In some traditional cultures Red Kidney Beans are cooked with a little bit of sugar. A group of scientists wondered if the sugar might act, in some way, to reduce lectin toxicity in the beans. In 2010 they put this to the test by feeding three groups of Sprague-Dawley rats different diets; standard rat chow, standard rat chow plus 26% raw Red Kidney Bean powder or standard rat chow plus 26% Red Kidney Bean powder plus sucrose.

All the groups were free to eat and drink water at will (ad libitum) with the water supply of the third group containing a small amount of table sugar (1milliMolar Sucrose).

After 24 hours the rats were tested for:

  • food intake;
  • body weight;
  • small intestinal bowel overgrowth (SIBO – Lactulose Hydrogen breath test);
  • overgrowth of bacterial mucosa in the intestine and colon (qPCR tracing of bacterial genetic signature 16s rRNA);
  • intestinal permeability (Lactulose Mannitol sugar challenge);
  • physical (morphological) damage to the intestinal or colonic lining (histological examination);
  • and bacterial translocation to the liver (qPCR tracing of bacterial genetic signature 16s rRNA).

A laboratory (in vitro) cultured cell layer (Caco-2), that mimics the intestinal lining, was also tested for permeability by Transepithelial Resistance (TER) when exposed to isolated Red Kidney bean lectin (phytohemagglutinin PHA) alone, sucrose alone or the isolated lectin plus sucrose together.

All groups ate the same amount of food and had no physical damage to the gastro-intestinal lining.

The first group that ate standard rat chow (the control group) put on weight.

The group that ate standard rat chow plus red Kidney Beans plus Sucrose lost some weight, had increased Intestinal Permeability, mucosal bacterial growth, SIBO and some translocation of bacteria to the liver.

The group that ate standard rat chow and Red Kidney beans, without any additional Sucrose, had SIBO, lost the most weight and had the highest levels of Intestinal Permeability, mucosal bacterial growth, and translocation of bacteria to the liver.

Laboratory testing of the pseudo epithelial layer found that isolated Red Kidney Bean lectin increased permeability whilst Sucrose alone had no effect either way. Isolated Red Kidney bean lectin, combined with Sucrose, helped maintain impermeability. From this the authors concluded that the lectins in the beans are the most likely agent promoting intestinal permeability and bacterial overgrowth and that Sucrose partially inhibits RKB lectin activity by either:

“binding to the lectin (lectin blocking) or interfering with the lectin binding on the epithelial surface. Since this latter protection is a non-specific binding to the lectins, it doesn’t follow a particular dose-dependent trend.”

Sucrose Co-administration Reduces the Toxic Effect of Lectin on Gut Permeability and Intestinal Bacterial Colonization

Balamurugan Ramadass • Karol Dokladny • Pope L. Moseley • Yatin R. Patel • Henry C. Lin

Received: 5 February 2010 / Accepted: 15 July 2010 / Published online: 5 August 2010

Springer Science+Business Media, LLC 2010

https://www.ncbi.nlm.nih.gov/pubmed/20686845

ID: AAA014