Calories In Vs Calories Out Myth
If you are over the age of 35 then you’ve probably believed or at least heard of “calories in, calories out” in the context of nutrition as a formula for weight management or solution to your weight “problem”. The scientific explanation of CICO is based on the law of thermodynamics, which states that energy cannot be created or destroyed, only converted from one form to another. In principle, this means that if you consume more calories than your body burns, you will gain weight, and if you burn more energy than you consume, you will lose weight. On its face, this principle is simple. From a scientific point of view, running a calorie deficit once you figure out your energy requirements works. After all, eating keto, paleo or Mediterranean can be a more complicated way to manage weight. Also, following the CICO method, there are no off-limit foods as long as you stay under the calorie threshold. Forget limiting dairy, cutting carbs or increasing protein or fats! But this simplified, mathematical approach to weight loss, while theoretically true, in practice is incredibly misleading, short-sighted and ultimately fails when accounting for individual differences.
First, we need to understand how science counts calories. How do we know the energy requirements to reduce our caloric expenditure in the first place? The BMR or basal metabolic rate refers to the amount of energy your body needs to maintain homeostasis. BMR is the energy your body uses at rest to maintain basic functions like breathing, circulation, and cell activity. Your BMR includes only the energy (calories) necessary for basic, life-sustaining functions. It does not include additional calories needed for daily activities, such as walking, moving, and exercising.
Factors influencing BMR include age, sex, body composition (muscle vs. fat), and genetics. Males generally have a higher BMR than females due to having more muscle mass. As you age, your BMR tends to decrease, which means that your body requires less energy to perform basic functions, leading to a slower metabolism. Measuring your BMR can be calculated using direct calorimetry, indirect calorimetry, or a quick math equation. Direct calorimetry is the most accurate method. It involves spending time in a tightly controlled room, known as a calorimeter, with little to no movement. However, it’s typically used only in research settings and is difficult to access. Indirect calorimetry involves using an in-office device that measures the exchange of oxygen and carbon dioxide in your body. Knowing your BMR can provide some insight, but it does not paint a full picture of your health. Three main factors can affect how your body processes calories:
Processed vs Natural Food
According to a 2019 study that measured effective strategies for obesity prevention, it concluded that despite ultra-processed and unprocessed diets being matched for daily presented calories, sugar, fat, fibre, and macronutrients, people consumed more calories when exposed to the ultra-processed diet as compared to the unprocessed diet. Not all food is created equal and our bodies know this! Another study at The National Institute of Health found that ghrelin, a hormone that drives hunger, is higher when people consume ultra-processed foods compared to eating a well-balanced diet. If appetite and hunger are driving food choices it is clear how processed foods set up a dysfunctional loop: hunger leads to eating more (because you’re still feeling hungry), non-satiety signals to the body to conserve energy (energy is stored as fat to be converted later into energy) and the loop continues.
Gut Microbiome
The discovery of the gut microflora originated and was first written about in Western literature in the 1840s but in the last two decades, we have seen more studies and interest in understanding the gut microbiome. This research is rapidly changing the way we understand human health and medicine. Ever since the publication of the Human Microbiome Project in 2012, and the realization that our bacteria outnumber our cells, we have become more interested in this area of research.
It’s estimated that roughly 90% of the body's serotonin is produced in the gut, specifically cells that line the gastrointestinal tract. While a small percentage is produced in the brain, serotonin, also known as 5-hydroxytryptamine or 5-HT, is a neurotransmitter and hormone that plays a crucial role in various bodily functions, including mood, digestion and immune responses. It turns out the gut microbiome, a community of microorganisms that are found in the gut, plays a significant role in obesity, influencing nutrient absorption, energy storage and metabolism. A quick search online reveals that certain gut microorganisms are more efficient at extracting energy from food which may lead to increased calorie absorption and storage in overweight individuals as well as regulating metabolic processes, including lipid metabolism and glucose regulation which plays a direct role in diseases such as diabetes. Gut bacteria also help regulate appetite and energy which we know influences food intake. According to this source, some researchers have come to think of the gut microbiome as an endocrine organ, facilitating and responding to homeostatic and physiological changes in the body.
Your Metabolism
It seems our bodies have a natural “set point” for weight and it is governed by the hypothalamus (a region in the brain that controls temperature) located at the base of the brain. Our weight set point is a reflection of several factors that include genes, environment and behaviour. Even after losing a large amount of weight, the body has what is recognized as ‘metabolic adaptation’ which makes it incredibly difficult to keep the weight off. So often, unless environment and behaviour are consistent with supporting the loss of weight, individuals will regain the same weight or more.
In a review on exercise and gut physiology, ‘…exercise has protective effects, reducing the risk of colon cancer, diverticulosis, and inflammatory bowel disease.’ There is clear and uncontested evidence that exercise in general not only plays a positive role in weight management but is also beneficial in cases where there is a high-fat diet, with exercise reducing inflammation, improving circulation and reducing colon diseases as well as supporting cognitive functions. While age, genetics and sex differences cannot be altered, increases in muscle mass (the constant variable that can be adjusted through exercise) result in a higher metabolic rate, energy expenditure as well as improved nervous system function. Improving or exciting parasympathetic nervous system function can trigger a reduction in stress and cortisol levels. Particularly relevant for women in peri and post menopause, on its own, can help regulate sleep and mood disturbances as well as support bone maintenance and health. Overall, exercise seems to have potent effects in signalling mTOR or muscle fiber adaptations leading to muscle growth and changes in body composition.
Consistent calorie tracking raises awareness of portion sizes and foods as well as appealing to simplicity and flexibility, so long as you adhere to the calorie restriction aspect of the diet. It cuts out all the excess information and sticks to a basic premise, which is to reduce energy/caloric consumption. Critics of CICO downplay the awareness factor that it may generate. Discovering that you consume excess calories in sweet drinks and processed foods can have a powerful effect on your food choices. The ‘awareness’ part of the CO can be extremely useful. Becoming more aware of your in/activity level on a weekly and daily basis will also help to create a plan that focuses on energy expenditure and exercise consistency.
The narrow focus on numbers can create a distorted view of health, which prioritizes restriction and can potentially lead to disordered eating and bingeing cycles, while the focus on exercise can become excessive as a weight management tool when the quality of the CI is not prioritized. From a purely calorie-counting perspective, muscle mass, age, hormones and genetics are largely ignored. Yet we all know that 300 calories from a donut will have different effects on the gut and the brain compared to 300 calories from lean protein and complex carbohydrates. Biomarkers for health consider age, muscle-to-fat ratios, blood-glucose levels and hormones.
Calories in, calories out is a formula that ignores a variety of metrics such as sex, age, energy levels, food quality, gut microbiome, insulin, etc.. The idea of weight loss should be replaced with an approach that views eating and food through the lens of choices that prioritize body composition, food quality and eating with more awareness. By dropping the language of “weight management” and calorie counting, we shift out of pathology and disease. Adopting an approach that considers why we are eating vast amounts of processed foods and asking where our food comes from, how it is prepared and how it connects and fuels us, we judge ourselves less critically, view food less clinically and more fundamental to our well-being.
