What is resistant starch?
Carbohydrates are grouped into either sugars or starches (polysaccharides). Sugars can include natural sources such as fruit or milk or added to foods such as sweets and cakes. Starches are long chains of glucose and can be found in foods such as cereals, bread, rice, pasta, pulses and starchy vegetables. All starches are then categorised further into two types, amylopectin and amylose (see Fig. 1). Amylopectin has a branched structure which essentially provides more surface area for digestion. This means that it is broken down quickly and therefore causes a larger rise in blood glucose and subsequently insulin. Amylose, however, is a straight chain structure with a reduced surface area and therefore does not give rise to large spikes in glucose and insulin. It is amylose that is rich in resistant starch, and unlike most other starches which are broken down by enzymes in the small intestines, resistant starch is not digested or absorbed there but in the large intestine (colon), where it is fermented by intestinal bacteria similar to fibre.
Figure 1. Amylopectin and Amylose
Types of resistant starch
- Type 1: found within the fibrous cell walls of starchy foods and cannot be broken down / digested by enzymes.
- Type 2: found in some starchy foods such as unripe bananas and raw potatoes, fruits, corn and some legumes. The rawer the food is then the more resistant starch it tends to have.
- Type 3: this type is formed when starchy foods such as potatoes, rice and bread are cooked then cooled, this is because the starch changes form which is called retrogradation.
- Type 4: this is man made by chemical alteration usually from corn and is used mainly in processed foods and commercial resistant starch supplements.
Benefits of resistant starch
- Better digestive system: the intestinal bacteria convert resistant starch into short-chain fatty acids such as acetate, butyrate and propionate (similar to fibre), the most important of these being butyrate. Butyrate provides nutrition for the cells that line the colon as well as feeding the good bacteria that reside in the gut. Other benefits include better blood flow to the colon, inhibition of pathogenic bacteria, absorption of minerals and a reduction in the absorption of toxic carcinogenic compounds. The short chain fatty acids not used by the cells in the colon will travel to the bloodstream or liver where they can have various beneficial effects. As with fibre, resistant starch can add bulk and water to the stool which can assist in keeping the bowl regular.
- Weight loss – There are a few mechanisms of action that resistance starch plays to assist in weight loss. Many studies have shown that whole foods which are less processed compared to refined highly processed foods provide fewer calories. This is because we actually absorb fewer calories from the food, the reason being fibre and resistant starch are incompletely digested (2 calories per gram versus 4 calories per gram from other starches), in other words, 50 grams of resistant starch provides 100 calories compared to 200 calories from other types of starches. It has been estimated that most developed countries which have a processed diet are consuming approximately 3-9 grams of resistant starch per day compared to developing countries eating whole plant foods where resistance starch intakes are approximately 30-40 grams per day. Similar to fibre, resistant starch slows down the release of nutrients from food into the bloodstream which helps with satiety, feelings of fullness and reducing appetite, in addition, short chain fatty acids can stimulate the release of important satiety hormones such as leptin, PYY and GLP.
- Metabolic health – Several studies have shown that resistant starch can improve insulin sensitivity. Insulin resistance is a major risk factor for many serious conditions which can include type 2 diabetes, dementia, obesity, cardiovascular and heart disease. However, as with most nutrition studies, these beneficial effects depend on the individual and the amount and type of resistant starch consumed.
Adding resistance starch to your diet
To include more resistant starch in your diet you can either eat whole unprocessed foods or supplement, see examples below:
- real foods: oats, rice, grains, beans, peas, lentils, potatoes, green bananas
- supplements: raw potato starch, maize flour
You must bear in mind that these examples have a high carbohydrate content and it may be difficult to include these if following a very low carb (< 50 g per day) dietary approach, therefore supplementation could be an option here and these can be added to meals by sprinkling it on foods after cooking or mixing into smoothies. However for a low carb (< 130 g per day) or Mediterranean approach (200 g per day) you could include some of these foods as part of a balanced dietary approach. Beneficial doses have been seen in the range of 20-40 grams per day and it is important to introduce this gradually to avoid flatulence and discomfort, this will allow time for the gut bacteria to ferment the starch. There seems to be no benefit of consuming high amounts which is more than 50g because excess amounts seem to pass through the digestive tract.
Typical amounts (g) of resistant starch present in selected foods relevant to the UK diet (Lockyer & Nugent, 2017)
||Per 100 g (range)
|White bread rolls
|Wholemeal bread rolls
|Mixed grain bread rolls
|Breakfast cereal, wheat biscuits
|Bran breakfast cereal
|White rice (long grain, cooked)a
|Brown rice (cooked)a
|Wheat pasta (white, cooked)
|Wholewheat pasta (cooked)
|Hot potatoes (e.g. boiled, mashed, baked chips)
|Cold potato dishes (e.g. potato salad)
|Potato products [e.g. hash browns, wedges (cooked)]
- Values provided represent total RS, individual RS types not stated. Ranges given were reported. Items with no superscript, values derived from Landon et al. (2012).
- a Values derived from Murphy et al. (2008).
- b Serving sizes as per Food Portion Sizes (FSA 2006) or 80 g for fruit, vegetables and pulses.
Take home message
Following an unprocessed whole food dietary approach has many benefits, especially when this includes legumes, whole grains and vegetables. Including resistant starch containing foods may be one option if you are trying to break through weight loss plateaus, have poor glucose control or wish to improve your good gut bacteria.
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