How does the body turn “carbs” into “sugar”?

We hear this all the time, but what does it actually mean? I decided to look into this process and find out more …

Carbohydrates are commonly classified as being either simple or complex. The difference between a simple and complex carbohydrate is in how quickly it is digested and absorbed – as well as its chemical structure.

Simple carbohydrates

  • Often referred to as simple sugars, these carbohydrates are composed of sugars such as fructose, glucose and galactose which have simple chemical structures composed of only one sugar – monosaccharides, or double sugars – disaccharides, which include sucrose (table sugar), lactose and maltose.
  • Sugars are found in a variety of natural food sources including fruit, vegetables and milk, and give food a naturally sweet taste.
  • Simple carbohydrates are easily and quickly utilised for energy by the body because of their simple chemical structure. But they also raise blood glucose levels quickly.

Complex carbohydrates

  • These carbohydrates have more complex chemical structures, with three or more sugars linked together, known as oligosaccharides and polysaccharides.
  • Many complex carbohydrate foods contain fibre, vitamins and minerals, and they take longer to digest – which means they have less of an immediate impact on blood sugar, causing it to rise more slowly.
  • However other so called complex carbohydrate foods such as white bread and white potatoes contain mostly starch but little fibre or other beneficial nutrients.

Dividing carbohydrates into simple and complex does not account for the effect of carbohydrates on blood sugar and chronic diseases. To explain how different kinds of carbohydrate-rich foods directly affect blood sugar, the Glycaemic Index (GI) is considered a better way of categorising carbohydrates, especially starchy foods.

NOTE: the term complex carbohydrate refers to any starches, including the highly refined starches found in white bread, cakes, most pastries and many other food sources. However, when dietitians and nutritionists advise having complex carbohydrates, they are usually referring to whole grain foods and starchy vegetables which are more slowly absorbed than refined carbohydrate.

What is the Glycaemic Index?

The glycaemic index ranks carbohydrates on a scale from 0 to 100 based on how quickly and how much they raise blood sugar levels after eating. Foods with a high glycaemic index, like white bread, are rapidly digested and cause substantial fluctuations in blood sugar. Foods with a low glycemic index, like whole oats, are digested more slowly, prompting a more gradual rise in blood sugar.

  • Low-glycaemic foods have a rating of 55 or less, and foods rated 70-100 are considered high-glycaemic foods. Medium-level foods have a glycaemic index of 56-69.
  • Eating many high-glycaemic-index foods can cause powerful spikes in blood sugar. This can lead to an increased risk for type 2 diabetes and coronary heart disease.
  • Foods with a low glycaemic index have been shown to help control type 2 diabetes and improve weight loss.
Many factors can affect a food’s glycaemic index, including the following:

Processing: Grains that have been milled and refined (removing the bran and the germ) have a higher glycaemic index than minimally processed whole grains.

Physical form: Finely ground grain is more rapidly digested than coarsely ground grain. This is why eating whole grains in their whole form like brown rice or oats can be healthier than eating highly processed whole grain bread.

Fibre content: High-fibre foods don’t contain as much digestible carbohydrate, so it slows the rate of digestion and causes a more gradual and lower rise in blood sugar.

Ripeness: Ripe fruits and vegetables tend to have a higher glycaemic index than un-ripened fruit.

Fat content and acid content: Meals with fat or acid are converted more slowly into sugar.

You can find out more about the Glycaemic Index at Diabetes UK >>

These look rather tasty!

Carbohydrates and blood sugar

When we eat food containing carbohydrates, the digestive system breaks down the digestible ones into sugar, which then enters the blood.

  • As blood sugar levels rise, the pancreas secretes insulin, the hormone that enables you to digest starches and sugars. This release of insulin is sometimes called an insulin spike.
  • As cells absorb blood sugar, levels in the bloodstream begin to fall.
    When this happens, the pancreas starts making glucagon, a hormone that signals the liver to start releasing stored sugar.
  • This interplay of insulin and glucagon ensure that cells throughout the body, and especially in the brain, have a steady supply of blood sugar.
  • If you have a metabolic disorder such as diabetes that keeps you from producing enough insulin, you must be careful not to take in more carbs than you can digest.

The NHS advises that added sugars shouldn’t make up more than 5% of the energy (calorie intake) you get from food and drink each day. This is about 30g of sugar a day for those aged 11 and over.

See more about how much sugar is good for you at NHS Choices >>

Eat sensibly and enjoy good carbohydrates!

It’s important to remember that the somewhat much maligned carbohydrates are your body’s main source of energy and in fact your muscles and brain cells prefer carbs more than other sources of energy, such as triglycerides and fat, for example.  If you’re active and eating appropriately for your activity level, most of the carbs you consume are more or less burned immediately. However, if you’re eating a lot more calories per day than you are burning, then your liver will convert excess calories from carbohydrate into fats. If you consume too many calories from simple sugars like sucrose and fructose, then your body will more readily take some of those sugars and turn them into triglycerides (fat) in your liver.

  • Thanks to diabetes.co.uk
  • The Harvard School of Public Health
  • NHS Choices

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