Science Blog #1 Starch Dilemma – Is it beneficial nutrient or toxin? You be the judge.

Know thy enemy’ – this has stood true on a battlefield, and often in life. Is starch the source of energy; our enemy? Consumers are in a dilemma. We, either in west or east have a starch-dependent culture. On any given day, not only rice which is like the ‘staff of life’, our day starts and ends with varied number of starch sources like toast, roti, idli, biscuits, cakes, noodles, potato and many more.
The lifestyle disease poll, 2016 showed that we have a huge target crowd with varied beliefs, the more we aware, the more we confused. About 50% of our populations check their sugar levels on monthly basis which exemplifies the fact that, India is the diabetic capital of the world. According to the California based CADI (Coronary Artery Disease among Asian Indians) Research Foundation, India has around 62 million heart patients in 2015. As the calorie restriction is the easiest way out, there is a huge outcry for healthy diet with whole grain and less carb mediated health supplements. But for common people, the most mind boggling question is - Starch the source of energy, good or bad?

A number of dietary charts and dietitians, insist more on wheat, oat and whole grain diet, making white rice aliens; another group of researchers and nutritionist who work on starch quality emphasize the point that it’s not the rice or the starch the villain, but the way we store, cook and eat it. Interesting updates on Resistant starch (RS) is igniting consumer interest these days.

For a layman what is resistant starch? How it differ from the normal starch?

Quality of starch is biochemically governed by the ratios of amylose and amylopectin fractions (components of starch). Commonly consumed Indica varieties in India are rich in amylopectin; hence more prone to rapid amylase hydrolysis and thus spikes the glucose, necessary for metabolic reactions leading to high glycemic Index (GI). But this generation including me, you and we have saturated with access to cheap, palatable junk food rich in calories. Such carbaholic diet with sedentary life habits have aggravated the alarming aftermath in terms of life style disorders like diabetes, obesity, cardio vascular diseases and various cancers But, the very same starch or a proportion of it can escape enzymatic (amylolytic) digestion due to its structural difference and are known as resistant starch (RS). As a boon itdoesn’t add to the glycemic load too. Thus resistant starch content and glycemic index are inversely proportional. In addition they act as dietary fibers which act as carbon source for the intestinal flora,releaseshort chain fatty acids, which assist gut health. Based on structural modifications, RS has been divided into five sub types (Table 1).

Types of Resistant starch.

(Raigond et al., 2015)

Isolated and extracted resistant starch and foods rich in resistant starch have been used to fortify foods to increase the dietary fiber content. Typically, food fortification utilizes RS2 resistant starch from high amylose corn, RS3 resistant starch from cassava and RS4 resistant starch from wheat and potato, as these sources can survive varying degrees of food processing without losing their resistant starch content. Resistant starch has a small particle size, white appearance, bland flavor and low water-holding capacity. Resistant starch typically replaces flour in foods such as bread and other baked goods, pasta, cereal and batters because it can produce foods with similar color and texture of the original food. It has also been used for its textural properties in imitation cheese. Some types of resistant starch are used as dietary supplements in the United States. RS2 from potato starch and green banana starch maintain their resistance as long as they are consumed raw and unheated. If they are heated or baked, these types of starch become rapidly digestible. RS2 resistant starch from high amylose corn can be consumed raw or baked into foods.

Being so important RS is a major area of interest from more than a decade. Biochemists are unraveling the various types and pathways involved; bio technologist keen to explore on how to engineer the pathways; food technologists playing a role in improving RS content in food stuffs by various processing methods and nutritionists are the bridging factor which connects these research community to consumers. More than a decade research which explored the RS content and glycemic index in various food stuffs (Table 2) and the potential mechanisms underpinned in them have gained great attention of the nutritional world (Sajilata et al., 2006)

Comparison of resistant starch content and glycemic index for commonly consumed starchy foods.

It is high time for us to intensify our fight against these metabolic syndromes like diabetes, obesity, colon cancer etc on our very own tables by increasing our intake of quality starch. Even though the etiology of diabetes in India is multifactorial, the rapidly and slowly digested proportion of starch spikes rapid blood glucose levels and underlines the fact that physiochemical properties of starch influence the nutritional value of the carbohydrate rich diet. The studies revealed consistent evidence that consumption of RS can aid blood sugar control bypassing the digestion in small intestine and reaching the colon where bacteria ferment to release short chain fatty acid (SCFA) like butyric acid, propionic acid and acetic acid that support gut health. Here, RS acts as a nutraceutical and its consumption leads to many health benefits (Table 4). A new study in the British Journal of Nutrition found that insulin response was significantly lower in people who ate RS-rich bread for just 3 days, compared with those in the control group, who consumed normal wheat bread.

Benefits of Resistant Starch for human health.

(Sajilata et al., 2006)

Starch has been consumed by people and animals for thousands of years. Thus, foods containing resistant starch are already commonly consumed. It has been estimated that average resistant starch intake in developed countries ranges from 3-6 grams/day for Northern Europeans, Australians and Americans., 8.5 grams/day for Italians and 10-15 grams/day in Indian and Chinese diets. The higher consumption of starch-containing foods like pasta and rice likely accounts for higher intake of resistant starch in Italy, India and China. Several studies have found that the traditional African diet is high in resistant starch.Rural black South Africans consume an average of 38 grams of resistant starch per day by having cooked and cooled corn porridge and beans in their diets. According to RDA, 30g/day dietary intake of resistant starch is important. Few more examples are in Table 4.

Resistant starch in naturally occurring source and serving size.

There are varied processing conditions which increase the RS content like high pressure, refrigeration, enzymatic treatment, extrusion etc., as well parallel certain household strategies (Figure 1) are also instrumental to increase the RS content (Vaidya et al., 2011).

House-hold strategies to increase RS content.

Even though different household strategies were seen to increase the RS content of starches; however, their effectiveness is largely a function of botanical origin and inherently tailored to suit a specific type of starch based on amylose-amylopectin ratio. Higherlevels of RS will impact the rheological and sensorial characteristics of the food, that affect the palatability but to note, these simple practices can improve our health conditions. To end with, along with quantity it’s the quality of starch that we consume determines our health and hence it’s very important that we being consumers should be aware about the starch quality metrics of what we intake.

Written by

Veda Krishnan, Haris Iqbal, Archana Singh, Haritha Bollineni, Ashok.K.Singh and Shelly Praveen

References

• Raigond P, Ezekiel R, Raigond B (2015)Resistant starch in food: a review. Journal of the Science of Food and Agriculture. 15;95(10):1968-78.
• Sajilata MG, RekhaSS,Pushpa RK (2006) Resistant starch – A review. Comprehensive reviews in food science and food safety. 5(1): 1-17.
• Vaidya RH and Mini SK (2011) Processing and storage of Indian cereal and cereal products alters its resistant starch content. Food Science Technology. 48(5): 622–627.