The search has been on for some time to identify dietary strategies to tackle diabetes, which is estimated to affect around 4.8m people in the UK, including about a million undiagnosed individuals, and carries considerable cost to the NHS.
Type 2 diabetes accounts for about 90% of diabetes cases. It is the result of a progressive decline in the capacity of specialised cells in the pancreas to secrete insulin, the hormone that controls blood glucose levels. This decline can be accelerated by a poor diet and unhealthy lifestyle, and for some time a beneficial role for resistant starch in the diet has been recognised.
Resistant starch is a carbohydrate that resists digestion in the upper parts of the digestive tract, with some reaching the large bowel (colon) where it is fermented by the bacteria that reside there. Details can be found in a paper by Lockyer and Nugent. This process generates products known as short chain fatty acids which are thought to improve insulin secretion by acting on the specialised cells in the pancreas known as beta cells. Although a variety of fruits and vegetables contain resistant starch, UK diets generally contain low amounts.
The research is a collaboration between Imperial College London, the Quadram Institute and the John Innes Centre. It set out to study which features of starch structure are important in determining resistance to digestion, whether resistant starches from different food sources differ in their capacity to improve beta cell function and whether cooking method is important. The project aspired to identify strategies to reduce type 2 diabetes risk through development of new forms of common foods containing resistant starches.
There is evidence that pulses beneficially affect control of blood glucose. The new research from Petropoulou and colleagues focused on peas because there is a range of naturally occurring genetically defined variants known to contain different types of resistant starch.
Wrinkled pea improves blood glucose control
The resistant starch content of peas varies with the degree of maturity and between varieties. The research found evidence that, compared to regular smooth peas, a wrinkled type of pea improved blood glucose control by preventing harmful sugar spikes following a meal. The same effect was seen when flour made from the peas was incorporated into a meal. Processing and cooking techniques were also found to influence the effect on blood glucose levels.
This type of wrinkled pea contains a naturally-occurring variant gene that means the peas have a high resistant starch content. It has been commercially cultivated for several decades as a fresh vegetable crop. Efforts to expand the range of food uses is underway, to provide ingredients for a wide range of applications. This includes exploring whether the genetic variation responsible for the effects is present in other pulses, such as beans, and whether the variant can be bred into other starch-containing crops such as grains and seed crops.
This research is an excellent example of how investment in plant research involving a multidisciplinary research team can help tackle major public health challenges.
Judy Buttriss is director general of the British Nutrition Foundation