Carbohydrates: The Quintessential Energy Source

By Dr. Sadhna Sharma

Carbohydrates, proteins and fats are macronutrients and are needed in large amounts in our body. Vitamins and minerals form the micronutrients and are required in small amounts by our body. All of these are necessary for physiological and biochemical processes of the human body and help assimilate and utilize food for carrying out activities and maintaining health. 

Carbohydrates are an essential part of any diet. Carbohydrates are the body's main source of energy. They are called carbohydrates because, at the chemical level, they contain carbon, hydrogen and oxygen. Carbohydrates are the sugars, starches and fibers found in fruits, grains, vegetables and milk products. Carbohydrates provide fuel for the central nervous system and energy for working muscles. They also prevent protein f r o m being used as energy source and enable fat metabolism. Carbohydrates provide the body with the energy it needs and are a good source of many vitamins. Our body uses these foods to make glucose, which is body's main energy source. Glucose is a type of sugar that can be used right away for energy or stored away to be used later. 

Quality Matters

Carbohydrates are either simple or complex, and are major sources of energy in all human diets. They provide energy of 4 Kcal/g.  The digestive system breaks down carbohydrates in foods and drinks into simple sugars, mainly glucose. This simple sugar is then carried to each cell through the bloodstream. The pancreas secretes a hormone called insulin, which helps the glucose to enter cells f r o m the blood. Inside a cell the glucose is ‘burned’ along with oxygen to produce energy. Red blood cells exclusively and the brain and nervous system mainly rely on glucose as their main fuel to make energy. The body converts excess glucose f r o m food into glycogen. Glycogen acts as a storage form of glucose within the muscle tissue and the liver. Glycogen supplement blood sugar levels if they drop between meals or during excessive physical activity. About 100gm of glycogen is stored in the liver which can supply a day of glucose need of RBC and brain during fasting. Our different body muscles store about 200-250gm of glycogen for need in increased physical exercise. 

The simple carbohydrates, glucose and fructose, are found in fruits, vegetables and honey, sucrose in table sugar and lactose in milk, while the complex polysaccharides are starches in plant products such as cereals, pulses, millets and root vegetables and glycogen in animal foods. The other complex carbohydrates mainly plant products are resistant to digestion in the human digestive tract are cellulose in vegetables and whole grains, and gums and pectins in vegetables, fruits and cereals, which constitute the dietary fibre component. In India, 70-80% of total dietary calories are derived f r o m carbohydrates present in plant foods such as cereals, millets and pulses. Dietary fibre retards absorption of carbohydrates and fats and creates a feeling increased satiety. Diets rich in fibre reduce glucose and lipids in blood and increase the bulk of the stools. Diets rich in complex carbohydrates are healthier than low-fibre diets based on refined and processed foods.

Managing Carbohydrates

Many people are confused about eating carbohydrates or not, but it is important to keep in mind to eat carbohydrates f r o m healthy foods than to follow a strict diet limiting or counting the number of grams of carbohydrates consumed.

One of the best weight-loss guidelines is to eliminate sources of simple sugars such as soda, sweets, candies, cakes, cookies, and similar snack foods. One needs to choose foods with few or no grams of simple sugar. Other carbohydrates to eat in moderation or avoided entirely include white rice, white potatoes, white bread and fruit juices, especially those with added sugar. These carbohydrates are rapidly digested and absorbed and cause a sharp rise in blood sugar. This causes increased insulin release, making it easier for your body to store fat. It also contributes to insulin resistance. 

Rapidly absorbed carbohydrates aren’t as satiating either. When one eats carbohydrates that are quickly absorbed, it raises blood sugar and drops it quickly. This stimulates portions of our brain that trigger cravings, meaning one’ll be looking for next meal sooner. Some research even shows that processed and refined carbohydrates activate a portion of the brain called the nucleus accumbens that’s linked with addiction.

Whole foods are also more filling because your body has to work harder to digest them, and they move more slowly through your intestinal tract. High-fiber carbohydrates f r o m whole food sources have a greater “thermal effect,” meaning your body has to expend more energy to digest and process them. That gives our metabolism a temporary boost so it burns more calories.

A deficiency of glucose, or low blood sugar, is called hypoglycemia. Carbohydrates are the primary fuel source for muscles and eating a diet deficient in healthy Carbohydrates could leave one feeling exhausted, especially for those who regularly work out.  A low Carbohydrate diet can also interfere with ability to build lean body mass since body breaks down a certain amount of protein to amino acids to use as energy when one have depleted glycogen stores i.e. during starvation or diabetes mellitus. Where does that protein come f r o m? Primarily, muscle tissue! That’s not what one wants if one is trying to build lean body mass. Using protein for fuel instead of carbohydrates also puts stress on the kidneys, leading to kidney damage. Additionally, without sufficient glucose, the central nervous system suffers, which may cause dizziness or mental and physical weakness. People who don't consume enough carbohydrates may also suffer f r o m insufficient fiber, which can cause digestive problems and constipation.

Plan your Carbohydrate Diet

A balanced diet should provide around 50-60% of total calories f r o m carbohydrates, preferably f r o m complex carbohydrates, about 10-15% f r o m proteins and 20-30% f r o m both visible and invisible fat. The glycemic index (GI) is a new way to classify foods and drinks according to how quickly they raise the glucose level of the blood. It is replacing classification of carbohydrates as either simple or complex. The GI scale ranks carbohydrate-containing foods based on their effect on blood sugar levels over a period of two hours. Carbohydrate-containing foods are compared with glucose or white bread as a reference food, which is given a GI score of 100. The GI compares foods that have the same amount of carbohydrate, gram for gram. Carbohydrates that break down quickly during digestion have a higher glycaemic index (GI more than 70). These high GI carbohydrates, such as a baked potato, release their glucose into the blood quickly.

Carbohydrates such as oats break down slowly and release glucose gradually into the bloodstream. They have low glycaemic indexes (GI less than 55). The blood glucose response is slower and flatter. Low GI foods prolong digestion due to their slow break down and may help with feeling of fullness. People with type 2 diabetes are resistant to the action of insulin or cannot produce insulin rapidly enough to match the release of glucose into the blood after eating carbohydrate-containing foods. This means their blood glucose levels may rise above the normal level if they eat a high GI food. Therefore for them, Porridge (low GI) is a better choice of breakfast cereal than cornflakes (high GI). It will also provide more sustained energy for people without diabetes.

The glycaemic load (GL) is another concept that builds on GI, as it takes into account both the GI of the food and the amount of carbohydrate in a portion. GL is based on the idea that a high GI food consumed in small quantities would give the same effect on blood glucose levels as larger quantities of a low GI food. GL is easily calculated by multiplying the GI by the amount of carbohydrates (in grams) in a serving of food.

A low GI diet has commonly been promoted as an effective way to help lose weight by controlling blood sugars and appetite. Eating low GI foods two hours before endurance events, such as long-distance running, may improve exercise capacity. On the other hand, high GI foods are recommended during the first 24 hours of recovery after an event to rapidly replenish muscle glycogen.

Some examples of the GI rating of various carbohydrates include:

  • Low GI (less than 55) – soy products, beans, fruit, milk, pasta, grainy bread, porridge and lentils
  • Medium GI (55 to 70) – orange juice, honey, basmati rice and wholemeal bread
  • High GI (greater than 70) – potatoes, white bread and short-grain rice.
  • In conclusion, maintaining an ideal body weight by eating the right kind and amount of carbohydrates is a prerequisite to a healthy life. It goes a long way in proper growth and development of the body and to stay active.  

The author is A. Professor, Zoology at Miranda House, University of Delhi 

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