Carbohydrates are probably the most important group of nutrients for you to understand when it comes to diabetes. They come in all shapes and sizes and really do consist of the good, the bad and the ugly. The bottom line, though, is that they are digested to release their simplest components: sugars!
The carbohydrates that we consume vary in terms of their structures and complexity. Some carbohydrate-rich foods are made up of a lot of fibre, with very few actually digestible elements that can give us sugars for absorption. These are the higher fibre foods such as grains, beans, pulses and so on. Others are very simple, meaning that they are either sugars that are ready or almost-ready for immediate utilisation, or that they are foods that require very little digestive effort in order for your body to liberate their sugars from them: think sweets, or white bread.
The more complex carbohydrates are called polysaccharides, meaning they are a very complex bundle of lots of sugars bound together (poly = many; saccharide = sugar). The more simple variety tend to come in the form of disaccharides, while the simplest of all are the monosaccharides, such as glucose. These distinctions will become drastically important later on. Being carb-wise will be one of the most important factors for safeguarding your future health.
MOUTH
Carbohydrate digestion starts almost immediately in the mouth. When we chew a food, we secrete saliva. This serves two purposes. Firstly, it softens the food and lubricates it in order to make it easier to swallow. Secondly, saliva contains an enzyme called salivary amylase. This enzyme kick-starts the first steps of carbohydrate digestion, beginning to break starches down into disaccharides (simpler sugar molecules). You may have noticed that when you chew a baked potato, you detect a sweetness from it pretty quickly. That taste is the simpler sugars being released by salivary amylase. This enzyme by no means liberates all of the sugars, it merely begins the process, to make things a little easier later on.
STOMACH
Very little digestion of carbohydrate takes place in the stomach. The stomach is an acidic environment and there are no enzymes present to break the complex bonds of polysaccharides. But stomach acid can break the disaccharide sucrose (the granulated stuff you put in your tea) into the monosaccharides fructose and glucose. Depending on the composition of a meal, foodstuffs can stay in the stomach for up to six hours (though the average is three or four). Food will leave in little dribs and drabs, rather than in a sudden flood. (This is going to be a vital thing to think about later on in this book, so I want you to remember this little nugget; it is an important justification for thinking about meal composition.) As soon as the food leaves the stomach, it enters the small intestine, where carbohydrate digestion continues.
SMALL INTESTINE
Once food leaves the stomach, it enters the small intestine. At this stage the pancreas releases an array of enzymes, including pancreatic amylase (the rock-hard big brother of salivary amylase), which splits polysaccharides (depending on composition) into disaccharides: sucrose, lactose and maltose being most common.
As these travel through the small intestine, the intestinal walls secrete enzymes called sucrase, lactase and maltase that split these disaccharides into their monosaccharide components, which are then ready for absorption.
The rate at which food enters the small intestine, the meal composition, as well as the complexity of the carbohydrates, will all be vitally important factors to consider later on. I know I keep saying that, but with good reason. All will become clear!
LARGE INTESTINE
Some of the more complex fibrous carbohydrates don’t get degraded too much by pancreatic enzymes and intestinal secretions. They are pretty tough customers and are resilient to much of the digestive onslaught. This is partly why they are so beneficial to health. Some of them do get broken down to a certain extent in the large intestine, by another unique method.
The large intestine is the home to a massive array of bacterial life. You have heard of probiotics, right? Those little bugs that come in little funky yogurt drinks, or capsules. Well, these are a small cross-section of the population of bacteria that live in our gut. These bugs play a vast array of important roles, but one of the things that they can do is ferment and break down certain complex carbohydrates. Some of the complex polysaccharides will ferment and break down into smaller components, releasing some sugars. They also release a range of fat-like compounds that can offer some localised repair to gut tissue.
Once carbohydrates have been digested and broken down into their smallest components, they are sent into the bloodstream as glucose ready for use. Once the body has taken as much as it needs, excess glucose is stored as glycogen (the storage form of glucose) in our liver and muscles, as a type of ‘rainy day fund’ for use later on.