Macronutrients Explained: Protein, Carbs, Fat & Alcohol

Nutrition basicsMacronutrientsEvidence based

Macronutrients ("macros") are the nutrients your body needs in large amounts every day. Three of them — protein, carbohydrate and fat — are the foundation of every meal and the only components of food that supply energy, measured in calories (kcal). A fourth source of energy, alcohol, also belongs on this page: it provides calories, but unlike the others your body has no actual need for it. Everything else you need — vitamins and minerals — comes in tiny amounts and are called micronutrients (covered in their own section).

Understanding macros isn't about counting every gram. It's about knowing what each one is for, which foods deliver it, and the difference between a higher-quality and a lower-quality version of the same macro. That single idea — quality, not just quantity — runs through this whole page.

The four energy sources at a glance

Each gram of a macronutrient releases a fixed amount of energy. These conversion factors (the "Atwater factors") are how every nutrition label is calculated.¹

Notice fat carries more than twice the energy of protein or carbohydrate per gram — which is why fatty foods are so calorie-dense, and why alcohol (closer to fat than to sugar in energy) adds up faster than people expect.

What it is & how it's built

Protein is built from small building blocks called amino acids, strung together like beads on a chain and then folded into a working shape. There are 20 amino acids in human nutrition. Your body can make most of them itself, but 9 are "essential" — meaning you must get them from food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.⁴ When you eat protein, you digest it back down into those amino acids and reassemble them into the proteins you need.

What it does

Protein is the body's construction material. It builds and repairs muscle, skin, hair and organs, and it forms enzymes, many hormones, antibodies for your immune system and the carriers that move things around in your blood. It also keeps you feeling full longer than carbs or fat, which is why higher-protein meals help with appetite.

Where you find it

"Complete" vs "incomplete" protein: a complete protein contains all 9 essential amino acids in good amounts. Animal foods and soy are complete; most single plant foods are lower in one or two amino acids. This is easy to solve — eating a variety of plants across the day (for example beans with grains) covers the full set, so a well-planned vegetarian or vegan diet reaches all essentials.⁴

How much you need

The official baseline (RDA) to prevent deficiency in healthy adults is 0.8 g of protein per kg of body weight per day⁴ — about 56 g for a 70 kg person. That is a floor, not an optimum: people who are older, very active, building muscle, or losing weight generally do better with more, and many researchers now point to roughly 1.2–1.6 g/kg for those groups.⁴

What it is & how it's built

Carbohydrates are made of sugar units. One sugar unit on its own (like glucose or fructose) is a simple carbohydrate; many units linked into long chains (like starch) are a complex carbohydrate. During digestion your body breaks most carbohydrates back down into glucose, which travels in your blood as your main fuel. Fibre is a special kind of carbohydrate: the chains are bonded in a way humans can't digest, so it passes through largely intact — and that is exactly what makes it valuable.

What it does

Glucose is the body's preferred quick energy, especially for the brain and for hard-working muscles. Carbohydrate not needed right away is stored in the liver and muscles as glycogen. Fibre, meanwhile, feeds your gut bacteria, slows the rise in blood sugar after a meal, helps lower cholesterol and keeps digestion regular.

Where you find it — and the quality ladder

The single most useful distinction in carbs isn't "carbs vs no carbs" — it's fibre-rich and whole vs refined and sugary. Whole-food carbohydrates come packaged with fibre, vitamins and minerals; refined ones have had most of that stripped away.

How much you need

Carbohydrate typically makes up the largest share of energy — about 45–60% of daily calories.² For fibre, aim for at least 25–35 g per day, an amount most people fall short of.² The clearest target to cut back on is free/added sugar: the WHO recommends keeping it under 10% of energy, and ideally below 5%.⁵

What it is & how it's built

Dietary fat is built from fatty acids — chains of carbon atoms — attached in threes to a small backbone (a "triglyceride"). The shape of those chains decides everything about how a fat behaves and how it affects your health:

• Saturated — straight, tightly packed chains; usually solid at room temperature (butter, fatty meat, coconut).
• Unsaturated — chains with one or more "kinks"; usually liquid (olive oil, rapeseed oil, nuts, fish). Split into mono- and polyunsaturated.
• Trans — mostly artificial unsaturated fats reshaped to act like saturated; the worst type for the heart.

What it does

Fat is concentrated energy and far more than a fuel. It builds the membrane around every cell, is the raw material for many hormones, cushions organs, and is required to absorb the fat-soluble vitamins A, D, E and K. Two polyunsaturated fats — omega-3 and omega-6 — are essential: your body can't make them, so they must come from food.

Where you find it — the types matter most

How much you need

Total fat of around 25–40% of energy fits a healthy diet — what matters most is the type.² The WHO recommends keeping saturated fat under 10% of energy and trans fat under 1%, replacing them with unsaturated fats from plants and fish.⁶

What it is & how it's built

The alcohol in drinks is a single small molecule, ethanol, made when yeast ferments sugar. It is not a nutrient — your body has no requirement for it — but it does carry energy: 7 kcal per gram, almost as much as fat, and these are "empty" calories with essentially no vitamins, minerals or benefit attached.¹

What it does in the body

Your body treats ethanol as a toxin and prioritises clearing it, mainly in the liver — which is why fat-burning and normal metabolism pause while alcohol is being processed. Beyond the calories, the more important issue is health risk.

This doesn't have to read as a lecture — but on a site about health, honesty matters: there is no amount of alcohol that improves your health, and from a nutrition standpoint it adds significant calories while displacing better food. Less is genuinely better.

Putting it together

You don't need to weigh your food or memorise percentages. The principles on this page do most of the work:

• Include protein at each meal — from a mix of animal and/or plant sources.
• Make carbohydrates mostly whole and fibre-rich — vegetables, fruit, whole grains, legumes — and keep added sugar low.
• Choose unsaturated fats — olive/rapeseed oil, nuts, oily fish — over saturated and trans fats.
• Keep alcohol to a minimum, knowing there is no health benefit to it.
• Favour variety and whole foods — the quality of each macro matters as much as the amount.

From here, the natural next steps are the micronutrients (the vitamins and minerals that work alongside these macros) and our supplement guides, where the same evidence-first approach applies.