Carbohydrates and Diabetes: Breaking it down

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If you have diabetes it’s important to know how carbs can affect your blood glucose levels. If you eat too many carbohydrates, or the types of carbohydrates that process rapidly, then your blood glucose levels will fluctuate dramatically, increasing health risks. Even if you don’t have diabetes, it’s good to know the ins and outs of carbs and how they affect your body.

So how do you learn to moderate your carb intake effectively? You need to get a good understanding of two things: carbohydrate distribution and carbohydrate quality. Carbohydrate distribution refers to when you eat and the amount of carbohydrate you eat. Carbohydrate quality refers to the types of carbohydrates you eat, and can be moderated using the glycemic index or load. If you familiarise yourself with both these aspects of carbohydrate intake, and make any necessary changes to your diet, you’ll be well on your way to effectively managing your blood glucose levels.

Carbohydrate distribution

Carbohydrate distribution refers to when you eat and the amount of carbohydrate you eat.

If you have diabetes, regular meals with an even distribution of carbohydrate over the day are important for good control of blood sugar levels. If you eat large quantities of carbohydrate foods at main meals, and little or none between meals, you risk excessive fluctuations in blood sugar levels. It’s better to eat smaller amounts of food more frequently, as this results in steadier, more even blood glucose levels. In general, the recommended daily eating pattern for good blood glucose control is:

  • Three meals and three snacks for people with Type 1 diabetes and normal blood glucose variations
  • Three meals (and 1-2 snacks as needed) for those with Type 2 diabetes

If you are diabetic, your doctor or dietitian can advise you on the level of calories and carbohydrate most appropriate to your weight, medication, and activity. You should also check your blood glucose regularly for feedback on how carbohydrate intake is affecting blood glucose levels.

Whether or not you have diabetes, a rough rule-of-thumb for carbohydrate intake is 13g of carbohydrate per 100 calories; this is equivalent to about 50% of total calories. Variations on this rule are shown in the Carbohydrate Intake table below.

Daily Total Calories Daily Total Carbohydrates Percentage of Carbohydrate Calories Each Main Meal (3) Between Meals (3)
1200 calories 120g 40% 30g 10g
1500 calories 170g 45% 40g 15g
2000 calories 250g 50% 60g 25g
2500 calories 345g 55% 70g 45g
3000 calories 450g 60% 90g 60g

From Allan Borushek’s Pocket Calorie, Fat & Carbohydrate Counter, 2005 edition.

Carbohydrate quality

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Moderating your carbohydrate intake involves more than just eating the right amounts of carbohydrate at the right times. You also need to choose the right kinds of carbohydrate foods.

Various forms of carbohydrate affect blood glucose levels in different ways. The same amount of carbohydrate from different foods may affect blood glucose differently. For example, white and brown rice have approximately the same amount of carbohydrate, but white rice will cause your blood glucose levels to rise faster than brown rice.

The aim is to choose carbohydrate foods that cause a slow, steady release of glucose into the bloodstream. These tips can help you towards that goal:

  • Choose carbohydrates containing soluble fibre as these can help slow the release of glucose. The best sources of soluble fibre are fruits, vegetables, oat bran, barley, dried beans and peas.
  • The physical form of the carbohydrate food (whether it is solid, puree, or liquid), can influence the rate of glucose release. Choose solid forms of food, rather than liquid – for example, choose oranges instead of orange juice. In general, the more refined the food substance, the quicker the release of glucose into the bloodstream.
  • Choose raw carbohydrate foods rather than cooked ones, and whole foods rather than processed foods. These are generally more slowly absorbed, even though the carbohydrate content is often the same.
  • Avoid carbohydrate foods high in simple sugars, such as white bread, biscuits and lollies, as these will speed up the release of glucose.

Using the glycemic index and the glycemic load

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Originally developed as research tools, the glycemic index (GI) and glycemic load (GL) can also be used to help predict how different types of carbohydrate foods will affect blood glucose levels. The term “glycemic” means “sugar in the blood”. The GI and GL rank carbohydrates on a scale from 0 to 100, based on their immediate effect on the “sugar in the blood” after eating. This is called the glycemic response.

Foods with a high GI/GL are those which are rapidly digested and absorbed, resulting in marked fluctuations in blood sugar levels. Low GI or GL foods produce gradual rises in blood sugar and insulin levels, and have proven benefits for health. However, keep in mind that for diabetes and weight control, portion size is also vital, regardless of a food’s GI/GL rating.

To have stable blood glucose levels, the bulk of your carbohydrates should be of low GI/GL. Mostly this means eating less sugars and refined grains and more vegetables and unrefined grains, but there are a few surprises – some of the complex carbohydrates behave more like simple sugars, with a quick release of glucose. For example, white potatoes, French fries and many breakfast cereals, such as cornflakes, all have a high GI/GL.

Although GI/GL can be helpful for understanding how carbohydrates work in the body, research has not yet proven that a low GI/GL diet will prevent diabetes. The GI/GL should by no means be used in isolation, but as a tool to manage diabetes.

Calorie King
CalorieKing's mission is to provide the best information, tools and education to Australians to help them conquer their weight.

CalorieKing is the brainchild of Allan Borushek, registered dietitian, co-found here at food.com.au and author of "Allan Borushek's Pocket Calorie & Fat Counter", Australia's best-selling calorie counter for over 30 years.

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