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Resistant Starch: Foods, Low Amylose Diets, Benefits & More

Resistant Starch: Foods, Low Amylose Diets, Benefits & More

Zack West
  • Resistant starches have emerged as gut-health superfoods for some and BIG problems others. Knowing a granule or two about starch might help you better navigate your own health and nutrition!
amylose foods optimus medica

Amylose, a.k.a. resistant starch, is found in foods like potatoes, carrots, and many other root vegetables. It has many known health benefits such as supporting healthy colonic bacteria, stabilizing blood sugar, and lowering cholesterol.

However, some health concerns warrant caution when approaching higher-amylose foods. For example, a low amylose diet is recommended for Chronic Inflammatory Response Syndrome (CIRS), SIBO, and other cases where bacterial or fungal dysbiosis is present. In addition, a low amylose diet has been shown to influence cholesterol and blood sugar (27)(28).

Highlights

  • Starch consists of two compounds: amylose and amylopectin
  • Amylose describes resistant starch, which is non-digestible
  • Cooling foods like potatoes and rice for 24-hours then reheating increases resistant starch amounts by as much as 300%
  • The terms “sticky,” “sweet,” “glutinous,” and “waxy” all describe high-amylopectin ratios resulting in stickier foods after cooking.
  • The term “glutinous” refers to amylopectin content and has nothing to do with Gluten or Gliadin
  • Amylose/amylopectin ratios and total starch yields can differ greatly for varieties of the same food.
  • Higher amylose starches result in lower glycemic responses

Understanding Starch

Starch (a.k.a. amylum) is chemically made of many units of glucose—the simple sugar structure we humans use for energy. It is produced abundantly by plants as a means of energy storage to be used in times of decreased photosynthesis (2).

Starch consists of two primary compounds: amylose and amylopectin. On average, amylose accounts for 20-30% of total starch content with amylopectin accounting for the rest (1). Amylose is also referred to as resistant starch to describe its inability to succumb to digestion among us humans (11).

Starches higher in amylopectin tend to be “stickier” when cooked (3). For example, the starch content of Glutinous (a.k.a. sweet rice) rice is almost entirely amylopectin which gives it the characteristic sticky consistency when cooked.

Note: Glutinous rice is gluten-free (4). The term originated from the characteristic of being “glue-like” when cooked and has remained an unfortunately confusing term.

Amylopectin/Amylose Ratios of Foods

A functional ratio of amylopectin to amylose among all foods is 70/30 (7). However, this ratio varies based on the type of food and several other properties. Below is a table displaying several common starchy foods and their respective ratio of amylopectin and amylose.

Starch Amylopectin Amylose Ratio
Maize 75 25 1:3
Waxy-maize 100 0 1:0
Amylomaize-5 47 53 1:0.89
Amylomaize-7 30 70 1:0.43
Potato 78 22 1:3.55
Wheat 77 23 1:3.35
Rice 81 19 1:4.26
Tapioca 83 17 1:4.88
Banana 80 20 1:4
Shotis 70 30 1:2.33

Fitzer, 2016

Keep in mind that these are only ratios of the amylopectin to amylose and not reflective of relative amounts of starch. In other words, just because tapioca has a lower amylose percentage doesn’t mean the total amount of amylose is lower compared to a lower starch food.

Waxy vs. Non-Waxy (a.k.a. Glutinous vs. Non-Glutinous)

Generally, the terms waxy, glutinous, or even sweet (in the context of certain rice) describe foods that have higher ratios of amylopectin compared to amylose.

These foods are stickier when cooked whereas non-waxy variations are harder and more easily separable. The difference in waxy vs. non-waxy starches is not universal, however. For example, a 2018 study found that non-waxy broomcorn millet has more amylose content than waxy proso millet (5).

Note: The term glutinous means that a food contains a higher ratio of amylopectin. This term, while semantically confusing, does not mean a grain contains gluten. However, it also does not mean that grain does not contain gluten.

Varieties of Same Food Have Different Starch Content

Total starch yield, as well as the amylose vs. amylopectin ratios, can vary for a single food-based on specific genetic variation. In other words, a red-skinned sweet potato may have a higher starch content compared to a yellow-skinned sweet potato. For example, a 2013 study found total starch yield ranging from 33%-65% among only seven varieties of sweet potatoes (6).

Impacts of Cooking

Cooking greatly influences the levels of starches in food. In rice, the cooking process causes the leaching of starches into the water. Research has shown that a significantly greater amount of amylopectin leeches into the water compared to the amount of amylose (7).

Amylose content has been considered crucial to evaluating the “hardness” of grains such as rice (7) though not always associated with stickiness. Less analytical methods, such as grain length, have traditionally been used to predict the stickiness of different types of rice.

Starch composition changes when cooked foods are allowed to cool as well. In one study, researchers noted a 280% increase in the resistant starch content of boiled potatoes when they were allowed to cool in the refrigerator overnight (9).

In a similar study, researchers found that the resistant starch content of boiled rice increased more than 150% after cooling for 24 hours (10). This study also found that—as one might hope and expect—the foods with higher resistant starch resulting from a 24-hour cooling period had a lower glycemic impact.

Also worth noting is that reheating does not lower the level of resistant starch after the cooling period. In other words, one does not have to eat cold rice to get the benefits of higher resistant starch!

Amylose Content of Foods

Below is a table displaying the amounts of total amylose compared to total starch for a number of foods. These foods, selected somewhat randomly, are those I’ve found common among discussions related to low amylose diet foods. I’ve pieced these together from a number of sources and tried, when confident, to indicate if measures were from dried or cooked sources.

Food Amylose (g/100g) Starch (g/100g) Ref.
Sorghum, dry 43.7 86.6 18
Kidney Beans, dry 32.3 43.9 20
Bananas, raw 16.7 5.38 20, 17
Cashews 12.9 23.49 20, 17
Soybeans 11.4 10.3 19, 17
Quinoa, cooked 8.4 17.6 19, 17
Water Chestnut 8.05 9.01 20
Black Beans, cooked 6.1 30.4 25
Pumpkin 5.63 37.1 20
Peas, cooked 4.99 35.36 20
Russet Potato 4.37 17.45 18, 17
Waxy Millet, cooked 3.9 64.13 23
Kidney beans, cooked 3.9 33.2 21
Lentils, cooked 3.4 31.8 21, 24
Buckwheat, Cooked 3.11 76 26, 18
Barley, cooked 2.4 n/a 21
Glutinous Rice 2 4.2 22, 18
Sweet Potato 1.97 5.22 20, 17
Pinto Beans, cooked 1.9 15.15 21, 17
Buckwheat, cooked 1.8 n/a 21
Brown rice, cooked 1.7 86.95 21, 24
White rice, long-grain, cooked 1.4 n/a 21
Amaranth, cooked 0.25 65.25 17
Garlic, raw 0 1.36 17

There are several key aspects of starch measurements to be aware of. First, many foods’ amylose content varies based on the stage of their maturation. For example, unripe bananas have a higher level of resistant starch compared to ripe ones (15).

Another key consideration is that several foods have “waxy” varieties with lower amylose content.

Yet another aspect, I’ll bring up again here, is related to cooking and its effect on starch content. Cooking greatly impacts the content of starch in foods, especially amylose, lowering it in most cases I have seen. Again, similar to cooking, the cooling and subsequent reheating will result in higher levels of amylose in many foods such as potatoes and wheat.

Health Benefits of Resistant Starch

Looking beyond diets meant to limit amylose intake—there are many health benefits associated with resistant starch intake. It is emerging as an economical, readily available, and convenient means of supporting digestive health.

Gut bacteria with known benefits to human health have been shown to feed on resistant starches (12). These bacteria, including Bifidobacterium and Bacteroides, are common species found in many consumer probiotics.

Recent research suggests that longer, healthier lives are significantly correlated with a more diverse range of bacteria, with a specific benefit from Bacteroides spp. (13).

More directly, the research describes diets high in resistant starch improve outcomes associated with fasting triglyceride and cholesterol levels as well as insulin responses (14). Simply put, this is a partial scientific explanation of the benefits of low-glycemic index foods in the context of resistant start.

See this article by SelfHacked for a fuller discussion on the benefits of resistant starch.

Final Thoughts

Planning a low amylose diet (or a high one for that matter) should go beyond the simple lists of amylose foods commonly circulating on the Internet. These lists, while functionally accurate in many cases, leave out a lot of relative comparison and context.

Particularly, the “sticky” variety of many foods offer low-amylose options. Also, the effects of cooking and cooling can greatly impact the starch content of many foods. Research on the health benefits of resistant starches is relatively new. However, initial findings suggest that it may play an essential role, similar to dietary fiber, in supporting long-term health.

References

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