Dr Tracey Robertson

Resistant starch (RS) is classed as a dietary fiber and does not contribute to the postprandial glucose excursion. Two types may be formed during food processing: RS3 when a starchy carbohydrate cools; RS5 when starch is heated in the presence of lipid. It is unknown whether RS5 can be produced under domestic cooking conditions or whether different fat types would affect the amount formed. Nor is it known whether sufficient RS3 remains after a chilled meal is reheated to have a significant impact on the postprandial glucose response. The aim of this study was to determine if different solid fat spreads (of varying fatty acid composition) incorporated into a mashed potato meal, served either freshly cooked or chilled and reheated, would produce different effects on the postprandial glucose and insulin responses. Ten healthy adults (age: 29 ± 5 y; BMI: 21.7 ± 2.6 kg/m2) attended six study days in a randomized crossover design. On each day, they consumed mashed potatoes (203 g) prepared with one of three solid fat spreads (butter, sunflower oil, olive oil, each providing 20 g fat). Each meal was consumed freshly cooked or microwave-reheated (after two days refrigeration at 4°C). Capillary blood samples were taken for 180 min postprandially. Plasma glucose and insulin were measured by glucose-oxidase method and ELISA respectively. Glucose incremental area under the curve (IAUC) was significantly lower for the reheated meal with butter, compared to the equivalent freshly cooked meal (P = 0.030). Insulinogenic Index (IGI), a surrogate measure of first phase insulin response, was significantly lower for the freshly cooked butter meal in comparison with the reheated equivalent (P = 0.031). There were no other differences between meals, either for fat type or preparation method. Differences in RS formation may explain these results; work is underway to measure both total RS and RS5. Other possible explanations are differences in effects on glucose absorption, such as via delayed gastric emptying. Whilst a beneficial effect on postprandial glucose and IGI was observed for the reheated butter meal, in comparison to the freshly cooked, it should be remembered that butter contains saturated fat, which has detrimental effects on blood lipids and should only be consumed in moderation. Biotechnology and Biological Sciences Research Council, UK.

Increased postprandial glycaemia and reduced insulin sensitivity are associated with development of Type 2 Diabetes (T2D). Maintaining a normal glucose response is important both for healthy individuals, for disease prevention, and for those with T2D, to prevent development of diabetes-related complications. Chilling previously-cooked starchy carbohydrate (CHO) results in retrogradation of some of the starch to form resistant starch (RS). RS is not absorbed in the small intestine and consequently does not contribute to the postprandial glucose excursion. Reheating the CHO, however, reverses this process, reducing some of the RS content. RS type 5 is formed in the laboratory by heating starch with free fatty acids; there is limited evidence for its formation using domestic cooking methods and real foods. Furthermore it is unclear whether this would translate into a noticeable effect on postprandial glucose metabolism. In this randomised crossover study, 8 participants attended two study days; at one they consumed a freshly cooked mashed potato meal (203 g boiled potato, 25 g butter) at the other they consumed an identical meal which had been chilled for 66 h then microwave reheated. The potatoes were intrinsically labelled with [U-13C]starch, and participants received a variable [6,6-2H2]glucose infusion, allowing detailed glucose flux modelling. Venous blood samples were taken for 6 h postprandially. There was no significant effect on postprandial glucose, however repeated measures ANOVA on postprandial insulin time-point data found a significant difference between meals (p = 0.026), with a 24% reduction in incremental area under the curve (0–120 min) and 21% reduction in insulin peak between freshly cooked and reheated meals. There were no significant effects on rate of appearance of glucose into the plasma from the gut (Ra) or on endogenous (hepatic) glucose production (EGP), however there was a strong trend for a reduced rate of glucose disposal (uptake into tissues, Rd) following the reheated meal (p = 0.054). It is hypothesised that RS was formed in the reheated meal by the chilling and reheating process; this will be verified by in vitro work later in the project. The attenuation of the postprandial insulin response with no significant effect on EGP suggests enhanced hepatic insulin sensitivity following the reheated meal as a possible mechanism for the effects of RS on postprandial glycaemia. This study demonstrates that making simple changes to the way a starchy carbohydrate meal is prepared can have significant beneficial effects on postprandial glucose metabolism.

This pilot study explored the feasibility of a moderate time-restricted feeding (TRF) intervention and its effects on adiposity and metabolism. For ten weeks, a free-living TRF group (n=9) delayed breakfast and advanced dinner by 1.5-hours each. Changes in dietary intake, adiposity and fasting biochemistry (glucose, insulin, lipids) were compared to controls (n=7) who maintained habitual feeding patterns. Thirteen participants (29±2kg/m2) completed. The average daily feeding interval was successfully reduced in the TRF group (743±32 to 517±22 mins/day (p

Previous work has shown increased insulin sensitivity, increased hepatic insulin clearance and lower postprandial insulin responses following treatment with resistant starch, a type of dietary fibre. The objective of this study was to further explore the effects of resistant starch on insulin secretion. Twelve overweight (BMI 28.2±0.4 kg/m(2)) individuals participated in this randomized, subject-blind crossover study. Participants consumed either 40 g type 2 resistant starch or the energy and carbohydrate-matched placebo daily for four weeks. Assessment of the effect on insulin secretion was made at the end of each intervention using an insulin-modified frequently sampled intravenous glucose tolerance test (FSIVGTT). Insulin and C-peptide concentrations were significantly higher during the FSIVGTT following the resistant starch compared with the placebo. Modelling of the data showed significantly improved first-phase insulin secretion with resistant starch. These effects were observed without any changes to either body weight or habitual food intake. This study showed that just four weeks of resistant starch intake significantly increased the first-phase insulin secretion in individuals at risk of developing type 2 diabetes. Further studies exploring this effect in individuals with type 2 diabetes are required.

This pilot study investigated the effects of chilling and reheating a pasta-based meal on the postprandial glycaemic response. In this single-blind crossover study, 10 healthy volunteers consumed identical pasta meals (pasta, olive oil and tomato sauce), served either freshly prepared, chilled or chilled/reheated, on three separate randomised occasions. Capillary blood samples were taken for two hours postprandially. A significant difference in glucose Incremental Area Under the Curve (IAUC) was observed (p = 0.006), with the greatest difference observed between the freshly cooked and chilled/reheated meals (p = 0.041). Significant differences in incremental peak glucose were also observed (p = 0.018). These results suggest that making simple changes to domestic food processing methods can reduce the glycaemic excursion following a pasta meal, with the potential for health benefit.

Potatoes have been an affordable, staple part of the diet for many hundreds of years. Recently however, there has been a decline in consumption, perhaps influenced by erroneous reports of being an unhealthy food. This review provides an overview of the nutritional value of potatoes and examines the evidence for associations between potato consumption and non-communicable diseases. Potatoes are an important source of micronutrients, such as vitamin C, vitamin B6, potassium, folate, and iron and contribute a significant amount of fibre to the diet. However, nutrient content is affected by cooking method; boiling causes leaching of water-soluble nutrients, whereas frying can increase the resistant starch content of the cooked potato. Epidemiological studies have reported associations between potato intake and obesity, type 2 diabetes and cardiovascular disease. However, results are contradictory and confounded by lack of detail on cooking methods. Indeed, potatoes have been reported to be more satiating than other starchy carbohydrates, such as pasta and rice, which may aid weight maintenance. Future research should consider cooking methods in the study design in order to reduce confounding factors and further explore the health impact of this food.

There is much epidemiological evidence suggesting a reduced risk of development of type 2 diabetes (T2D) in habitual coffee drinkers, however to date there have been few longer term interventions, directly examining the effects of coffee intake on glucose and lipid metabolism. Previous studies may be confounded by inter-individual variation in caffeine metabolism. Specifically, the rs762551 single nucleotide polymorphism (SNP) in the CYP1A2 gene has been demonstrated to influence caffeine metabolism, with carriers of the C allele considered to be of a “slow” metaboliser phenotype. This study investigated the effects of regular coffee intake on markers of glucose and lipid metabolism in coffee-naïve individuals, with novel analysis by rs762551 genotype. Participants were randomised to either a coffee group (n=19) who consumed 4 cups/day instant coffee for 12 weeks or a control group (n=8) who remained coffee/caffeine free. Venous blood samples were taken pre- and post13 intervention. Primary analysis revealed no significant differences between groups. Analysis of the coffee group by genotype revealed several differences. Prior to coffee intake, the AC genotype (“slow” caffeine metabolisers, n=9) displayed higher baseline glucose and non esterified fatty acids (NEFA) than the AA genotype (“fast” caffeine metabolisers, n=10, p