Why cold potatoes and green bananas are better for you?
Heard of prebiotics? The fact that my spell check wants to auto-correct it to probiotics makes me think most of you have not. Well it turns out prebiotics are just as important as probiotics for gut health.
So what are prebiotics?
Just to clarify, probiotics are live microorganisms, the so-called ‘good’ bacteria and yeast, that keep your gut healthy. Prebiotics on the other hand are foods that induce the growth or activity of these beneficial microorganisms. Basically, they feed the friendly flora.
Prebiotics are typically carbohydrate compounds, primarily oligosaccharides, that resist digestion in the small intestine and then feed the advantageous bacteria that colonise the colon.
The most well documented example of probiotics are fermentable carbohydrates such as fructans and galactans. However, a particular type of dietary fibre known as resistant starch (RS) is emerging as a highly beneficial prebiotic.
How does resistant starch work?
The term “resistant” simply refers to this starch’s ability to resist digestion. Instead, it passes to the large intestine where it is fermented and encourages the growth of beneficial bacteria. These good bacteria confer a multitude of health benefits through the production of short chain fatty acids, such as butyrate. These acids lower the pH of our bowel, this in turn improves absorption of minerals and suppresses the growth of harmful bacteria(1,2,3). Additionally, butyrate is the preferred energy source for colon cells. As a consequence, populations at low risk of bowel diseases have high dietary resistant starch intake and high butyrate levels(4).
Benefits of resistant starch
Cholesterol: RS consumption is associated with a decrease in the levels of cholesterol and triglycerides(11).
Prevention of haemorrhoids(16).
Best sources of resistant starch
RS is found in all starchy foods albeit in variable amounts. The net amount can be influenced by the way you prepare the starch-containing foods, as cooking and processing destroys most resistant starches. However, you can "rescue" the resistant starch content of some foods by letting them cool after cooking. For example cooling potatoes and rice after cooking helps to salvage their RS content. This is because after the cooked starch is cooled, the starch molecules crystalise and become less digestible. A process is called retrogradation.
Examples of naturally occurring RS(21):
- Raw oats
- Cooked and cooled legumes and beans: white beans have the highest amount of resistant starch, followed by lentils, green peas, chickpeas and kidney beans.
- Green bananas and plantains: green bananas contain up to 70-80% starch and during ripening, the starch is converted into sugars and ends up being less than 1% when the banana is fully ripe.
- Cooked and cooled potatoes. Think potato salad.
- Cooked and cooled rice. Think sushi or even fried rice.
While there is no official recommendation for the intake of resistant starch, studies showing health benefits typically range from 15-30 grams per day.
So what does this look like:
- 100g of roasted and cooled potatoes provides 19.2g RS, whereas the boiled version provides only 0.16g.
- 100g uncooked rolled oats contain 11.3g RS.
- 1/2 cup cooked (100 g) lentils contain 6.62g RS.
- 1 medium green banana has 19g RS
- Cashews contain 12.9g RS per 100g (1/2 cup)
- Brown rice cooked and cooled provides 5.48g per 100g serve
Seems rather easy to meet the requirements so enjoy some potato salad and your gut will thank you.