the glory of the green – tipped banana [a primer on resistant starches]

As the pandemic ran its course over 2020, the humble banana shone brightly in family kitchens and social media posts showcasing a love for banana bread. Now don’t get me wrong, banana bread is a delicious treat and a great way to use up overripe fruit. However, the unripe, green-tipped banana is truly the fruits’ superhero alter ego. So what makes green-tipped bananas the
Wonder Woman to the overripe banana’s Diana Prince? Resistant starch.

Not all starch is created equal. Most starch that we eat gets digested in the GI tract into simple sugars and used for energy. Resistant starch is different. Aptly named, it is a starch that is resistant to digestion. Much like dietary fiber, it passes through the small intestine without being absorbed. It reaches the large intestines intact, where it becomes fuel for our microbiome. In the large intestine, it becomes fermented by the microbes, producing short-chain fatty acids (SCFA) as a result. And these SCFA’s are like the pot of gold at the end of the digestive rainbow. SCFA’s, especially butyrate, promote the health and integrity of the colon.

Gut health
Think of butyrate as a superfood for your gut. Butyrate is the preferred fuel source for the colon cells, ensuring they have ample energy to do their job. SCFA’s act as powerful anti-inflammatory agents that may be beneficial for people with inflammatory bowel conditions like ulcerative colitis or Chron’s disease. It has been associated with the inhibition of cancer-causing genes in the colon. Butyrate is essential for maintaining the colon’s mucus layer, helping to keep the lining of the gut healthy and functioning properly.

Improved blood sugar
Resistant starch has benefits that travel outside of the gut as well. Multiple studies have shown that eating resistant starch can improve insulin sensitivity, improving blood sugar metabolism. Better blood sugar metabolism means better energy, fewer cravings, and decreased risk for diabetes, obesity, heart disease, and Alzheimer’s disease.

Reduced appetite
Resistant starch appears to impact the chemical messengers that play a role in appetite regulation. It increases leptin and peptide YY (PYY), hormones that signal to the body you are full.

Brain health
SCFA’s may have a positive impact on the brain. It has long been known that the gut microbiome plays a role in brain health, but emerging evidence has linked SCFA’s in the communication between the gut and the brain. SCFA may play a beneficial role in mood disorders and neurological disorders such as Parkinson’s’ Alzheimer’s, autism, and multiple sclerosis.

Food sources
So, where can we find a gold mine of resistant starch in the diet? Well, we know green-tipped bananas are one source. As bananas ripen, the resistant starch gets converted into sugar, making the banana sweet, so to get an ample dose of resistant starch the banana must be underripe. Besides green-tipped bananas, a few favorite food sources are potatoes and rice that have been cooked and then cooled. The cooling initiates a process called retrogradation, where resistant starches are formed. Legumes and rolled oats are other excellent sources of resistant starch.

Incorporating more of these foods in your diet, balanced with other fiber rich foods is an ideal way to ensure gut health and reap the benefits of this lesser known wonder starch.


References:
1. Keenan MJ, Zhou J, Hegsted M, et al. Role of Resistant Starch in Improving Gut Health, Adiposity, and Insulin Resistance. Adv Nutr. 2015;6(2):198-205. doi:10.3945/an.114.007419
2. Maziarz MP, Preisendanz S, Juma S, Imrhan V, Prasad C, Vijayagopal P. Resistant starch lowers postprandial glucose and leptin in overweight adults consuming a moderate-to-high-fat diet: a randomized-controlled trial. Nutr J. 2017;16. doi:10.1186/s12937-017-0235-8
3. Lockyer S, Nugent AP. Health effects of resistant starch. Nutrition Bulletin. 2017;42(1):10-41. doi:https://doi.org/10.1111/nbu.12244
4. Tan J, McKenzie C, Potamitis M, Thorburn AN, Mackay CR, Macia L. Chapter Three – The Role of Short-Chain Fatty Acids in Health and Disease. In: Alt FW, ed. Advances in Immunology. Vol 121. Academic Press; 2014:91-119. doi:10.1016/B978-0-12-800100-4.00003-9
5. Zimmerman MA, Singh N, Martin PM, et al. butyrate suppresses colonic inflammation through HDAC1-dependent Fas upregulation and Fas-mediated apoptosis of T cells. Am J Physiol Gastrointest Liver Physiol. 2012;302(12):G1405-1415. doi:10.1152/ajpgi.00543.2011
6. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol. 2020;11. doi:10.3389/fendo.2020.00025

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