“How Many Calories Should I Eat?”: The Guide
This is up there with “Is this food bad for me?”, as one of the most asked questions I seem to get asked. First, let me be honest with you, the process of estimating calorie intake has numerous limitations. Having said that there is a way you can go about it to guide nutritional intake, although this will require re-evaluation.
Calculating calorie intake requirements is not necessary for everyone. For some, just concentrating on dietary behaviours can provide decent progress. However, for others some quantitative guidance can play a role in directing their nutrition efforts.
So, where do you start?
Stage One – Resting Energy Expenditure
Quantifying required energy intake can be achieved via the utilisation of energy expenditure prediction equations. However, it is important to stress the word ‘PREDICTION’. These equations provide an ‘ESTIMATE’ of energy expended at rest – Basal Metabolic Rate (BMR) or Resting Metabolic Rate (RMR).
What is BMR/RMR?
This is simply the calories you expend at rest to maintain important functions for life. For example, just being sat there breathing whilst you are reading this article excited with the anticipation of what is coming next!
Note: To gain an accurate measurement of energy expended at rest a laboratory test would be required (this can be quite expensive, require a visit to a testing facility and therefore unnecessary for your average fitness trainee).
Three popular equations for estimating BMR/RMR include:
(1) Harris and Benedict – incorporates height (cm), weight (kg) and age (years)
(2) Schofield – incorporates weight (kg) and age (years)
(3) Mifflin-St Joer – incorporates heigh(cm), weight (kg) and age (years)
There are also two other popular equations for estimating BMR/RMR. However, these require lean body mass (kg), which many individuals will not be able to accurately quantify (testing would be required):
(1) Cunningham – incorporates fat-free mass (kg)
(2) Katch-McArdle – incorporates fat-free mass (kg)
The above equations have been created from differing populations and it is therefore important to consider this limitation. For example, some have been used to predict energy expenditure within the general population and some within active or athletic individuals. Even though an equation has been used within athletic individuals this is not to say that it is applicable to all athletes, as some sports will have individuals of lower body mass (e.g. distance runners), whereas other sports will have athletes of higher body mass (e.g. rugby).
Research amongst professional rugby league players found that measured RMR was 16.5% (approximately 310kcal) lower than that predicted via the Cunningham equation. Furthermore, Cunningham, Harris-Benedict and Schofield equations typically underestimated total energy expenditure for u16 to u24 rugby league and union players, although an over prediction was seen in some instances, highlighting the great individual variability in predictions.
Energy expenditure prediction equations are not perfect and have their limitations. However, having said that, they can provide a rough initial figure for calorie intake, from which you can then re-evaluate progress (e.g. body mass) and make the necessary changes.
Not sure how to monitor your progress? Click here for a simple guide through the common methods.
Stage Two – Incorporating Physical Activity Demands
As mentioned above to calculate estimated total energy expenditure you must first utilise a prediction equation to estimate the energy you expend at rest. This is then multiplied by a Physical Activity Level (PAL) value that corresponds to your self-estimated activity demands. Below is a table outlining the range of PAL values from which to base your estimation.
Although useful, the above can be confusing for individuals when trying to estimate both their expenditure during the day (e.g. job) and training. We are not all professional athletes and therefore have to consider expenditure at work etc. This highlights a further limitation when predicting energy expenditure as be ability to accurately quantify your activity is difficult. This is why your initial estimate made need re-evaluating based upon your progress.
A PAL of 1.6 represents the average activity level of a normally active individual, but sedentary for periods. 2.0-2.5 is considered the PAL for athletes engaging in normal training, whereas a PAL of 2.5-4.0 for athletes engaged in rigorous training/competition
I have created a calculator which can estimates of energy intake based upon the energy expenditure prediction equations discussed above
Stage Three – Goal Adjustments
So you have calculated how many calories you may need to consume. But remember, this is to maintain your current body mass. What if you want to increase or decrease your body mass? Well, to do this you would need to implement a calorie surplus (increase body mass) or calorie deficit (decrease body mass).
There are two ways you can go about implementing the necessary changes:
This refers to a set a number. For example, to lose 0.5kg (1lb) of fat it is typically stated that a weekly calorie deficit of 3500kcal is needed. So if implementing the linear approach, this equates to a daily calorie deficit of 500kcal. You would therefore subtract 500kcal from your estimated daily calorie intake:
For those looking to increase size are therefore aiming for a calorie surplus, a typical strategy to increase body mass is to again utilise a weekly 3500kcal surplus to add 0.5kg (1lb) of muscle/mass per week. Technically muscle is not the same as fat, as there is only 800kcal in 1lb (0.5kg) of muscle. However it is an energy costly process to build muscle, so an additional kcal buffer from 3500 kcal can assist this muscle building process. However, caution must also be used with the utilisation of a higher than required surplus, as there is a risk that such an increase could result in excessive additional fat accumulation. Interestingly, it has been suggested that a 200-300kcal day surplus is more appropriate than 500kcal per day for individuals who have been resistance training for some years, as their rate of muscle gain will be much slower, and the smaller surplus will minimise fat mass gain.
This value is in reference to body mass. For example, you may wish to lose/gain X% body mass per week. Utilising a relative approach may be of consideration for lighter individuals with smaller total daily calorie intakes, as the absolute approach does not take into account the body mass of the individual. The utilisation of an absolute deficit of 500kcal+ may take calorie intake so low that you may struggle to fuel your training and recovery. From a psychological aspect the prospect of eating such low calorie intakes is not appealing! Utilising a % of body mass loss per week therefore may be a more appropriate method when estimating calorie intake for lighter individuals when reducing body mass.
I have created a calculator which can provide estimates of energy intake based upon the energy expenditure prediction equations discussed above. This also includes adjustments depending upon goal.
Before we go making changes, a quick word on rate of progress. The size of the calorie deficit or surplus can dictate the quality of the weight loss or gain. What do I mean by this? If in a deficit, a more extreme deficit could increase the risk of losing greater amounts of muscle mass, than if the individual were in a less severe calorie deficit. Whereas, when in a calorie surplus a moderate surplus may be more appropriate than an excessive surplus to minimise the accumulation of fat mass.
When some individuals set out on their fat loss or muscle gain journey the primary focus might be to see the numbers drop or increase on the scale and fast! Of course you want to see return for your efforts, but it is important to consider the quality of your returns.
However, there may be certain instances where a higher rate of weight loss may be desired, for example individuals that hold larger amounts of fat mass. In fact, it has been shown that fast initial weight loss enhanced motivation and aided dietary adherence amongst dieters. With regards to the size of calorie deficit implemented, when opting for a slower (0.7% weekly loss of bodyweight), compared to a faster rate (1.4% loss of bodyweight), individuals were able to preserve, or in some instances enhance, muscle mass and performance with greater fat mass loss.
When we think of muscle, thoughts immediately turn towards aesthetically pleasing physiques or performance. However, the maintenance or development of muscle mass should also be considered important from a health perspective. The greater the amount muscle mass an individual holds the greater the contribution to resting metabolic rate. Muscle is also a disposal site for glucose and lipid (fat) oxidation. Additionally, sarcopenia is a condition commonly seen amongst older individuals with a progressive loss of muscle mass and function with ageing.
What are suggested rates of muscle gain or fat loss? I typically refer to the approximate guidelines put forward by Alan Aragon:
Stage Four – Structure
It is important to re-iterate that consistency is needed when implementing such a nutritional strategy for the achievement of daily targets, and ultimately your weekly targets. It is easy to sell yourself short by not being consistent with energy intake and therefore not progressing at the expected rate. It is important to opt for a dietary setup that you will be able to adhere to, whilst suiting your individual training schedule. I shall now highlight two example dietary intake structure options.
In the above scenario I have highlighted the goal of fat loss. The individual is looking to decrease body mass and hoping to achieve a body mass loss of 0.5kg per week. As mentioned above, this would approximately require a weekly surplus of 3500kcal.
Option 1: Linear Approach
This would be considered a linear approach, as calorie intake is the same each day of the week. To lose 0.5kg per week then you would need to increase weekly intake by an additional 3500kcal. This on average over the week would require a daily decrease of 500kcal per day from your maintenance calorie intake, which would bring your new average daily intake.
If muscle gain/increase body mass is your goal, then you would do the opposite and implement a consistent daily calorie surplus. For example, if looking to gain 0.5kg per week, you would consider implementing adding an additional daily 500kcal to your estimated maintenance daily calorie intake.
Option 2: Non-Linear Approach
This would be considered a non-linear or undulating approach, as calorie intake varies across the days of the week. For example, if your daily maintenance intake is 3000kcal and you are looking to lose 0.5kg per week then you would need to decrease weekly intake by an additional 3500kcal. As above, this on average over the week would require a daily 500kcal per day decrease from maintenance calorie intake 3000kcal. However, the intensity/volume of your training sessions (e.g. weights, conditioning) or rest day would require varying amounts of daily energy expenditure. Therefore, you could vary your energy intake over different days to accommodate this and fuel training. When averaged out over the week you would still require a 3500kcal surplus.
If muscle gain/increase body mass is your goal, then you would do the opposite and implement a weekly calorie surplus. For example, if looking to gain 0.5kg per week, you would add an additional 3500kcal to your estimated maintenance daily calorie intake. The way you divide this across the week will be based upon personal preference and training demands.
Stage Five – Re-evaluation
This is often the part trainees often fail to implement optimally. As we discussed earlier, the energy expenditure predictions are just estimates – a starting point. It is therefore important to monitor your progress and make any necessary changes based upon re-evaluating your current strategy.
What could you monitor?
- Body Mass
- Body Composition
- Training/Competition Performance