By: Steph F., Lagniappe Wellness Dietetic Intern

High-fiber diets are an important component of diabetes management. These nutritious carbohydrates add so many benefits including controlling daily blood sugars, decreasing HbA1c, reducing insulin resistance, decreasing LDL and total cholesterol, and keeping us feeling fuller longer. We will discuss each of these fantastic benefits plus much more within this blog.

Many people are under the misconception that all people with diabetes should be consuming a ketogenic diet. A ketogenic diet can reduce blood sugar, but this doesn’t mean it’s right for everyone. When following a ketogenic diet, you restrict carbohydrates, including grains and fruits. A ketogenic diet is 70-80% fat, 5-10% carbohydrates, and 10-20% protein. When following a strict ketogenic diet, carbohydrates are as low as 20 grams a day. Although this decrease in carbohydrates may lead to lower blood sugar, hypoglycemia (lower than normal blood sugar) is a real concern for people with diabetes and should be avoided. The risk of hypoglycemia becomes even greater after adding medications/insulin used to control diabetes and the co-morbidities that come along with this diagnosis.¹ A study performed by Morrison et al. in 2020, found that after feeding a ketogenic diet to mice for 7-21 days the mice showed impaired glucagon release in response to hypoglycemia. Glucagon is a hormone made by the pancreas to regulate blood glucose levels. Consuming a ketogenic diet leads to a reduction in liver glycogen (the stored form of glucose) which most likely was the culprit that led to this response.²

Another cause for concern when following the ketogenic diet is insulin resistance and the increased risk of T2D (Type 2 Diabetes). We are told that a high-carbohydrate, high-fat, western-style diet is linked to developing T2D and obesity, but consuming a low-carbohydrate, high-fat, ketogenic diet is healthy. Questions were raised on the validity of this information in a study that was published in the Journal of Physiology in 2018 where mice were fed a ketogenic diet. The study showed that even though keto-fed animals seem to be healthy in a fasted state, they exhibited a decreased glucose tolerance to a greater extent through the suppression of liver glucose production by insulin.³

Lastly, we cannot forget the importance of working with the individual client and their own lifestyle. Many people enjoy carbohydrates, and it is important for them to keep carbohydrates in their daily diet. The key is to give our clients the power of knowledge on how to safely keep carbohydrates in their daily lives and what kind of carbohydrates they should be focusing on. 

The Difference Between Starch, Fiber, and Sugar

There are three main types of carbs: starch, fiber, and sugar. Simple carbohydrates (sugar) are easily broken down by our bodies due to their simple chemical structure which leads to a faster blood sugar rise and insulin secretion from our pancreas (i.e., rapid blood sugar spike.)  However, complex carbohydrates (starches and dietary fibers) such as whole grains and legumes can instead help to control blood sugar. Complex carbs are filled with vitamins, minerals, and fiber and they are digested slower than refined carbohydrates. This makes them less likely to cause rapid spikes in blood sugar. 

Fiber 

One of the keys to controlling blood sugar and supporting insulin sensitivity is adding fiber-rich carbohydrates to the diet. Dietary fibers are not digested or absorbed in the small intestine. They are usually fermented in the colon which results in SCFA (short-chain fatty acid) production and some of those can be used for energy sources. They include non-starch polysaccharides (cellulose, hemicellulose, pectin, gums, and beta-glucans) all of which are from the plant cell wall. These can further be divided into soluble and insoluble fiber. Soluble fibers (oats, psyllium, pectin, and guar gums) can impact glucose and lipid absorption. Insoluble fibers are slowly and incompletely fermented in the large intestine and affect our bowel habits significantly. Notably, fiber is unable to be broken down and digested and instead passes through our bodies and digestive system undigested.

Soluble Fiber vs Insoluble Fiber

Soluble fiber can be found in apples, bananas, oats, black beans, and avocados. This type of fiber slows digestion because it dissolves in water and forms a gel-like substance in our stomachs. This makes us feel fuller longer and helps with weight loss and maintenance. It helps to control cholesterol and LDL (low-density lipoprotein aka “bad cholesterol”) by binding with cholesterol in the intestine and removing it from the body. Since soluble fiber is unable to be broken down and absorbed, blood sugar spikes are not the same as with other carbohydrate sources.⁴ 

Insoluble fiber acts differently than soluble fiber in that it doesn’t dissolve in water and usually remains whole while passing through the stomach. Insoluble fiber is found in things such as whole wheat flour, bran, nuts, seeds, and fruit and vegetable skins. It supports insulin sensitivity and has been shown to reduce insulin resistance. A strong correlation has been shown between insoluble fiber and a decreased T2DM risk.⁵ It has low energy density and can improve post-prandial satiety (after a meal) to reduce appetite, which can lead to reduced body weight and may lead to lowering blood pressure.⁶ In addition, insoluble fiber also promotes movement through the digestive system and gives stool bulk. Fiber has a scrub-brush effect that helps to rid bacteria and promote gut health. It decreases the overall transit time by about half. Hence, carcinogenic concentrations are reduced, and the risk of colon cancer is reduced.⁷

The Facts

Based on three recent systematic reviews and meta-analyses conducted by Reynolds et al. (2020), Ojo et al. (2021), and Chen et al. (2021), the following key findings regarding the effects of dietary fiber on various health markers are as follows: ^{8, 9, 10}

• Lipid Profile
  • Total cholesterol, LDL cholesterol, and triglycerides were reduced with increased fiber intake. The effect was significant and independent of diabetes type, diabetes medications, or fiber types used.^{8, 9}
  • High fiber intakes were associated with a greater improvement in total cholesterol levels.⁸
• All-Cause Mortality
  • High fiber intakes were associated with a significant reduction in all-cause mortality compared to low-fiber intakes.⁸
  • A 35% reduction in all-cause mortality was observed with an intake of 35 grams of fiber per day compared to 19 grams per day.⁸
• Glycemic Control
  • Increased fiber intake was shown to improve glycemic control, as indicated by improved HbA1C levels, regardless of the type of fiber. Fasting glucose levels also improved with increased fiber intake.^{8, 5}
  • Moving from low to moderate or higher fiber intakes was associated with greater benefits in glycemic control.^{8, 5}
  • Dietary fiber was found to be beneficial for all types of diabetes.⁸
• Inflammatory Markers
  • Dietary fiber consumption was associated with significant reductions in C-reactive protein (C-RP) levels, indicating a decrease in inflammation.⁹
• Gut Microbiota
  • Fiber-rich diets were shown to increase the abundance of beneficial bacterial species (Faecalibacterium prausnitzii and Akkermansia muciniphila) known for their anti-inflammatory effects.⁹
• Weight Loss and BMI
  • Increasing fiber intake was associated with reduced body weight, BMI, and waist circumference.^{8, 9}
  • The difference in BMI between the dietary fiber group and the control group was statistically significant.^{8, 9}
• T2DM Risk
  • An intake of > 30 grams a day of insoluble fiber and whole grains correlated strongly with a decreased T2DM risk.⁵
  • Soluble fibers were associated with the post-prandial (after a meal) response by having a delayed and reduced glucose absorption effect which causes a flattened post-prandial blood sugar level and reduces insulin.⁵

In Summary

Current fiber recommendations for people with diabetes are the same as for all Americans. The recommendation put forth by The Dietary Guidelines for Americans (DGA) is a minimum of 14 grams/1000 kcals which equates to a minimum of 28 grams in a 2,000-calorie diet. More specific recommendations are found in the DGA depending on age and gender.¹⁰ Reynolds et al. suggests increasing daily fiber intake by 15g or to 35 grams/day may be a reasonable target that would be expected to reduce the risk of premature mortality in adults with diabetes.

Excellent sources include vegetables, pulses, whole fruits, and whole grains. By following a balanced plate method put forth by the American Diabetes Association and adding fiber to a consistent carbohydrate diet for a person with diabetes, we can provide a lifestyle that has fewer blood sugar spikes and reduces insulin resistance. Cardiovascular disease is a well-known comorbidity that may come along with a diagnosis of diabetes. By choosing fiber, we can help to control total cholesterol and LDL and help to combat CVD. Fiber can also help with post-prandial satiety which in turn helps with weight maintenance and weight loss. Lastly, by choosing fiber we can keep the digestive tract working properly, avoid constipation, and reduce colon cancer risk.¹¹ This is not an all-inclusive list of the benefits fiber offers all of us, but I’m hoping it helps to put fiber-rich carbohydrates into the correct perspective. Putting a stop to the mindset that carbohydrates are inherently bad can help people with diabetes live a happy, healthy life that fits their own lifestyle and culture. 

References

1. Cleveland Clinic. (2022, August 23). The pros and cons of keto to manage diabetes. Cleveland Clinic. https://health.clevelandclinic.org/is-the-ketogenic-diet-safe-for-people-with-diabetes/ 

2. Morrison, C. D., Hill, C. M., DuVall, M. A., Coulter, C. E., Gosey, J. L., Herrera, M. J., Maisano, L. E., Sikaffy, H. X., & McDougal, D. H. (2020). Consuming a ketogenic diet leads to altered hypoglycemic counter-regulation in mice. Journal of Diabetes and Its Complications, 34(5), 107557. https://doi.org/10.1016/j.jdiacomp.2020.107557

3. Grandl, G., Straub, L., Rudigier, C., Arnold, M., Wueest, S., Konrad, D., & Wolfrum, C. (2018). Short-term feeding of a ketogenic diet induces more severe hepatic insulin resistance than an obesogenic high-fat diet. The Journal of Physiology, 596(19), 4597–4609. 

4. Centers for Disease Control and Prevention. (2022, June 20). Fiber: The CARB that helps you manage diabetes. Centers for Disease Control and Prevention. https://www.cdc.gov/diabetes/library/features/role-of-fiber.html 

5. Chen, L., Wei, D., Zhu, X., Huang, F., & Mao, T. (2021, April 15). Effects of dietary fiber on glycemic control and insulin sensitivity in patients with type 2 diabetes: A systematic review and meta-analysis. https://www.researchgate.net/publication/351730520_Effects_of_dietary_fiber_on_glycemic_control_and_insulin_sensitivity_in_patients_with_type_2_diabetes_A_systematic_review_and_meta-analysis 

6. Dong, Y., Chen, L., Gutin, B., & Zhu, H. (2018). Total, insoluble, and soluble dietary fiber intake and insulin resistance and blood pressure in adolescents. European Journal of Clinical Nutrition, 73(8), 1172–1178. https://doi.org/10.1038/s41430-018-0372-y 

7. Yang, H., Bixiang, W., Liankui, W., Fengzhong, W., Hansong, Y., Dongxia, C., Xin, S., & Chi, Z. (2022). Effects of dietary fiber on human health. Food Science and Human Wellness, 11(1), 1–10. 

8. Reynolds, A. N., Akerman, A. P., & Mann, J. (2020). Dietary fibre and whole grains in diabetes management: Systematic review and Meta-analyses. PLOS Medicine, 17(3). https://doi.org/10.1371/journal.pmed.1003053 

9. Ojo, O., Ojo, O. O., Zand, N., & Wang, X. (2021). The effect of dietary fibre on gut microbiota, lipid profile, and inflammatory markers in patients with type 2 diabetes: A systematic review and meta-analysis of Randomised Controlled Trials. Nutrients, 13(6), 1805. https://doi.org/10.3390/nu13061805 

10. American Diabetes Association. (2023). Get to know carbs. Get to Know Carbs | ADA. https://diabetes.org/healthy-living/recipes-nutrition/understanding-carbs/get-to-know-carbs 

11. American Diabetes Association. (2023). Eating well. Diabetes.org. https://diabetes.org/healthy-living/recipes-nutrition/eating-well#:~:text=You%20want%20to%20fill%20half,yourself%20a%20well%2Dbalanced%20plate!