Four important rules of thumb about eating fiber

TIME magazine recently interviewed my colleague Walt Willet, Harvard professor of epidemiology and nutrition, about the best “high-fiber foods.”

Of course, as I explained a few weeks ago, the issue of dietary fiber is complicated.

In fact, it’s one of the most-complicated, most-discussed topics in medicine today. I even tackled it in the very first issue of my Insiders’ Cures newsletter (“Dietary fiber: Cancer cure — or cause?”).

Of course, Walt can also help clarify this topic.

In fact, he’s probably the single, most knowledgeable person I know when it comes to the science of diet and nutrition. I first started corresponding with him back in 1977 regarding some of my findings in Southeast Asia.

A few years thereafter, I frequently saw him at the National Cancer Institute when he would come to meet with us in the mid-1980s. I remember he cited my own research in the New England Journal of Medicine, showing that dietary factors during childhood are important in determining long-term cancer risk.

So, I pay attention when Walt speaks out, especially on complex topics — like fiber — that baffle the mainstream researchers.

The right kind of fiber, in the right amounts

Walt says the human body likes a bit of challenge…such as moderate exercise, intermittent fasting, and getting out into the elements of Nature from time to time. These activities give your physiology a workout and help preserve your longevity.

At the cellular level, these activities can induce “hormesis.” This biological phenomenon illustrates how your body can benefit positively from low amounts of a substance that’s otherwise harmful in higher amounts. For example, exercise benefits your body in moderate amounts. But in excess, it can be incredibly damaging to your joints, bones, heart, kidneys, reproductive organs, and GI tract.

Walt says eating dietary fiber works somewhat in the same way…

Moderate amounts of it challenge your digestive system, “tuning it up,” so to speak. And on a cellular level, moderate amounts of dietary fiber will stimulate your cells.

Walt also cited numerous studies that linked a diet moderately higher in fiber to lowered risk of cardiovascular disease, Type II diabetes, and weight gain.

Plus, a new review published in the American Journal of Clinical Nutrition (AJCN), which I think is one of the best sources on diet and nutrition science, shows higher fiber is associated with lower risks of pancreatic cancer and deaths from any cause (including heart disease).

Nevertheless, I want to caution you regarding another statement that came later in the TIME article…and it’s quite a common misconception.

Wendy Dahl, an associate professor of food science and human nutrition at the University of Florida, said, “there is no upper limit on [the amount of] fiber — you can’t get too much.”

Well, that’s just plain wrong.

Your body processes various types of fiber differently

As you probably know, there are two kinds of fiber.

Soluble fiber dissolves in water, so it’s easier for your body to digest. It’s found in bran, barley, beans, lentils, nuts, oats, peas, seeds, and some fruits and vegetables. Research associates soluble fiber with better control of blood sugar and lower levels of fats in the blood.

The second kind of fiber, insoluble fiber, doesn’t dissolve in water. It’s found in the outer, bran layer of whole grains and in the skin of many whole fruits and vegetables. (That’s why I always recommend eating the skin of fruits and vegetables.)

Insoluble fiber helps bulk up your stools, pushing the waste through your intestines in a timely manner. The fibers actually act like little “brooms” on the inside of the colon, removing old and damaged cells, which is thought to reduce the risk of cancer.

But, as I first published 30 years ago, too much scraping and stimulation of the cells in the colon can signal the cells to proliferate, which is a risk factor for colon cancer.

This finding may explain why there hasn’t been any real evidence of lowered cancer rates among people who follow popular macrobiotic diets, which are centered on eating a plant-based, low-fat, high-fiber diet. (They’re mainly focused on consuming whole grains, vegetables, and beans/bean products.) So, consuming too much fiber can be quite counter-productive.

As I always advise, achieving balance in your diet is key…

Moderation in all things — including fiber

When it comes to working fiber into your diet, there are a few simple rules of thumb:

1.) Opt only for whole grains

As I always advise, avoid processed grains, like white flour. They break down too easily in the GI tract, so they essentially run right through your digestive system without offering much nutritional benefit.

Also, eating them leads to spikes and surges in blood sugar. Plus, people tend to eat too much.

Instead, I always advise you to opt for whole grains, which break down slowly in the GI tract.

2.) Seek variety

It’s also important to eat a variety of grains, fruits, and vegetables as they contain different types of dietary fiber and bioactive substances. This diversity helps support the health of your GI microbiome — the environment in your gut where billions of healthy probiotic bacteria thrive.

Of course, fruits and vegetables also contain a wide variety of other healthy substances besides fiber — including carotenoids, flavonoids, indoles, isothiocyanates, lignans, phenols, minerals, and vitamins.

So, aim to buy fresh produce, in all shades of the rainbow. Think of adding not just green…but also orange, purple, red, and yellow fruits and vegetables to your plate.

The same goes for grains…

Strive to eat a variety of different types of whole grains — such as buckwheat, bulgur, couscous, millet, 100 percent whole wheat, rye, steel-cut oats, and wheatberries.

3.) Make sure it’s organic

I’m writing more and more about the importance of choosing organic full-fat dairy, grains, produce, and meat.

For one, organic foods don’t come from genetically modified seeds (GM). Nor are they contaminated with glyphosate, also known as Roundup. This pesticide — and known human carcinogen — poisons your GI microbiome and probably much more. Plus, as you’ll recall — a new study found that eating organic slashes your risk of developing a particularly deadly cancer by an impressive 73 percent.

I most recently reported on the dangers of glyphosate and GM foods in the October 2017 issue of my monthly Insiders’ Cures newsletter (“REVEALED: Poison in your pasta”).

4.) Aim for the moderate middle

The Institute of Medicine’s recommendation for daily dietary fiber intake is 38 grams for men and 25 grams for women. But I find people follow this advice best when it’s illustrated in servings of food— not specific, weighed amounts.

So, I’m going to put my recommendations in easy-to-follow, whole-food terms…

  • Aim to eat seven to eight servings of colorful, varied, fresh fruit or vegetables a day.
  • As for whole grains, aim to eat two to three servings per day.

Hopefully, I’ve made it clear that despite what some random “expert” in TIME magazine says, just eating loads and loads of “fiber” isn’t the be-all, end-all of good health.

And more importantly, I hope you’re coming to realize that most mainstream reporting on nutrition simply misses the mark.

Instead, stay tuned here to my Daily Dispatch and my Insiders’ Cures monthly newsletter for the truth behind the headlines, and the commonsense, science-backed advice you really need in order to live a long, healthy life. Not yet a subscriber to Insiders’ Cures? No worries — it just takes one easy click.


“These are the best high-fiber foods, according to experts,” TIME ( 10/18/2018

“Dietary fiber and health outcomes: an umbrella review of systematic reviews and meta-analyses,” The American Journal of Clinical Nutrition 1 March 2018; 107(3):  436–444