Image: John Innes Centre
A type of wrinkled ‘super pea’ may help control blood sugar levels and could reduce the risk of type 2 diabetes, suggests a new study.
The research, from scientists at Imperial College London, The John Innes Centre, Quadram Institute Bioscience and the University of Glasgow, suggests incorporating the peas into processed foods, in the form of pea flour, may help tackle the global type 2 diabetes epidemic.
The work, published in the journal Nature Food and funded by the BBSRC, focused on a naturally occurring type of pea. Unlike regular peas, they contain higher amounts of ‘resistant starch’, which takes longer for the body to break down.
The study reveals that compared to eating normal peas, wrinkled peas prevented ‘sugar spikes’ – where blood sugar levels rise sharply after a meal. The same effect was seen when consuming flour made from wrinkled peas incorporated in a mixed meal.
According to the researchers, this could be important as regular, large sugar spikes are thought to increase the risk of diabetes. They add that flour from their ‘super peas’ could potentially be used in commonly consumed processed foods which, if eaten over the long term, could prevent these sugar spikes.
Dr Katerina Petropoulou, first author of the research from the Centre for Translational and Nutrition Food Research at Imperial College London, said: “Despite national campaigns to promote healthy eating, type 2 diabetes diagnosis rates continue to rise. An alternative dietary strategy to maintain normal blood glucose rates among the population is to improve the composition of commonly consumed foods. There is much evidence that diets rich in a type of carbohydrate called resistant starch have a positive impact on controlling blood glucose levels, and hence reduce susceptibility to type 2 diabetes.”
The peas used in the research are similar to the frozen peas you can buy in the supermarket. They are also the same as those used by the famous scientist Gregor Mendel in the 1800s, to show how dominant and recessive genetic traits can be passed on through selective breeding.
However, in the latest experiments researchers used larger, more mature versions of those typically found in the freezer aisle. This is because larger, older peas contain more so-called ‘resistant starch’.
Cell from wrinkled pea before cooking with exposed starch granules
Starch is a compound that the body breaks down to release sugar, but resistant starch is broken down more slowly, so that sugar is released more slowly into the blood stream, resulting in a more stable increase rather than in a spike.
In the latest study, the researchers used a type of ‘super pea’ – wrinkled peas with a naturally occurring genetic mutation, or variant, that produces a greater amount of resistant starch, but which have a lower overall carbohydrate content.
Over a series of experiments, the team gave healthy volunteers a mixed meal including 50 grams of wrinkled peas, and in a series of control experiments gave them regular ‘smooth’ peas. Working with the University of Glasgow, researchers also added a tracer molecule the peas, so that they could trace how they were absorbed and digested by the human gastrointestinal tract.
They repeated the experiments using flour made from wrinkled peas or control peas. To further investigate the impact of long-term consumption they recruited 25 volunteers and asked them to consume pea hummus and mushy peas (made from wrinkled or control peas) for a period of 4 weeks.
Professor Gary Frost, lead author of the study and head of Imperial’s Centre for Translational and Nutrition Food Research, said: “The ‘super pea’ contains a naturally-occurring genetic variant that means they are high in resistant starches. These starches are not completely digested in the upper parts of the digestive tract and are available for fermentation by bacteria in the colon.”
Micrographs of cooked smooth (left) and wrinkled (right) peas: The plant cells remain intact and the cell wall (“dietary fibre”, stained light brown) surrounds and protects the starch (stained blue) inside the cells from digestion. The wrinkled pea starch granule structure is more resistant to cooking and digestion. Image: the Quadram Institute
Previous research from the same group has suggested that as these bacteria ferment the starch, they produce compounds called short chain fatty acids. These compounds in turn help boost the function of cells that produce insulin, which helps control blood sugar.
Further tests using a mimic of the human gut, carried out by researchers at Quadram Institute Bioscience, showed that the way that the peas were prepared and cooked affected how quickly they were digested. Researchers also showed that there were significant benefits to our gut microbiota because of the fermentation process taking place there.
Professor Pete Wilde of the Quadram Institute said that “This study has shown us that by preparing these peas in certain ways we can further reduce these blood sugar spikes, opening up new possibilities for making healthier foods using controlled food processing techniques.”
The researchers are now planning further trials involving volunteers with early stage type 2 diabetes. This will also involve a major pea breeding programme with help from industry partners to grow more ‘super peas’ with the resistant starch.
Professor Claire Domoney of the John Innes Centre in Norfolk said: “This research has emphasized the value of making these pea lines which involve many years of work to develop.”
The study authors points out that it is not just peas that have the resistant starch mutation. Other research is focusing on breeding the mutation into staple crops, such as rice and wheat. With modern genomic tools there is the potential for discovery or generation of the mutation across a range of seed and grain crops – which make up many of the carb-rich foods we consume.
Professor Domoney added: “Longer term it could become policy to include resistant starch in food. We have precedents for this kind of intervention, such as iron being added to bread to tackle anemia. We could potentially make it policy to say that food can contain a certain amount of resistant starch to tackle type 2 diabetes and other metabolic illnesses.”
A mutation in a starch branching enzyme gene alters starch assembly in Pisum sativum L. (pea) and improves glucose homeostasis in humans, Katerina Petropoulou, Louise Salt et al, Nature Food doi: 10.1038/s43016-020-00159-8