From a young age, most people hear about the idea of a caloric balance. That is how to balance how much energy we take in and how much energy we "need" to expel to reach an ideal ratio. Most of us hear about CICO (Calories in/Calories out) from a weight loss/diet culture lens. Why would we even talk about this ratio if it weren't for society's obsession with weight loss? The connection that most of society has drawn is that if someone takes in more Calories than they burn off, they will gain wait. If they consume and burn off the same amount of Calories, they will maintain their weight and if they burn more Calories than they consume, they will lose weight. Easy and straightforward, right? Well, the reality is not actually that easy.
Firstly, I want to acknowledge that I do not subscribe to society's obsession with weight loss and thinness. I prefer to focus on someone's actual wellbeing and their body size is not part of that equation. Also, I want to acknowledge that I am an "anti-counting" dietitian. I try to steer away from fixating on numbers to determine how much or little anyone should eat. The focus is meeting needs, right? And when we're talking about holistic nutrition, Calories (kcals) aren't the be all end all of what our "needs" are. We have to consider all of our macro and micro nutrients, electrolytes, and fiber. We also have to consider our mental health, and counting all markers of nutrition may have a negative impact on our quality of life.
So, let's get into some of the reasons that CICO isn't a reliable way to determine dietary needs.
Reliability: It's extremely difficult to know how many Calories are in the foods that we have on a regular basis. To truly figure out how many Calories are in food items, we would need a bomb calorimeter, which is likely expensive and also primarily exists in labs and would be very difficult to get ahold of. What we're left with are estimations. Even though our food labels use pretty specific numbers (i.e. 41 kcals per serving), it's all still an estimate. This applies not just too our food labels, but any of your favorite Calorie counting apps, websites, or formulas.
When talking about Calories, those apply to all food items, so it's important to talk about the difference in where we get our Calories from. Eating 100 kcals of kale is not the same as 100 kcals of pizza. I am not saying that one is better than the other. We get important nutrients from both of these foods, however, we get different nutrients from those 100 kcals depending on the food.
Accuracy: We typically use formulas to estimate our energy needs as a reference point when thinking about CICO. These formulas vary and are again, estimations. All of these formulas are helpful in a pinch for registered dietitians, however, they all have their flaws. The only way to truly get a baseline of how many Calories you need is to measure resting metabolic rates (RMRs) through a metabolic cart, which is again, expensive, in a lab and therefore difficult to access. Let's say you run one of those estimated energy need equations and it pops out that at rest, you burn 1000 kcals, but when you do a gold standard RMR test, it shows that you're actually burn 1500 kcals at rest. That's a big difference! It may seem like that is rare, but it surprisingly isn't. I actually worked in a metabolic lab for 2 years and saw this result on a daily basis. If anything, it was rare to see someone's actual RMR within even 100 kcals of what an equation predicted for that person.
Physicality: CICO is a very simplistic outlook, which is why it is likely so comfortable for most people. We like concrete facts most of the time. However, our bodies are complex and unique to us, and most of the time, our own physiology will get in the way of CICO. Certain disease and disorder states can have a large impact on our metabolisms as well as medications and our mental states. Thyroid disorders are very common hormonal conditions that affect how fast or slow metabolism is. Physical trauma also plays a huge role. If I get a concussion, my metabolic rate is likely going to go up just from that head trauma alone.
CICO also tends to ignore our body's actual needs and usually leads to eating too little, be that intentionally or accidentally. When we don't give our bodies what they need, our bodies have to slow down to preserve the energy that we take in. To do that, metabolism will slow down. We can enter starvation mode and our bodies start to hang on to fat for survival. Needless to say, if you're trying to decrease your Caloric intake to lose weight, that may not happen. Our bodies will start to break down stored carbohydrates in our muscles and liver. Our brain gets up to 90% of the energy that we consume and that's where most of our intake will go just so that or organs can continue to function. Because our body is focusing on survival, we are at a higher risk for illness, injury, and other physical signs of malnutrition that are invisible many times (osteoporosis, inappropriately low resting heart rate and blood pressure, etc.).
When we place our bodies into energy deficits on a regular basis, it will confuse our bodies because the amount of energy that it receives becomes chronically unreliable. This is what leads to weight cycling. Maintaining an energy deficit long term is extremely challenging and eventually, we physically and mentally give up, which usually manifests as overeating or binging just to make up for all of the derprivation.
Our bodies are smart and will do what they need to protect us at any costs. If you notice that you regularly restrict your Calories and aren't losing weight, that's your body protecting you.
References:
University of Sydney (2023) It's Time To Bust the 'Calories In Calories Out' Weight Loss Myth
Chika Anekwe, MD, MPH (2022) Exercise Metabolism and Weight: New Research From the Biggest Loser at https://www.health.harvard.edu/blog/exercise-metabolism-and-weight-new-research-from-the-biggest-loser
Shawna Williams (2021) Extreme Exercise Carries Metabolic Consequences: Study at https://www.the-scientist.com/news-opinion/extreme-exercise-carries-metabolic-consequences-study-68581
Woods, A., Rice, A., Garvican- Lewis, L., Wallett, A., Lundy, B., Rogers, M., Welvaert, M., Halson, S., McKune, A., Thompson, K. (2018) "The effects of intensified training on resting metabolic rate (RMR), body composition, and performance in trained cyclists" PLoS One 13(2) doi: 10.1371/journal.pone.0191644