A Carb is a Carb is a Carb… RIGHT!?
The war on carbohydrates has been raging for about 10 – 20 years now (depending on which side of the diet adoption curve you sit), and after vilifying fat, grains, dairy, meat, cooking, and certain proteins… I’m not looking forward to eating what’s left (well, at least not every day). It’s about time we sat back and had a look where this war on carb’s started, and approach this from a (hopefully) more objective vantage. In part 1, we’re going to look at what carbohydrates actually are, before getting into how we use them in part 2!
…Carb’s essentially mean glucose (end product). Glucose means fuel for your body. Where did we go wrong…???
Now We’re Cooking With Carbon!
So let’s get started! A carbohydrate is (oddly enough) a combination of carbon molecules, hydrogen molecules and oxygen molecules (think hydrogen + oxygen = water which hydrates => carbo-hydrate or hydrated carbon!) which are connected together with a covalent bond (generally called a glycosidic bond). The length/size of the carbohydrate (meaning how “complex” it is) is dictated by the number molecules connected together, with simple carb’s (like glucose, fructose, sucrose, lactose, galactose etc.) all being short, and with starches, fibres and other complex carb’s being longer. For carbohydrates to be absorbed they must be broken down into their basic constituent, which means they must be metabolised into single carbohydrate molecules (or, more correctly, a mono-saccharide). There are different kinds of monosaccharides which have different functions in the body, the most common of which is glucose (in its many forms), which is used for energy!
When a carbohydrate is eaten, enzymes in our saliva begin to break it down; so that when it reaches the stomach, your body has already begun digesting it (hence why people tell you chewing is so important). The glucose produced is absorbed in the small intestines and into the bloodstream where the body decides what to do with it. Its primary role should be to replenish glycogen stores in muscles (and organs, aka smooth muscle), as glycogen is the body’s primary source of fuel. Excess sugar is stored as fat (adipose tissue) to be used in times of scarcity (which is pretty much never if you live in a 1st World Country).
The takeaway here is that Glucose = Glycogen, and Glycogen = fuel source for the body! While that IS kind of necessary, there are obvious dangers of excessive carbohydrate consumption, but before we look at that… let’s take a quick meander to look at how carb’s are made.
Plant Magic (… Solar Power??)
There are times when one feels truly lucky to be able to share something special, and discussing photosynthesis is one of those times (bear with me…). Try to imagine having the power to use the sun’s light as energy… you now have every plant you’ve ever seen. Yes, we have now had solar power for all of seven minutes, but for the thousands of years before that we were outsmarted by shrubbery… and to some extent still are. To think that they require a little water and sunlight to grow belies the truly amazing nature of what’s really happening (and connects all living creatures), which would not be possible, were it not for all of the mind-boggling reactions happening in every cell of EVERY living organism!
When a plant absorbs water from the ground, it’s really absorbing hydrogen and oxygen (H2O). This means that when said plant now absorbs carbon dioxide (a carbon and two oxygen molecules) from the environment around it, it now has:
• A carbon molecule
• 2 hydrogen molecules
• 3 Oxygen molecules
Now, using the energy from the sun (and some rather complex reactions), a carbon, 2 hydrogen and an oxygen molecule are fused to make a carbohydrate that can be stored as fuel, and the remaining 2 oxygen molecules are released (as is the case when making the simplest possible carbohydrate, a C•H20). Plants are the only natural source of carbohydrates on the planet, as in they produce their own. All other life forms (us included) must ingest carbohydrates through their diet (the only carbohydrate produced by animals is lactose, produced by mammals). Seeing as we know that carbohydrates are the body’s primary fuel source (let’s not start arguing about ketogenic dieting just yet…), it’s clear how a better understanding of both plant based nutrition and carbohydrates will benefit our health.
Not All Carb’s Are Created Equal
Carbohydrates come in many, many forms. The simplest being a monosaccharide. Saccharide is just the scientific term to denote sugar, so every time you see the word saccharide you can just think single carbohydrate molecule.
Glucose, Fructose, Galactose, D-Ribose, etc.
Sucrose, Lactose, etc.
Mannitol, Sorbitol, Xylitol, Glycerol etc. (alchohol sugars)
Maltodextrin, Fructo-Oligosaccharides (FOS’s such as inulin), etc.
Starch (amylose/amylopectin) & Non-Starch (cellulose, hemi cellulose, pectin)
Monosaccharides are the foundation of all carbohydrates and are incredibly important for the body. While the term mono-saccharide describes that they are only 1 carbohydrate long, it’s a little misleading in that this one molecule can itself be different lengths depending on the monosaccharide in question. The most common monosaccharide is glucose (which has a 6 carbon chain), though there are other kinds, including fructose and galactose. D-Ribose has come to prominence recently due to its part in energy creation (it’s used in the creation of Adenosine, which is used to form both ATP and RNA) and may have potential therapeutically for some ailments, though much of this requires further research. It has been tested as a means of reducing symptoms in fibromyalgia and, anecdotally, seems to have some success. It has also been tested with some success on ischemia though, again, these were both adjunct treatments, not a primary means to deal with these ailments.
One area of contention with regards monosaccharides is their metabolism. Some monosaccharides are metabolised in the liver (fructose and galactose) which can cause confusion for consumers. By being metabolised in the liver, they don’t cause the same glycemic spike that other sugars do, causing many to believe that they are healthier than other high GI carbohydrates. This (and other issues) has led to the understanding that the GI index is a somewhat limited tool for analyzing how appropriate certain carbohydrates are. Carbohydrates metabolised in the liver can also, if consumed in excess, put undue pressure on the liver and even lead to fatty liver deposits. This isn’t to say that fructose or galactose are bad, they are healthy and useful but should be eaten in moderation.
Next come di-saccharides. These, as you can see in the diagrams below, are just 2 simple sugars connected. They are connected by a “glycosidic bond”. These will generally be digested down into simple sugars and absorbed in the intestines. Disaccharides are extremely common sugars (such as sucrose – a glucose and fructose molecule, maltose – two glucose molecules, and lactose – a glucose and a galactose) and are metabolised using special enzymes that break down the glycosidic bonds
Issues with lactose can occur due to a lack of the metabolatory (that’s a completely made up word) enzyme (lactase) needed to break down the bond holding the two sugars together. At birth, our levels of lactase are quite high due to the fact that all of our sustenance would have come in the form of milk. As we get older, our lactase levels drop significantly. This is more prevelant in people of Asian (and sometimes African) ethnicity, whereas Caucasians tend to be better equipped to metabolise lactose.
There have been studies done in recent years that show the medicinal benefits of Trehalose (a disaccharide found in mushrooms) which can increase apoptosis, though it must be taken intravenously as oral consumption will result in it being broken down by trehalase (the enzyme for breaking down trehalose) into it’s singular counterparts (glucose). Oddly enough, it has also been found to be very effective against dry eyes and is now used in some eye drop formulas. While both trehalose and maltose have 2 glucose molecules, they differ in the bonds that hold the 2 glucose together.
Polysaccharides are complex carbohydrates, meaning starches, fibre and any other carb’s of substantial length. These generally fall into 2 categories: soluble and insoluble fibre. Soluble fibre generally expands in the stomach and slows the digestion of food. It is useful as a diet aid, as it can help you to feel full and reduce food cravings. It is also helpful in regulating blood sugar, as it can lower the glycemic response. Insoluble fibre (aka “ruffage” roughage) is actually just a carbohydrate that your body isn’t able to break down. As was mentioned before, complex carb’s are really chains of carbohydrates attached with bonds. If we don’t have the correct enzymes to break down these bonds, that carbohydrate will pass through our body undigested (hence fibre having little or no calories).
While we discussed above that carb’s come in different groups/categories, it may be more useful to think of them in other terms. The problem is this: Carb’s are generally absorbed in the small intestines, but not all carb’s can be metabolised and therefore end up in the large intestines. These carb’s will ferment and either be partially digested or not digested at all, MEANING that they will have varying degress of glycemic response and will offer less calories to the body.
With this in mind, it can be misleading to call a carb complex or simple and assume that this classification gives clear indication to the biological properties of the carbohydrate in question. For example, some complex carb’s (think modified carb’s like Vitargo) are metabolised very quickly, while a simple di-saccharide like fructose is actually metabolised more slowly. From a health (and even sports performance) perspective, it makes sense to look at some of the other classifications used!
Starch and Non-Starch Polysaccharides
This is a division in the complex carb category and is really a means of distinguishing between the major starches (Amylopectin and Amylose) and other forms of complex carb’s. Carb’s such as “fibre” (Hemicellulose) and Cellulose (pictured in the first set of carb diagrams) are non-starch and therefore make up the second half of the category, which is primarily seen as non-digestible carbohydrates. This isn’t entirely true as Pectin is a non-starch carbohydrate, but is partially digested which, as you will see below, is a vitally important distinction. Also, there are “resistant starches” which, while they are starches, cannot be broken down in the small intestines. The next two classifications provide a better way of approaching carb’s for your diet.
Soluble / Insoluble Fibre
This is primarily a means of distinguishing between digestible and non-digestible non-starch polysaccharides (NSP’s). NSP’s were shown to have different digestion/break down points in different pH environments, thus leading to the understanding that some NSP’s wouldn’t be broken down in our stomach. For our purposes though, Soluble Fibre (which is partially broken down in the stomach) slows down the digestion of other nutrients and can slow the absorption of glucose. It can also increase the feeling of fullness. Insoluble fibre, on the other hand, is very important both for keeping “transit” regular, and for maintaining healthy gut microbiota. Not all carb’s fall neatly into one of these ends of the soluble/insoluble spectrum, and pectin (mentioned above) is a soluble carb that helps slow absorption of cholesterol and sugar AND it also acts as a “prebiotic” in the large intestines by fermenting and feeding the bacteria there.
Another important point to note is that, contrary to popular belief, eating more insoluble fibre is not always better and can actually exacerbate conditions like constipation and IBS instead of healing them. If you are eating a balanced diet of leafy greens, tubers/roots, fruit, and grains, you should have enough “roughage” in your diet.
Available and Unavailable Carbohydrates
This terminology is worth mentioning as it is in some ways the clearest of all, and definitely allows for a good grasp of what a carb will do and what it’s useful for (allergies and intolerances aside). Any carb that is absorbed in the small intestines (starch and soluble carb’s) would contribute to sugars in the body and provide calories. Any carb that was not digested in the small intestines (mostly the NSP fibres cellulose and hemicellulose) would not contribute to glycemic load or calories. As with all carb classifications, the available/unavailable category should really be thought of as a spectrum, as most complex carb’s will be partially digested to varying degrees, meaning they will also provide some calories and feed your gut bacteria (or in some cases cause an upset stomach).
At this point it’s worth trying to clarify things a little, as all the terminology can get a bit overwhelming. Keep in mind that all we’re trying to do here is understand carb’s themselves (in isolation), before looking at how they impact on health (diabetes, obesity, fatty liver, etc.), sports performance, and digestion in Part 2. From a general health perspective, carb’s could be broken down into 5 categories:
Fast Acting, Slow Acting, Fermenting, Nutritive, Problematic