What Macros Are

What you’ll learn

  • The difference between each type of building block.
  • The roles of carbohydrates, protein, fats and fibre.
  • Why combining foods with different make-up changes how fast energy is released.
  • Why understanding macros helps steady energy and mood, so you hit your goals.

Let’s start simple

Food is made up of building blocks — macronutrients and micronutrients.

Macronutrients (macros) are the nutrients we eat in large amounts: they are carbohydrates, protein and fats.

Micronutrients (micros) — vitamins and minerals — are just as important, but we need them in much smaller amounts.

The macronutrients serve different main functions in our bodies:

  • Carbohydrates: a quick-acting energy source that powers our bodies
  • Proteins: the body’s building and repair blocks
  • Fats: our energy reserve and hormone support system, vital for survival when food is scarce

Macros can even be converted from one form to another. Sugar can be stored as fat; protein can be used for energy in a pinch. Your body constantly shifts between these options depending on what’s available. Your body is amazing.

Carbohydrates

Carbohydrates are your body’s preferred fuel. They come in different sizes — from small molecules to long chains. Large molecules (compounds) like starch — the white part in the middle of rice, wheat and potatoes — are long chains of a smaller carbohydrate called glucose. Granulated sugar is two glucose molecules joined together.

When you eat starch or sugar, your gut breaks them down into lots and lots of glucose molecules small enough to enter the bloodstream. It’s the glucose your body uses to fuel activity.

Once glucose hits the blood, your pancreas releases insulin — a hormone that unlocks your cells so glucose can move inside. If there’s more glucose than you need, the excess is stored as fat.

So, the first thing to realise is that even eating a low-fat diet doesn’t stop your body from making fat.

Key ideas:
There are many different carbohydrates. The skin on the outside of a potato is another type — made from fibre. The structure of a carbohydrate changes how fast it’s digested, and as we’ll see later, that’s very important.

Simple sugars (like those in coffee or soda) are absorbed very fast; starches take a little longer; and fibre is slow.

Protein

Your body is built from thousands of different proteins. Muscle fibres, skin, blood, and even your brain are made from them — and they perform an enormous range of functions, including helping to make other proteins.

Protein itself is made from smaller molecules joined together — like beads on a necklace. These smaller molecules are called amino acids. There are 20 different ones, and they’re like letter tiles in a Scrabble game. Some are used all the time (like A, E, S, T); others only occasionally (like X or Z).

Our bodies can make many amino acids (non-essential amino acids), but there are nine essential amino acids we must get from food. We don’t need each amino acid in the same quantity — some are used far more than others — but we do need a minimum of all nine essentials.

Meat contains all 20 amino acids used by humans in the right proportions, so it’s called a complete protein.
Beans and other plants also contain all 20 amino acids, but not in the proportions our bodies need — they’re often lower in one or two essentials such as methionine.

The fix is simple: combine plants. When one food (like beans) is low in a particular amino acid, another (like whole grains) provides it in abundance. Together they create a complete amino acid profile.

Meat, on the other hand, lacks fibre. So adding lentils or beans to a meat stew gives you the best of both worlds — complete protein and fibre — making it a much healthier, more balanced meal.

Your body continually breaks proteins down and rebuilds them. It can also use protein for energy, but it prefers to save it for repair and rebuilding.

Fats

Fats are a concentrated energy source and are vital for:

  • Energy for activity
  • Hormone production
  • Absorbing vitamins A, D, E and K

They provide more than double the calories per gram compared with carbs or protein — not “bad,” just powerful. Small amounts go a long way. Your body can use fats as an energy source, but it’s slow — fine if you’re walking or watching TV, but not fast enough if you need to sprint away from danger.

Fats are also crucial structural components — every cell in your body needs them to build membranes and perform vital functions. For the purpose of the 30 a Week approach, we’ll keep it simple and consider them mainly as a fuel source.

Fibre

Technically a carbohydrate — but one we don’t fully digest. Fibre slows glucose absorption, feeds beneficial gut bacteria, and helps you feel full.

Whole grains, beans and vegetables naturally contain more fibre, which lowers a meal’s glycaemic index (GI) — the measure of how fast glucose rises in the blood. We’ll discuss GI later.

Technically, fibre sits within the carbohydrate category — but it behaves differently in the body. Most carbs are broken down and absorbed as glucose (or similar simple sugars). Fibre is not. Instead, it reaches your gut bacteria, where it’s fermented to produce short-chain fatty acids (SCFAs).

That term sounds technical — but these compounds play a major role in stabilising hunger, supporting your gut lining, calming inflammation, and helping keep blood sugar responses smoother and steadier.

Fibre is incredibly beneficial — even though it doesn’t fuel your body the way other carbohydrates do.

So while the biochemistry textbooks will still file fibre under “carbs,” practically it functions as its own metabolic category. For the 30 a Week approach, fibre is important enough that we treat it as a fourth pillar, alongside protein, fats and carbohydrates.

It’s also worth knowing where fibre actually lives in food. People often think it’s only in the “chewy” or rough parts of plants. Yes — the skin of apples or potatoes is rich in fibre. But fibre is also in the soft flesh of fruits like peaches, in beans, lentils, nuts, seeds, and inside the structure of vegetables. It’s not just the bits you’d normally peel off — it’s built into the plant itself.

There are also different types of fibre, and they behave differently:

  • Soluble fibres (like pectin in fruit and beta-glucans in oats) dissolve in water and can slow digestion.
  • Insoluble fibres (like the cellulose in many vegetables) add bulk and keep everything moving through your system.
  • Resistant starches (in foods like cooked-and-cooled potatoes or legumes) act more like fibre because they resist digestion and reach your gut bacteria intact.

We’ll go into these categories later — but for now, the key takeaway is this: no single fibre type is enough on its own. Variety matters far more than megadosing one isolated fibre source.

Key point

This is a simplified view, but it helps to think in terms of immediate energy, building, and storage. It’s a practical way to understand how different foods affect your body.

Macros aren’t “good” or “bad” — your body is designed to make use of all of them. As with most things, balance is key. Processed foods can really mess with the natural balance of macronutrients.

For example, soda contains huge amounts of sugar but almost nothing else. That blast of sugar, delivered very fast, can really upset how your body reacts — as we’ll see later. For the record: yes, I still enjoy a can of cola now and then — just not with every meal.