There are a lot of resistant starch stories floating around – it is sometimes hard to know what to believe. Plant-based groups emphasize food sources like beans, green bananas and cooked and potato salad but refuse to consider resistant starch supplements. Paleo bloggers emphasize supplements of raw potato starch but will not eat foods with resistant starch. And natural foodies will not consider resistant starch from corn because it is from the mega-industrial crop of corn. These stories are definitely driven by the background beliefs and stories that people want to tell.
Here’s a science-based categorization that I think will help. For me, there are three major categories of resistant starch benefits, each correlating with different levels of consumption. I think that people with prediabetes just want anything they can find to help reverse their condition and stop staring down the dragon of diabetes.
Low levels for general health
Some plants naturally contain resistant starch. For instance, a slightly green banana contains ~4.7 grams of resistant starch, ½ cup of cooked lentils contain 3.4 grams, a ½ cup of green peas contains 2 grams, ½ cup of canned white beans had around 3.7 grams, and ½ cup of canned black beans had around 2 grams. (Reference). It all depends on the food and how it is cooked or processed. Unfortunately, not many foods contain resistant starch as currently consumed.
Intact whole grains also contain resistant starch, primarily because the seed or the hull protects the starch from being quickly digested. By the time the hull has been broken down or digested, the starch is fairly far down into the digestive process and a good portion of the protected starch reaches the large intestine. Here are examples:
|RS content raw
milled & cooked
|0.2 – 0.4%
|Whole grain wheat
|Whole grain corn
Note – % of dry mass – water and moisture not included.
Finally, other types of starchy-foods can increase their resistant starch when they are cooked and cooled. For instance, a recent study found that chilled potatoes contained more resistant starch (4.27 g/100g) than hot (3.00 g/100g) or reheated potatoes (3.45 g/100g). In my way of thinking, the resistant starch in cooked and cooled potatoes is still low. Let’s put this in perspective: 100 grams of potatoes (half of a medium size baked potato) = ~100 calories to get 3 or 4 grams of resistant starch. (Personally, I would not eat half of the potato – I would eat all 200 calories of it, but that’s just me. You might have more self control.) Is ½ or 1 gram of resistant starch enough of a reason to substitute cooled potatoes for hot potatoes in your diet? Is it worth 200 calories and a lot of rapidly digestible, high-glycemic starch to get 7 or 8 grams of resistant starch? Maybe, maybe not. If you want food-based resistant starch, one slightly green medium banana costing ~100 calories for almost 5 grams of resistant starch would be a slightly better choice.
Including these foods in your diet just makes sense. The science for eating a plant-based diet is really strong. The China Study helped to establish this. Plants contain a huge quantity of nutrients and compounds that help you stay healthy and strong – resistant starch is only one of them. But, these benefits come from eating a primarily plant-based diet, NOT from eating a few foods with resistant starch.
Yes, eating foods with resistant starch is beneficial, so I call this “healthy eating” option, but don’t count on the stronger benefits shown with higher levels of resistant starch with “healthy eating” levels of consumption. This is especially true for foods taken out of the context of a plant-rich diet.
Animal studies have shown that any and all resistant starch that reaches the large intestine is consumed by the bacteria, produces beneficial short-chain fatty acids, helps keep your intestinal barrier strong and working well and is good for general health. My take on it is that low levels of resistant starch will likely help you stay healthy and well, but is insufficient to more quickly address a health concern.
High Levels of Benefits
High doses of resistant starch (28-60 grams/day) have shown improved regularity (increased fecal bulking with softer stools), and reduced secondary bile acids, ammonia and phenolics. If too much resistant starch is eaten, it is simply lost in the feces with no side effects. One Australian researcher suggested that 20 grams of resistant starch/day or more may be needed to see the resistant starch’s fermentation-related benefits. (Baghurst FA 1996, Page S17) This would deliver enough resistant starch to ferment through the entire intestinal tract, including the distal portion, where the majority of digestive diseases occur.
Three studies have also shown that resistant starch helped to stop acute diarrhea in hospitalized adults and children with rotavirus, cholera or other diarrhea-causing diseases at the level of 50 grams/liter of oral rehydration solution. (Binder CGR 2014) Resistant starch’s fermentation directly helps to stimulate sodium and water absorption within the large intestine, significantly reducing stool output and aiding in patient recovery.
High doses of resistant starch improves insulin sensitivity. 60 grams of resistant starch/day improved insulin sensitivity in healthy people, (Robertson D 2003). Another study found 30 grams improved insulin sensitivity in healthy adults, (Robertson AJCN 2005) while a third study showed that 30 grams did not (Gower 2016).
It appears that insulin resistant people are the most responsive to resistant starch. Overweight, insulin resistant men consuming 15 grams of resistant starch improved insulin sensitivity by 56% while 30 grams improved insulin sensitivity by 73%. (Maki JN 2012) Insulin resistant, postmenopausal women consuming 30 grams of resistant starch improved insulin sensitivity by 34%, but these benefits were not seen at 15 grams/day or in women who were not insulin resistant. (Gower NM 2016) These amounts were added on top of the ~5 grams already in the diet of typical Americans. (Murphy JADA 2008).
O’Keefe NC 2015 fed African Americans 38 grams of resistant starch/day and reduced their fat consumption by 50%. He showed dramatic reductions in intestinal mucosal inflammation and markers for colon cancer risk, as well as large increases in microbiota diversity. This was a very big shift, as the typical diet of the African Americans contained only 14 grams of dietary fiber and this study increased it to 55 grams/day.
Johnston DM 2010 fed insulin resistant adults 40 grams of supplemented resistant starch/day and showed a trend toward improved vascular inflammation. This benefit was not large enough to be statistically significant, but it was seen.
Sirich CJASN 2014 demonstrated 18 grams of supplemented resistant starch/day improved toxins associated with kidney failure in patients with chronic kidney disease. Specifically, it reduced indoxyl sulfate and had a trend to reduce p-cresol sulfate in the bloodstream of these patients. Essentially, nitrogen is disposed of through the fermentation process (bacteria use nitrogen to grow and reproduce), which reduces the workload on the kidney. With good health, disposing of nitrogen is not problematic, but in individuals with chronic kidney disease, dialysis does not remove these protein-bound toxins, allowing them to accumulate in the blood. High levels of these compounds are associated with vascular injury and mortality in individuals with renal failure.
Animal studies have demonstrated improved eye health, improved liver health, reduced body fat and anti-aging benefits at high levels of resistant starch consumption. Of course, additional research is needed to determine if these benefits are seen in people.
Moderate Levels of Benefits
It is much more difficult to show benefits in clinical studies with moderate quantities of resistant starch. Some studies have been successful in certain groups while other studies have shown no benefits in other groups.
Moderate amounts of resistant starch will typically increase regularity by about 1 gram of fecal output per gram of resistant starch consumed. Unlike bulking fibers like wheat bran and cellulose, which absorb and hold onto water to increase regularity, resistant starch’s bulking consists of increased bacterial and microbial mass.
Dr. Janine Higgins and her colleagues at the University of Colorado showed that 5.6 grams of resistant starch/day increased lipid oxidation by 23% in healthy people. This means that the participants’ metabolism increased fat burning and decreased carbohydrate burning under a moderate dose of resistant starch. This 2004 study fed participants a variety of foods with supplemented resistant starch, but not foods naturally containing resistant starch.
In 2009, Holly Willis and her colleagues at the University of Minnesota found that 8 grams of resistant starch baked into a muffin increased the subjective feelings of satiety over three hours. In other words, people reported that they were less hungry and did not have as much desire to eat. This acute study did not measure subsequent food consumption. Additional studies have also shown increased satiety and reduced food intake at higher levels of resistant starch consumption. (i.e., Bodinham BJN 2010 and Anderson AJCN 2010)
Michelle Penn-Marshall and her colleagues fed 7 grams of RS/day to African American adults at risk for type 2 diabetes and found no benefit in insulin sensitivity. Gower NM 2016 also found no benefit in insulin sensitivity with 15-30 grams of resistant starch fed to women who were not insulin resistant. (This study demonstrated improved insulin resistance in postmenopausal women who were insulin resistant who ate 30 grams of resistant starch/day.)
Two large, international clinical trials by the Colorectal Adenoma/carcinoma Prevention Programme (CAPP1 and CAPP2) fed people at high risk of developing colorectal cancer from 9 grams (CAPP2) to approximately 20 grams (CAPP1) of resistant starch/day and found no effect in the development of colorectal cancer.
I believe that it is almost impossible to eat the quantity of resistant starch from natural food sources to see the strong level of benefits quickly seen with supplemented resistant starch. If you are healthy, it is a wonderful way to stay healthy. If you are not healthy, it may take a lot longer eating foods with resistant starch to potentially see benefits that are quickly seen with supplemented resistant starch.
It is wrong to assume that if 30 grams of resistant starch showed improved insulin sensitivity, then 5 grams of resistant starch from a different source will deliver the same benefit, especially if that source comes with a large quantity of glycemic starch as well. Yes, 10 grams of resistant starch is believed to help healthy people stay healthy, but there is no evidence that it will help reverse or improve serious health condition, especially ones as critical as insulin sensitivity.
Using the scientific evidence as a guide, it is as simple as 1-2-3:
- Choose the level of benefits you want or need,
- Select which source of resistant starch you prefer, and
- Consume enough resistant starch that has been shown to deliver that type of benefit.