What are carbohydrates?
Carbohydrates are molecules composed of carbon, hydrogen, and oxygen atoms. Since the ratio of hydrogen to oxygen atoms in carbohydrates is usually the same as the water that's the reason they are called carbo+ hydrates as in watered carbons.
What are the function of carbohydrates in the human body?
It has 3 main functions:
To supply energy to the body when it breaks down into glucose in the blood stream. Glucose is the brain's preferred source of fuel.
To prevent the breakdown of fatty acids in ketosis.
It has a protein-sparing effect i.e proteins are spared from breaking down to glucose (through gluconeogenesis).
Other functions:
Provide fibre that may be beneficial for certain medical conditions.
Production of glycosaminoglycans (GAGs), that play a crucial role in the cell signaling process, including regulation of cell growth, anticoagulation, and wound repair.
How are they classified?
Carbohydrates are classified as simple or complex. Simple carbohydrates with just one sugar molecule are called monosaccharides. They are glucose, fructose and galactose.
Foods high in glucose are honey, dried apricots, dates and prunes (dried plums). Foods high in fructose are honey, raisins, dates and dried figs. Foods high in galactose are mostly dairy due to them being high in lactose too. Besides dairy such as low-fat cheese and low-fat yogurt, galactose is also found in celery and cherries. When two monosaccharides combine, they form a disaccharide.
Examples of disaccharides are:
Sucrose= glucose + fructose
Lactose= glucose + galactose
Maltose= glucose + glucose
Sucrose is a natural plant sugar - cane sugar, brown sugar, palm sugar, maple syrup, sweet potato and table sugar are all high in sucrose. Foods high in lactose are all dairy products and infant formula. Foods high in maltose are breads (even sourdough), bagels, pancakes and sweet potato.
Complex carbohydrates are many single monosaccharides linked together and when hundreds of monosaccharides are linked together they are called Polysaccharides.
Complex carbohydrates are made up of sugar molecules that are strung together in long, complex chains. When they have 3 to 10 sugar molecules they are called oligosaccharides and when more than 10, they are polysaccharides.
Note: both simple and complex carbohydrates are turned to glucose (except fibre) in the body and are used as energy.
Types of Complex Carbs
Two known types of complex carbs are starch and fibre. Depending on how fast or slow starches take to digest and broken down, they can be categorized into rapidly digestible starches (RDS), slow digestible starches (SDS) and resistant starch.
Starches- are broken down by the enzyme Amylase, produced by the pancreas, into maltose (refer previous post about maltose). Usually RDS are high on the glycemic index. Excess consumption of RDS foods can lead to insulin resistance due to sustained high levels of insulin over time. Resistant starch resist digestion (hence the name) in the small intestine and ferments in the large intestine, acting similar to fibre.
R.D.S - white bead, pasta, white rice, baked or cooked potatoes.
S.D.S - white flour, lentils, roots/tubers like cassava, brown rice.
R.S - kidney beans, green bananas, peas, oats
Note: Glucose from sugar and starch are stored in the liver and muscles as glycogen. The body has limited capacity to store glycogen, so excess glucose is then converted to fat and stored in the adipose (fat cells) tissues through the action of insulin.
Fibre - Dietary fiber or roughage is the portion of food that cannot be completely broken down as the human body does not have the required enzymes for this to happen. Fibre adds bulk to our stool. It can be grouped (based on its properties) by their solubility, viscosity, and fermentability. For now, we'll stick to soluble and insoluble fibre. Soluble fibre dissolve in water and form a gel-like substance. Examples - pectin, gum, mucilage. Insoluble fibre, as the name suggests does not dissolve in water. Examples - cellulose, lignin.
Food sources for soluble fibre - apple with skin, barley, oats, beans, carrots.
Food sources for insoluble fibre - almonds, potato, lentils, avocado, apple.
Note: Short chain fatty acids are produced when fibre and resistant starch are fermented in the large intestines.
What is The Glycemic Index?
The glycemic index ranks food from 1-100 based on how quickly they are digested and get into your bloodstream. The higher the food is ranked, the quicker it raises your blood glucose levels. Rapid glucose conversion is something you want to avoid, as your body performs best when sugar levels stay consistent.
Note: G.I measures how 50 grams of carbohydrate of a certain food will cause your blood sugar levels to rise.
What is Glycemic Load?
Glycemic load is based on the glycemic index (GI), and is calculated by multiplying the grams of available carbohydrate in the food by the food's glycemic index, and then dividing by 100.
Note: G.L factors in how much of a specific food you would need to eat to obtain 50 grams of carbohydrate.
Which is more helpful?
The Glycemic load will help you know how high your blood sugar could go when you actually eat the food, and this measurement also lets you know how much glucose per serving a particular food can deliver. On the other hand, the lower a food's glycemic index, the slower blood sugar rises after eating that food.
Let's take the example of Watermelon. The glycemic index of watermelon is 72, which is very high—meaning that is causing your body’s blood sugar levels to rise rapidly. However, watermelon is just that, mostly water. The glycemic load in a serving of watermelon is only 4, which is extremely low, as the carbohydrate content of watermelon is very small. So, while your blood sugar levels may rise quickly, they will not remain elevated for very long, as there is very little carbohydrate in watermelon. (Another reason why I allow watermelon in the food plan of folks on my Fitness packages who have moderate to high intensity workouts)
What about fruits and fructose?
The fructose content in specific foods is not measured independently by the glycemic index or the glycemic load. Fructose is considered to be a low GI food, with a value of 19, meaning it causes less insulin secretion than glucose. Naturally occurring fructose is actually ranked lowest on the GI scale of all natural sugars. This is because fructose does not raise blood glucose levels, but rather blood fructose levels. Your body needs glucose for energy. Unlike glucose, fructose cannot be directly used as an energy source by all cells of the human body and needs first to be converted into glucose, lactate or fatty acids in the liver, intestine and kidney.
Conclusion...
So can we have a lot of fruits, just because they have low G.I and G.L numbers? NO! High levels of fructose in your body is not good, as it can cause cell damage. In fact, excess fructose in your body causes 7x more cell damage than excess glucose. This is another reason why you have to be careful when judging foods solely by their glycemic index value. Excess fructose consumption isn’t good for you, even though its glycemic value is only 19.
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