Many people wonder whether they'll lack the required amount of fiber if they cut wheat and other grains from their diets. The short answer is “absolutely not!” In fact, some of the healthier foods you're replacing wheat with (vegetables and fruit) have more fiber than the fortified whole grains you were eating before.
Now for the bigger question: Do you need as much fiber as the recommendations say (25 to 40 grams per day)? Yes, but it shouldn't come from fortified grains whose effect hinders absorption of other nutrients.
To understand what fiber does for the body, you first have to differentiate between the types of fiber:
Soluble fiber: Soluble fiber is considered water soluble, meaning it dissolves in water. It makes you feel full and slows down digestion because it expands in the gut. It also can produce sticky lumps in the intestine, which can lead to bloating and gas. Soluble fiber is more prone to fermentation, which helps feed the good bacteria in the gut. It's found in some vegetables, fruits, nuts, and legumes.
Insoluble fiber: Insoluble fiber is not water soluble. It passes through the body mostly unchanged and tends to speed up transit time, if you will. It's not as prone to fermentation but may help spread the process of fermentation to the entire colon. Insoluble fiber is found in the skins of vegetables and fruits and the bran portion of whole grains.
Much of the research is inconclusive as to fiber's benefits. One of the biggest claims made for eating fiber is the increased time for digestion, which keeps blood sugar levels down (obviously an important benefit for diabetics). However, blood sugar levels decrease anyway on a wheat-free diet, so the need to slow digestion isn't as much of an issue.
Well-controlled studies shows no benefit from diets high in fiber for the reduction of colorectal cancer, diverticulitis, irritable bowel syndrome, or constipation. In reality, such a diet can worsen these conditions, despite what conventional wisdom would tell you.
Insoluble fiber in particular can have some additional consequences:
Leads to osteoporosis: Because of the antinutritive effect, insoluble fiber inhibits the absorption of both calcium and zinc and depletes calcium the body already contains.
Increases vitamin deficiency diseases: Because of the increase in transit time caused by insoluble fiber, your body doesn't absorb the fat soluble vitamins (A, D, E, and K) or phosphorus, iron, or magnesium as easily, which can lead to a variety of diseases.
The takeaway is to eat soluble fiber from fruits, vegetables, and fermented foods and don't sweat trying to go overboard with your fiber intake. Follow the tenets of living wheat free , and you shouldn't have to give any extra thought to adding or supplementing with extra fiber.