Dietary Fiber And Insulin Resistance

By November 13, 2016Blog

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 [1], 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 [2], consuming more dietary had no effect on insulin resistance in obese diabetics [3]. 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 [4].

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 [5].

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 [6]. 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 [7]. 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.

References:

  1. Marshall JA, Bessesen DH, Hamman RF: High saturated fat and low starch and fibre are associated with hyperinsulinaemia in a non-diabetic population: the San Luis Valley Diabetes Study. Diabetologia 1997, 40:430-438.
  2. Tagliaferro V, Cassader M, Bozzo C, Pisu E, Bruno A, Marena S, Cavallo-Perin P, Cravero L, Pagano G: Moderate guar-gum addition to usual diet improves peripheral sensitivity to insulin and lipaemic profile in NIDDM. Diabete Metab 1985, 11:380-385.
  3. Cavallo-Perin P, Bruno A, Nuccio P, Bozzo C, Pagano G: Dietary guar gum supplementation does not modify insulin resistance in gross obesity. Acta Diabetol Lat 1985, 22:139-142.
  4. McKeown NM, Meigs JB, Liu S, Saltzman E, Wilson PW, Jacques PF: Carbohydrate nutrition, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort. Diabetes care 2004, 27:538-546.
  5. Chandalia M, Garg A, Lutjohann D, von Bergmann K, Grundy SM, Brinkley LJ: Beneficial effects of high dietary fiber intake in patients with type 2 diabetes mellitus. The New England journal of medicine 2000, 342:1392-1398.
  6. Lunde MS, Hjellset VT, Holmboe-Ottesen G, Hostmark AT: Variations in postprandial blood glucose responses and satiety after intake of three types of bread. Journal of nutrition and metabolism 2011, 2011:437587.
  7. Frost GS, Brynes AE, Dhillo WS, Bloom SR, McBurney MI: The effects of fiber enrichment of pasta and fat content on gastric emptying, GLP-1, glucose, and insulin responses to a meal. European journal of clinical nutrition 2003, 57:293-298.

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.

4 Comments

  • LaMar Dahl says:

    Hi Dr Bikman,
    I found this study interesting; relating to the increased insulin sensitivity in non diabetic hypertensives who were given Lisinopril. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1873694/ Your thoughts?

  • Ben says:

    Hi Lamar. That’s a nice study, albeit with some limitations. Nonetheless, lisinopril is a drug that lowers blood pressure by pushing more water from the kidneys (and out of the blood). By reducing water in the blood, blood volume and, thus, blood pressure goes down. Importantly, by making lifestyle changes to keep insulin low, the reduced insulin has a similar effect of lisinopril–lower insulin helps the kidneys remove excess water from the blood. I think it would be worth exploring the effects of altered diet, in particular limiting carbohydrates to keep insulin low, on blood pressure changes before taking a drug, which always has side effects.

  • Mike Ellwood says:

    Dr Bikman,

    Do you have any comment to make over Robert Lustig’s claim that while consuming refined carbohydrates containing a lot of sugar is bad for us, eating fruit is “ok”, because the fibre in fruit is enough to slow down absorption of the sugar.

    I’ve always been sceptical of this claim (I think fruit is generally not a good thing for people with severe IR), but has any science been done on people’s insulin response to a variety of fruit? (especially among people with existing insulin resistance).

    Thank you.

    • Ben Bikman says:

      Hi Mike. In general, I agree with Robert–nature intended fructose to be consumed with fiber, which does alter digestion of the sugar (i.e. fructose). However, “nature” didn’t make most of the fruit we eat. For example, apples are several times larger and sweeter (and the same could be said of probably every fruit we eat). Furthermore, for someone who “carb intolerant”, certain fruits, such as “tropical” fruits (e.g. banana, mango, etc.) should be eaten rarely due to the higher sugar content.

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