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.

Dietary starch is the largest component of the UK diet. A recent report (SACN 2015) concluded that total carbohydrate intake had no effect on obesity or diabetes, though discrepancies were found with starches. A problem with the current data on starch is that there is no attempt to account for the prior cooking and processing of the food (due to gaps in our knowledge with respect to the effects of food preparation), which will affect its bio-availability and health impact. For example, resistant starches (RS) do not contribute to glycaemia, contribute only 50% of the energy of a digestible starch and are dealt with by the body as a dietary fibre. Food processing which increases the formation of RS would therefore be considered beneficial on multiple levels. Historically, RS has been difficult to measure and so has effectively been omitted from the literature linking starch to health. A new form of RS (RS5) has recently been identified, which is formed by bonding of starch molecules to fat during the heating process when both are present within a meal or food. Starches are commonly eaten with fat and combining this with the potential effects of food processing may lead to significant and yet unknown effects on starch bioavailability. The aims of this research are to investigate the role of simple processing of a starchy food (potato) in the presence of fat on the formation of RS5 and the resultant impact on glycaemia using a 3-stage approach:(i) measuring total RS formation under a variety of experimental food processing conditions in the laboratory; (ii) testing the postprandial glycaemic response in humans using the experimental conditions demonstrating the highest increase in RS formation and finally by (iii) an in-depth analysis of how this change to starch structure impacts on the components of the postprandial glucose response (gut absorption, hepatic production and peripheral disposal) using intrinsic isotope labelling and mathematical modelling.

The main beneficiaries of this research proposal would be:
a) The food industry, specifically those within the areas of food processing, retail and marketing,
b) Academic researchers working in the fields of nutrition,
c) The public sector including Governmental policy makers,
d) The wider general public,
e) Those working in allied health fields such as Diabetes and Obesity,
f) The UK economy,
g) The researcher.

2) How will they benefit from the research?
a) Our study will provide important insights into what happens to starch during processing of currently available food products and how these might impact on the health of the consumer. The consumer is driven towards products which are more natural and are similar to those prepared "from scratch"; understanding the implications of simple aspects such as storage temperature, whether the food should be frozen, and the effects of reheating would have an important role in both the public image of prepared foods but also in food labelling and health promotion. Resistant starch should be classified as a dietary fibre and so understanding how different preparation methods could change the starch bio-availability and hence the carbohydrate/dietary fibre and energy content within foods is of universal interest to the food industry. Although in this trial we are using potato as our model system, the results of this work could be extrapolated to other carbohydrates such as rice and pasta, in addition to all pre-prepared foods containing carbohydrate.
b) At the moment there is significant interest within academia in terms of the role of carbohydrates in the diet and postprandial glycaemia (PPG) and also in understanding the variation in PPG and how this can reflect changes in hepatic production and peripheral disposal.
c) This research has the potential to inform on UK and European food policy. The latest SACN report on Carbohydrates and Health identifies variation in food cooking/preparation practice as a confounder to the interpretation of currently available cohort data linking starch to cardiometabolic risk, and may have resulted in significant discrepancies. Informing scientists now may result in the correct information being collected in the future, in order to have a more reliable evidence base.
d) There is considerable interest with respect to the effects of food preparation and the impact of convenience foods on health. Educating the public allows for autonomy in food choice and is important for public health; human behaviour cannot be legislated. Manipulating a food grouping which is consumed by ~100 % of the UK population has the potential for wide impact especially when the dietary change required at the individual level would be minor.
e) Minor changes to food processing which could result in reduced PPG and a reduced energy impact of food would be highly relevant to researchers/clinicians and dieticians working in diabetes and obesity. The nutrition evidence base is continually evolving and new, and importantly simple, strategies are always being developed in order to tackle the current crisis enveloping the NHS.
f) The annual spend on pre-prepared foods is increasing, with a higher profit-margin on these products, which can often be developed as part of premium ranges by retailers. Marketing/labelling such products in terms of digestible starch replacement, or relabelling with higher dietary fibre values has the potential to improve the image and profitability of this entire food sector. With an increasing financial burden of type 2 diabetes on the NHS, dietary manipulations to improve PPG and insulinaemia in individuals with normal or moderately compromised glycaemic control is of the highest importance in terms of public health.
g) The PDRA employed on this project will be provided with a comprehensive training which could be adapted to almost any biomedical discipline.