You can't really have a fiber deficiency, per se, since your body doesn't absorb it and there isn't a way to measure how much you have in your body. But it is possible to have too little fiber in your diet. When your fiber intake is lacking, you'll probably notice some gastrointestinal upset, and signs of a low-fiber diet may eventually show up during physical exams.
Average Intake Vs. Recommendation
On average, Americans tend to get just 15 grams of fiber per day, which is far less than the recommendation in the publication "Dietary Guidelines for Americans, 2010," You should actually be getting 14 grams for each 1,000-calorie increment in your diet. That means for a 2,000-calorie diet, you'll need 28 grams of fiber daily, almost double the typical intake.
How You’ll Feel
Fiber's most prominent role is helping with digestion. Insoluble fiber, also known as roughage, from fruit and vegetable skins, whole grains and nuts, is like a broom. It sweeps out your bowels, collecting waste so you can easily pass bowel movements on a regular basis. Soluble fiber, from the inner fleshy parts of fruits and veggies, oats and beans, ferments slightly in your gut. As it passes, the sludge that forms slows digestion and allows nutrients to fully absorb. So when fiber is lacking in your body, digestive processes suffer. You could have gas and bloating, as your system struggles to push out waste. Additionally, you might become constipated, leaving you backed up and struggling to pass stools. In some cases, you could even have diarrhea, since fiber isn't around to bulk waste together.
Reflections in Lab Work
Even though there isn't a way for your physician to check your fiber levels, other lab values could signify that you don't have enough fiber in your diet. One of the jobs of soluble fiber is to bind with excess cholesterol and push it out along with your waste. If your blood cholesterol runs high, your doctor might advise you to up your fiber -- particularly soluble fiber -- intake. Soluble fiber is even beneficial for keeping your blood sugar stable, an important benefit if you have diabetes or prediabetes. If your glucose shows up on the high end after a blood draw, it could be a signal that you need to up your fiber consumption.
Inadequate fiber in your system can lead to bowel problems that may not be obvious right away. For example, if you're straining while using the restroom and struggling to relieve yourself since your fiber intake is low, you'll be more likely to suffer from painful hemorrhoids. Over time, if fecal matter gets impacted, it can force bulges and pockets to form along the lining of your intestinal tract. This condition, known as diverticular disease, leads to poor nutrient absorption and uncomfortable inflammation. Low fiber concentrations in your body can also expose your system to toxins because waste sits in your bowels for a longer period of time. This could potentially increase your risk of developing colon cancer, explains the University of Colorado Extension, although more research needs to be conducted to know for sure.