Potatoes are rapidly digested, simple carbs, right? Depends on how you prepare them.

Updated: Jan 16, 2019


Resistant starch is a prebiotic that is 'resistant' to digestion in the small intestine. The body processes starches and resistant starches very differently:



Resistant starch remains undigested until it reaches the colon and feeds the microbes that live in your gut. This produces short chain fatty acids like butyrate that have important health-promoting effects, such as:

  • Reducing inflammation in the body.

  • Strengthening the intestinal wall, which promotes proper digestion and absorption of nutrients.

  • Reducing the caloric density of food. Foods high in resistant starch contain less usable calories because the body does not metabolise the calories from resistant starch like it does for other starches. Digestible starch provides 4 calories per gram while resistant starch yields around 2.5 calories per gram. The resistant starch content effectively dilutes the net caloric load of the food source.

  • Reducing the postprandial (after eating) blood sugar spike and insulin response.

  • Increasing the release of gut satiety peptides, signalling to the brain that 'I'm full.'

  • Increasing fat oxidation and protecting lean mass.


A case study: the humble potato

Did you know that how you cook certain foods actually alters its resistant starch content? Some examples of this include potato, rice and pasta.

Let's look at the example of the plain old white potato.

  • Uncooked potato: contains some resistant starch (type II).

  • Baked potato: the potato starches becomes highly digestible and the GI of the food increases. (GI of sweet potatoes, baked: 92. GI of waxy white potatoes, boiled: 82.)

  • Cooked and cooled potato (particularly if refrigerated): creates more resistant starches (type III).

Cook it, cool it, reheat it - less total calories and more microbe-friendly prebiotics

In fact, research indicates that if you cook and cool potatoes, this more than doubles the resistant starch content to about 5.8 grams per 100 grams of food. In addition, some studies suggest that if you later reheat the cooked and cooled potatoes, this dramatically increases the resistant starch in it and considerably reduces the amount of calories that your body will store from it because the body needs to use more energy just to digest the potatoes.

There is limited data on this, but it's an interesting finding that could have huge implications. It tells us that people can actually alter the caloric load of common, staple foods like potatoes, rice and pasta based on how they cook it, rather than just how much they eat. This is a nifty tool for people eating to promote fat loss. Or, if you just love eating potatoes but you're not particularly active, you could opt for cooked, cooled and reheated rice, or a home made potato salad that also contains slow-digesting fats and proteins. It is equally relevant to you if you're eating to gain size or to replenish glycogen storage after a brutal training session. If that's your goal, then it's better to eat baked potatoes hot out of the oven or freshly cooked rice to promote easy digestion and maximise the caloric potential of that food.

Sources

Gentile, Christopher L. et al. 'Resistant Starch and Protein Intake Enhances Fat Oxidation and Feelings of Fullness in Lean and Overweight or Obese Women.' Nutrition Journal (2015) 14: 113.

Keenan MJ, et al. 'Effects of Resistant Starch, a Non-Digestible Fermentable Fiber, on Reducing Body Fat.' Obesity (2006) 14(9):1523.

Slavin JL. 'Carbohydrates, Dietary Fiber, and Resistant Starch in White Vegetables: Links to Health Outcomes.' Advances in Nutrition (2013) 4(3): 351S.

Higgins JA. Resistant starch and energy balance: impact on weight loss and maintenance.'' Critical Reviews in Food Science and Nutrition. (2014) 54(9):1158.

Michael Mosley, The Clever Guts Diet. In particular, read pages 129-30, 268-9.