Sugar 101: Digestion of starch

Sugar 101: Digestion of starch

When I was at college I had the most amazing biology teacher. One day she brought in a beautiful loaf from Cranks-an up market whole foods restaurant in England. It was artisan, wholegrain, organic and made from sour dough. At that time there were test papers that on contact with glucose turned violet. She gave us one each and cut the loaf into 32 pieces for her pupils.

Then she instructed us to chew the piece of bread for 20 seconds. We put the paper on our tongues. It turned violet. This showed us that even in the mouth there are amylases, that is enzymes, that actively break down starch into it’s basic building blocks-glucose. This continues in the gut after we swallow.

Starches can raise our blood sugar very quickly. Rice cakes, which many consider to be a health food, do it more quickly than sucrose ie. table sugar. Foods are graded in terms of their glycemic index or the speed and extent they raise blood sugar. Portion size also has an effect.

We have 7 pints of blood on average. I often ask my patients how much glucose they think is circulating in their blood stream. Invariably they say things like 1-2 pints or 500 grams. The real figure is near to 5 grams. That is just a teaspoon of glucose in 7 pints of blood. When we eat something like a ripe banana we are taking on 6 teaspoons of sugar. A 150 gram serving of potatoes is the equivalent of 9 teaspoons of sugar.

It is not just the obviously sweet foods that are a problem. Starches that do not taste sweet are very readily digested into simple sugars.

Common foods can wreak havoc metabolically without our knowing. One way to find out how foods are affecting our blood sugar is to use a continuous glucose monitor. The monitor is attached to the upper arm for two weeks and the patient can, without using a lancet, measure their blood sugar with an app on their phone. They can then discover which foods are causing blood sugar excursions. This gives them valuable information. They are then able to make informed dietary changes that prevent future disease.

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