Resistant Starch Production and Glucose Release from Pre-Prepared Chilled Food; the SPUD Project

There are new evidence based guidelines concerning the recommended intakes of free sugars (<5% energy) and total carbohydrate (~50% energy) in the UK diet, however, there remains no direct advice regarding dietary starch, despite this potentially contributing upto 45% of daily energy requirements. Starchy-foods (pasta, rice potatoes for example) are unique within the diet in that they are always processed in some way before consumption. However, both manufacturers and consumers know very little about the impact of this processing on our health, for what represents a very large part of the UK diet. The digestion of starch generally results in the release of glucose which is absorbed by the body leading to an increase in blood glucose, but we know now that some starches are not broken during digestion. These starches are termed "resistant starch"; they have no effect on blood glucose when consumed and as an added benefit, they are classified as dietary fibre, which is low in the UK diet. Increasing resistant starch in the diet has been highlighted as being particularly beneficial in terms of the prevention of metabolic disease due to this combined effect on blood glucose and by increasing dietary fibre. A new form of resistant starch has recently been identified in food which is created by the interaction between starch and fat molecules when the food is cooled and reheated. This new form of starch has been designated as 'type 5 resistant starch' (RS5). The presence of a small amount of fat (~5% recommended daily intake) within the food matrix is now known to be critical for the formation of this resistant starch and highlights the importance of looking at whole "food" rather than simply the individual "nutrients". While published data on RS5 has so far been restricted to laboratory and animal models, our own human pilot data has revealed that the beneficial effects can be acquired through simple home processing (chilling and reheating) of starchy food (pasta/potatoes), which can reduce the glycaemic impact by at least 25% in a single serving. The potential translation for this research is far reaching, with starch contributing up to 45% of daily energy intake, simple changes to processing could have large-scale effects on public health. The overall aims of this project are to investigate the effects of processing on the formation and glycaemic impact of RS5 using the potato as a model of a starchy food. The potato represents an ideal food to study, as it remains in its native state from field to fork, thus minimising factors that could potentially confound the interpretation and translation of our results. The programme of research will be delivered in three stages: 1. Food processing effects: Measure resistant starch formation under a variety of experimental home food processing conditions in the laboratory, with different varieties of potato. 2. Evaluation of glycaemic response: Testing the postprandial glucose response in humans volunteers to potato samples that demonstrated the highest levels of resistant starch formation in Stage 1. 3. Mechanistic studies: An in-depth analysis of how increasing resistant starch content impacts on the individual components which make up the postprandial glucose response (absorption from the gut, liver production of glucose and glucose clearance from the blood). We will use potatoes grown under special conditions so that the starch is enriched with a natural isotopic label which will allow us to use mathematical models to specifically calculate the movement of glucose (released from the starch) around the body. We anticipate that our calculations will show that potatoes containing more resistant starch will release less glucose into the blood and therefore have beneficial effects on other metabolic parameters that we will measure.