This article was written by one of The Food Medic team; registered dietitian Maeve Hanan
What are macros?
Macronutrients (A.K.A. ‘macros’) are the nutrients that our body needs in larger amounts. These are carbohydrates, protein and fat.
Whereas our body only needs micronutrients, like vitamins and minerals, in relatively small amounts.
Macronutrients are essential for the body to function optimally. They provide energy and the main building blocks the body needs to function and for its structure.
Let’s look at each macronutrient in more detail.
Carbohydrates are a group that include sugars, starches and complex carbohydrates like fibre.
On a chemical level, they are made up of the molecules carbon, hydrogen and oxygen. These form single units of sugar called saccharides.
Depending on how many saccharides are present, carbohydrates are classified as either:
- Monosaccharide — contain one saccharide molecule
- Disaccharide — contain two saccharides molecules
- Oligosaccharide — contain up to 10 saccharide molecules
- Polysaccharide — contain more than 10 saccharide molecules
Functions of carbohydrates:
Carbohydrate in the form of the simple sugar glucose is the most efficient source of fuel for the body and provides 4 kcals per gram. This is also the preferred fuel source for the brain and is needed for optimal brain function (1).
Fibre is a type of carbohydrate that’s more difficult for the body to digest. This provides a number of important benefits for our gut health including keeping bowel movements formed and regular and feeding friendly gut bacteria (probiotics). This has further knock-on benefits such as keeping cells lining the gut healthy and reducing inflammation (2).
Certain types of fibre found in oats and barley called beta-glucans support healthy cholesterol levels (3). Fibre also helps with stabilising blood glucose (4). Having a good intake of fibre is also linked with a reduced risk of bowel cancer, heart disease and type 2 diabetes (3).
Carbohydrates are also important for athletes and those who are active to provide energy, optimise performance and support muscle recovery (4, 5).
Sources of carbohydrates
Starchy carbohydrates are found in:
- Bread, pita and wraps
Sources of sugars include:
- Table sugar
- Sweets, cake, sweet pastries and chocolate
- Sweetened drinks
- Honey and syrups
Sources of fibre include:
- Fruit and vegetables
- Beans and pulses
- Nuts and seeds
Recommended Carbohydrate Intake:*
In the UK, we’re advised that carbohydrates should make up roughly 50% of our total daily food energy (3). This includes upto 5% of daily energy intake from free sugars and at least 30g of fibre per day (3).
Athletes and those who are very active usually need a higher intake of carbohydrate to meet their requirements. This can be upto 10g of carbohydrate per kg of body weight per day, depending on the amount and intensity of activity (6, 7).
Proteins are made up of strings of molecules called amino acids. Amino acids contain carbon, hydrogen, oxygen and nitrogen.
There are 20 amino acids that the body needs, 9 of which are called ‘essential amino acids’ because the body can’t make these by itself and they need to be consumed in our diet (8).
A protein is said to be ‘complete’ or to have a ‘high biological value’ when it contains all 9 essential amino acids in an easily digestible form. Animal-based proteins tend to be complete, whereas only a few plant-based proteins are (i.e. soya, quinoa and buckwheat).
Functions of protein:
Protein is needed to form a number of structures in our body, including our muscles, bones, skin and other tissues. It also plays a vital role in the growth and repair of these tissues.
We also need protein for a number of functions within our body, such as (9, 10, 11):
- Creating enzymes
- Creating certain hormones e.g. insulin
- Cell membrane structure
- Cell signalling
- pH balance
- Immune system function
- Transporting nutrients in the body using a protein called haemoglobin
Protein can also provide energy, at 4 kcals per gram.
Sources of Protein:
Animal-based protein sources:
- Fish and seafood
- Whey protein
Plant-based protein sources:
- Soya milk
- Beans, lentils and chickpeas
- Mycoprotein e.g. Quorn
- Seitan and wheat protein
- Pea protein
- Nuts and seeds
- Plant-based protein powders
Note: Those who don’t consume animal products need to eat a variety of plant-based protein sources across the day in order to meet their amino acid needs.
Recommended Protein intake:*
The recommended intake of protein for adults in the UK is 0.75 g per kg bodyweight per day (12).
However, athletes and those who regularly exercise have higher requirements (7, 13):
- Endurance athletes: 1.2 – 1.8g per kg bodyweight per day
- Strength athletes: 1.4 – 2g per kg bodyweight per day
Protein requirements for older adults have been seen to be higher than younger adults at 1.2 – 2g per kg bodyweight per day, due to reduced protein turnover in the body (14).
Due to the way protein is absorbed and used by the body, it’s best to spread this across the day as 20-40g of protein every 3-4 hours (13).
Protein requirements also increase in a number of illnesses and medical conditions because of their role in repairing the body, and in order to maintain or restore muscle mass.
Fats are molecules made of carbon, oxygen and hydrogen.
These are classified as ‘saturated’ or ‘unsaturated’ based on whether all the carbons on the fatty acid are bound to hydrogen or not. Saturated fats are solid and unsaturated fats are liquid at room temperature.
Unsaturated fats can then be further sub categorised as:
- Monounsaturated (MUFA) – contain one double bond
- Polyunsaturated (PUFA) – contain more than one double bond
Omega-3 and omega-6 are types of PUFA and known to be ‘essential fatty acids’, so they must be consumed in the diet.
Trans fats can form when vegetable oils containing PUFA become solid or semisolid when heated at a high temperature (which usually only occurs in industrial settings as part of food manufacturing) .
Functions of fat:
Fats are rich in energy as they contain 9 kcals per gram.
In the body, fats are needed to:
- Form cell membranes
- Produce steroid hormones like estrogens, progesterone and androgens
Fat also plays a number of important nutritional roles. We need fat in order to absorb the fat-soluble vitamins A, D, E and K (15). Consuming fat along with a meal can help with stabilising blood glucose levels and can leave us feeling more satisfied and fuller for longer.
Omega-3 fats have specific important functions in the body including (16, 17):
- Optimising brain function
- Improving heart health
- Supporting eye health and function
- Balancing inflammation levels
- Brain development of a foetus
- Involvement in cell signalling
Sources of fat:
- Nuts and seeds
- Olive oil
- Rapeseed oil
- Sunflower oil
PUFA (DHA and EPA):
- Oily fish e.g. salmon, mackerel, trout, kippers, sardines and herring
- Microalgae-based supplements
- Flax and chia seeds
- Rapeseed and soybean oil
- Soya products e.g. edamame beans, tofu and tempeh
PUFA – Omega 6:
- Sunflower, corn and safflower oil
- Coconut oil
- Visible fat on meat
- Cakes, biscuits, pies and pastries
- Products containing ‘partially hydrogenated vegetable oil’
- Certain fried foods and takeaways
Recommended fat intake:*
The general population adult recommendations for fat intake in the UK is (12, 18):
- Total fat: no more than 35% of daily food energy
- MUFA: 12% of daily food energy
- EPA and DHA: 0.45g per day
- ALA: at least 0.2% of daily food energy
- Omega-6: at least 1% of daily food energy
- Saturated fat: no more than 10% of daily food energy
- Trans fat: no more than 2% of daily food energy
As you can see, macronutrients are vital for our health and everyday functioning. This is an important reason why a balanced diet should contain all macronutrients.
Combining these nutrients at meals and snacks can also lead to additional benefits in terms of both health outcomes and satisfaction.
So watch out for restrictive diets that advise avoiding or restricting specific macronutrients or food groups.
*Recommended intakes are based on UK public health guidelines, so may not apply to your specific circumstances. Always seek individual nutritional advice from a registered dietitian where needed.
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Understanding Macronutrients was last modified: May 5th, 2022 by