What are Carbohydrates?
Carbohydrates are a major component of the human diet. In this video, we will learn about their structure and how the human body metabolizes them. Carbohydrates are one of the three main macronutrients in the human diet. They come in many varieties, including breads, baked goods, and vegetables. In terms of their chemical composition, all carbohydrates are made out of carbon, hydrogen, and oxygen, and most have a ratio of one carbon for every one molecule of water. All carbohydrates can be classified as either simple of complex. Simple carbohydrates are often just referred to as sugars. There are two types: monosaccharides and disaccharides. Monosaccharides are the simplest form of sugar and the most basic unit of carbohydrates. There are three important monosaccharides in nutrition. The first is glucose, also known as blood sugar, which will be represented by this yellow hexagon.
The second is galactose, which is found is dairy products, which will be represented by this red hexagon. The third is fructose, which is found naturally in fruit, and will be represented by this blue pentagon. Two monosaccharides can be linked together via a hydrolysis reaction to form a disaccharide. There are three important disaccharides in nutrition. The first is maltose, which is formed by linking two glucose molecules together. Maltose is produced when starch is broken down as well as during the fermentation process that produces alcohol. The second is sucrose, which is formed by linking a molecule of glucose and fructose. Sucrose is commonly known as table sugar, which is the main ingredient in store-bought granulated sugar. The third is lactose, which is formed by linking a molecule of glucose and galactose. Lactose is the sugar found in milk.
Next, we have the complex carbohydrates. There are generally two types. The first are called oligosaccharides, which consist of 3 to 10 monosaccharides. The second type are called polysaccharides, which consist of any molecule made out of more than 10 monosaccharides. In the field of nutrition, there are three important polysaccharides. They are glycogen, starch, and fibre. Each one will be discussed next. Glycogen is a highly-branched polymer consisting of hundreds to thousands of glucose monosaccharides. In the human body, we store glucose in the form of glycogen for later use. It is predominately stored in the liver and muscles. Similar to how the human body stores glucose as glycogen, plants store glucose in the form of starch. The first is amylose, which is a linear chain of glucose molecules that form a spiral structure.
The second is amylopectin, which is a branched chain of glucose molecules. Both chains can contain hundreds to thousands of glucose molecules. Starches make up a large part of our diet. They can be found in grains such as rice, legumes such as peas, and root and tuber crops such as carrots. Dietary fibres are found in all plant-derived foods. Fibres make up the structural parts of plants, such as cell walls. Fibres consist of mostly polysaccharides that cannot be broken down our digestive enzymes, meaning they provide little to no energy. There are two general types of fibre: soluble fibre and insoluble fibre Soluble fibre is the first type of fibre. It can be dissolved in water and although we cant digest it, it can be digested by bacteria in our colon. Soluble fibre can be found in oats, legumes, and citrus fruits. It is thought to assist in promoting a healthy heart.
Insoluble fibre is the second type of fibre. Unlike soluble fibre, it cannot be dissolved in water and is not easily digested by the bacteria in our colon. Insoluble fibre mostly passes through us undigested. It assists in promoting bowel movements and alleviating constipation. When we eat carbohydrates, through digestion the body breaks them down into their monosaccharide components, mostly glucose, that the body can later absorb and use for its energy requirements. As soon as we consume carbohydrates, they immediately begin being digested in the mouth by the mechanical action of chewing and enzymatic action. Starch is broken down by an enzyme called amylase, which is present in our saliva. Amylase breaks down starch into maltose and other small polysaccharides. Food usually doesnt stay too long in the mouth, so little digestion occurs here.
When swallowed food enters the stomach, most of the amylase enzymes are inactivated by stomach acid, which can further break down starch to a small extent. However, very little carbohydrate digestion occurs in the stomach. Next, the swallowed food makes its way to the small intestine, which is where the majority of carbohydrate digestions occurs. Here, an enzyme called pancreatic amylase continues breaking down starch into smaller polysaccharides and maltose. This occurs until we are left with only maltose disaccharides. From here, specific enzymes break down specific disaccharides into their component monosaccharides. An enzyme called maltase breaks down maltose into two glucose molecules. An enzyme called lactase breaks down lactose into one glucose and one galactose molecule. Another enzyme called sucrase breaks down sucrose into one glucose and one fructose molecule.
Dietary fibre on the other hand cannot be broken down by our digestive enzymes, so it travels mostly undigested into the large intestine. Once here, it can be broken down by bacterial enzymes, which produce short-chain fatty acids and gas As mentioned, after digestion the monosaccharides glucose, galactose, and fructose are produced in the small intestine. From here, these monosaccharides are absorbed by the cells lining the small intestine called enterocytes. Glucose and galactose are transported across the cell membrane by the sodium-glucose transport protein-1. This process is powered by a sodium potassium pump that requires ATP. Fructose is transported by the transport protein called GLUT5.
Once inside the enterocyte, all three monosaccharides are transported out the other side of the cell into the bloodstream by the GLUT2 transport protein. Once inside the bloodstream, all monosaccharides are transported to the liver via the portal vein. Inside of the liver, most of the fructose and galactose is immediately processed, often being converted into glucose or other products. As for glucose, some of it can be absorbed by the liver to be stored as glycogen. The rest is transported back into circulation where it can be taken up by cells for their energy requirements. Every cell in the human body relies on glucose as a source of fuel to some extent. This is especially true for the brain. After consuming a meal containing carbohydrates, the concentration of glucose in the blood rises. A healthy person should have a blood glucose level of around 5 mmol/L. Whats astonishing is that the human body has approximately 5 L of blood.
With a concentration of 5 mmol/L, this corresponds to approximately 1 teaspoon of dissolved glucose in our entire blood supply! Lets discuss how the body maintains its blood sugar levels next. Blood sugar levels are tightly regulated by the bodys hormonal control system. After a meal, blood glucose levels rise. This causes the pancreas to secrete the hormone insulin. Once insulin is in the bloodstream, it can stimulate the uptake of glucose into cells for energy, or stimulate the muscle or liver cells to store glucose as glycogen, or if there is too much glucose in the bloodstream, then insulin will stimulate the conversion of glucose into fat for storage. As time goes on, blood sugar levels will decrease. This causes the pancreas to release another hormone called glucagon into the bloodstream.
What in the world are Carbohydrates?
Let’s take a closer look at what carbohydrates are. So let Science Tyler come and put on my lab coat and find my glasses. Here we are all right, so for carbohydrates they are a living molecule made up of carbon hydrogen and oxygen. When something like this is primarily involved in dietetics, it forms a group of sugars and cellulose called saccharides. It is important to remember that very simple carbon is quickly converted into glucose in your bloodstream, then a spoonful of refined sugar will throw your body’s blood sugar level, and then you will get a high level of sugar. Then you will usually break down the phrase you have heard about empty calories in the food you eat, and what it means is basically that this is about simple carbon with added sugar. Since simple carbohydrates are not so good, let’s talk about complex carbon from foods based on complex carbon plants, which in a more complex sense have a more complex molecular structure and take longer to break down around the body. You can still get sugar at the end of the day. It takes longer to contain other useful nutrients as it is of a more complex origin and we are talking about fish foods with high fiber pasta grains. Others of the same kind can be called glycemic index in a spectrum or abbreviated as G. It is basically a measure of how quickly blood glucose or sugar levels rise after eating certain foods. It is a simple carbon and complex carbon glycemic index with a low GI score of about 10, producing pea rye and white bread between 70 or 71. So carbon is important but y you need to make up part of the energy you need to eat the right type of carbon. If you eat too much, most of your carbon should be complex carbohydrates. The result is a very simple weight gain. It’s not a bad idea to have a plate in front of you and take 1/4 of a pie and put a high protein ingredient in it and take another quarter of that plate and think of it as a high carb content rice potato. Whatever the other half of the plate, you can’t go wrong with about 25% protein, about 25% carbon and 50% fresh vegetables.