Macro is Latin for large, and micro is latin for small. Macronutrients are compounds that you need to eat bowls of every day to survive. This is commonly known as food. Micronutrients are required only in trace amounts, but they are just as necessary. These are vitamins and minerals. You can go weeks without certain vitamins, but eventually it catches up with you. More on this in a later article.
there are three kinds of macronutrients: proteins, carbohydrates, and fats, also known as oils. Let's look at these one at a time.
Proteins are the structures of life, the compounds that build muscle, skin, organs, enzymes, and even some of the neurotransmitters that facilitate thought. They build you and me, and animals, and plants, and bacteria, and all life on earth. Assembling a protein is a bit like playing with lego. There are 20 different blocks to choose from, 20 different pieces, 20 different amino acids. You might have the standard 2 by 4 brick, (the workhorse of lego construction), the 2 by 3 brick, the 2 by 2 brick, the 1 by 8, the 4 by 8 flat, the wheel and axel, the 6 dot window, the 4 dot slanted roof, the 10 by 20 base, the 2 by 2 tile, and 10 others. amazing how many things you can build using these 20 pieces. But wait, the protein in meat is already assembled. When you eat a hamburger, you must digest the protein and take the bricks apart, then reassemble the pieces according to your needs. If you couldn't do this you'd have no use for cow protein, unless of course you were a cow. Every animal would have to be a cannibal to survive, and that is rather impractical. So all life on earth, even bacteria, has the ability to take proteins apart and put them back together according to the DNA blueprint that determines who we are.
If you're an adult, like me, you're not growing any more, at least not in a good way. You don't need a lot of protein for construction purposes, though you do need to replace dying blood and skin cells, and repair minor injuries as they occur. Dieticians agree; the meat on your plate should be the size of a deck of cards. And yet we eat more than that, don't we? Double cheese burger, 10 ounce steak, meat lover's omelet, giant slab of ham, and the like. The excess protein provides net energy as you take the blocks apart, break them down, and excrete them. What we don't require for maintenance we use as fuel. This is not surprising. Evolution hates waste. If you couldn't take advantage of a food source that was close at hand, one of your cousins, with different genes, might. He would survive through the famine, while you did not. His genes would propagate into the next generation, while yours did not. This mechanism is universal, and thus there just isn't any waste in nature. By now, 3.5 billion years after life began, we can all make use of protein, as building blocks for life or as an energy source.
The next molecule is comparatively simple. The glucose molecule, the most common form of sugar, has 6 carbons, 6 oxygens, and 12 hydrogens arranged in a ring structure. This is currency for energy storage, like putting money in the bank. Honey, for example, is almost all glucose, and it keeps the hive well fed throughout the winter. This valuable energy source is sometimes taken by force, as when a bear reaches into a hive and steals the comb. Thus, over millions of years, bees have developed stingers to defend the hive, while bears have developed thick skin and fur to render these stings ineffective. Evolution is like 3 dimensional chess, with all the pieces moving at once.
In contrast to honey, which is fiercely guarded, plants offer sugar as a treat to passers by. It's not a gift really, for that would be a waste. When Milton Friedman said, "There is no such thing as a free lunch.", he was referring to capitalism, and the predilections of human beings, but his maxim also applies to nature. A plant offers you a berry because it wants you to spread its seeds far and wide. Without sugar, you wouldn't bother - so sugar is your reward. In tandem, we have evolved the ability to taste sugar, and it brings us pleasure. We eat all the sweet treats we can lay hands on, and that was a survival trait until the 20th century, when grocery stores were stocked with cakes and pies and ice cream. Many of our behaviors that seem self-destructive are actually adaptive, if you turn the clock back a few thousand years.
At the other end of the spectrum, cats can't taste sugar at all. They have eaten meat for so long, meat and nothing but meat for millions of years, that there is simply no attraction to sugar. If something sweet falls into their bowl, they'll eat it, and turn it into energy, but they can't taste the difference.
Dogs land somewhere in between these two extremes. They can taste sugar, but it doesn't seem to trigger their pleasure center as it does for us. I have two dogs, sunny and Oreo. My wife and I share an apple at night, trying to be good, trying to eat fruit instead of cupcakes. The two dogs stare at us, wondering what is on our plate. When I offer a slice to Oreo, she sniffs it and turns away. Sometimes she takes it in her mouth for analysis, then spits it out onto the carpeted floor, thus rendering it inedible as far as I'm concerned. So I offer the same slice to Sunny. She sniffs it, and pauses, as though the wheels are turning in her lemon-sized brain. After some deliberation she eats it, slowly. Here is what she might be thinking.
"That's an interesting smell, kind of sweet. It's a nice smell. I guess it's ok to eat. Not great, not like a piece of steak or even my snacky bones, but it's ok. The humans are eating it, so there must be something to it. I'll give it a try."
Then, after Sunny eats her piece, Oreo wants one too.
"Hey, am I missing out on something? It didn't smell that great, but Sunny is eating it, and she's a dog, and I'm a dog, so maybe it's a good thing after all. I better get my share."
So sweets are not a significant part of a dog's diet, but they'll eat fruit and enjoy it if it lands in front of them. Of course fruit in the wild is not as attractive as fruit from the grocery store. I went on vacation in Vermont, and strolled through the woods, eating the wild grapes. Each is about the size of a blueberry, with a snappy sweet sour taste and 3 to 4 seeds inside. There's a lot of seeds in there, relative to the volume and mass of the grape. Still, I would eat it. There is just enough sugar to make it worth my while, and that's as it should be, as you would expect from nature. In contrast, farmers have selected ever larger grapes with ever smaller seeds for centuries. This is called artificial selection (in contrast to natural selection), using evolution to our advantage. Grapes in the store are now 2 to 3 centimeters across, with seeds so tiny they are simply called seedless. Watermelon is also "seedless", although it too contains some very tiny, soft seeds that you hardly notice as you chew and swallow the fruit. These seeds, selected for inconspicuousness, are a far cry from the seeds of 50 years ago that inspired spitting contests.
At the molecular level, nature loves chains. Proteins are chains of amino acids, chains of lego blocks attached in a line, then folded back onto themselves to make a dizzying array of shapes. Sugar molecules can also be put together into chains, but in this case there is just one lego block, the glucose molecule. You're not going to get a lot of different shapes with just one block to choose from, but the chains are useful for energy storage. This is a compact way to store sugar, in tightly packed chains, and these chains are called starch. Potatoes, rice, corn, wheat, and other grains are high in starch. They don't taste sweet, because the sugar is locked up in chains and does not trigger the sweet receptors on your tongue. Still, the starch is broken up into sugar in the small intestines, where it acts as an energy source. For most of us, eating a gram of sugar is no different than eating a gram of starch. After digestion, it's a gram of sugar either way. That's why sugar and starch are lumped together into a class of compounds called carbohydrates, or carbs for short. If you're on a low carb diet, you can't eat a lot of sugar, nor a lot of starch.
glucose ⇔ glucose ⇔ glucose ⇔ glucose ⇔ glucose
Wolves can't digest starch, at least not very well. They don't have the necessary enzymes, the appropriate bolt cutters to cleave the starch chain into its sugar molecules. The energy in this food is locked away and inaccessible to them. That's ok, because a wolf hardly ever eats a potato or an ear of corn. Grains are just not on his diet. Dogs, on the other hand, digest starch quite well. Dogs and wolves are close relatives, capable of interbreeding in fact, so what happened?
Humans began growing crops ten thousand years ago, more or less. This was the dawn of agriculture. Domestication of wolves began around the same time, thus transforming the wolf into all the dog breeds we know and love today. After threshing, there was plenty of grain left over for our new canine companions. As mentioned above, wolves don't usually eat corn and wheat and potatoes, so this represented a novel food source for the ancestors of our modern day dogs. Within a couple thousand years, a couple hundred generations, dogs developed the enzymes necessary for starch digestion. They weren't going to let that food go to waste, not for very long. Today, after ten thousand years of domestication and table scraps, dogs can eat wheat with the best of us. I had a dog named Remmy who was absolutely a bread hound. One day she snatched a loaf off the counter, still warm from the breadmaker, and scarfed down half of it before we could intervene. She loved the taste of bread, especially homemade bread. I have to laugh at the commercials that proudly advertise premium, grain-free dog food, for a premium price of course. I can just imagine a dog thinking,
"Really? I spent ten thousand years evolving the ability to digest grains, and now you're afraid to put them in my dog food? Well that's up to you I suppose, just make sure you keep giving me those pizza crusts and crispy fries. Don't you dare throw those away."
Actually I have a friend whose dog is allergic to corn, so yes, grain-free pet food has its place and purpose.
The last macronutrient is organic oils, also known as fats, or triglycerides. It is once again a chain. The basic building block of this chain is CH2, a carbon with two hydrogens attached. Put 4 to 22 of these together in a chain, then attach one end of this chain to a glycerol backbone, along with two other chains. That's three chains tied together, thus the term triglyceride. Chain lengths, along with some double bonds here and there, determine the properties of the oil. If there are no double bonds, then the oil is saturated, sporting as many hydrogens as it can. A saturated chain of length 6 has 11 hydrogens, 2 hydrogens on 5 of the 6 carbons, and one more hydrogen capping the free end. The innermost carbon has the oxygen connection to the glycerol backbone. A saturated chain of length n has 2n-1 hydrogens. In this depiction, G stands for glycerol. Only one of the three chains is shown.
A monounsaturated oil has one double bond, with 2 fewer hydrogens attached, and a polyunsaturated oil has multiple double bonds. A double bond is sometimes indicated by an equals sign.
These diagrams are a simplification; the chains actually flop around in 3 dimensions, and do not lie flat on the page.
Peanut oil, sunflower oil, canola oil, olive oil, soy oil, coconut oil, palm oil, butter, animal fat, and blubber are all examples of organic oils. This is the most efficient method of energy storage by far. If sugar is money in a savings account, then fat is money in a long term CD. When an animal eats too much, and gets "fat", he is storing energy in the form of fat. Granted, animal fat doesn't look like oil, it's not a liquid, but it is essentially the same molecule. The chains are longer, so that the triglycerides clump together into a solid known as animal fat. A camel's hump, for instance, holds fat, not water. The fat does not surround him, like other animals, for then he would get too hot. A bear lives on fat through the long winter, and plants pack their seeds with vegetable oil for the next generation. Cottonseed oil, sunflower oil, coconut oil, canola oil; these come primarily from the seeds of the plant.
Let's put some numbers on these macronutrients. A Calory is a unit of energy, measuring the nutritional content of food. Technically, a Calory, also known as a kilocalory, is the amount of heat needed to raise one kilogram of water one degree celsius. A gram of protein contains 4 Calories, and a gram of carbohydrate (be it sugar or starch) also contains 4 Calories. Burn either of these in a crucible and you could (theoretically) heat a kilogram of water from 20°c to 24°c. But a gram of fat has 9 Calories, more than twice as much. The reason is simple. Sugar is already half burned. Glucose contains six oxygens, well on its way to water and carbon dioxide. But a molecule of peanut oil has almost no oxygen in it at all. Just carbons and hydrogens in chains, ready to be burned in the presence of oxygen, giving water and carbon dioxide. The gasoline that you put in your car has a similar structure. There are 8 blocks of CH2 put together in a chain, with a hydrogen at either end, and no oxygen at all. Because the chain is 8 units long, the molecule is called octane, as in octane fuel. Yes, some organic oils are also 8 units long, particularly those from coconut oil, but don't confuse the two. That small modification at the end of the chain, where COO connects to glycerol, makes all the difference. Coconut milk is delicious, especially in Thai curry, while gasoline is highly toxic. Unlike living creatures, some cars, having a modified diesel engine, are more forgiving, and can run on either gasoline or filtered cooking oil.
If you are on a lo Calory diet, you can see why fats are your enemy. A pat of butter is 36 Calories. You'll have more room for protein and carbohydrates in your Calory budget if you cut back on fats. Fast food, dripping with soy oil, is not for you.
There is another variation on carbohydrates that doesn't get much attention, because we can't digest it. Sometimes it is simply called fiber. But it is a form of food, and other animals digest it very well. I'm talking about cellulose, a vital constituent of plants. This is another chain, a chain of glucose molecules in fact, but the connections are different than those of starch. You need a different set of bolt cutters to take them apart, and we don't have it. Cows do however, and sheep and goats and horses and elephants etc. They can eat grass all day, slicing cellulose into sugar and deriving energy from the plant material. A cow looks out upon a green pasture and thinks to himself, "Yum - carbohydrates."
In summary, there are three macronutrients: proteins, carbohydrates, and fats. Carbohydrates include sugars (of various types), starch, and cellulose. Some animals can metabolize starch, and some cannot. Some animals, primarily herbivores, can digest cellulose, while others cannot. Each animal obtains energy from the food that it routinely eats, and some animals can store energy in times of plenty, to get through a cold winter or an unexpected famine, which are all too common in the history of life.