What Are Macronutrients? Carbs, Protein and Fat Explained

Macronutrients come up everywhere, from food labels to gym chat, and the word can make healthy eating sound more technical than it needs to be. At heart it's a simple idea: a handful of nutrients you eat in large amounts, which give your body energy and the raw materials it uses to grow and repair.

I've pulled together a plain-English guide from the NHS, the government's Scientific Advisory Committee on Nutrition (SACN) and the British Nutrition Foundation. It's general information to help you understand the basics. If you've got a health condition or specific dietary needs, a GP or a registered dietitian is the right person to talk to.

Macronutrients versus micronutrients

Nutrients are often split into two groups by how much of them we need. Macronutrients are eaten in relatively large amounts and provide bulk energy. The three you'll hear about most are carbohydrate, protein and fat. Some definitions also count water as a macronutrient, even though it provides no energy.

Micronutrients are the vitamins and minerals your body needs in much smaller quantities. They matter just as much, but they don't supply energy themselves. Fibre sits slightly apart: it's a type of carbohydrate found in plant foods, but most of it isn't absorbed in the gut.

Energy per gram from each macronutrient

Each macronutrient supplies a different amount of energy, which is why foods with similar weights can have very different calorie counts. SACN, which advises the UK government, lists these conversion factors:

Nutrient	Energy per gram	Everyday food examples
Carbohydrate	3.75 kcal (SACN factor; the NHS rounds this to 4 kcal)	Potatoes, bread, rice, pasta, cereals, fruit
Protein	4 kcal	Beans, pulses, fish, eggs, meat, dairy, tofu
Fat	9 kcal	Oils, butter, cheese, nuts, oily fish, avocado
Alcohol (not a nutrient you need)	7 kcal	Beer, wine, spirits

The NHS points out that fat is the most energy-dense of the three, and that any excess energy, whether it comes from fat, carbohydrate or protein, is stored as body fat. That's why it's the overall balance of your diet that counts, not one food or one nutrient on its own.

Carbohydrates: the main energy macronutrient

The NHS describes starchy foods as our main source of carbohydrate and a good source of energy. Foods such as potatoes, bread, rice, pasta and breakfast cereals also bring a range of other nutrients with them. The NHS notes that, gram for gram, starchy foods contain fewer than half the calories of fat.

Fibre is the part of carbohydrate many of us don't get enough of. The NHS describes it as a range of substances found in the cell walls of vegetables, fruits, pulses and cereal grains, and says it helps food and waste move through the gut and can help you feel full. SACN recommends about 30g of fibre a day for people aged 16 and over. Easy swaps include:

• Wholegrain bread and breakfast cereals instead of white versions.
• Brown rice or wholewheat pasta.
• Potatoes with the skins left on.
• Adding beans, lentils or extra vegetables to meals.

Protein: the building-block macronutrient

The British Nutrition Foundation explains that protein supports growth, repair and maintenance in the body, particularly of bones and muscles, and also provides energy. Proteins are chains of amino acids. Around 20 are commonly found in food, and nine are essential for adults, which means they have to come from your diet.

Protein comes from both animal and plant foods. Animal sources include meat, poultry, fish, eggs, milk, yoghurt and cheese. Plant sources include lentils, chickpeas, beans, peas, tofu and other soya foods, nuts and seeds, plus smaller amounts from bread, pasta and oats.

The UK reference intake for adults is 0.75g of protein per kilogram of body weight a day. The British Nutrition Foundation says that, on average, UK adults already eat more than this, including vegetarians and vegans. The Eatwell Guide suggests choosing lean meat, eating less red and processed meat, and having at least two portions of fish a week, one of them oily.

Fat: the most energy-dense macronutrient

Fat often gets a bad name, but the NHS is clear that a small amount is an essential part of a healthy diet. It provides essential fatty acids your body can't make itself, and it helps you absorb vitamins A, D and E, which only dissolve in fat.

What matters most is the type of fat:

• Saturated fat is found in fatty meat, sausages, butter, ghee, lard, hard cheese, cream, cakes, biscuits and pastries, as well as palm and coconut oil. The NHS says men should have no more than 30g a day and women no more than 20g.
• Unsaturated fat is found mainly in plant oils, nuts, seeds and fish. Olive oil, rapeseed oil, avocados and oily fish such as salmon, mackerel and sardines are examples.
• Trans fat occurs naturally in small amounts in some meat and dairy foods, and in partially hydrogenated vegetable oil.

How macronutrients fit on the NHS Eatwell Guide

You don't need to count grams to eat a good balance of macronutrients. The NHS Eatwell Guide shows what a healthy, balanced diet looks like over a day or a week, and it covers most of the work for you:

1. Fruit and vegetables make up just over a third of what you eat: at least five portions of a variety each day.
2. Starchy carbohydrates make up just over another third, ideally higher-fibre or wholegrain versions.
3. Beans, pulses, fish, eggs, meat and other protein foods form a smaller section.
4. Dairy or fortified alternatives add protein, calcium and vitamins.
5. Unsaturated oils and spreads are used in small amounts.
6. Six to eight cups or glasses of fluid a day keep you hydrated.

Foods high in fat, salt and sugar, such as chocolate, cakes, biscuits and sugary soft drinks, sit outside the main guide because they aren't needed for a healthy diet. The guide doesn't apply to children under two.

Macronutrients and exercise

If you're more active, your energy needs go up, and the NHS says energy needs vary from person to person. People who train regularly often take more interest in their macronutrients, especially carbohydrate for fuel and protein for recovery. If you're curious about steady, lower-intensity cardio, I've also explained what zone 2 training is and how people gauge their effort.

Specific targets for athletes or people with medical conditions are personal. A registered dietitian can work out what suits you, and your GP can refer you if you need specialist support.

Common macronutrient myths

• "Carbs are bad for you." The NHS recommends basing meals on starchy carbohydrates, ideally wholegrain.
• "All fat should be avoided." Some fat is essential. The aim is to swap saturated fat for unsaturated fat and use it in small amounts.
• "Most people need extra protein." The British Nutrition Foundation says the average UK adult already eats more than the reference intake.
• "You must hit the perfect balance at every meal." The Eatwell Guide says to aim for balance across a day or a week.

Sharing nutrition knowledge

Clear, accurate information helps people make better food choices, and qualified voices are the ones worth listening to.

Dietitians and nutrition writers can share evidence-based articles through nutrition blogs that accept expert contributions.

Frequently asked questions

What are the three main macronutrients?

Carbohydrate, protein and fat. They're eaten in relatively large amounts and provide energy. Some definitions also include water, which provides no energy.

How many calories are in a gram of each macronutrient?

SACN lists 3.75 kcal for carbohydrate, 4 kcal for protein and 9 kcal for fat. The NHS rounds carbohydrate to 4 kcal. Alcohol provides 7 kcal per gram.

Is fibre a macronutrient?

Fibre is a type of carbohydrate found in plant foods, but most of it isn't absorbed in the gut. SACN recommends about 30g a day for people aged 16 and over.

Do I need to count my macros?

Most people don't. Following the NHS Eatwell Guide gives a good balance over a day or a week. A registered dietitian can help if you have specific goals or health needs.

Who should I ask about my diet?

Your GP is a good starting point, especially if you have a health condition. They can refer you to a registered dietitian for personal advice.