The Benefits Of Resistant Starch For People With Type 2 Diabetes
Starch is a form of carbohydrate with a complex molecular structure. This structure slows the speed that cells can process its stored energy. Compare that to carbs with simpler molecular forms, which get processed faster.
The carbs with the simplest structures are sugars, or monosaccharides in science speak. These include glucose (grape sugar, also known as dextrose), galactose (a milk sugar) and fructose (a fruit sugar). Two of these simple sugars can also join together to form a 'double sugar' (disaccharide). Examples are regular table sugar (sucrose), lactose (a milk sugar) and maltose (a sugar found in cereals). But sugar can also form into longer molecular chains and combine with a lot of sugars. These are called polysaccharides.
If any of this sounds complicated, just remember that we're looking at how difference molecular structures of carbs act in your body.
Now, on to starches.
Starch is a long sugar molecule (polysaccharide) made by plants to store the energy they get from the sun. Polysaccharides look like long chains of identical glucose strings linked together. For the science nerds, there are two types of starch: amylose is made of long straight chains of glucose molecules whose structure resembles a necklace, while amylopectin is made of highly branching chains whose structure is more tangled.
In short, starch is a more complex (less simple) form of carbohydrates.
Starch comes from different plants. From their leaves, tubers, fruits, seeds and nuts. When we eat these foods, the starch's structures are broken down by 'amylase', which is a digestive enzyme found in saliva and pancreatic juices.
'Resistant starch' is a form of 'insoluble fiber. That means that human enzymes cannot fully digest them. So, they reach the colon as a fiber or ‘roughage’ where it is fermented by bacteria.
Resistant starch is found naturally in some foods such as green bananas, potatoes, grains and legumes. Some is also produced during food processing. It's also sometimes made artificially and added to some food products. The average person eats about 3g -10g of resistant starch per day.[i]
Types of resistant starch
There are five different types of resistant starch.[ii]
Type 1 starches can't be digested since they are sealed inside cells and do not come into contact with amylase, the digestive enzyme. Type 1 starch is found in coarsely ground grains and wholegrains. Milling and chewing these grains can help make their starch less resistant.
Type 2 starches are found in very compact starch particles. Their compact structure makes them less digestible. Raw potatoes, green bananas, legumes and some grains such as high-amylase corn or maize all contain Type 2 starch.
Type 3 resistant starch is formed when starch particles are modified during cooking or processing. This modification (known as retrogradation) causes some of the bonds attaching the glucose molecules to each other to change so they can no longer be broken down by amylase enzymes. Cooling those foods allows the newly modified starch to form a 'crystalline' structure. That's why cooking potatoes, pasta or grains, and then allow them to cool is a better choice for diabetes friendly meals. Thing cold potato, pasta and grain salads.
Type 4 starch is made artificially during food manufacturing. Chemical processes are used to make starch less digestible. These can then be added to increase the fiber content in breads and cakes, or whatever else.
Type 5 is a type of starch that forms bonds with certain fats, preventing the starch particles from expanding. This means digestive enzymes cannot reach the starch to break it down. A small amount of this type of resistant starch is found in native starch granules and processed starches.
Type 2 diabetes should eat foods with resistant starches to help improve blood glucose control and support a weight loss.
Resistant starch and glycaemic index
Now remember, there are two types of starches: amylose and amylopectin. The ratio of amylose and amylopectin in starchy foods affect how quickly they can be digested. The more amylose there is, the slower the digestion and the lower its glycemic index. This is because amylose molecules are smaller than amylopectin, so the connective chains pack more tightly together. As a result, more cooking is needed to separate the chains, digest the starches, and soften these vegetables. Foods with a higher ratio of amylose also have higher levels of resistant starch than those with lower concentrations.[iii]
Tubers (underground root veggies) such as potatoes, yams and sweet potatoes change texture when they are cooked. When raw, their starch is packed into hard granules but when cooked, the granules swell with water to form a gel which gives them a softer, tender texture. White potatoes typically only contain around 20% amylose.
Grain starches typically consist of 15% to 28% amylose, although short-grain rice has almost none.
Peas, beans, and pulses (legumes) tend to have a higher ratio of amylose (typically 33%) than other starchy foods. This makes them better for diabetics than short grain rice.
Fruits, however, are designed to be sweet and tasty (so that animals eat them and spread their seeds). Unripe fruits are full of starch, which then break down into sugars as the fruit ripens. Green bananas have around 70% to 80% starch content, of which around 25% to 30% is amylose. As bananas ripen, their starch content drops to less than 1% as sugars are released.
Effects of resistant starch on glucose levels
Since resistant starch is not digested, it slows the speed at which the stomach can empty. Thereby acting like a sponge that slows the release of glucose from other foods that you ate. It's officially recognized (in the EU) that baked goods with at least 14% resistant starch reduces blood glucose levels after eating.
As an example, a study of people with abdominal obesity showed that eating a muffin with 75g of digestible carbohydrates and 30g resistant starch significantly lowered glucose levels and insulin responses during the following 2 hours.[iv]
Effects of resistant starch on appetite
Since resistant starch slows stomach emptying, it promotes feelings of satiety (how full you feel). People therefore tend to eat less at latter meals. Resistant starch can also reduce cravings because of how it positively reacts the gut hormones that control appetite. It's also absorbed into your blood circulation and has positive effects on the liver, as well as the satiety control centres in the brain.
The results from seven clinical trials suggest that consuming at least 25g of resistant starch per day can significantly reduce appetite and support weight loss.[v]
Probiotic effects of resistant starch
Because resistant starch reaches the colon, it helps feed the good bacteria found in the large bowel. This 'Good Gut Food' is called Probiotics. Gut microbes ferment the probiotics 'resistant starch', making the gut's contents more acid. Which is a good thing. This promotes the growth of healthy, bacteria (like Lactobacilli, Bifidobacterium) and fortifies your body to fight the bad bacteria, which loves simple sugars.
When study volunteers with insulin resistance consumed supplements with 66g of resistant starch (type 2) per day for 2 weeks, their insulin sensitivity increased and their ratio of ‘good’ bowel bacteria increased.
The effects of apple cider vinegar
Adding apple cider vinegar as a dressing to foods like potatoes and rice is a good idea. That can stimulate the chemical formation of resistant starch, and reduce the glycemic index (GI) of those foods.
For example, a study investigated the effects of adding apple cider vinegar to potatoes, and storing them cold in the fridge.[vi] The study showed that cold storage of boiled potatoes increased their resistant starch content from 3.3 to 5.2%. When a vinaigrette dressing was added to the cold potatoes their glycemic index was significantly reduced by 43%. And insulin responses were reduced by 31%. And when vinegar is added to rice it decreases its GI value by 20% to 30%.[vii]
This effect was also tested in a small group of people with type 2 diabetes. They consumed two tablespoons of cider vinegar with water at bedtime. Their morning blood sugar (after breakfast) was reduced by 4% to 6%.[viii]
In another study, 14 people with type 2 diabetes were asked to drink 8 fluid ounces (236ml) of apple cider vinegar sweetened with stevia, twice a day with meals, for 12 weeks. They saw significant improvements in fasting blood glucose levels. The study also showed a 19% increase in colonic fermentation (from probiotics, as mentioned earlier).[ix]
Increasing your intake of resistant starch
- Aim to eat at least 5 servings of fruit and vegetables each day (and ideally more). A good target is to eat a total of at least 450g fruit and vegetables per day
- Eat more nuts and seeds
- Go for wholegrain cereals, brown bread, whole-wheat pasta, brown rice and other minimally processed starchy foods
- Eat potatoes and pasta cold in salads
- Add a vinaigrette dressing containing apple cider vinegar.