Fiber flakes out again

Dieticians love fiber. Diet magazines love fiber. Celebrities love high-fiber diets.

They all say it helps you lose weight and keep it off. But a new study pokes some holes in that widespread and long-standing advice, as I’ll explain in a moment.

Protein is the real key to long-term weight management and healthy aging, as I explained on Tuesday.

Of course, for decades, the government doled out faulty advice to cut cholesterol and saturated fats. And since people eat foods, not nutrients, they began to cut out foods that contain cholesterol and fat–such as eggs, meat and seafood. These very same foods are important sources of protein as well.

Thankfully, the government finally admitted their advice about cholesterol and fat was all wrong all along. But apparently, the dietary and nutritional issues involved with “fiber” are too complex for the government nutrition research experts to really get their minds around.

Fiber is indeed fundamental to diet and health. But it’s not the be-all, end-all of weight loss. Or even cancer prevention. (I explained all about the complex role of fiber in the body in the August 2012 issue of my Insiders’ Cures newsletter.)

For this new study on fiber, researchers recruited 240 middle-aged adult patients with metabolic syndrome. They divided the participants into two groups: low- and high-fiber dietary groups.

Researchers told participants in the high-fiber group to increase their daily fiber intake to 30 grams per day. They also received instructions on how to reduce calorie intake, minimize sugar and salt, limit alcohol, and eat fish at least twice weekly.

Participants in the lower fiber group simply followed the American Heart Association (AHA) diet.

After 12 months, the researchers found no significant difference in weight loss between the high- and low-fiber groups. In fact, after 12 months, the AHA diet group lost slightly more than the high-fiber group.

But both groups showed improvements in diet, blood pressure, and insulin levels. (Probably associated with the similar weight losses that occurred in both groups.)

But here’s where things got interesting…

The patients in the high-fiber group were more likely to develop Type II diabetes over the course of the 12 months (measured by a hemoglobin A1C level of 6.5 percent or higher).

Here’s another interesting point…

The researchers admitted they designed the study expecting to find the high-fiber diet would confer greater benefits. But since they didn’t get the expected results, the researchers went ahead and published various complicated rationalizations about why the high-fiber diet didn’t work as well as expected.

Also, unlike a real diet study, researcher relied on study participants to voluntarily follow dietary guidelines they were given. This kind of study design leads to muddy results.

By contrast, in studies I helped design as far back as the mid-1980s at the USDA Human Nutrition Research Center, we fed participants a controlled diet. Nutritional studies with a controlled diet design leads to much stronger, more reliable results.

So why do researchers keep doing these poor-quality diet studies after all this time? It simply casts more confusion. (Of course, these new studies come from a whole, new generation of researchers with no sense of the past…no sense of what we already found 30 years ago. Yet they seek grants, faculty positions, and academic tenure all the same by publishing studies like these. And since their political bosses don’t really know any better, they get what they seek from massively expanded federal research spending.)

It seems everything gets complicated, when it comes to fiber. And it’s certainly not the magic bullet for health or weight that dieticians proposed years ago.

When it comes to medical researchers, nutrition and health, as I have said before, “in the land of the blind, the one-eyed man is king.”


“Single-Component Versus Multicomponent Dietary Goals for the Metabolic Syndrome: A Randomized Trial Comparison of High-Fiber and AHA Diets,” Ann Intern Med. 2015;162(4):248-257