Undigested or resistant starch (RS), a type of dietary fibre, was the subject of a review paper that assessed its role in different health outcomes such as postprandial glycaemia, satiety, and gut health.
Researchers from University College Dublin, and the British Nutrition Foundation (BNF) compiled and evaluated a body of human evidence that strongly leaned towards its ability to reduce the glycaemic response, and may be particularly useful for managing diabetes.
The wealth of evidence linking RS to reduced postprandial glycaemic responses has resulted in an EU-approved health claim back in 2011.
The European Food Safety Authority (EFSA) approved the wording ‘Replacing digestible starch with resistant starch induces a lower blood glucose rise after a meal.’
This statement sets out the minimum amount (at least 14% of the total starch content must be RS) that is needed to replace digestible carbohydrates in order to produce the desired effect.
The review, which was financially supported by ingredients provider Ingredion, also remained unmoved on RS’ impact on other metabolic markers, such as blood pressure and plasma lipids.
“It should be noted that there is limited evidence suggesting that RS does not influence vascular function, including peripheral or vascular stiffness or blood pressure,” the review stated.
“Furthermore, there does not appear to be a role of RS in mediating effects through the activity of the adipose tissue derived hormones, adipokines, such as adiponectin.”
Fibre as a prebiotic
The team of researchers thought that RS’ credentials as a prebiotic needed more convincing evidence in order to fulfil proposed classification criteria.
The team referred to a paper that attempted to provide these guidelines. These were: a resistance to gastric and gastrointestinal digestion; an ability to be fermented and used by gut microbiota; and an ability to selectively stimulate activity of one, or a limited number of, gut bacteria with health properties.
Whilst the researchers stated that current literature on RS did not quite fulfil these criteria, they did acknowledge that fermentation rates (and thus certain changes in the composition and/or activity of the gastrointestinal microbiota) could vary according to RS type.
The review went on to comment on RS’ greatest challenge for the future, which was to prove its ability to selectively stimulate beneficial microorganisms.
This obstacle is made all the more complex by the health claim restrictions imposed on probiotics and prebiotics by EFSA.
Additional considerations include the individual variations in gut microbiota and diet-induced responses, as well as factors such as age and geography.
Fibre effects on gout
Finally, Brazilian researchers were able to demonstrate fibre’s instrumental role in interfering in the inflammation associated with gout in a separate study.
More specifically, the findings point to a mechanism of action that leads the gut to produce short chain fatty acids (SCFAs).
These SCFAs were found to promote the death of neutrophils—a type of white blood cell that forms part of the immune response. This includes inflammation that is linked to progressive tissue damage and debilitating pain.
Mice placed on a high-fibre diet appeared to prevent the inflammation caused by injections of monosodium urate (MSU) crystals into the knees of mice – the prime characteristic of gout.
As well as neutrophil cell death, the experiments also showed the removal of this dying/dead cell debris.
Reduction of inflammation was also joined by increased production of anti-inflammatory substances in the knee joint, further preventing knee damage and dysfunction.
The study provides an example of how tweaking inflammatory circuits is possible by harnessing diet to microbial products producing significant effects on an inflammatory disease that affects the joints.
“By understanding the way foods interact with living organisms, we may be able to create diets that help people with the disease, as well as their health overall," said Dr Mauro Teixeira, a researcher at the Institute of Biological Sciences at the Federal University of Minas Gerais in Minas Gerais, Brazil.
Source: Nutrition Bulletin
Published online ahead of print: DOI: 10.1111/nbu.12244
“Health effects of resistant starch”
Authors: S. Lockyer, A. P. Nugent
Source: Journal of Leukocyte Biology
Published online ahead of print: DOI: 10.1189/jlb.3A1015-453RRR
“Dietary fiber and the short-chain fatty acid acetate promote resolution of neutrophilic inflammation in a model of gout in mice.”
Authors: Mauro Teixeira et al.