Weight Loss & Calorie Restriction

Weight loss is a commonly held goal for many individuals undergoing body transformation.  Many people pursuing this objective exhaust cardiovascular exercise, like running or cycling, as strategies for accelerating weight loss goals.  However, few understand how weight loss occurs and the potentially damaging side effects of rapid, calorie restricted diets.   Read more to learn about best approach to safe and rapid weight loss.


Weight loss can be an incredibly challenging goal that can carry potentially health damaging effects .  Using an evidence-based approach to weight loss gives guidance to the safest and most effective approach to accelerating weight reduction goals.  Also, reviewing the literature provides insight into important considerations in weight loss that can potentially slow progress and reverse gains.  As a starting point, it is first important to understand a client’s physique goal.


  1. Weight loss
  2. Weight gain
  3. Weight maintenance

Once a goal is established, using optimal calorie intakes and macronutrient (fats, proteins, carbohydrates) combinations will largely determine whether a client meets their physique goal within the desired time frame.  Estimating food intake is useful for approximating how much food is necessary to direct daily eating habits.

Caloric Intake for Weight Loss

To generate weight loss, energy expenditure must exceed energy intake [3].  The danger arises if a client consumes high calorically-dense foods while maintaining a sedentary occupation with little daily, general movement.  Under these circumstances, weight gain is highly likely.  The scientific literature indicates that a single pound (0.45kg) of pure body fat metabolised yields about 3500 kcals, therefore a daily caloric deficit of 500 kcal would theoretically results in fat loss of 1lbs (0.45kg) per week [2].  A number of methods can be used to determine caloric intake.  One approach includes determining daily maintenance calories then reducing approximately 15% below maintenance food intake levels.  An alternative method, described below, sets a target body weight (TBW) then factors in weekly personal training hours and intensity.

How to Calculate Daily Calories

Calorie intake formulas are only a rough estimation that should be used as a starting point from which to make adjustments based on individual response.  Formulas are hypothetical at best and it ultimately comes down to the response of the individual.

Many formulas fail to account for TBW and weekly workouts.  Alan Aragon, a leader in evidence-based fitness and applied nutrition, accounts for both TBW and hours of training.  Aragon’s formula for daily caloric intake is one of many that can be applied [5].  Here is Aragon’s approach [5]:

Select a Target Body Weight

Step 1: Determine lean body mass

According to Aragon, lean body mass can be estimated by taking 25 percent of total body weight [5].  For example, an individual weighing 70kg would retain approximately 17.5kg of fat and 52.5kg of lean body mass.  Alternatively, a number of online calculators are available to compute lean body mass.

Step 2: Select lean body mass and multiply by 100

Even in losing body fat, an individual will typically aim to increase lean body mass to improve tone and definition in their physique.  A realistic target for an intermediate-level lifter is 1lbs or 0.45kg a month, which would equate to 3lbs or 1.35kg of lean muscle mass gain in 12 weeks.

Here is an example of a hypothetical client with goals to decrease overall body fat and increase lean muscle mass:

Client Current Total Body Weight: 70kg

Client Lean Current Body Mass: 52.5kg

Client Current Body-Fat Percentage: 25%

Client Goal: Increase lean body mass by 1.35kg and reduce body fat by 9% in 12 weeks

Target Lean Body Mass: 53.85kg (52.5kg + 1.35kg)

Target Body-Fat Percentage: 16% (25% – 9%)

Lean Body Mass Multiplied by 100 (Step 2): 53.85kg x 100 = 5,385

Step 3: Subtract Target Body-Fat Percentage from 100

Indicated in the chart below, Aragon sets realistic rates of monthly body-fat reduction [5]:

Monthly body fat reductions for weight loss

According to this chart, at 25% body-fat, a realistic rate of reduction is 2-3% body-fat per month.  Therefore, the example above of a client with a target body-fat percentage of 16% would be 100 – 16 = 84.

Step 4: Calculate Target Body Body Weight

To calculate target body weight, the figure in Step 2 is divided by the results of Step 3.


53.85kg x 100 = 5,385

100 – 16 = 84

5,385 / 84 = 64.1kg

In this example, the target body weight would be 64.1kg for a 12 week program.  The net loss for this client is 5.9kg (70kg total body weight minus 64.1kg target body weight).  Since the target weight in this example includes an additional 1.35kg of lean muscle mass, the actual loss is greater at 7.25kg over 12 weeks.

Calculating Daily Calories 

Step 1: Estimate Total Weekly Training Hours

This includes strength training and any cardiovascular exercise.  Also, recreational activities or sports like hiking, cycling or landscaping are further included.  For example, an individual who participates in two gym workouts a week of strength training lasting 1 hour, and 2.5 hours of cycling a week, engages in a total of 3.5 weekly hours of training.

Step 2: Estimate Weekly Training Intensity

This refers to intensity of effort and is defined numerically by the following:


Woman or less active person:

8 = low intensity training

9 = moderate intensity training

10 = high intensity training


Man or more active person:

9 = low intensity training

10 = moderate intensity training

11 = high intensity training


Step 3: Calculate Daily Calories Using the Formula


Target bodyweight (TBW) (lbs) x (8-10 or 9-11 + total weekly training hours) = Daily Calorie Intake


Target bodyweight (TBW) (kg) x ((8-10 or 9-11 + total weekly training hours) * 2.2) = Daily Calorie Intake


Here is an example of calculating daily caloric intake using the previously indicated hypothetical client:

Client gender: Female

Client weight: 70kg

Client target bodyweight: 64.1kg

Total weekly training hours: 5 hours

Weekly training intensity: 9 (moderate intensity training)

64.1 x ((9 + 5) *2.2) = Daily Calorie Intake

64.1 x 30.8 = Daily Caloric Intake

1,974.28 = Daily Caloric Intake

The daily caloric intake of this individual would be 1,974.28.

Important Considerations in Weight Loss

Lean Body Mass Changes in Weight Loss

Important to consider during a caloric deficit is the amount of simultaneous tissue loss [3].  It is accurate in saying that greater caloric deficits lead to accelerated weight loss, however a percentage of weight loss occurring from lean body mass (LBM) will simultaneously incur as caloric deficit increases [3].  Garthe and colleagues (2011) compared weekly weight loss using either a slow reduction of 0.7% or fast reduction of 1.4% of total body weight [1].  Their study found that fat mass decreased to a greater extent in the slow reduction group compared with fast reduction (31% vs 21%) [1].  Also, LBM increased by 2.1% in the group that used a slow reduction (0.7%) of weekly weight loss compared with no change in the group that used a fast reduction (1.4%) weekly weight loss [1].  The authors of this study suggest that a slower weekly reduction of 0.7% LBM is more effective for body weight loss and LBM gains compared with faster rates of weight loss [1].

An additional consideration in weight loss is the initial level of LBM.  The less adipose (fat) tissue available, or, the leaner a client, the greater the possibility of LBM loss [3].  This may have observable consequences in the physique of an individual, which may run contrary to the desired look.

Metabolic Adaptation in Weight Loss

Also, with increased calorie restricted diets, a process called metabolic adaption occurs whereby unfavourable changes in energy expenditure, circulating hormones and mitochondrial efficiency end up slowing weight loss and actually promoting weight gain [6].  In humans, metabolic adaptation is the body’s way of conserving energy and returning it to baseline body mass [3].

Changes in Energy Expenditure to Weight Loss

Interestingly, research has consistently shown that in weight loss, total daily energy expenditure (TDEE) decreases [6].  TDEE is composed of a number of components including basal metabolic rate (BMR), non-exercise activity thermogenesis (NEAT), thermic effect of food (TEF) and exercise activity thermogenesis (EAT) [6].

Because weight loss results in a loss of metabolically active tissue, there is a drop in BMR (the amount of energy burned at rest), therefore a reduction in TDEE [6].  Some research suggests that this resulting drop on BMR from weight loss is due to the body attempting to restore baseline body weight [6].  This process, deemed adaptive thermogenesis, could be used to explain why weight loss plateaus even during caloric deficit and why weight is commonly regained following weight loss [6].

Even energy expended during exercise, know as exercise activity thermogenesis (EAT), is found to decrease with weight loss [6].  With reduced body weight, the body requires less energy to complete a given activity [6].  With respect to TEF, which relates to the energy expended while eating and metabolising food, dietary restriction means that less calories are consumed, therefore directly decreasing absolute TEF [6].  Finally, there is evidence demonstrating that non-exercise activity thermogenesis (NEAT) levels are decreased in calorically restricted subjects [6].  A reduction in NEAT can subsequently result in weight-gain following a diet period [6].

Changes in Hormonal Response to Weight Loss

A number of studies report endocrine (hormonal) changes in response to calorie restricted diets.  Research examining calorie restricted diets show leptin, a hormone regulating energy intake and expenditure by inhibiting hunger, is decreased, while the appetite promoting hormone ghrelin is found to increase with hypocaloric (low-calorie) diets [6].  Likewise, additional endocrine hormones like insulin, testosterone and cortisol have all been found to potentially increase hunger and reduce metabolic rate and lean body mass maintenance in response to a calorie restricted diets [6].

Changes in Mitochondrial Efficiency

Adenosine triphosphate (ATP), a molecule in the body that stores and transports energy used for all activity, requires a number of different chemical reactions to take place [6, 4].  In aerobic metabolism, ATP is produced by transporting protons across the inner mitochondrial membrane [6].   During this process, protons may leak in the mitochondrial membrane and release energy [6].  In animal studies, this process of proton leak can account for about 20-30% of BMR [6].  In circumstances of dietary calorie restriction, proton leak declines, therefore reducing the amount of energy expended [6].  In the context of weight loss, this reduction in proton leak can make losing weight more challenging and even encourage weight gain [6].




Weight loss personal trainers Edinburgh

Proton leak in mitochondrial membrane resulting in released energy


With the majority of our clients sharing weight loss goals, understanding the safest and most effective method for achieving this goal is imperative.  Using formulas to estimate food intake and rate of loss are useful for setting realistic expectations of progress applying more specificity to the reduction process.  Importantly, a number of metabolic adaptation occur during weight loss that can slow and even reverse progress as a way for the body to restore baseline body mass [6].  It is advocated that a weight loss process using slow and small, incremental energy deficits are best for weight loss.  Also, to ensure retention and development of lean body mass, a progress resistance gym program and attention to sufficient protein intake are essential [6].



1. Garthe, I. et al. 2011. Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. International Journal of Sport Nutrition and Exercise Metabolism. April. Vol.21, No.2, pp.97-104.


2. Hall, K.D. 2008. What is the required energy deficit per unit weight loss? International Journal of Obesity. March. Vol.32, No.3, pp.573–576.


3. Helms, R. E. et al. 2014. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition. May. Vol.11, No.20. pp.1186/1550-2783-11-20.


4.  May, P. Adenosine Triphosphate: ATP – Nature’s Energy Store. Retrieved from: http://www.chm.bris.ac.uk/motm/atp/atp1.htm.


5.  Schuler, L. & Aragon, A. 2014. The Lean Muscle Diet. How to Calculate Daily Calories. Rodale Inc. New York, NY.


6.  Trexler et al. 2014. Metabolic adaptation to weight loss: implications for the athlete. Journal of the international Society for Sports Nutrition. February. Vol.11, No.1. pp.1186/1550-2783-11-7.



Leave a Reply