Shows importance for plant breeding programs to incorporate human health traits into crop improvement strategies.
New research on waxy starch in sorghum by University of Nebraska-Lincoln researchers shows that waxy starches can have undesirable effects on the human gut microbiome. The gut microbiome is an ecosystem of microorganisms living in the gastrointestinal tract.
The Nebraska Food for Health research project focused on sorghum starch content, and its findings, were recently published in the journal “Gut Microbes”: “The waxy mutation in sorghum and other cereal grains reshapes the gut microbiome by reducing levels of multiple beneficial species.”
While starch is part of a healthy diet, it’s important to note that not all starches are created equal. Typically, native starch comprises 20 to 25% amylose and 75 to 80% amylopectin, while waxy starches contain no amylose and are composed almost entirely of amylopectin molecules due to a naturally occurring mutation in starch synthesis genes. Normal starches often have physicochemical properties that are undesirable for food processing, while waxy starches are known for their high digestibility, desirable viscous properties in food processing, and unique organoleptic characteristics, such as sticky rice.
We know little about the health effects of consuming waxy starch compared to normal starch, particularly in context of a whole grain. Our gut contains trillions of microbes, which are influenced by our diet and impact our health through host-microbiome interaction. Could waxy vs normal starch have different effects on our gut microbiome and our health?
Using plant genetics and advanced research platforms, scientists at Nebraska Food for Health Center studied the in vitro fermentation of six pairs of near-isogenic sorghum lines. These lines were created through years of breeding and only differed in starch characteristics.
“It’s a gold mine!” exclaimed Dr. Qinnan Yang, lead researcher, discussing the exceptional plant materials studied. Analyzing fermentation profiles across diverse human microbiomes, they discovered that grain from parental lines of sorghum stimulate growth of many species of gut microbes that are known to be beneficial to our health whereas grain from waxy derivatives lacks this capacity. Thus, there is a trade-off effect between the desirable characteristics of waxy starch for food processing and an undesirable effect on the human gut microbiome.
Waxy starch lacks amylose, a component more resistant to human digestion, which can reach the colon and fuel beneficial gut microbes to produce short chain fatty acids. The amylose content of normal starches drives growth of beneficial microbes and their desirable metabolites whereas waxy starch does not. Adding extracted normal sorghum starch to waxy sorghum restores the beneficial microbiome changes, demonstrating the causal effect of amylose on the gut microbiome. Their work also showed that this effect also applies to waxy derivatives of other commonly consumed grains like corn, wheat, rice, and millet.
They also showed that humanized gnotobiotic mice fed waxy sorghum have different microbiome composition and gain more weight than those on a normal sorghum diet.
The conclusion drawn is that while waxy starches offer benefits in terms of food functionality, they can also have unintended consequences on both the gut microbiome and host physiology. This could be especially relevant in human populations in parts of Asia that consume significant quantities of waxy grains (e.g. sticky rice).
This study marks the third major discovery from the Nebraska Food for Health Center demonstrating the substantial impact that naturally occurring genetic variation in food crops can have on the human gut microbiome.
This growing list of food crop components identified by these genetic analyses now includes levels of amylose in wildtype vs. waxy starch (https://www.tandfonline.com/doi/full/10.1080/19490976.2023.2178799), levels of condensed tannins influenced by major tannin regulatory loci in sorghum (https://www.nature.com/articles/s41467-022-33419-1), and the effects of mutations in the opaque-2 locus on seed protein composition in maize (https://www.frontiersin.org/articles/10.3389/fmicb.2022.921456/full).
“Collectively, these findings point toward the importance of plant breeding and genetics in human health-associated traits and should open the door for breeding programs to consider incorporating human health traits into crop improvement strategies,” said Dr. Andrew Benson, director of the Nebraska Food for Health Center.