Why Is Fiber So Important in Your Diet?

The REAL Reasons You Need To Get Enough Fiber

Why do we need so much fiber?. Patrizia Savarese/Getty Images

You've probably heard you need to get more fiber in your diet: women are supposed to consume 25 grams per day, while men should seek out a whopping 38 grams per day. That's a lot of fiber — for men, more than two cups of lentils ... each and every day. So why do we need so much fiber?

Well, there are several reasons, including one you may not have seen before. But first, we'll cover a myth that turns out not to be quite true.

You may have read that fiber can help to "scrub out" your intestines and move things along quickly, leading to a lower risk of colon cancer (it's an interesting mental image, isn't it?).

However, it isn't accurate: while early studies indicated that fiber could protect against colon cancer, more recent studies haven't always replicated that protective effect, meaning the jury's still out. So right now, you can't count on a bowl of beans or a plateful of crunchy vegetables to guard your gut against colon cancer.

So What Is Fiber Good For?

Even though fiber might not protect you against colon cancer, there are still plenty of reasons to get plenty in your diet.

First, medical research shows fiber can help you "bulk up" your stool, which may lead to improvements in diarrhea (a frequent problem for those of us with celiac disease and non-celiac gluten sensitivity). Fiber also can help soften your stool, a plus if you tend to be constipated (many celiacs suffer from constipation, not diarrhea, and constipation can plague those with gluten sensitivity, too).

Certain types of soluble fiber (fiber that dissolves in water) also may help you lower your cholesterol and assist your body in controlling your blood sugar levels — both important considerations if you suffer from diabetes or heart disease, or if you have metabolic syndrome, a common, often undiagnosed medical condition that in turn raises your risk for heart disease and diabetes.

If you're a woman, studies have shown that fiber — especially fiber from vegetables — may be associated with a reduction in your risk of breast cancer.

Research also indicates that fiber may protect you from esophageal cancer and from a condition called Barrett's esophagus, which can result from long-term gastroesophageal reflux disease (GERD). Since Barrett's esophagus raises your risk of esophageal cancer, this is important to know.

Finally, fiber in your diet may even help you lose weight. Scientists thought this possible benefit came because fiber takes longer to eat (you have to chew it more) and because it makes you feel fuller more quickly.

But more recent research indicates that various types of fiber — especially insoluble fiber, or fiber that doesn't dissolve in water — may trigger alterations in our metabolism even more directly by shifting the balance of microbes living in our large intestines.

Microbes? Really??

Yes, really. This is the reason you may not have heard before.

There's been lots of interest lately in the gut microbiome.

As it turns out, our guts are home to literally trillions of microbes, some beneficial to us and some, well, not so much.

Growing evidence in the medical literature indicates that the "good" microbes living in our guts like fiber. When you eat fiber, your microbes get to eat it, too. Feeding them more fiber may help increase their numbers and possibly create some of the beneficial health effects (and yes, weight loss) we see when we boost our fiber intake.

It's not clear why this effect occurs, although interest has focused on the short chain fatty acids produced by these microbes as they eat fiber. Short chain fatty acids may help to boost your metabolism (leading to the aforementioned weight loss effects of more fiber), and also may exert anti-inflammatory effects that could be protective against cancer and other serious diseases.

So there you have it: dietary fiber may feed not only you, but also the tiny helpful microbes who live in your gut. And getting enough fiber may in turn lead those microbes to help you improve your own health.


Coleman HG et al. Dietary fiber and the risk of precancerous lesions and cancer of the esophagus: a systematic review and meta-analysis. Nutrition Reviews. 2013 Jul;71(7):474-82.

Deschasaux M et al. Prospective association between dietary fiber intake and breast cancer risk. Plos One. 2013 Nov 14;8(11):e79718. doi: 10.1371/journal.pone.0079718.

Michels KB et al. Fiber intake and incidence of colorectal cancer among 76,947 women and 47,279 men. Cancer Epidemiology, Biomarkers and Prevention. 2005 Apr;14(4):842-9.

Wong JM et al. Carbohydrate Digestibility and Metabolic Effects. The Journal of Nutrition.  2007 Nov;137(11 Suppl):2539S-2546S.

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