Macronutrients

I intend for this to be a fairly basic but informative post regarding macronutrients- what they are and what bits of information about each of them are useful to know so that this can be applied practically to one's diet and saved in your nutrition knowledge bank as a tool for making future food choices and plans. Roughly speaking all food can be broken down into constituent macro- (from Greek makros "long, large") and micro- (from Greek smikros "small, little, petty, trivial, slight"... seems slightly harsh) nutrients. This post will focus on the macronutrients. 

As I am sure most people are abundantly aware foods are made up of Carbohydrates, Fats and Proteins, these are the 3 macronutrients, the big dogs so to speak. The nutrients big (macro) enough and bold enough to make it on to the back of every food packet across the land, and sea. "But what about fibre?" I hear you ask, well technically not a macronutrient and I will discuss that later, vitamins? salt? pffft too micro to be macro, sugar? well kinda. 

Carbohydrates

So lets kick this off with carbs. Not only because that sentence sounds good, but also they happen to fall first alphabetically. Carbohydrates provide our body with 4kcals per gram. When people think of carbs, the foods that most likely come to mind are bread, pasta, rice and potatoes. And these are all good examples of carb heavy foods- i.e. foods which contain a large proportion of carbohydrates, carbs we could say are their dominant macro. 100g of white rice for example contains 80g carbs, 7g protein and 0.7g fat - therefore it is very much carb dominant at 80% carbs. But while carbs are the dominant macro of rice, it isn't technically correct to say rice is a carbohydrate in and of itself as you can see it also contains other nutrients- protein, fat (macros) along with vitamins and minerals (micros) also.

Just what are carbohydrates then? Well, carbohydrates are macromolecules made from carbon, hydrogen and oxygen. They are structures of varying complexity (ooh mysterious). They are the structural materials which plants are made from. They are put simply, sugars and when consumed they provide our body with energy (kind of).

Carbohydrates fall in to one of four categories, which vary in complexity- monosaccharides, disaccharrides, polysaccharides and oligosaccharides

    - Monosaccharides - simple single (hence mono-) sugars for example glucose, fructose, galactose. These are the most easily absorbed of the four listed due to the relative simplicity of their structure requiring little in the way of digestion before being small enough to enter the blood stream. 

    - Disaccharides - made up of two basic sugars bonded together (hence the di- prefix), for example lactose (of milk fame) is made up of subunits of glucose and galactose, and sucrose (prefers the pseudonym table sugar) of subunits of glucose and fructose. When consumed and digestion occurs enzymes such as amylase or lactase (found in your mouth, stomach, intestine) must act to break the bonds between these subunits to leave the constituent simple sugar molecules which made up the disaccharide structure. These are then small enough to absorb in to the blood and transport around the body.

    - Oligosaccharides - a short chain of simple sugars 3-10 molecules in length (so larger than the puny 2 molecule long disaccharide). For example maltodextrin consists of a chain of glucose molecules and raffinose a chain composed of glucose, galactose and fructose molecules. These lesser known carbs are found in various food sources, raffinose in the delicious brussels sprouts, cabbage and broccoli. Maltodextrin is generally added to foods such as crisps and drinks to "improve mouth feel" (food just gotta have that good mouth feel). Just as with disaccharides, in order to digest these once consumed they will need to be chopped down in to their smaller simple sugar pieces by enzymes before being ready to be absorbed.

- Polysaccharides - are made up of long (and I mean long) chains of monosaccharide subunits, the term polysaccharide itself means many sugars, so I guess it has a lot to live up to, and it certainly does. They can consist of up to 10,000! subunits of simple sugars. That's 10,000 units of sugar all bonded together to form a chain. The best known of these goliaths are probably starch, glycogen and cellulose- all three are made up of many many subunits of the monosaccharide glucose. Polysaccharides must be broken down in to their smaller subunits prior to absorption in to the blood and this work again is carried out by our favourite little helpers enzymes, throughout the digestive system. 

So we can summarise the above information as such- monosaccharides are simple sugars which are easily absorbed- they can be easily absorbed into the blood across the oral membranes of the mouth on consumption or later in transit across the membrane of the small intestine (the first of the intestines in a food item's travels through the gut) they require no enzymatic action to break anything apart prior to absorption. All the other more complex saccharides (from Latin saccharum "sugar") the dis, oligs and polys all must be broken down in to simple sugars (monos) by enzymes before absorption in to the blood at some point along the small intestine. 

We can therefore say that all carbohydrates absorbed in to the bloodstream are monosaccharides no matter in what form they were consumed. The length of time from consumption to absorption will vary though depending on whether it is a mono- or a poly- saccharide that is eaten. But when push comes to shove what all carbohydrates, no matter the complexity, provide us is units of energy. 

Glucose is a simple sugar (sorry mate), a monosaccharide. Sometimes it links up with a ton of its buddies and creates a super structure polysaccharide called starch, but ultimately they all get separated when an enzyme comes and breaks up the party. So they're back in their glucose simple sugar form cruising around the blood stream. What use can we even make of this simple cruising glucose molecule? 

When glucose is travelling around in the blood it would be referred to as blood sugar (a term ubiquitous with diabetes). Insulin is a hormone produced by the pancreas and it is responsible for ushering glucose from blood to cells where it can be used by mitochondria to produce energy, or within muscle cells all of the glucose molecule buddies can be reunited and stored in a super chained up polysaccharide called glycogen. Another hormone Glucagon can then be used to break this back down in to glucose again at a later date as needed. 

In the cells of the body glucose, like all simple sugars, is used for energy. Or maybe that should read to produce energy. Strictly speaking the energy currency of the body is ATP (that's adenosine triphosphate to you, thank you very much), however in order to create this ATP it is glucose that is the crucial first component. You see, glucose is the key molecule used by humans to begin aerobic respiration. A (lengthy and wordy) process which to put it simply involves taking glucose and oxygen and undergoing a miracle transformation which ultimately creates carbon dioxide, water and ATP (energy). ATP is then used to  power amongst other things all muscular contractions (think biceps and quads, but also heart and stomach) as well as the brain, all of this is made possible thanks to glucose. 

To add confusion to the mix the body is actually capable of creating its own glucose through a process called gluconeogenesis (generation of new glucose - clever). This is a process whereby constituent components of fats and proteins can be magically transformed into glucose which can then be used to create energy. This is not a process that is constantly occurring in the body, nor is it a process which it is particularly favourable to be using as all it does is add a step, when actually glucose is easily available from diet. Putting this aside, the fact that glucose can be created within the body means, strictly speaking, glucose and ergo carbohydrates are not considered an essential component of the diet. They provide nothing to us other than energy (ok, ok, a means for creating energy). They do not, as we will see with fats and proteins, provide anything considered ESSENTIAL to the body for maintenance, growth or repair. 

Summary

Carbs provide our body with 4kcals per gram, they are all sugars, they come in simple and complex varieties, they help us create energy, they are technically a non-essential component of the diet. 

Lipids/Fats

Moving on to the macro that everyone loves to hate, the macro that is surely the most misunderstood, the macro that just can't seem to catch a break, it's fat. I feel the need to make it clear that 'Lipids' is actually the technical term for a group containing fats and oils. Fats are solid at room temperature and oils are liquid. However colloquially we just call them all fats and that's where it gets confusing to talk/write about the subject as you will surely find out - I am just going to refer to this macro group as fats however it would probably more accurately be called lipids.

Fats (lipids) provide our body with 9kcals per gram. When people think of fats the foods that most likely come to mind are butter, oils, nuts, cheese and olives. And these are all good examples of fat heavy foods- i.e. foods which contain a large proportion of fat, fat we could say is their dominant macro. 100g of butter for example contains 81g fat, 0.9g protein and 0.1g carbs - therefore it is very much fat dominant at 81% fat. But while fat is the dominant macro of butter, it isn't technically correct to say butter is a fat in and of itself as you can see it also contains other nutrients- protein, carbs (macros) along with vitamins and minerals (micros) also.

Fats are triglycerides, they are made up a molecule of glycerol with three fatty acids attached (hence tri), it is these fatty acids that we will be paying most attention to later. Fats are insoluble in water. They are ubiquitous throughout nature and can be found in large amounts throughout both animal and plant foods. Fatty acids, the sub-units of fats, are the main building materials of our brain and nervous system. They provide structure to every cell in our body in the form of the cell membrane. 

When consumed fats as triglycerides undergo lipolysis in the small intestine, glycerol is separated from the fatty acids. The free fatty acids can be used as energy through a process called fat metabolism whereby the fatty acids undergo beta-oxidation which converts them in to acetyl coenzyme A (Acetyl-CoA) molecules which can then be used in the same process as glucose - that is respiration - to create our energy unit, and all round great guy, ATP.

Dietary fats can be classified in to distinct types dependant upon their structure and the types of fatty acids they have.

    - Saturated fats - the fatty acids of saturated fats (SFAs) are made up of a carbon chain with single bonds, they do not have any double bonds between carbon atoms. SFAs are more stable in their structure as the carbon atoms are fully saturated with hydrogen atoms (makes sense). Saturated fats are more solid at room temperature. Rich dietary sources of SFAs are mostly animal fats - tallow, lard, butter, milk, cheese, but also coconut oil and palm oil. 

    - Unsaturated fats - the fatty acids of unsaturated fats (UFAs) have carbon chains with one or more double bonds, they are divided in to two groups depending on the number of double bonds (mono- and poly-). UFAs are more unstable than SFAs as they are not fully saturated (duh), this also means they are more vulnerable to rancidity. They are also less solid at room temperature as a result of being less saturated.

    - Monounsaturated - the fatty acids of monounsaturated fats (MUFAs) have a single double bond (that makes sense). The most common found in the human diet is oleic acid, this is a major constituent of olive oil. These fats are more stable than polyunsaturated due to having less double bonds, they are therefore more resistant to oxidative stress than polyunsaturated fatty acids.

    - Polyunsaturated - the fatty acids of polyunsaturated fats (PUFAs) have multiple double bonds. There are two classes of PUFA- Omega 3 and Omega 6 (ah, we've been expecting you). The distinction between the two relates to where the first double bond resides within the fatty acid. In Omega-6 it is between the 6th and 7th carbon atom and in Omega-3 between the 3rd and 4th (that checks out). Omega-3 and Omega-6 are known as essential fatty acids, as humans cannot create them within the body and therefore must ingest them. Polyunsaturated fatty acids are classed as unstable compared to saturated due to the fact that their Carbons are not fully saturated with Hydrogen atoms.

    - Trans - trans fatty acids exist in nature in trace amounts in milk and meat, this is one version of trans fats. There are also artificial trans fatty acids, human-made as a direct result of the hydrogenation process, an industrial process which adds hydrogen to fatty acids enabling them to be converted from polyunsaturated to saturated fats. This process is used (was used in the past more so before the dangers of trans fats were identified) in the creation of margarine, the process is utilised to turn a proportion of the primarily polyunsaturated fatty acids in oils such as rapeseed oil in to saturated fatty acids making them more stable and more solid at room temperature so that they can be used as spreads and in making cakes (for any children you don't like). These fats would then be termed partially-hydrogenated vegetable oils (mmm sounds delicious). The human made trans fats which occur as a result of the hydrogenation process are different in structure to the naturally occurring trans fats found in small amounts in milk and meat. Substantial evidence has shown that consumption of hydrogenation produced trans fats i.e those in margarine made from partially-hydrogenated vegetable oil has been shown to increase the likelihood of fatty liver disease, insulin resistance (ergo diabetes), cardiovascular disease and cancers. So please do watch out for the term partially hydrogenated vegetable oils on all foods (or preferably don't buy foods where you need to check a label).

Summary

Fats(lipids) provide our body with 9kcal per gram. They are actually triglycerides and consist of a glycerol head and three fatty acid tails. The fatty acids can be saturated or unsaturated (mono- or poly-). Saturated are more stable and more solid at room temperature e.g butter. Unsaturated are less stable and less solid at room temperature e.g oils. They can be used for energy through conversion to acetylCoA. Omega-6 and Omega-3 fatty acids are important structural components of all cells - making up all cell membranes. They are also important structural components of the brain, making up high proportions of grey matter and playing a crucial role in nervous system function. O-3 and O-6 are essential, meaning they must be consumed in our diet, because our bodies do not have the apparatus to manufacture them ourselves. P.S avoid artificial trans fats at all costs.

Proteins

Last but by absolutely no means least we have proteins. Proteins provide our body with 4kcals per gram. When people think of proteins the foods that most likely come to mind are chicken breast, steak, tuna, eggs, milk, and also (I write this begrudgingly) quorn, legumes and tofu (my begrudging attitude will be clarified at later date when I post regarding the disparities in bio-availability of amino acids from plant and animal sources, but also those three things taste like crap in my humble). These are all examples of protein heavy foods- i.e. foods which contain a large proportion of protein, protein we could say is their dominant macro. 100g of tuna for example contains 28g protein, 1.3g fat and 0g carbs - therefore it is very much protein dominant with regards to macros. But while protein is the dominant macro of tuna, it isn't technically correct to say tuna is a protein in and of itself as you can see it also contains other nutrients- fat, trace carbs (macros) along with vitamins and minerals (micros) also.

Proteins are biopolymers made up of many amino acids. Proteins are described as having up to four structural levels (primary, secondary, tertiary and quaternary). Amino acids connect in a sequence to make up a polypeptide chain (primary structure). The chain is folded in certain ways due to interactions between atoms of the chain thus forming a secondary structure of a repeated pattern, this can be a sheet or a helix pattern. Further interactions and bonds between groups of amino acids within the chains then make up its 3-d tertiary structure. And finally a protein with more than one polypeptide chain can form in to a quaternary structure. Anyway... enough with all that stuff, let's just say for simplicity that amino acids are the building blocks of proteins, amino acids align in a sequence to create polypeptide chains, polypeptide chains fold and interact in certain ways to form the 3-d structures of proteins.

Amino acids are made up of an amine group, a carboxylic acid group and a side chain (R). The side chain (R) varies between different amino acids. There are quite a few amino acids around, 20 are classified as common amino acids. These 20 are the building blocks of animal and plant proteins. These various animal and plant proteins found in nature contain different amounts of each amino acid within their primary structure giving them differing protein (tertiary/quaternary) structures (see, all that rambling in the last paragraph is helpful). 

Here for your enjoyment are the 20 common amino acids listed in alphabetical order (to keep it tidy): alanine, arginine, asparagine, aspartic acid, glutamic acid, cysteine, glytamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine (a really fun one to say), proline, serine, theronine, tryptophan, tyrosine and valine. Love a list.

Nine of these are said to be essential, meaning they can not be synthesized by the human body and must be ingested (just like O-3 and O-6 fatty acids). These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, theronine, tryptophan and valine. That's right I made another list for you to not read. 

The other amino acids would therefore be classified as non-essential, as your body is able to synthesise them itself using the essential amino acids that you, hopefully, consume. However in times of illness, stress or consuming a diet low in the essential amino acids make it more difficult for this synthesis to occur. That's right, not consuming enough essential amino acids makes producing non-essential amino acids difficult, therefore they are required more so through diet, thus making them essential - wrap your head around that one.

To make it slightly more complicated arginine, cysteine, glutamine, glycine, proline, ornithine, serine and tyrosine, are considered to be conditionally essential. The body's ability to synthesise them is insufficient during physiological periods of growth such as pregnancy, puberty and trauma recovery.

Proteins are a fundamental molecule of life and therefore the amino acids that make them are crucial components of our diet. Proteins make up around 15-20% of our body mass.  Once consumed protein is broken down in your small intestine into its constituent amino acids by enzymes called proteases. These amino acids are then used to synthesise and repair all of the proteins needed throughout your body (which is a lot, as mentioned). Your muscles, bones, skin, organs, blood cells, antibodies, hormones, neurotransmitters, enzymes (and more) are all proteins or mostly made up of proteins. Abundant processes throughout your body rely on proteins to work correctly. All of these proteins are synthesised with the amino acids you consume or manufacture (using the amino acids you consume). Underlining the critical importance of ensuring an adequate (at the very least) consumption of essential amino acids, not forgetting those conditional essentials during periods of growth.

Protein is broken down into amino acids and the primary use we then have for them is to re-synthesise them into proteins the human body needs to function. It therefore may not make much sense to say that protein offers us 4kcal of energy per gram (as I indeed did earlier). Amino acids can be used to produce energy, I am not going to detail how, because quite frankly you don't want to know (gluconeogenesis, transamination, deamination...). Suffice to say it is more difficult than conversion of sugars or fatty acids to energy, mostly because of the presence of nitrogen in amino acid composition. Using amino acids to produce energy (ATP- remember) is therefore third choice energy producing method (of three) and thus if there are sufficient sugars (glucose) and fatty acids around the third choice won't be utilised. However if we consume amino acids in excess they can be converted into fat and stored or into glucose and used for energy. 

Summary

Proteins are made up of many amino acids. There are 20 common amino acids. Amino acids are primarily used by the body to synthesise the proteins we require to function - muscles, skin, immune cells, enzymes, neurotransmitters, hormones etc. There are essential amino acids - which we need to consume within our diet. There are non-essential amino acids - which we are able to manufacture ourselves using the essential ones (there are also conditionally essential amino acids). Amino acids can be used to produce energy but it is a difficult process and they are third in line behind sugars and fatty acids as a fuel source.

Aaaaand breathe...

Ok well, that's quite enough of all that for now. But I hope that this wasn't too much and that you perhaps learned a thing or two along the way. My idea for this post is that hopefully it can serve as a good reference point to refer back to when reading future posts whereby I use a lot of the terms that I have tried to define here. I am sure a lot of the terms listed are in most people's general vocabulary, however whether people truly know their meaning is another question. I think the information here serves as a good foundation for further nutritional investigation.

Thanks for reading (I know you didn't read the lists of amino acids, but that's alright!)