Written by Sophie Conant
Our bodies need energy, we can’t live without it. Energy, in the form of food, is required for our bodies to carry out normal functions and activities. At present, the general energy requirement recommended by the NHS for the general public is 2000kcal for women and 2500kcal for men (1), but how seriously should we follow this? How much energy do our bodies really need, and what factors influence our individual energy requirements?
How were the recommended energy requirements calculated?
When it comes to nutrient and energy requirements, there are a number of terms that are used when referring to and calculating them in research. It can be a little confusing! The 2000kcal - 2500kcal reference amount that we know as our estimated energy requirement (the UK’s dietary reference value or DRV for energy) is also referred to as the average reference value (EAR) for the population.
The DRV for energy (or estimated energy requirement) was created by collecting data from reference populations of what their energy expenditure values, and consequently their energy requirements, were. For adults, this was a group of approximately 1000 people and their energy requirements were evaluated using doubly labelled water – a method generally viewed by researchers as the most effective way of calculating the energy expenditure of individuals over a period of days or weeks.
The data gathered was then compiled and a typical (average) value was produced (2). It is important to note that the EAR data was collected from a group of healthy adults aged 30-80, predominantly of European and White American origins. The EAR is an average and therefore, doesn't show the energy range of the reference group (we were unsuccessful in finding the range too), and has its limitation in the age range and ethnicities captured in the data.
Energy requirements were defined by the Committee on Medical Aspects of Food and Nutrition Policy (COMA) in 1991 as “intakes of nutrients which were likely to ‘meet the needs of some or all within population groups” (3), further reinforcing that energy requirements which are recommended to us at a population level will not apply to everyone.
Adult EAR Summary (3)
What are the components of energy expenditure?
Our metabolic rate is made up of three different components, which all add up to form the total energy expenditure of any given day:
1. Basal Metabolic Rate (BMR)
BMR is the energy expended by our bodies at rest (i.e. the amount of energy we need for our organs to simply function). This is the largest component of our energy requirements, making up between 60-70% of the total.
A study looking into the energy requirements of each organ highlighted the significant amounts of energy required for the body to simply survive (4). They outlined how many calories each organ would need, on average in a healthy adult, in a day to perform its functions:
Brain - 336kcal
Heart – 120kcal
Liver – 360kcal
Muscle – 364kcal
Kidneys – 360kcal
When the energy requirements of the organs listed above were added together, this highlighted that to just survive at rest, a healthy adult will require between 1200-1500kcal. Many diets recommend a caloric intake even lower than 1200-1500kcal. These are unmaintainable and can have damaging effects if followed long term, as key organs and body systems do not have enough energy to perform their functions at optimal levels.
2. Activity energy costs (energy for physical activity)
Making up approximately 20-35% of our total energy requirements, activity energy costs include not only exercise but also sitting, standing, walking, cleaning, brushing your teeth, showering and all other activities you may undertake during the day. This is the most variable aspect of our energy requirements. The activity levels of a healthy person will differ daily, meaning that on some days the amount of energy required by our activity levels will be higher and on others, they will be lower.
3. Postprandial thermogenesis (the thermic effect of food)
Did you know that 5-10% of the energy we expend is used to digest the food we eat? Although postprandial thermogenesis sounds like a complicated term, it simply means the energy our body uses when digesting, absorbing, transporting, and storing the food we’ve eaten.
Different foods will require various amounts of energy to break down, so will each have differing thermogenic effects. This means that while on paper it may look like we are consuming a certain number of calories, the amount of energy we actually get from different foods will be different. Read more about this in our blog Are All Calories Equal?
What factors influence our total energy requirements?
Our total energy requirements can be influenced by a wide variety of factors, many of which are completely out of our control as they are predetermined by our genetics.
Body size - this is largely determined by the genes we receive from our parents. Some people will naturally thrive at a larger body size, whereas others' natural body size will be smaller. The size of our body will have an impact on how much energy we need and expend.
Gender - largely due to physical differences in body size and composition
Age - generally, as we age, our BMR tends to decrease, meaning that our overall energy expenditure declines also. Lifestages like puberty, pregnancy or lactation can also make an impact.
Body composition - lean muscle is more metabolically active (uses more energy) than fat mass
Injury or illness
What impacts how we digest our food and how much energy we get from it?
As mentioned above, the thermogenic effect of food affects how much energy we get from it, however, there are several other physiological factors that can also influence food metabolism.
Research has been done investigating a link between our gut microbiome and food metabolism, showing that our gut health can impact how we extract energy from food. One animal-based study found that test subjects with a ‘healthier’ gut microbiome were more able to adapt to variations of fat in the diet (5). Although further research is needed to say for certain that the human gut microbiome plays a significant role in altering our energy requirements, it is possible that it has a significant effect on food metabolism.
Injury and trauma can also increase our energy requirements due to an additional necessity of energy for defence and repair processes. This is not only the case for people suffering from injuries and illnesses such as a broken bone or virus but can also be the case for recovery from an eating disorder. During recovery from a restrictive eating disorder, an individual may have increased energy requirements than ‘normal’ as their bodies will need to repair the damage that starvation has caused. Sometimes this can develop into a process called hypermetabolism which has a significant effect on calorie requirements in the early stages of eating disorder recovery.
How much energy do we really need?
Whilst it may be the case that on average, a large proportion of the population will require around 2000-2500kcal, for a significant number this will not be the case. It is also worth noting that although a person’s intake may average out to be a number close to the average, that doesn’t mean that this will be the case every day; some days it may be more and others less, but this will average out over time.
Energy Requirements for Athletes
For some, their requirements for energy will be significantly higher, perhaps even double, that of the recommended amount. This is the case for individuals whose daily routine involves high levels of physical activity. The importance of meeting these increased energy requirements was shown as athletes who did not consume adequate energy showed a decrease in both performance and recovery (6).
Energy Requirements in Eating Disorders
Calorie requirements for eating disorder recovery are significantly different to everyday requirements. Chronic dieting and starvation are states that often result in a lowered metabolic rate (called hypometabolism) as the body and its organs adapt by slowing their overall energy expenditure to preserve energy - conserving it for another time. However, in contrast, it has been found that during the process of refeeding, a state of hypermetabolism is often induced as the body starts to repair the damage done by starvation, raise core body temperature and the thermic effect of food (4). The induction of this state could result in a raising of energy requirements to as high as 3500-4000 calories per day for weight restoration to be achieved (7).
Following energy intake guidelines
Although there is a general recommendation for daily energy requirements, it must be stressed that this is only a guide. Energy requirements are very individualised and can differ from day to day and over the years. Energy requirements differ from person to person, some people require more energy to thrive, others less. It's not a good or bad thing. It's just science.
There are so many factors that influence how much energy we each require. Although an app may theoretically be able to tell us how much energy we have eaten in a given day, in practice, it doesn’t take into account the differences in which each of us metabolises the food we eat, and how different food sources are metabolised. Calorie counting is not as black and white as we are often led to believe. Our bodies are not simply machines requiring the same amount of energy each day, a number of intertwining factors cause our daily energy requirements to change as we move through life. With this in mind, how many calories you need during eating disorder recovery is best to be calculated and guided by a registered dietitian.
Part of overcoming disordered eating or an eating disorder is learning to trust that the body can regulate energy intake through hunger and fullness cues. This process can take time and self-compassion but is possible to achieve again (remembering we were all born with this inbuilt mechanism).
If you feel as though you are struggling with your relationship with food or your body, book a free discovery call with us. We would be delighted to guide you towards finding balance again.
Sophie Conant
TCN Intern
Sophie Conant is a 2nd year Dietetics student at the University of Nottingham. Her own journey to finding food freedom has given her a passion to help others to do the same. In her spare time, she enjoys yoga, climbing and cooking for friends.
REFERENCES:
[1] NHS, 2019, What should my daily intake of calories be?, Accessed: 26th April 2022, Available at: https://www.nhs.uk/common-health-questions/food-and-diet/what-should-my-daily-intake-of-calories-be/
[2] SACN, 2011, Dietary Reference Values for Energy, Accessed on: 26th April 2022, Available at: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/339317/SACN_Dietary_Reference_Values_for_Energy.pdf
[3] Department of Health, 1991, Dietary Reference Values – A Guide, Accessed: 26th April 2022, Available at: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/743790/Dietary_Reference_Values_-_A_Guide__1991_.pdf
[4] McClave S and Snider H, 2001, Dissecting the energy needs of the body, Curr Opin Clin Nutr Metab Care, Vol. 4
[5] Martinez-Guryn K, Hubert N, Frazier K, Urlass S, Musch M, Ojeda P, Pierre J, Miyoshi J, Sontag T, Cham C, Reardon C, Leone V and Chang E, 2018, Small Intestine Microbiota Regualte Host Digestive and Absorptive Adaptive Responses to Dietary Lipids, Accessed: 27th April 2022, Available at: https://pubmed.ncbi.nlm.nih.gov/29649441/
[6] Woods A, Rice A, Garvican-Lewis L, Wallett A, Lundy B, Rogers M, Welvaert M, Halson S, McKune A and Thompson K, 2018, The effects of intensified training on resting metabolic rate (RMR), body composition and performance in trained cyclists, PloS one, Vol. 13
[7] Robbins S, 2021, Hypermetabolism in Eating Disorder Recovery, Gaudiani Clinic, Accessed: 1st May 2022, Available at: https://www.gaudianiclinic.com/gaudiani-clinic-blog/2021/1/28/hypermetabolism-in-eating-disorder-recovery
Talia Cecchele Nutrition is a team of registered dietitians that specialise in eating disorder recovery, disordered eating, digestive issues and sports nutrition. We aim to bring balance back to nutrition, help you to break free from food rules and find food freedom. We offer virtual consultations and group programs so whether you are based in London, the United Kingdom or around the world we would love to support you. To enquire about a private consultation please fill out a contact form.
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