How Much Fibre Should You Eat Every Day?
Written by: Michael Greger M.D. FACLM on March 14th, 2017
High dietary fibre intake may help prevent strokes. The belief that dietary fibre intake is protectively associated with certain diseases was postulated 40 years ago and then enormously fuelled and kept alive by a great body of science since. Today it is generally believed that eating lots of fibre-rich foods helps prevent obesity, diabetes, and cardiovascular diseases such as stroke.
Strokes are the second most common cause of death worldwide. Moreover, stroke is a leading cause of disability, and so preventing strokes in the first place—what’s called primary prevention—should therefore, be a key public health priority (see How to Prevent a Stroke).
The best observational studies to date found that fibre appears to significantly protect against the risk of stroke. Different strokes for different folks, depending, evidently, on how much fibre they ate. Notably, increasing fibre just seven grams a day was associated with a 7% reduction in stroke risk. And seven grams is easy, that’s like a serving of whole grain pasta with tomato sauce and an apple.
What’s the mechanism? Maybe it’s that fibre helps lower cholesterol and blood sugar levels. Or it could just be that those eating more fibre are just eating more vegetables, or fewer calories, or less meat and fat, or improving digestion, all of which may slim us down and lower our blood pressure and the amount of inflammation in our bodies. Does it really matter, though? As Dr. Burkitt commented on the biblical passage, “A man scatters seed on the land—the seed sprouts and opens—how, he does not know,” the farmer doesn’t wait to find out. Had the farmer postponed his sowing until he understood seed germination, he would not have lasted very long. So yes, let’s keep trying to figure out why fibre is protective, but in the meanwhile, we should be increasing our intake of fibre, which is to say increasing our intake of whole plant foods.
It’s never too early to start eating healthier. Strokes are one of many complications of arterial stiffness. Though our first stroke might not happen until our 50’s, our arteries may have been stiffening for decades leading up to it. Hundreds of kids were followed for 24 years, from age 13 in through 36 and researchers found that lower intake of fibre during a young age was associated with stiffening of the arteries leading up to the brain. Even by age 13, they could see differences in arterial stiffness depending on diet. Fibre intake is important at any age.
Again, it doesn’t take much. One extra apple a day or an extra quarter cup of broccoli might translate into meaningful differences in arterial stiffness in adulthood. If you really don’t want a stroke, we should try to get 25 grams a day of soluble fibre (found concentrated in beans, oats, nuts, and berries) and 47 grams a day (just over 3 table spoons full) of insoluble fibre (concentrated in whole grains). One would have to eat an extraordinarily healthy diet to get that much, yet these cut-off values could be considered as the minimum recommended daily intake of soluble and insoluble fibre to prevent stroke. The researchers admit these are higher than those commonly and arbitrarily proposed as “adequate” levels by scientific societies, but should we care about what authorities think is practical? They should just share the best science and let us make up our own minds.
Someone funded by Kellogg’s wrote in to complain that in practice, such fibre intakes are “unachievable” and that the message should just be the more, the better—like maybe just have a bowl of cereal or something.
The real Dr. Kellogg was actually one of our most famous physicians, credited for being one of the first to sound the alarm about smoking, and who may have been the first American physician to have recognize the field of nutrition as a science. He would be rolling in his grave today if he knew what his family’s company had become.