Dr. Michael Ruscio, DC is a clinician, Naturopathic Practitioner, clinical researcher, author, and adjunct professor at the University of Bridgeport. His work has been published in peer-reviewed medical journals and he speaks at conferences around the globe.
Are you confused about fiber? There’s so much information out there talking about how we need to increase our fiber intake to achieve better health, feed our microbiome, and prevent colon cancer. But is this really true? Is fiber friend or foe?
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The Truth About Fiber – Everything You Need to Know About Fiber Consumption
People are confused about fiber. Many microbiota enthusiasts feel we need to eat a bunch of fiber to feed our gut bugs and increase the diversity of our microbiome. However, that may not be the best option for everyone.
There’s definitely a subset of people such as those with IBS or IBD, who do not respond well to high fiber intake.
There’s so much information out there talking about how we need to increase our fiber intake to achieve better health, feed our microbiome, and prevent colon cancer. Probably the biggest fear among people is colorectal cancer, and the thought that if they don’t eat enough fiber they’re at great risk for cancer.
There’s also a concern with regularity and if you don’t eat enough fiber, then you’ll be constipated.
Insoluble vs. Soluble Fiber for Regularity
When it comes to fiber for regularity, soluble fiber shows the most benefit with the least harm compared to insoluble fiber.
The group of IBS patients who do the best with soluble fiber are those with constipation. Soluble fiber has been shown to increase stool frequency, stool bulk, and ease of passing stools.
Insoluble fiber has the highest side effect profile potentially causing gas, bloating, cramping, or worsening of constipation.
You may be wondering what the difference is between soluble vs. insoluble fiber. Soluble fiber dissolves in water, insoluble fiber does not. Soluble fibers are actually more fermentable, which you would think would be worse for IBS, when in fact it’s better tolerated. Insoluble can’t be broken down by your gut bugs and is less fermentable, but it causes more side effects. This is actually counter-intuitive which demonstrates the importance of making decisions based on clinical outcomes rather than theoreticals or hypotheses.
What about fiber and GI cancer?
We’ve evaluated a multitude of studies that looked at both supplemental fiber and dietary fiber and its relationship to gastrointestinal cancer.
Supplemental fiber and GI cancer
Clinical studies show minor positive impact or no impact in preventing GI cancer. In a systematic review of 9 trials, 8 of the trials showed no benefit of supplemental fiber preventing colorectal cancer. Six of these studies used resistant starch as the fiber supplement, and there was no reduced risk of colorectal cancer. Most of the data shows no positive impact on fiber supplementation to reduce the risk of colon cancer.
Rather than trying to eat the way that all the experts say you should eat, it will likely benefit you more to eat intuitively. Listen to your body. Eat the way that makes you feel best, and that may be on a lower fiber diet. Generally, when you eat in a way that makes you feel healthiest, then your body is going to be the healthiest.
Dietary fiber and GI cancer
It appears supplemental fiber doesn’t impact GI cancer risk, but what about dietary fiber? Several systematic reviews and meta-analyses have shown that increased fiber consumption reduces the risk of colorectal cancer. Increased fiber consumption has also shown to be protective against stomach and esophageal cancer. A couple of meta-analyses have shown increased fiber consumption to be protective against cancer, heart disease, and death by any cause.
Is there a preferential type of fiber – fruit, vegetable, or grain – that seems to be more protective? Studies have shown that increased consumption of fruit and vegetables reduce the risk of GI cancer. A meta-analysis of 20 studies and 11,000 subjects found that dietary fruit fiber, vegetable fiber, and cereal grain fiber all protected against colorectal cancer.
However, some research suggests that grain fibers are slightly more protective. A meta-analysis of 25 studies found dietary fiber intake was protective with the greater fiber intake leading to the greatest protection. Total fiber, cereal fiber, and whole grain fiber were shown to be protective, whereas fruit and vegetable fiber did not show protection.
Another meta-analysis showed that cereal fiber and, to a lesser extent, vegetable fiber were protective against death from any cause. Fruit fiber consumption provided no protection.
What we can conclude is that all fiber types seem to offer protection, however, grain fibers might be a little more protective. It may also be that we see more protection from grains because worldwide, healthy diets are more commonly centered around whole grains rather than fruits and vegetables. Therefore, we have more data on whole grains.
This might be alarming considering the bad reputation grains have received recently. Obviously, if gluten is a problem for you, then you should avoid gluten-containing grains. But whole grains, with or without gluten, may offer health benefits. There are studies showing that increased grain consumption correlates with better health.
A meta-analysis of 11 studies and over 1.7 million people found that whole grain consumption was protective against colorectal cancer. Another meta-analysis found that whole grain consumption reduced the risk of cardiovascular disease, cancer, and death from any cause.
A meta-analysis of 14 clinical trials showed that dietary fiber consumption caused a slight but significant decrease in c-reactive protein, an inflammatory marker. Many of the fibers consumed were derived from grains. Eight of the 14 studies used fibers containing gluten. If grains were as toxic as some people claim, we wouldn’t see these types of results.
Of course, this doesn’t mean you to need to consume gluten or any types of grains, but it does mean, you don’t necessarily need to be fearful of them.
What if you don’t tolerate grains very well. What if eating too many grains or carbs causes GI symptoms, weight gain, or inflammation? While there’s much data showing dietary fiber to be beneficial, there’s also data showing the opposite to be true.
A systematic review of 43 studies examined the association of cereal fiber intake, whole grain intake, or both to cancer risk. The vast majority of the studies showed that neither cereal fiber or whole grain fiber protected against cancer.
Another study of over 88,000 women tracked for 16 years evaluated if dietary fiber intake impacted risk for colorectal cancer. No association between fiber intake and cancer was found.
One study looked at the diets of 816 people with colorectal cancer compared to healthy controls. Increased fiber consumption did not protect against colorectal cancer. However, both rice and fruit consumption appeared protective against colorectal cancer, while vegetable intake showed no benefit. Additionally, a high intake of non-rice cereals increased the risk of cancer.
A systematic review with meta-analysis showed no significant association between overall fiber intake and small intestinal cancer. Although grain fiber intake did show a small benefit.
On thing we must consider, is other lifestyle changes people might make when they start eating healthier. Perhaps they start eating more fiber from fruits, vegetables, and whole grains, but they also start exercising, reducing stress, and stop smoking.
The journal of the American Medical Association examined 13 prospective cohort studies involving 725,000 people and the relationship between fiber intake and colorectal cancer risk. The researcher adjusted for these other variables such as exercising. They found no protective effect of fiber intake of any kind on colorectal cancer.
Hopefully, now you can see that fiber is not the colorectal cancer preventing miracle it’s often believed to be.
As suggested earlier, focus on eating intuitively. Eat fresh, healthy food that you tolerate well. If fiber worsens your symptoms, then don’t try to eat a ton of fiber. Eat what you tolerate and gradually try to find the broadest diet that makes you feel good.
To learn more about the effects of fiber, click here to listen to this week’s podcast where Dr. Ruscio shares an excerpt of his upcoming book on the microbiota.
If you need help with your digestive health, click here
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