The US Food and Drug Administration just approved a Level “C” Qualified Health Claim that resistant cornstarch  reduces the risk of type 2 diabetes. Click here for the link to the FDA site with this announcement. This is a huge development that happened in a quick 13 years, as the first clinical trial was published in 2003. Maybe 21 years if you consider that the first rat study demonstrating improved insulin sensitivity was published in 1995.

Health claims are extraordinarily difficult to achieve. Only a few foods or ingredients have achieved this milestone. This is the highest claim achieved for a food or dietary ingredient in reducing the risk of type 2 diabetes. This is a breakthrough and enhances the credibility of resistant starch!

The approved claim is:

“High-amylose maize resistant starch may reduce the risk of type 2 diabetes. FDA has concluded that there is limited scientific evidence for this claim.”

One of the graphics that the FDA used in its 2005 consumer research as an option to communicate this type of evidence is shown to the right. Another way to say a “C” level claim is “Some evidence suggests that resistant starch from high amylose corn may reduce the risk of type 2 diabetes.”

So, while the “limited scientific evidence” disclaimer might sound a bit questionable, it in fact communicating that the FDA considers that some credible evidence exists suggesting that resistant starch helps to reduce the risk of type 2 diabetes.

Background

Insulin, made in the pancreas, plays a major role in metabolism – it significantly impacts the way the body uses digested food for energy. Insulin helps cells throughout the body absorb glucose. Insulin sensitivity is a measurement of how effective insulin works in helping cells absorb glucose from the blood. When insulin sensitivity is lost, it is called insulin resistance and causes a build up of glucose in the blood because glucose is not being effectively absorbed. Insulin resistance is biomarkers for prediabetes and the further development into type 2 diabetes. Additional information on insulin resistance and prediabetes is available at the National Diabetes Information Clearinghouse.

A closer look at the evidence

Nine relevant clinical intervention studies were published between 2003 and 2016 in which healthy (non-diabetic) people consumed resistant starch from corn and changes in their insulin sensitivity was measured. The studies are profiled in Table 1, below. The focus in all of the studies was on measuring improvements in insulin sensitivity.

Unfortunately, there is not one standard way to measure insulin sensitivity. The Clamp method is recognized as the gold standard method, as it directly measures the body’s uptake of glucose into tissue, but it is very expensive to perform. Additional methods calculate insulin sensitivity, generally from glucose and insulin response data, and are considered indirect methods. These include the Minimal Model Approach (MMA), homeostasis model assessment (HOMA), oral glucose tolerance test (OGTT), and the frequently sampled intravenous glucose tolerance test (FSIVGTT). Finally, the simplest of them all, fasting blood glucose (FBG) is also an indicator of insulin sensitivity. As you can see from Table 1, a wide variety of measurements were utilized across the 9 studies. I am not going to focus on the merits and advantages of each of these methods – you can investigate them in the scientific literature if you want to better understand these methods.

The very first study, Robertson, 2003 was considered insufficient by the FDA because the length of the study was just one day. Perhaps the FDA does not think resistant starch is supposed to be beneficial within one day, but the data reports that it is! Dr. Denise Robertson at the University of Surrey fed healthy people 4 doses of 15 grams of resistant starch mixed into jelly in one day and tested their insulin sensitivity the next morning. This added 60 grams of dietary fiber to their diet – a very high dose, given the recommended intake of dietary fiber is 28 grams for adult women and 35 grams for adult men. She reported a 69% improvement in insulin sensitivity as measured by the minimal model approach, MMA.

The FDA also discounted the Gower 2016 study, citing that more than half of the participants did not complete the study, resulting in its sub-segment analysis completed with small number of participants. Even though it reported 34% improved insulin sensitivity in postmenopausal, insulin resistant women, and 16% improved insulin sensitivity in insulin resistant women, these results were considered not acceptable.

With the remaining studies, the FDA concluded that five studies had mixed results of surrogate endpoints within each study (Bodinham 2012, Dainty 2016, Maki 2012 for men only, Robertson 2005 and Robertson 2012). They specifically noted that not all of the studies demonstrated improved insulin sensitivity in all of the measurements. As a result, they found the total body of evidence to be inconsistent. This is a fair assessment given the rigor required for health claim evaluation.

However, additional insights can be gained from two considerations: 1) the potential for a theshold level, and 2) the metabolic profile of the participants.

The best explanation for 4 studies showing no effect is that the quantity of resistant starch fed to the individuals was too low and that a threshold quantity probably exists for insulin sensitivity benefits. Three out of the four studies reporting no effect fed people 15 grams of resistant starch/day or less. It is relatively common for nutritional ingredients to have threshold quantities, but this consideration was not mentioned in the FDA’s health claim decision.

The metabolic profile of the participants is also important to consider. It appears that individuals with higher insulin resistance responded more strongly to resistant starch’s insulin sensitivity benefits. This was most evident in Barbara Gower’s study, which found improved 16% insulin sensitivity in insulin resistant women consuming 30 grams of resistant starch/day but not in insulin sensitive women. Dr. Gower also reported that all of the African Americans in this study were insulin resistant and responded while all of the Caucasian women were insulin sensitive and did not respond. When Dr. Gower identified a sub-group of postmenopausal women with insulin resistance, their insulin sensitivity improved 34% with resistant starch compared to the control. It is very important to note that African Americans and postmenopausal women are at higher risk for type 2 diabetes than the general population. While we may not understand all of the intricacies of why these segments responded to resistant starch, it is wonderful that the people who need improvement the most responded while the people who did not saw no improvement. In my opinion, this is a very positive outcome.

I agree with the FDA that the data is inconsistent, but I think it is highly relevant that improved insulin sensitivity by at least one measurement was found in 8 out of 9 reports from the 8 clinical trials feeding more than 15 grams/day and in 9 out of the 13 reports from the 9 clinical trials. This is remarkable as a measurement of metabolism of which we know relatively little. This is the first time that a completely safe food ingredient has shown significant benefits related to reversing prediabetes and reducing the risk of type 2 diabetes in numerous peer-reviewed, placebo controlled intervention trials in healthy people. Nobody knew that this was possible only a few years ago.

I cannot stress this enough – resistant starch is completely safe because this is how our bodies are supposed to work. People eating unprocessed foods could get 30-50 or grams or more of resistant starch each day, but our modern daily diet only contains about 5 grams of resistant starch. (Murphy JADA 2008) Resistant starch is fermented by the bacteria already in the gut and animal studies shows that it changes the expression of hundreds of genes – some of which are connected to insulin sensitivity and glucose metabolism. (Keenan JNN 2012) Resistant starch improves insulin sensitivity within hours because of this previously unknown mechanism. It does not take weeks or months to see the benefit – it is generally seen within hours and it is maintained after at least 3 months. The worst side effect seen across the 130 published clinical trials with all sources of resistant starch is a mild amount of gas resulting from the intestinal fermentation.

One more important item to emphasize – these studies did not require the participants to lose weight or to exercise! They sprinkled resistant starch supplements onto their foods or consumed foods specifically baked to contain resistant starch. The existing recommendations to reverse prediabetes focus on losing weight and exercise, so this is an entirely new approach to reversing prediabetes.

I applaud the FDA for recognizing the credibility of resistant starch’s benefits in improving insulin sensitivity. I would LOVE to see larger clinical trials to more fully investigate the benefits in populations with different metabolic profiles and to understand why different methods (i.e., clamp, HOMA or fasting blood glucose) reported different results. I think we have a lot to learn about how resistant starch improves metabolism.

In the meantime, people who have been diagnosed as prediabetic, African Americans, postmenopausal women or people who are worried about their risk of developing type 2 diabetes have more credible options than they did before. Increasing resistant starch is a great tool to increase insulin sensitivity if you are facing down the dragon of prediabetes and type 2 diabetes.

This new field is truly exciting. I absolutely love Nutrition. Don’t you agree?

Abbreviations –

NSD = Not Statistically Different

Clamp = euglycemic hyperinsulinemic clamp method (the gold standard)

FBG = fasting blood glucose

FSIVGTT = frequently sampled intravenous glucose tolerance test

HOMA = homeostasis model assessment

IR = insulin resistant

IS = insulin sensitivity

MMA = minimum model analysis

OGTT = oral glucose tolerance test

T2D = type 2 diabetes