Good carbs and bad carbs – what’s the difference?

Carbs or carbohydrates are a macronutrient, the other two being protein and fat (learn more here). Carbohydrates are used by our bodies as an energy source. After food which contains carbohydrate is eaten, it is broken down into glucose, fructose and galactose, all of which are small units of sugar.

These sugars are then absorbed by the small intestine into the bloodstream and transported to the liver. The liver converts fructose and galactose into glucose. Glucose is very important as it is used by different parts of your body, including muscles and organs, as a source of energy. This is done with the help of insulin, a hormone which instructs cells in your body to absorb glucose from the blood stream.

Any glucose that is not used by the body is stored in the liver and muscles as glycogen, a substance which is made up of many glucose molecules joined together. Glycogen acts as a backup energy source; when glucose is not readily available, glycogen is broken down into glucose. The body is only able to store a certain amount of glycogen (approximately 2000 calories worth). Any glucose which is not stored as glycogen is stored as fat – this is probably why carbs get such a bad rep.

Carbohydrates obtained from food can be split into 3 different categories:

  • Starches – these are a complex type of carbohydrate and are made up of many glucose molecules that have been bonded together. Starches are converted back into glucose by the digestive system. Foods which contain starches include beans, potatoes and green leafy vegetables.
  • Sugars – people usually associate “sugar” with the white crystalline substance used in many households (very bad for you by the way!). This sugar is called sucrose; however there are a many other different types of sugars including fructose and lactose. Fructose occurs naturally in fruits and some vegetables, whereas lactose can be found in milk.
  • Fiber – also known as roughage, it’s obtained from plant based foods and cannot be digested by the body. As fiber moves through your digestive tract it absorbs water and this helps tremendously when you go to the loo. There are 2 types of fiber, soluble and insoluble; the former dissolves in water whereas the latter does not. Good sources of dietary fiber include fruits, vegetables and legumes.

Refined carbs


These are considered the “bad” kind of carbohydrates and rightly so as they provide almost no benefit to the body, but cause plenty of problems. Refined carbohydrates have been processed and so have most of the naturally occurring fiber removed from them.

Refined carbs include white bread, white rice and white pasta, fruit juices and candy, to name a few. When you eat these refined carbs, they are broken down very quickly and glucose is released into the bloodstream at a much faster rate than with complex carbs (more on these later). This leads to large spikes in blood sugar levels and therefore a greater release of insulin is needed. As you can imagine this is especially problematic to diabetics, who are unable to produce adequate amounts of insulin.

Eating refined carbs barely fills you up and because of the quick spike in blood sugar, you are left feeling tired, moody and hungry. I am sure you have experienced this before (I know I have) – having a bowl of oatmeal and bananas (complex carbs) compared to a doughnut (simple carb) for breakfast makes all the difference in your energy levels. The former can keep you filled up and full of energy until lunch time, whereas the latter makes you crave even more sugary food by 10am!

Adding sugar to foods (cakes, ice cream, pastries etc) causes an even bigger problem. Numerous studies have shown that refined sugar is one of the worst components of the modern diet and is responsible for ailments such as diabetes, obesity and even cardiovascular disease.

Whole carbs


These are considered the “good” kind of carbohydrates – they are carbohydrates which have not been refined, meaning they contain the fiber which comes naturally with them. They are also known as unprocessed carbohydrates because no changes have been made to them. As opposed to refined carbs, scientific studies have shown that whole carbs actually reduce the risk of type 2 diabeteslower mortality rates and also reduce your risk of coronary heart disease.

Whole carbs are a vital part of your diet for a number of reasons.

They provide energy

As mentioned above, carbohydrates are a source of energy. Your body can use protein and fat as a source of energy, however carbohydrates are the most efficient at doing this. Additionally, the main use of protein is to build muscle tissue – using it as an energy source is both inefficient and can put a tremendous burden on your kidneys.

Complex (whole) carbohydrates are broken down at a slower rate than simple (refined) carbohydrates. This means that glucose is supplied to your blood stream at a much more constant rate, which prevents you from “crashing”. This also means that insulin is released more slowly, which is particularly important for diabetics.

They fill you up and help with egestion

The fiber in complex carbohydrates is not digested, which means they help give you a feeling of “fullness”. This is especially great for people who are trying to lose weight as it means they end up eating less throughout the day. Complex carbohydrates are an excellent source of fiber.

Fiber also helps with egestion; another word for pooing. The fiber adds bulk to your stools, making them softer and easier to pass. Without fiber, visiting the loo would be a painful nightmare!

The foods that contain them are also a great source of essential vitamins and minerals

I am sure you have heard before how important vitamins and minerals are to your overall health. They are responsible for hundreds of different important roles in your body including supporting your immune system, healing wounds and helping to convert the food that you eat into energy. Particularly important vitamins and minerals include the B vitamins, vitamin C, vitamin D, vitamin K, iron, calcium and potassium.

Using our healthy food finder tool you will see that many legumes, fruits and vegetables are sources of these vitamins and minerals. They are also sources of complex carbohydrates.

The glycemic index and glycemic load


As seen above, carbs can be broken down into whole or refined, but another way to classify them is using the glycemic index. This is a common term used by nutritionists and dietitians.

The glycemic index gives you an indication of the effect a food will have on your blood sugar, both in terms of the speed and amount it raises your blood glucose by.

The index uses glucose as a reference to compare all other foods to – glucose has a glycemic index of 100. Below are some common foods with their glycemic index:

  • Apples – 38
  • Bananas – 52
  • Oatmeal – 58
  • White rice – 64
  • Brown rice – 55
  • Sweet potatoes – 53
  • Bagel – 72
  • Potato chips – 54

A much more important factor to take into consideration is the glycemic load of  a food.

This is calculated by taking the glycemic index of the food and multiplying it by the amount of carbs found in 1 gram of that food.

The same foods above have the following glycemic loads.

  • Apples – 6
  • Bananas – 14
  • Oatmeal – 12
  • White rice – 33
  • Brown rice – 23
  • Sweet potatoes – 13
  • Bagel – 38
  • Potato chips – 30

What you will quickly notice from the list above is that refined carbs have a much higher glycemic load than whole carbs. The refined carbs have a very high sugar content (with very little fiber) whereas the whole ones contain more fiber and water. This means that the whole carbs cause less of a blood sugar spike than the refined ones.

Reducing bad carb intake to aid weight loss


If you are trying to lose weight, following a low carb diet can be extremely effective. Many scientific studies have shown that low carb diets have a significant impact on weight loss, even more than low fat diets. Some of these studies include : 1, 2, 3. However it is refined carbs and those with added sugar which contribute to weight gain, not whole carbs.

The first thing you should do if you are trying to lose weight is eliminate all processed carbohydrates from your diet. This includes sugary drinks, most desserts, candy, and baked products like cakes & cookies.

Replace them with foods that are sources of whole carbs including vegetables, fruits, whole grains, nuts and seeds. Doing that alone will have a tremendous effect on your weight loss efforts.

Not all carbs are bad. In fact some carbohydrates are very important, especially for individuals who are lean and physically active – they tend to have fewer fat energy stores. Everyone is different and a lot of factors such as your age, gender, metabolic rate and weight play a part in determining how much carbohydrate you should consume. To get a better idea of what’s best for you, you should speak to a qualified dietitian or nutritionist before making any drastic changes to your diet.

That being said, to keep things simple you should eat those carbs which occur naturally and have not been processed in a factory. Conversely, stay away from carbohydrates that have had some kind of processing done to them as this strips them of fiber and other essential nutrients.

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