what makes wedges of an orange firm enough to peel off and pop into your mouth. It’s the envelope that encases and preserves the freshness of each individual kernel of wheat and other whole grains.
And, while fiber is edible, it is mostly indigestible by the human digestive tract. So it passes through the small intestine and arrives in the large intestine a bit puréed, but largely undigested.
How does fiber help our health?
When fiber arrives in the large intestine, billions of friendly bacteria take over. They, not we, digest the fiber, breaking it down with enzymes and fermenting the resultant sugars into a variety of prebiotics (food for the bacteria themselves) and short-chain fatty acids (SCFA).
Among other functions, the SCFAs help the bacteria nourish and heal the colon’s delicate lining and keep the gut operating at peak efficiency.
There are two main categories of fiber: soluble (found mostly in fruits, vegetables, nuts and oatmeal), and insoluble (found mostly in cereals, whole grains, legumes and vegetables).
Soluble fiber absorbs water in the intestines and becomes a gel, which gets fermented in the large intestine and produces two hormones that tell the brain, “I’m full.” It also sends a chemical signal to the liver to reduce its production of cholesterol, and increases the amount of cholesterol dumped out in the feces—improving cholesterol numbers from two angles.
Importantly, it interferes with absorption of sugars into the bloodstream—clearly a boon for people with diabetes. So we get direct protection against plaque-clogged arteries, and indirect protection by reducing the inflammation that results from obesity and diabetes.
Insoluble fiber, on the other hand, travels through the digestive tract like a bulky scrub-sponge, scouring residual flotsam from the intestines’ nooks and crannies and bulking up the feces. It also, through more intricate mechanisms not yet completely figured out, reduces several cardiovascular risk factors.
For one, it lowers numerous chemical markers of inflammation. And it decreases pro-inflammatory chemicals that make arterial plaque prone to breaking loose and causing strokes.
Additionally, while soluble fiber sends a hormonal message of fullness to the brain, insoluble fiber creates actual, physical fullness earlier in the course of a meal so that you don’t overeat. This not only dramatically enhances weight loss and helps us maintain healthy body weight, it also pushes the food we’ve eaten through the digestive tract a little faster, before all its calories can get absorbed. In general, fiber intake and body weight are like a child’s see-saw: As fiber goes up, weight goes down, and vice versa. In one study, middle-age women gradually lost an average of 4.4 pounds over a 20-month period, and all they did was increase their fiber intake by eight grams per 1,000 calories.
Finally, the glycemic index of meals, post-meal blood glucose levels, and therefore our risk for type 2 diabetes, all are lowered when insoluble fiber is consumed. It also reduces total and LDL cholesterol, lowers BMI and body fat, and shrinks belly fat. All great stuff for heart and cardiovascular health.
Fewer than five percent of Americans eat enough fiber. One review study found that the average fiber intake in the US was about half of what it should be (15.7 to 17 grams per day), with men at the lower end of the spread. In a Swedish study, fiber gave women greater protection against heart attack and stroke than it gave the men, but again, the women consumed more fiber than the men did (even though both sexes were well below the minimum).
The latest recommendation from the U.S. Food and Drug Administration is 25 grams of fiber per day for women, and 35 grams for men. For both sexes, at least 6 grams of their fiber intake should be soluble.
This is not to say women need less fiber than men; they simply need fewer calories than men do. So let’s put it another way: Everybody should get 14 grams of fiber per 1,000 calories eaten. This is based on the protection against cardiovascular disease, for which the epidemiologic evidence is very strong.
The average 15.7 to 17 grams of fiber Americans consume is roughly ½ to ⅓ the recommended amount. We have some catching up to do.
Upping your fiber—and loving it
Let me assure you, eating more fiber does not mean chewing on cereal that tastes like cardboard. On the contrary, some of our most delicious foods also happen to be fiber rich.
Here are some links to what I consider to be the best lists of food fiber content. By choosing varied whole foods and mixing it up from day to day, you’ll cover all the fiber bases for the best heart health protection possible.
Gene Smart Healthy Eating Guide
Mount Sinai Health System fiber chart
Today’s Dietitian fiber chart
Fiber supplements are also an option, but they tend to be made from single, isolated sources and therefore lack the healthy array of fiber varieties found in whole foods. As a result they can cause abrupt changes in gut bacteria, which can lead to bloating and gas. They also often fail to provide adequate amounts of the many types of fiber. This is why your best bet is whole foods.
Finally, be sure to increase your water intake as you increase your fiber. Doing so can help prevent unpleasant digestive side effects while your body gets used to this positive dietary change.