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Why is Calories in Versus Calories Out so Confusing?

Written By

Jeremy Boyd


Nutrition, Personal Training

Posted On

8 December 2014

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At the time of writing, one of the greatest divides in the field of nutrition is the debate over the calorific model for weight loss.

But why?

The first law of thermodynamics is often touted as irrefutable proof of the CICO model. The law itself states that:

“The increase in internal energy of a closed system is equal to the heat supplied to the system minus work done by it.”

i.e. Take the energy supplied to the body, remove from that amount what you use, and what you have left is stored.

Because the underlying foundation of the CICO model is a law of physics, the CICO evangelists can have a hard time even considering anything else that lacks an equivalent scientific basis. As a result of this potentially myopic viewpoint, there may be other factors that play a part in the long term success of CICO as a strategy.

The most commercially successful weight loss programmes in the world all use a CICO model as the main principle behind their method. Whilst their short term results show a high degree of success, the long term picture shows a high percentage of customers regaining the lost weight (for one company, over 90%).

So what do you need to know?

Technical Factors

1. Based on every piece of scientific literature available at the time of writing and decades of research, the first law of thermodynamics is irrefutable.

2. Calorific needs are almost impossible to quantify with a formula. You might be able to get a predicted baseline, that’s fairly accurate, but the reality could be a long way off in either direction. This is because there are a large number of variables that play a part in the energy equation:

  • Digestion Speed
  • Gut Permeability
  • Excretion
  • Nutrient Density
  • Metabolic State
  • Activity Levels
  • Body Composition
  • Time of Day
  • Thermic Effect of Food
  • Sleep Patterns
  • And many more...

3. Everyone is different. There have been examples of individuals who’ve consumed nothing but potato for weeks on end and seen a number of health markers improve and lost weight. Other people have overeaten by thousands of calories a day with very little to show in terms of weight gain. One of the greatest flaws when evaluating evidence is to assume that if a result occurs from a particular strategy when n=1 (n = number of subjects), then it can occur for everyone.

4. Macronutrients affect where the weight is gained and/or lost, but do not always affect the total amount.

5. Whilst not true in every case, protein seems to be the most important macronutrient to track. Research shows that having adequate levels of dietary protein can help increase satiety, reduce catabolism, raise metabolism and enhance nitrogen synthesis.

6. Long term average intake matters more than daily intake. This means that fluctuations from day to day are less important than the overall mean intake. So for an individual that requires an average of 2000 calories a day, having 1600 on one day and 2400 on the next, doesn’t matter as much as some people think. It should be noted that this applies predominantly to weight loss rather than performance.


  1. There’s a big difference between calorie reduction and calorie counting. It’s possible that this is in essence the cause of the divide between the two camps. The CICO group may be approaching the debate from a literal perspective, whereas the Anti-CICO crowd may be interpreting these two terms identically. Calorie reduction means exactly that, regardless of whether its obtained directly (eating less) or indirectly (consuming more nutrient dense, but less calorie dense foods). Calorie counting means the deliberate and detailed tracking of calorie consumption. This distinction is an important one as the arguments from both sides seem largely to be as follows:
  2. Anti CICO “You don’t have to count calories to lose weight” CICO “You can’t lose weight without a reduction in calories”

    Both statements are correct, but they’re often perceived as conflicting, when in fact they simply represent two completely different perspectives.

  3. From a psychological perspective, focussing on calories directly at the outset may result in individuals ignoring other aspects of nutrition, such as food quality, meal timing, portion control and macronutrient ratios. Equally, trying to address all of these at the same time may overwhelm people.
  4. One of the reasons that the Anti-CICO group argue so vehemently, is that the long term results for individuals who create a caloric deficit indirectly, by choosing less calorie dense versions of, or alternatives to particular foods, are much better in terms of sustainability.

    Also, by addressing eating habits, coaches can address the underlying cause of the weight issue, rather than the symptom.

    That said, it is still possible to over-consume calories whilst avoiding processed and refined foods, particularly with naturally calorie dense ‘health foods’ such as nuts, olives and avocadoes. In these instances, being aware of the average number of calories consumed daily is critical to achieving a successful long-term outcome.

  5. If weight loss stops and more is required, a reduction in calories is necessary.
  6. Stalling and stopping are not the same thing. Weight loss is very, very rarely linear. Therefore changes in bodyweight should be tracked and monitored continuously and ideally on a weekly basis. If there is no movement for a period of 4 weeks or more, then weight loss has probably stopped and calories should be adjusted (either directly or indirectly).
  7. Body-fat is not the only source of energy. In the presence of a caloric defecit, the body has a number of options:
    • Use fat for fuel
    • Use glycogen for fuel
    • Use muscle for fuel
    • Reduce internal cellular activity

    The last is another one of the reasons for the conflict between the two positions on calorie intake. Whilst energy cannot be created from nothing, it does not all have to come from the same source or be used the same way. Some individuals respond to calorie deficits (typically those that are too aggressive and too prolonged), by calorie sparing. This means that instead of using fat for fuel, they simply defer or slow down things like tissue repair, digestion and other internal functions. These cases are normally rare, but can occur and are normally evidenced by above healthy bodyweight AND poor health, despite significantly lower than suggested calorie intake.

  8. Deliberate calorie reductions should be as small as possible to promote weight loss. If you can stimulate weight loss with a reduction of 50 calories a day, why reduce calories by 100 calories a day? The body is always seeking homeostasis and as such will try and find ‘normal’ as quickly as possible. Reducing calories too quickly, limits options in the future. Always go with the minimum effective dose (MED in pharmacology is the lowest dose or amount of a drug that produces a therapeutic response or desired effect in the subjects taking it).
  9. Most of the CICO debate is for debate’s sake as the facts are undeniable. They are unfortunately often misinterpreted or misrepresented, which is what causes the disagreement.

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