Macronutrients Explained — Protein, Carbs & Fat (UK)

Macronutrients Explained: Protein, Carbs and Fat

Macronutrients — “macros” — are the three nutrients your body needs in large amounts and uses for energy: protein, carbohydrate and fat. Understanding what each does, and how much of it you need, is the single most useful piece of nutrition knowledge for anyone who trains. It is the foundation the rest of an optimised nutrition approach is built on, and it underpins everything from body composition to recovery.

This guide explains each macronutrient, how many calories they provide, and how to think about balancing them — for masters athletes and anyone over 40, of any sex.

Calories: The Common Currency

Every macronutrient provides energy, measured in calories (kcal), but not in equal amounts per gram:

Protein — 4 kcal per gram
Carbohydrate — 4 kcal per gram
Fat — 9 kcal per gram
Alcohol — 7 kcal per gram (not a nutrient, but it does supply calories)

Fat is the most energy-dense, at more than double protein or carbohydrate per gram — worth remembering when portioning oils, nuts and fatty foods. Your total daily calories are simply the sum of the macros you eat, which is why macros and calories are two sides of the same coin. (For how many calories you actually need, see our guide to daily calorie needs and TDEE.)

Protein

Protein is the structural macronutrient — the raw material for muscle, connective tissue, enzymes and more. For anyone over 40 it is arguably the most important macro to get right, for three reasons:

Muscle maintenance — protein provides the amino acids that build and repair muscle. Because muscle responds less readily to training with age (anabolic resistance), adequate protein matters more, not less, as you get older.
Satiety — protein is the most filling macronutrient, which makes it a powerful tool for managing appetite and body composition.
Thermic effect — the body burns more energy digesting protein than it does carbohydrate or fat, so a higher-protein diet has a small metabolic edge (more on this in our thermic effect of food guide).

For active adults, protein intakes in the region of 1.6–2.2 g per kg of bodyweight per day are commonly used to support training and lean-mass retention — higher than the basic government minimum, which is set to prevent deficiency rather than to optimise an athlete. Good sources include lean meat, fish, eggs, dairy, and legumes and soy for plant-based eaters.

Carbohydrate

Carbohydrate is the body’s preferred fuel for higher-intensity effort. It is stored as glycogen in muscle and liver and drawn on when you train hard. Its reputation swings with diet fashion, but for anyone doing meaningful training, carbohydrate is a performance tool, not the enemy:

Training fuel — glycogen powers sprints, heavy sets and sustained efforts; running low blunts performance and recovery.
Quality matters — whole-food sources (oats, rice, potatoes, fruit, vegetables, pulses) bring fibre and micronutrients; heavily processed, sugary carbohydrates spike blood sugar and add little else.
Fibre — a form of carbohydrate the body cannot fully digest, important for gut health, satiety and steady energy.

How much you need scales with how active you are: the more and harder you train, the more carbohydrate supports it. Timing more of your intake around training is a simple, effective habit.

Fat

Dietary fat is essential — it is not optional. It supports hormone production, the absorption of the fat-soluble vitamins A, D, E and K, and cell structure, and it supplies the essential fatty acids the body cannot make:

Unsaturated fats — from olive oil, nuts, seeds, avocado and oily fish; the omega-3s in oily fish are a standout for heart and brain support.
Saturated fats — found in fatty meat, butter and many processed foods; most guidance suggests keeping these moderate.
Don’t go too low — very low-fat diets can compromise hormone health, which is particularly relevant to anyone focused on hormonal optimisation over 40.

Because fat is calorie-dense, it is easy to over- or under-eat; a sensible baseline is roughly a quarter to a third of daily calories from predominantly unsaturated sources.

Putting It Together

A practical way to set your macros:

Protein first — anchor your intake around a target based on bodyweight (e.g. ~1.6–2.2 g/kg).
Fat next — set a sensible minimum for hormone and vitamin health, then flex it.
Carbohydrate fills the rest — use it to fuel training and fill the remaining calories to your total.

Get protein right, base most of your carbohydrate and fat on whole foods, and let your total calories match your goal — that is 90% of nutrition handled. Supplements sit on top of this foundation, not instead of it; see the Supplements Over 40 guide for what fills the remaining gaps.

Frequently Asked Questions

What are the three macronutrients?
Protein, carbohydrate and fat. Each supplies energy (calories) and each has distinct roles — protein for structure and repair, carbohydrate for fuel, fat for hormones and essential functions.

How many calories are in each macro?
Protein and carbohydrate provide 4 kcal per gram, fat provides 9 kcal per gram, and alcohol provides 7 kcal per gram.

How much protein should I eat over 40?
Active adults commonly aim for around 1.6–2.2 g of protein per kg of bodyweight per day to support training and preserve muscle — more than the basic anti-deficiency minimum.

Are carbs bad for you?
No. Carbohydrate is the body’s main training fuel. The quality and quantity matter — whole-food sources scaled to your activity, rather than large amounts of refined sugar.

Do I need to count macros?
Not necessarily. Understanding them helps you build better meals; tracking is a useful tool for specific goals but is not mandatory for everyone.

Macronutrients Explained — Protein, Carbs & Fat (UK Guide)