When it comes to weight loss, there’s no topic so hotly debated than the old ‘calories in vs calories out’ (CICO) adage. At one end of the argument, nutritional and weight loss advocates typically promote the 'eat less, move more' angle. In contrast, endocrinologists at the other end of the conversation suggest that hormonal issues may be the pesky cause of weight gain.

Understanding CICO is simple: when we consume more energy than we burn, we gain weight, and when we consume less energy than we burn, we lose weight.

It's a fundamental concept in regulating body weight and as close to scientific facts as we can get, so why is the discourse around CICO so volatile?

Here, I attempt to unpack different arguments in the CICO saga, which should hopefully paint a picture that CICO isn't just black and white but a multifaceted, many-layered proposition.

To Fitbit, Or Not To Fitbit

Fitbits and fitness apps are a huge industry, with the fitness app market revenue expected to hit $298.3bn by 2026. Following the CICO train of thought, Fitbits' main selling point is tracking steps and counting calories to encourage a calorie deficit. While this is all well and good, it doesn't consider the bigger picture of weight loss.

For example, not all calories are created equal. A calorie tracker doesn't differentiate between whether or not you blow your daily calorie intake on Haribo or high-fibre, high-protein foods: as long as you stay within your calorie budget, the tracker will give you a digital pat on the back.

Another phenomenon that such apps perpetuate is moral licensing – the psychological rationalisation that we can overindulge because we’ve done an hour on the cross-trainer, which often leads to us negating the calories we burned while working out.

While CICO is a way to instigate weight loss, fitness products tend to place too much emphasis on a calorie deficit rather than establishing a foundation of proper nutrition or considering other determining factors.

Understanding your BMR

If you're a self-confessed gym bunny, then the chances are you've had your basal metabolic rate (BMR) calculated at some point. However, if you're reading this and thinking, 'what the hell is a gym?!' then it may not be a concept that you're familiar with.

Your BMR is a calculation of the number of calories your body burns at rest to maintain your normal bodily functions. It’s also a calculation of the number of calories your body burns daily, irrespective of exercise. Everything from your heart pumping blood around your body to your lungs admitting and expelling oxygen burns calories, with up 60-75% of your daily calories being burned by these processes.

While an 18-year-old may have a high BMR (damn those pesky youngsters), it's something that can slow down with age. Taking into account vital extremities such as a person's age, weight, height, and activity levels, understanding your BMR can help you to figure out how many calories your body burns each day, and there are a number of online BMR calculators that provide a crucial starting point for those wanting to lose weight, maintain their current weight, or gain weight.

What is TDEE?

Total Daily Energy Expenditure (TDEE) calculates the calories you burn per day, but unlike BMR, it includes physical activity.

While BMR touches upon the calories burned by our body’s everyday processes, TDEE takes into account anything physical, such as working out, climbing the stairs in the M&S car park, or taking the bins out: if it includes movement, TDEE is at play.

If you’ve calculated your BMR, then you can use your TDEE to calculate an estimate of how many calories you need for your level of physical activity.

BMR x 1.2 (sedentary, little/no exercise)

BMR x 1.3 (light exercise, typically 1-3 days per week)

BMR x 1.55 (moderate exercise, 3-5 days per week)

BMR x 1.725 (heavy exercise, 6-7 days per week)

BMR x 1.9 (highly physical job and heavy exercise, 6-7 days per week)

This calculation works out the number of calories your body needs to maintain your current weight. A 500-calorie-per-day deficit is one method to lose weight. Still, many experts instead recommend reducing your calorie intake by 10-20% of your TDEE, as a reduction of 500 calories can often make your calorie goal less than your BMR, which can force your body into starvation mode, whereby your body stores emergency energy, much like a squirrel stores nuts for a long, cold winter.

A NEAT little trick

I'm aware I'm just throwing every weight loss acronym at you but bear with me.

Non-Exercise Activity Thermogenesis (NEAT) is the energy we burn that isn’t sport-like exercise, bodily processes, or sleep. Opening the curtains in the morning, getting showered, or walking to the staff room to make a cup of tea are all forms of NEAT.

As the word implies, thermogenesis is the process of heat production in most living things. Burning calories generates heat, so any activities (and even some foods) that encourage a boost in our metabolism or burn fat are considered thermogenic.

NEAT exercise is a supplementary form of burning more calories. We've all been told to ditch the car and pound the pavement to work or give the elevator the middle finger and take the stairs instead, and these minor changes can help increase our TDEE and, in turn, our overall calorie burn.

Other affecting factors

While all the above are excellent ways of managing your energy consumption and expenditure, other factors outside of CICO can affect weight gain, maintenance, and loss.

Genetic makeup, age, health conditions, and environmental/social factors ensure that CICO isn’t just plain black and white.

As touched upon earlier, health professionals know that everything from hormone imbalances, polycystic ovary syndrome (PCOS), and insulin resistance can affect our metabolism, and indeed our weight journey; geneticists suggest that some racial and minority groups are more likely to be obese due to their genetic makeup; and sociologists advocate that environmental factors can affect weight, such as proximity to (and the quality of) neighbourhood restaurants and supermarkets.

If you've got this far through all the acronyms and mind-boggling information, you've probably made up your own mind that CICO isn't the straightforward proposition that some sources purport.

What I do hope you’ve taken away from this, though, is that flexibility of thought is likely to help you succeed on your weight journey. If you’re willing to experiment with the different ways to influence CICO and to trial what does and doesn’t work for you, then you’re well on your way to finding a strategy that helps you master an energy balance that’s in your favour.

Calories In, Calories Out: Is It That Black and White?