In terms of human nutrition, there are a number of essential and conditionally essential nutrients. An essential nutrient is a nutrient that the body can’t produce in adequate amounts, so we must get it from our diet. A conditionally essential nutrient means normally the body can produce the nutrient in the amounts we need, but under certain conditions, such as in heart disease, the body can’t.
These nutrients can be divided into macronutrients (carbohydrate, protein and fat) and micronutrients (vitamins and minerals).
Regardless of which specific elements are consumed, the primary requirement of food and drink is energy. The metric units for measuring energy are kilojoules (kJ), but calories are the more commonly referred-to unit when talking about food energy. Although the word ‘calories’ is often used, strictly speaking, kilocalories is the correct term and the abbreviation is kcal.
As we are all different, so are our calorific requirements. This can vary based on a variety of factors including age, sex, height and weight. There are two figures that are often referred to when determining how many calories are needed in order to sustain an individual:
Basal metabolic rate (BMR) – the amount of energy expended while at rest, i.e. when not moving. BMR is often used interchangeably with resting metabolic rate (RMR). However, they are slightly different with BMR being more accurately based on testing conditions. BMR/RMR is what is referred to when talking about the body’s metabolism.
Total daily energy expenditure (TDEE) – the daily calories required to maintain your weight. This is the combined total of your BMR plus the amount of energy you require for your level of activity/exercise.
If more calories are consumed than the body needs, the calories will either be stored as fat or, if the right stimulus is provided, used to build muscle. If fewer calories are consumed than the TDEE, fat will be lost and, if TDEE is matched, body weight will be maintained.
The basic rough rule of thumb is:
A pound of fat is roughly 3,500kcal, so a 500kcal deficit per day for seven days will be 3,500kcal under the TDEE, and therefore 1lb of fat per week should be lost and vice versa if weight gain is the goal. In regard to weight loss, some people may think it doesn’t really matter what is eaten to lose weight. However, it’s important to eat a balanced diet to ensure the body is getting everything it needs to stay healthy while weight is lost. This key point can often be forgotten even if the weight loss period is relatively short.
To work out how many calories the body needs and to get a rough idea of the number of calories needed to lose/gain weight, a calorie calculator can be used to give an estimate. Once a calorie target is obtained, the next step is to work out a macronutrient split.
A macronutrient is a nutrient required in large amounts in the diet. This includes carbohydrate, fat and protein. Fibre is technically a carbohydrate but can be classed as a separate macronutrient.
As a guide, carbohydrate and protein contain 4kcal/g, fat contains 9kcal/g while fibre can vary between 0 and 4kcal/g depending on how well it is digested. Though alcohol contains 7kcal/g. Alcohol is not a macronutrient as it is not required in the diet, despite those Friday night thoughts!
Macronutrient split refers to the percentage of calories provided by each macronutrient and is often referred to as a ratio. For example, in Huel Powder 37% of the energy comes from carbohydrates, 30% from fats, 30% from proteins and 3% from fibre. This is written as 37:30:30:3.
More detail about how the energy value of food is calculated can be found here.
Fat is a word which conjures up negative thoughts when heard; we tend to mentally associate the word with poor nutrition and have traditionally been encouraged to cut down the levels of fat in our diet in order to promote good health. However, as time has gone on, it appears the negatives of fat have been overstated[1], resulting in a decline in fat intake which isn’t necessarily a good thing because it may be replaced with an intake of sugar[2].
Fat is needed for growth, development and cell function among many other roles[3]. Fat is also important for the absorption of fat-soluble vitamins such as vitamins A and E. As we will see with carbohydrates there are different types of fats. Some are better than others. As a rule of thumb, avoid trans fats, consume some saturated fat but not at the expense of mono- and polyunsaturated fats which should be your main sources of fats. Rich sources of unsaturated fats include olive oil, flaxseed, sunflower seeds and oil, rapeseed oil, soya, peanuts, avocados and oily fish.
Read more about fats in our article Good Fats & Bad Fats.
Carbohydrates are an effective energy source[4]. Carbohydrates also play an important role in the structure and function of cells, tissues and organs[5].
There are essentially two types of carbohydrates: simple and complex. Simple carbohydrates are sugars; the majority in a typical Western diet are consumed through processed foods where the sugars have been added[6]. Simple carbs are fast acting; in other words, they are digested quickly resulting in a rapid increase and then decrease in a person’s blood glucose.
Complex carbohydrates tend to be digested more slowly causing a steady rise and gradual fall in a person’s blood glucose. Complex carbohydrates include rice, oats, potatoes, couscous and quinoa.
More information on carbohydrate digestion can be found here.
Fibre is a type of carbohydrate which can’t be digested. As a result, it passes into the large intestine, where the majority of the body’s gut bacteria are. These bacteria can digest some of the fibre, which goes on to provide energy for the body[7].
Fibre has several benefits such as promoting gut health and being filling[8]. High fibre foods include whole grains, such as wholewheat bread and pasta, and oats, pulses, nuts, fruit and vegetables.
Protein is critical for many bodily functions. It’s necessary for the immune response, transport of other substances around the body and the proper functioning of DNA[9].
Amino acids (AAs) are the building blocks that make up a protein. There are 20 principal amino acids and nine of them are essential. All protein sources are not equal; some are classed as ‘complete proteins’ and some are not. A complete protein source is one that contains an adequate amount of all nine essential AAs.
Generally, proteins derived from animal foods (meat, fish, poultry, milk, eggs) are complete.
Proteins derived from plant foods can be complete (soy, quinoa, chickpeas) or incomplete (wheat, beans, rice). Incomplete protein sources are low in one or more of the essential AAs.
By pairing incomplete protein sources a meal can be created which provides all the AAs that the body needs. For example, rice and beans are a complete protein source despite the two individually being incomplete protein sources. Even if a protein source is complete, sufficient quantities of that source need to be consumed to obtain enough of the essential AAs. So, protein quality and quantity are important.
Read more about proteins in our article Guide to Protein Quality, Digestion and Absorption.
While macronutrients are required in large amounts in the diet, micronutrients are required in much smaller amounts. They are important for a wide variety of reasons from helping our vision in dim light to helping wounds heal properly[10]. Micronutrients are vitamins and minerals. Through lots of medical research, a list of essential vitamins and minerals were published by the UK government in 1991 as Dietary Reference Values (DRVs), and there are also the EU Reference Intakes which are pretty similar[11].
There are DRVs for most, but not all nutrients. A population has a wide range of requirements, so the DRV Panel devised the Estimated Average Requirement (EAR), which is enough to cover 50% of the population, and the Reference Nutrient Intake (RNI), which is sufficient to cover at least 97.5% of the population[12]. There will always be extremes, so it is considered that, for most nutrients, supplying an intake equal to or above the RNI will be sufficient.
Ensuring sufficient quantities of all the listed vitamins and minerals are consumed can be tricky, so a wide variety of different foods must be eaten, including plenty of fruit and veg.
Read more about vitamins and minerals in our article The 26 Essential Vitamins and Minerals.
If you want to read in more detail about the topics mentioned in this article, check out Fats, Carbs, Protein, Fibre & Salt – What do we need?.
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