The Hazards of High Fiber Diets

Too much fiber? How is that possible!? The experts are always telling us to eat more fiber because it’s so good for us. And good for us it is, but only in certain amounts and in healthy people. There are possible physical risks if you don’t know what to watch for when trying to take in a high fiber diet.

The recommendations for dietary fiber intake are about 25-35 grams per day. Most Americans don’t get half this much, so I’m certainly not suggesting you avoid fiber! But there are always exceptions: people who believe if this much is good then more must be better. This assumption is untrue: very high intakes of fiber can actually be harmful:

It is possible that large amounts of fiber can bind to certain minerals and other nutrients and keep them from becoming absorbed. However, there are very few know cases of mineral deficiencies from high fiber diets. You see, the people who get a lot of fiber in their diet are also ingesting a great deal of these other nutrients from the healthy foods they are eating.

Fiber supplements and fiber-fortified foods are the sources from which people are most likely to ingest the extremely high amounts of fiber that will cause health problems. You can see on the label of powders and cereals that contain high levels of fiber, the warning to consume adequate fluids when you take these. There have been cases of obstruction, either in the stomach or the intestines, when people take well over the recommended amounts and do not follow the label directions and consume enough water along with the foods.

Prevent problems by using common sense and reading labels. If you know that 25-35 grams of fiber per day are recommended, and that whole grain products provide just 3, 5, or 7 grams of fiber in a suggested serving size, you should be suspicious that consuming large amounts of foods (or supplements) that provide 13-15 grams of fiber per serving might not be the best idea.

There have been strange and unusual cases: I had a patient once who was too lazy (his words) to spit out the watermelon seeds while he was binging on an entire watermelon; he swallowed dozens of seeds. Not the little flexible white seeds, but the larger, hard black seeds. A few hours later he was in the emergency room with an intestinal blockage that required surgery. See previous paragraph: use common sense.

Because fiber is not digested (that’s the point–it ‘sweeps’ out waste products and keeps your intestines “clean’) it can have a laxative effect. If you suddenly and greatly increase your fiber intake you will likely suffer from bouts of diarrhea. Just scale back and re-introduce more fiber into your diet gradually.

Another drawback of fiber consumption is intestinal gas. While not harmful it can be an embarrassing and uncomfortable consequence of taking in too much fiber. I observed this in a friend of mine who was devouring bing cherries when they first came into season one year: an entire quart passed his lips within a few hours. He suffered intense abdominal pain the rest of the day. There aren’t permanent health consequences from flatulence, but it can cause abdominal distention and discomfort until it has all passed (and there could be permanent social consequences!). Again, just reduce the amount of fiber and add it gradually back to your diet–your system will adjust over a period of just a few weeks.

The usual dietary fiber intake for Americans is only about 15 grams–about half the recommended amount. Adequate amounts of fiber have benefits, like helping you feel more full (thereby helping you eat less when you are trying to watch your weight) and reducing risk factors associated with chronic diseases. Fiber definitely has its benefits. Aim to get the recommended amounts, but don’t try getting too much of a good thing–it comes with risks!

Image by: Sue R B, SXC

2 thoughts on “The Hazards of High Fiber Diets

  1. Is there any evidence pointing to protein and, umm….intestinal gas? I have experienced this after consuming large quantities of protein, although I never considered that it could have been the fiber in what I ate – some protein powders have fiber, along with the typical big meal with lots of vegetables accompying the meat.

  2. Dan,
    There are many factors that can contribute to intestinal gas and it varies from individual to individual. Sometimes it’s fiber, sometimes it’s dairy, sometimes it’s just eating too fast, or having too many carbonated beverages. Often it is due to the bacteria acting on undigested materials in our large intestines and fiber is undigestible.
    If you notice an increase in, umm … flatulence after eating certain foods you may want to avoid them on certain occasions 😉 I’ve also heard that bean-o (an over-the-counter product) works very well to prevent this condition.

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