The low-down on low glycaemic carbohydrates

The concept of regulating carbohydrate intake has hit the mainstream. A phenomenal 75 per cent of the UK population believes a reduction in consumption of carbohydrates is a healthier way to eat¹, and carbohydrate content is increasingly driving food selection.

When talking about carbohydrates, it is important to explore the fundamental differences between them, and the key to this is to understand the digestion profile.

Classifying carbohydrates ? physiologically

Foods rich in refined or processed, high glycaemic carbohydrates (eg sugars, white bread, cooked potatoes, biscuits, snacks, cakes, muffins, sweetened extruded cereals and pizza) cause sharp rises in blood sugar (post-prandial blood glucose levels). This makes the body secrete insulin, which moves the glucose from the blood into the cells where it can be used for energy. However, high peaks can result in lower crashes of blood sugar, due to the impact of excess insulin secretion (as a response to the high peak of sugar). Therefore, these foods are best kept to a minimum.

Conversely, less refined or less processed, low glycaemic carbohydrates (eg some types of fruit, vegetables and intact wholegrains which contain dietary fibre and resistant starch) break down slowly in the digestive system and cause a slow and steady rise (and fall) in blood sugar. Moderating the spike-and-crash fluctuations in blood sugar leads to a more controlled and sustained release of energy.

Low glycaemic carbohydrates and health

National Starch recently questioned state-registered dietitians, senior gastroenterologists and nutrition nurses on their perceptions of carbohydrates and awareness of their potential health benefits. From the questionnaire answers of the 187 respondents we conclude that the different types of carbohydrates are well-known amongst nutrition-influencing professionals.

Nearly all (97 per cent) of respondents were aware of the different types of carbohydrates, and, significantly, 86 per cent currently recommend foods containing low glycaemic carbohydrates. They cite energy management issues, such as diabetes (100 respondents), weight control (82 respondents) and blood sugar / insulin control (34 respondents), as their main reason for this.

Studies support these findings. Research indicates that maintaining energy balance throughout the day by choosing a healthy diet based on low glycaemic carbohydrates can help individuals feel full for longer, fewer calories being consumed and portion control being more easily achieved². Other studies suggest that the potential health benefits of selecting foods that deliver a lower glycaemic response may extend beyond weight control. Maintenance of healthy blood glucose levels may also be connected with reduced risk of diabetes, heart disease and obesity³.

The role of resistant starch

Most starches are digested and absorbed into the body through the small intestine, but some resist digestion and pass to the large intestine where they act like dietary fibre. This is called resistant starch, and further investigation into the role of this form of carbohydrate, which has a low glycaemic response, is important to overall understanding of the subject.

Foods with naturally present or added resistant starch generally have a lower glycaemic response than other carbohydrate-rich processed foods. In addition, resistant starch delivers dietary fibre and can contribute to a healthy digestive system by reducing faecal pH, increasing mineral absorption, improving regularity and stimulating beneficial bacteria while suppressing the viability of harmful bacteria in the large intestine⁴. Resistant starch also produces very high levels of the short-chain fatty acid butyrate, a key biomarker for digestive health, which may reduce risk of colon cancer and help some common digestive disorders⁵.

In our survey 72 per cent of respondents showed awareness of the health benefits of resistant starch. However, only 51 per cent said they currently recommend foods including resistant starch. Here diabetes (40 respondents), weight control (34 respondents), irritable bowel syndrome (26 respondents) and general healthy eating /digestive system (24 respondents) were the major factors.

Increasing resistant starch intake

Resistant starch has a long history of safe consumption in humans and is naturally present in many foods including raw fruit and vegetables and intact wholegrain cereal products.

The resistant starch content of foods varies depending on how it is prepared and eaten ? raw potato starch is approximately 70 per cent resistant starch⁶ but this drops to less than 1 per cent after boiling, baking or frying. If, however, a boiled potato is left to cool overnight the resistant starch level can rise to as much as 5 per cent. In other words, food processing can destroy the crystal structure of starch but retro-degradation can allow it to re-crystallise.

The dietary intake of resistant starches has been estimated at 3-6 grammes per person per day in Europe⁷. As diets become more and more “processed” the consumption of naturally-occurring resistant starch decreases, and so processed foods with added resistant starch are particularly valuable sources of this form of dietary fibre and can increase resistant starch consumption. New forms of process-tolerant resistant starch can, in essence, make processed foods act physiologically more like unprocessed foods, without changing their taste or appearance.

Conclusions

A clear picture emerged from our survey, indicating that while understanding of the role of carbohydrates in general is high amongst nutrition-influencers, awareness of resistant starch is lower. Consequently a significant proportion of healthcare professionals do not currently recommend it in the diet.

In terms of health benefits, the role of resistant starch for energy management is well-known, but the other main health advantages, namely anti-constipation benefits, prebiotic properties and potential protective role for diseases such as colon cancer, are not.

Nutrition-influencing professionals are in a unique position to be able to portray the multiple benefits of low glycaemic carbohydrates, and in particular, resistant starch, and to encourage consumption of these specific dietary carbohydrates for a health-promoting, balanced diet.

References

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For further information on carbohydrates and resistant starch, and references detailing clinical studies using National Starch?s Hi-maize, a rich source of resistant starch, increasingly being incorporated into everyday processed foods, visit www.carbohydratenutrition.com Mike Croghan is the global business director of nutrition for National Starch