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Updated 15 October 2015

Why you need carbs

People seem to regard carbohydrates as "Public Enemy No 1" when it comes to losing weight, participating in sport or trying to build muscles, says DietDoc.

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I have once again received so many questions from readers about carbohydrates that I feel compelled to address the issue of carbohydrates again.

Knee-jerk reaction

The first food group that most people dump when they decide to lose weight, is always carbohydrates (starches and sugars). Many potential slimmers proudly report that they have cut out all sugar, bread, pasta, rice and other carbohydrates to lose weight and then add that they can’t understand why they are not losing or only losing small amounts of weight at irregular intervals. These slimmers usually also complain that they are constantly tired and find it hard to do exercise as part of their weight reduction regimen.

Many sportsmen and women are just as misinformed about the role of carbohydrates in their diets. “I aim to build muscle and get my six-pack, so I have cut down on carbs and am concentrating on protein” is a well worn refrain that I hear from budding bodybuilders. Then there are the cases of runners or cyclists who complain that they are too exhausted to train, participate or finish their races. Some of these carbohydrate-starved individuals even get ill because they insist on stressing their bodies to the utmost without providing their muscles with the necessary fuel.

Are carbohydrates fattening?

Carbohydrates on their own in reasonable quantities, are NOT fattening. Basically one gram of carbohydrate provides 16 kJ of energy, which represents the lowest energy content of all the macronutrients.

Energy provided by macronutrients per gram:

Carbohydrate       - 16 kJ
Protein              - 17 kJ
Alcohol             - 29 kJ
Fat                  - 37 kJ

One can see that alcohol and fat are much more energy-dense than carbohydrates and protein, and fat has more than double the kilojoules found in carbohydrates.

As long as you eat carbohydrates like bread, rice, pasta, potatoes, porridges and breakfast cereals in sensible quantities without lashings of fat, you will be saving 21 kJ of energy for every gram of fat you avoid.

Carbohydrates with a high dietary fibre content like unsifted maize meal, wholewheat and brown or low-GI bread, brown rice, wholewheat pasta, high-bran cereals, oats, samp and crushed wheat tend to contain even less energy because the fibre ‘dilutes’ the energy content.

High-fibre carbohydrates are also rich in B vitamins and minerals and most of the listed foods have a low glycaemic index (GI) which makes them ideal for slimming and to counteract insulin resistance, diabetes, metabolic syndrome and other diseases of lifestyle such as constipation.

The best fuel

Energy balance studies have shown that carbohydrates are by far the best source of energy or "fuel" for physical activity and to maintain our Resting Energy Expenditure (REE). The REE is that amount of energy our bodies require to keep body processes like digestion, circulation, and breathing going. These processes continue even when we are asleep or resting and it is estimated that up to 75% of our energy requirements are used to maintain the REE. In other words, an adult woman with an energy requirement of 8400 kJ (2000 kcal) per day, will utilise as much as 6300 kJ (1500 kcal) for REE.

Carbohydrates are the best fuel available to human beings for physical activity because the body uses carbohydrates preferentially above fat and protein as a source of energy. Sportsmen and -women will know that glycogen is essential for sustained performance. Glycogen is carbohydrate that is stored in the liver and the muscles as a reserve supply of energy. After a strenuous exercise session or a sporting event, the glycogen stores are often totally depleted and need to be replenished before the athlete can exert him- or herself again.

Consequently serious athletes use carbo-loading before big events to ensure that their liver and muscle glycogen stores are at maximum levels. During and after a race these athletes also increase their carbohydrate intakes to replace their glycogen stores. Without carbohydrates, no athlete would be able to deliver a top performance.

Athletes planning their food intake should also always remember that carbohydrates have what is called a "protein-sparing effect". Thus it is more important to eat plenty of carbs when you are trying to build up your muscle mass, than to overload your body with protein. If you only eat protein and fats, your body will have to use some of the protein as a source of energy which means there is less protein available for muscle growth.

The Food-Based Dietary Guideline

The nutrition experts who compiled the Food-Based Dietary Guidelines (FBDG) for Healthy South Africans, regard carbohydrates as so important that they devoted one of the 11 FBDG exclusively to this macronutrient.

 “Make starchy foods the basis for most meals”

The public on the other hand, blithely cut out all carbohydrates in the erroneous belief that this will help them to lose weight, build a six-pack or improve their athletic performance.

Only individuals who have tested positive and are allergic or intolerant to certain carbohydrates (e.g. gluten allergy or intolerance to lactose in milk and dairy), need to cut out the offending carbohydrates. This does not mean that people with wheat allergies need to avoid all carbohydrates, they can still eat 100% rye bread, potatoes, sorghum, rice, maize meal, corn on the cob and fruits and starchy vegetables as a ready supply of energy.

The sensible approach is not to avoid carbohydrates, but to include low-fat, high-fibre carbohydrates in your diet especially if you do a lot of physical activity or participate in sporting events.

Any questions?  Ask DietDoc


Read more:

Weight loss: will you succeed?
Carbo facts for sport fanatics
The SA Food-Based Dietary Guidelines


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