Macronutrients
Fats, carbohydrates and proteins
You must have seen variations of these food pyramid diagrams most of your life. They hang in doctors’ clinics everywhere and attempt to classify foods based on how much of each should be consumed—but don’t really tell what’s in them or why that matters. Let’s fix that.
Harold McGee’s magisterial On Food and Cooking is the book to read if you really want to understand what’s in your food. It’s somewhat expensive, but a PDF version is available courtesy some kind soul. Read chapter 15 from page 792 onwards. Please buy the book if you like what you’re reading. McGee is a central figure in molecular gastronomy, an approach to food that builds up from the basic molecules rather than down from the raw materials.
If you aren’t up to looking at a chapter that starts all the way at page seven hundred and ninety two, here’s a quick summary.
There are four basic classes of molecules in your food: water, lipids (fats, oils and others), carbohydrates, and proteins. You know what water is. It’s the bulk of your food—75% of meat and 95% of fruits and vegetables—but it’s not an energy source, so let’s get to the others.
Lipids: fats and oils
Fats and oils are part of the larger chemical family of lipids. One of their key characteristics is that they don’t mix with water. Thanks to this, they are an essential ingredient of all life: they’re used to make cell boundaries. Chemically, they’re what are called “triglycerides” because of a structure of three acid chains anchored to a glycerol compound:
An acid chain can be said to be saturated when it has no carbon double bonds (double lines in the diagram), or unsaturated when there is one or more, meaning it can take on more hydrogen atoms to replace those double bonds. This diagram represents three chains that are saturated, monounsaturated and polyunsaturated. When an unsaturated acid chain lays out in a straight line (as in this diagram), it’s said to be trans-unsaturated (or trans-fat in common parlance). The opposite is cis-unsaturated wherein the chain has a bend at the double bond and goes off in a different direction.
Why does this detail matter?
- Unsaturated fats are prone to attack from reactive chemicals, including oxygen. They have a shorter shelf life. Saturated fats are stable and last longer. Long lasting food can be mass produced food.
- Saturated and trans-fats, by virtue of their straight lines, pack down tighter and tend to be solid at room temperature (think butter vs oil). They are considered unhealthy because they can lay down deposits in your body.
- There’s a large variety in fats and oils, and in their chemical properties, because each of those chains could be of a different length, saturation, and trans or cis. This variety merits separate discussions for each nuance.
Carbohydrates
Carbohydrates are compounds made of carbon, hydrogen and oxygen, and serve as a basic energy store in all plants and animals. Of the many types, the primary ones are sugars, oligosaccharides (“several-unit sugars”), polysaccharides (“chains of sugar”) such as starch, and fibre (also chains, but with a different chemical structure) such as cellulose.
Sugars
Sugars are the simplest of the carbohydrates. Two of them, fructose and glucose, are commonly found in nature linked together with an oxygen bond as sucrose or table sugar—a disaccharide comprised of two monosaccharides. A third monosaccharide, galactose, is a variant of glucose. Here are some common disaccharides.
Glucose is a natural fuel of our body. Fructose needs processing in the liver. Fructose is also sweeter than either glucose or sucrose and is often used as a sweetening additive. This difference has some interesting consequences for our metabolism that merits a separate discussion.
Starches
A starch is a long chain of glucose molecules. When it’s a linear chain, it’s called an amylose. When it’s a branched chain, it’s an amylopectin. Starch is the primary component of foods like rice, wheat, maize (corn), and potatoes. The enzyme amylase present in our saliva breaks down starch into maltose, a disaccharide of glucose+glucose. Maltose passes through to the small intestine where the enzyme maltase further breaks it apart into the individual glucose molecules.
Fibres
Fibres are also chains, but with a different chemical structure that makes them harder to break down. They pass through our digestive system unprocessed. “Fibre” is sometimes spelt as “Fiber”.
Proteins
While carbohydrates and fats are mainly passive energy stores or structural materials, thereby forming stable compounds, proteins are the active machinery of life. Their behaviours change with the smallest change in conditions. Like with starch, proteins are large polymers of smaller units called amino acids. There are about 20 amino acids present in food, of which roughly half cannot be produced by your body and must be consumed in food.
What’s in your food?
If you got this far and need help correlating these basic building blocks with what’s in your food, here’s a simple method: Google for any ingredient name followed by the term “nutrition facts” and look at the table that shows up. It includes a breakdown of these macronutrients along with some important micronutrients. Try a few: onion, rice, eggs. This data is from the US Department of Agriculture (USDA) and is generally reliable, but is only available for food items recognised by the USDA.
Pay attention to the “total carbohydrate” section. Sugar and fibre are listed separately. If you subtract them from the total, you get starch. However, since fibre isn’t processed by your body, many diets ask you to use the “net carbohydrate” number of total minus fibre. You’ll have to do the math yourself. It’s not part of the label standard.
As these labels are typically per 100g of the item, you can use that to determine percentage. 1g = 1%. In this case, onions are 7.3% net carb. The three macronutrient groups add up to only 10.2% of the onion—the remaining is water and micronutrients.
Labels like “sugar” and “protein” don’t specifically identify which sugars or amino acids. Tomorrow we’ll look at just why this distinction is important in the case of sugar.
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