A colleague of mine asked if I would write this Nutritionist’s View on resistant starch and its effects on type 2 diabetes mellitus. I thought this would be an interesting article to write. Before discussing research on resistant starch and health, it is first necessary to define what resistant starch is.

WHAT IS RESISTANT STARCH?

Starch is the primary form of plant carbohydrate; however, the digestibility of starch can vary among different starchy foods. There are different types of starches, and they are classified as rapidly digestible starch, slowly digestible starch, or resistant starch (1,7). These classifications are based on the rate of glucose released and the absorption of that type of starch within the body. Resistant starch is not digested in the small intestine. Resistant starch can be fermented in the large intestine, and because of this, purported health benefits include increased absorption of some minerals, fuel for probiotic microorganisms, prevention of colon cancer, decreased risk of gall stone production, prevention of fat accumulation, and a reduction in serum glucose and cholesterol concentrations (6). Foods high in resistant starch have sometimes been referred to as fat burners; however, one must view that term with caution. Of the aforementioned list of purported benefits of resistant starch, their fuel for probiotic microorganisms in the intestine and a reduction in serum glucose concentrations have been researched most often. The Table provides a short list of foods that are high in resistant starch.

TABLE: Foods High in Resistant Starch

RESISTANT STARCH AND TYPE 2 DIABETES MELLITUS

Koh et al. (5) studied five lean Zucker rats that were fed a control diet and fed five Zucker rats with diabetes with either a control diet, 10% resistant starch diet, or a 20% resistant starch diet. Although they did not report any changes in blood glucose concentrations or glycosylated hemoglobin (hemoglobin A1c) percentage, adiponectin concentrations were 77% higher in rats fed the 20% resistant starch compared with the rats fed the control diets. Adiponectin concentrations were correlated significantly with serum calcidiol (vitamin D) concentrations. Adiponectin is a protein, secreted by the fat cells that can help regulate blood glucose concentrations. Only the rats that consumed the 20% resistant starch diet increased blood calcidiol concentrations and decreased urinary loss of calcidiol. Koh et al. (5) also reported improved renal function markers only in rats that consumed the 20% resistant starch diet. Although resistant starch maintained serum vitamin D concentrations and renal function in rats with diabetes, it did not affect blood glucose concentrations and hemoglobin A1c percentage. In addition, there was a dose required to affect these biological markers.

In a similar dose-response study in humans, Gower et al. (3) studied the effects of resistant starch in 40 healthy women aged 22 to 67 years. Although these women did not have type 2 diabetes, they had a large body mass index range from 20.6 to 47.4 kg/m2, and thus, were normal weight to obese. This was a placebo-controlled, double-blind, crossover study; thus, each woman was her own control. The researchers evaluated two doses of resistant starch: 15 and 30 grams/day, which were provided in the form of cookies. Participants consumed one cookie (15 or 30 g) a day for four weeks, had a four-week washout period, then would consume the other cookie (15 or 30 g) each day for four more weeks.

Although the participants did not have established diabetes mellitus, Gower et al. (3) evaluated insulin resistance in all participants at the end of each four-week period.

Like Koh et al. (5) reported, Gower et al. (3) reported that 30 g of resistant starch resulted in a significantly greater improvement in insulin sensitivity in women who had insulin resistance compared with 15 g or placebo.

Karimi et al. (4) examined the effect of resistant starch on glucose control and markers of oxidative stress in 56 women with type 2 diabetes mellitus. Women were assigned randomly to receive either 10 grams/day of resistant starch (n = 28) or a placebo (n = 28) for eight weeks. After the eight-week intervention, the researchers reported a significant improvement in insulin sensitivity as well as significant reductions in hemoglobin A1c percentage, insulin concentrations, and markers of oxidative stress compared with the control group. They also reported a significant increase in total antioxidant capacity compared with the control group. Although insulin sensitivity was improved, serum glucose concentrations did not change significantly with resistant starch.

Gargari et al. (2) investigated the effects of resistant starch as an alimentary prebiotic in women with type 2 diabetes mellitus. Sixty women were assigned randomly to either a group who received 10 grams/day of resistant starch (n = 28) or a placebo (n = 32). They reported significant decreases in hemoglobin A1c percentage, serum triglyceride concentration, and a significantly increased high-density lipoprotein cholesterol concentration compared with the placebo. Although the researchers did not report significant changes in prebiotics in women, the improvement in glucose management and inflammatory markers demonstrate a role for resistant starch in managing type 2 diabetes mellitus.

SUMMARY

Resistant starch can be found in foods or added to products, although consumption in plant-based foods is the better choice. Resistant starch may help to manage blood glucose concentrations and oxidative stress in individuals with type 2 diabetes mellitus. More research is required to evaluate the role resistant starch plays in the management of type 2 diabetes mellitus.