Understanding Macronutrients: Fat, Carbs & Protein

By Alok 29th October 2021 Category: Advice

What are macronutrients?

Macronutrients are essential components of the diet and include three distinct nutrient categories: fats, carbohydrates and protein. They are termed macronutrients because they are needed in large amounts to enable proper functioning.

One thing that all macronutrients have in common is that they provide a source of energy. However, each one has a specific set of properties and functions in the body. This blog focuses on each macronutrient in turn to explain the function of each and the role of macronutrients in weight loss.


Fat is an energy rich macronutrient that provides fatty acids that the body must obtain from the diet.

Why do we need fat in the diet?

Alongside the role of fats as an energy source, they play an essential role in multiple processes including hormone production and absorption of vitamins A, D, E and K.

Within the main macronutrient group are several different types of fat. Each type plays a specific role and is required in varying amounts.

  • Saturated fat
  • Trans fat
  • Monounsaturated fat
  • Polyunsaturated fat

Saturated fats are often considered to be “unhealthy” as excess consumption causes an increase in LDL (or “bad”) cholesterol in the blood and is linked to increased risk of cardiovascular disease. Unsaturated fats include monounsaturated and polyunsaturated fats and are able to reduce the amount of cholesterol in the blood and help to reduce cardiovascular disease risk.


Carbohydrates, or carbs, are a group of molecules that are made up of simple sugar units called monosaccharides. The types of carbohydrates include simple carbohydrates which are made up of only one or two sugar units, complex carbohydrates that contain more than three sugar units, starches which contain large numbers of sugar units connected in complex structures, and fibre which is a complex carbohydrate that cannot be digested and contributes towards gut health.

The difference between the types of carbohydrates is not limited to structure. Simple carbohydrates such as white bread, processed or refined sugars and sugary drinks can cause sharp increases in the amount of sugar in the blood and although acceptable in small amounts, excess consumption is linked to obesity and increased risk of cardiovascular disease. Complex carbohydrates or “healthy carbs” such as vegetables, legumes, whole grains and wholemeal products on the other hand are more difficult for the body to digest and cause a more gradual rise in blood sugar.

What do carbohydrates do?

Carbohydrates provide a source of energy, help to regulate the amount of glucose in the blood, play a crucial role in metabolism and are critical for brain function.


Protein is made up of long chains of smaller units called amino acids. These chains of amino acids then fold to form complex 3D structures that are complementary to their function. Amino acids can be classified according to whether they can be made by the body or if they need to be obtained from the diet:

  • Non-essential amino acids – can be generated by the body and also obtained from the diet

  • Essential amino acids – cannot be generated by the body and must be obtained from the diet
  • Conditionally-essential amino acids – under normal, healthy circumstances, can be generated by the body. But in under certain conditions these amino acids become essential and must be obtained from the diet.

What does protein do?

The major role of protein in the diet is to provide a source of amino acids for the body to use to produce specific proteins. Proteins are involved in virtually every process that takes place in the human body in the form of enzymes which are special molecules that help to regulate reactions that take place in the body. Protein is crucial for growth and repair which is particularly important in the context of exercise. When muscle fibres become damaged during exercise, they must be repaired, and protein provides the source of amino acids required for this process.

Dietary protein can be found in both plant- and animal-based foods including meat, dairy, eggs, nuts, seeds, lentils and tofu. It isn’t important if the dietary protein source is plant-based, animal-based or an alternative/substitute providing that all of the required essential amino acids are obtained. Once ingested, the digestive system breaks down the dietary protein into its constituent amino acids that can then be absorbed into the blood and transported around the body.

Why are macronutrients important for weight loss?

The ‘calories in, calories out’ paradigm is central to weight loss. The number of calories in is determined by the amount of food (or drink) consumed and all three macronutrient groups will contribute to the total number of calories. The number of calories out is determined by the amount of energy that is used at rest, or the resting energy expenditure, in combination with the amount of physical activity undertaken and the amount of energy used to process the food that is consumed. In order to reduce body weight, a calorie deficit needs to be achieved. This means the number of calories out needs to exceed the number of calories in.

So where do macronutrients come into this? Some macronutrients are more calorie dense than others and it is important to consider this when designing a diet plan. At Mediweight, diet plans are designed by experts around your personal weight-loss goals to ensure that macronutrient proportions are appropriately balanced.

Consuming any one macronutrient group in excess or excluding one macronutrient from the diet will not alter the fact that body weight is regulated by the balance of calories in vs calories out. However, if is sustainable for somebody to reduce their total calorie intake by consuming less of any particular macronutrient this can be helpful in achieving goals, although it is very important to ensure that any diet plan does not lead to macronutrient deficiencies.

Macronutrient based diets

There are a whole host of diet plans out there with aim of adjusting the relative proportions of the macronutrients, often restricting one macronutrient and providing another in excess. In order for any diet to provide an effective weight-loss strategy, there must be a calorie deficit. So what all of these diet plans have in common is that they advise an individual to consume fewer calories than they burn.

    Low fat diet

    The world health organisation recommends a total fat intake of between 20 and 35% of total calories. Reducing fat intake is often a useful strategy in helping to decrease calorie intake because it is the most energy dense macronutrient at 9 calories per gram.

    Low carb diet

    45 to 65% of total calorie intake should be obtained from carbohydrate sources. Even though carbohydrates are considerably less calorie dense than fat at 4 calories per gram, the macronutrient is often overconsumed so reducing dietary intake can be an easy, sustainable approach to weight loss.

    Low carbohydrate diets are often associated with high fat intake. This is commonly referred to as a ketogenic (or ‘keto’) diet. For many people, with appropriate medical supervision, ketogenic diets can help with achieving weight-loss goals. The Mediweight programme is centred around medically supervised ketosis to facilitate weight-loss, whilst ensuring adequate intake of essential vitamins and minerals.

    High protein diet

    The world health organisation recommends that at least 10% of daily calories should come from protein, but no more than 35%. Although maintaining a calorie deficit is a priority with any weight-loss diet, it is also important to achieve a sense of fullness and limit feelings of hunger to prevent weight regain following weight loss. A high-protein diet is an effective method of increasing fullness and preserving what is known as fat-free mass.

At Mediweight, medical professionals work with patients to develop detailed, personalised diet plans that make safe, controlled weight-loss achievable. This combined with the use of specialist ultrasound body contouring technology to target stubborn fat deposits and avoid loose skin makes the Mediweight programme a truly unique and comprehensive weight-loss experience for all.

Back to Articles

Related Articles


Dec 2021


Nov 2021

Arrange your consultation

One of our friendly sk:n advisors will contact you to answer your questions, and get you started on your journey to better skin.

  • Qualified and regulated medical experts
  • An NHS Partner organisation
  • Rated excellent by our clients on Trustpilot
  • Strict safety measures in place

Explore sk:n






& Support

Aftercare & Support

Skin Products

Skin Products


Medical Team

Expert Medical Team