POST SUMMARY: What this means for you…
It can be tricky to get good fiber without the insulin-spiking starches. In general, as you’re choosing good vegetables (i.e. any leafy greens, broccoli, cauliflower, and many more that have low glycemic loads) to eat with your fatty meals, you’re getting a good amount of fiber. If you choose to take a fiber supplement, just be sure it doesn’t contain sugar in the ingredient list—it’s remarkably common in fiber supplements.
Dietary fiber enjoys a special place in the hallowed halls of the nutritional pantheon; it is almost universally embraced as being essential to a modern healthy diet.
While there are many reported benefits, the role of fiber in insulin sensitivity is equivocal, albeit with a general indication that fiber helps improve insulin sensitivity. Multiple epidemiological studies (i.e., those studies that get data from questionnaires) find a correlation with fiber consumption and improved insulin sensitivity , but results from clinical trials are more mixed and require some scrutiny in interpreting in the context of insulin resistance.
High-Fiber Meals, Glucose, and Insulin Levels
Some studies have found that when study subjects eat a high-fiber meal, glucose and insulin levels are lower than those compared with subjects who eat a low-fiber meal, but again—these findings are not the consensus; the results vary based on the subject population.
For example, men with higher fasting insulin levels (i.e., insulin resistance) enjoyed a lower post-meal insulin spike when consuming a high-fiber meal versus a low-fiber meal, but there was no difference in insulin levels in the men with otherwise normal fasting insulin (i.e., insulin sensitive).
When explored over the long term, the results get even more confusing. While increasing dietary fiber over a period of several weeks was shown to improve insulin sensitivity in a non-obese diabetic study group , consuming more dietary had no effect on insulin resistance in obese diabetics . Altogether, these studies suggest an insulin-sensitizing effect of fiber in insulin-resistant subjects, if not insulin-sensitive subjects.
The Type of Fiber
An important weakness in the studies exploring the insulin-sensitizing benefits of a high-fiber diet is the type of fiber—virtually every dietary fiber trial uses fiber supplements in the form of guar gum (i.e., galactomannan); this is not the fiber that is part of most carbohydrates. Thus, while guar gum is available in most health food stores, it is not part of a normal diet, which suggests the results of a high-fiber diet in the form of increased guar gum consumption should not be extrapolated to assume other sources of fiber (e.g., vegetables, legumes etc.) will have the same results .
Nevertheless, placing insulin-resistant individuals on a high-fiber diet (50 g) where the fiber comes not from supplements, but from fruits, vegetables, legumes, and selective grains, significantly improves insulin sensitivity after six weeks .
Studies Increase Fiber at the Expense of Fat
An unfortunate aspect of almost every study exploring the role of dietary fiber in insulin resistance is that the study increases fiber at the expense of fat—the high-fiber study diets are low-fat diets.
In light of the fact that dietary fat elicits no effect on blood insulin, the relative absence of fat in the high-fiber diets leaves unanswered the question of whether a diet high in fat and fiber is more effective than a diet high in fiber and low in fat.
Two published reports touch on this conflict, albeit without actually addressing insulin resistance, only the glucose response. One gave study subjects three distinct types of bread—low fiber/low fat, high fiber/low fat, and high fiber/high fat . The low fiber/low fat resulted in a far greater blood glucose response than the other two and it was the least satisfying (suggesting that perhaps the person would be inclined to eat more). Whereas the blood glucose response was similar between the two high-fiber breads, regardless of fat content, the high-fiber/high-fat bread was more satisfying. Unfortunately, the study did not assess insulin levels, which prevents any conclusions touching on insulin resistance directly. A second study fed subjects four types of pasta meals—normal pasta, pasta with psyllium (fiber), pasta with fat (oil), pasta with pysllium and fat . Psyllium alone did nothing to mitigate the insulin or glucose effect of the carbohydrate-rich pasta. While the addition of fat lowered them somewhat, the addition of pysllium and fat lowered them the most. Moreover, the addition of fat and pysllium lead to the greatest satiety.
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This blog post (and all other posts and content on this website) is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.
About Benjamin Bikman, Ph.D. – Ben earned his Ph.D. in Bioenergetics and was a postdoctoral fellow with the Duke-National University of Singapore in metabolic disorders. Currently, his professional focus as a scientist and professor (Brigham Young University) is to better understand chronic modern-day diseases, with special emphasis on the origins and consequences of obesity and diabetes. He frequently publishes his research in peer-reviewed journals and presents at international science meetings.