What does “calories in, calories out” really mean – and is it still valid for weight loss?
Despite all the noise online and on TikTok, the CICO principle is still fundamentally true: if you consistently eat more calories than your body burns, you’ll gain weight. If you consistently eat fewer, you’ll lose weight. But that doesn’t mean it’s simple. Hormones, appetite, movement, and mindset all affect how easy or hard that calorie gap is to manage. Understanding how CICO actually works – and how it fits into real life – is still essential for sustainable fat loss.
So, let’s break down CICO and see what it’s all about:
What are Calories?
In layman’s terms, a calorie is a unit of energy. Think of it like the petrol you put in your car. Everything we eat and drink, barring water, provides us with calories, which our bodies use to power every function, from running a marathon to simply breathing.
Calories In
This refers to the calories we consume through food and drinks. Every slice of bread, every sip of a drink, and every bite of cake introduces calories into our system. The amount of calories in different foods can vary widely.
Calories Out
Here’s where things get active – literally. Our bodies are continuously expending calories in several ways:
- Basal Metabolic Rate (BMR): This is the energy our bodies use at rest for essential functions like breathing, keeping our heart beating, and maintaining body temperature. Even if you lay in bed all day, your body would still burn calories!
- Physical Activity: This is the energy we expend doing everything from intensive exercise sessions to simple tasks like walking to the shop or tidying up the living room.
- Thermic Effect of Food (TEF): Believe it or not, eating burns calories too! Our body uses energy to digest, absorb, and process the nutrients in our food.
- Non-Exercise Activity Thermogenesis (NEAT): This involves the calories burned during everyday activities that aren’t considered formal exercise – think fidgeting, standing, or even the act of typing on a keyboard. NEAT can vary significantly from person to person and can make a big difference in daily caloric expenditure.
Balancing the Equation
The CICO principle revolves around balancing the ‘calories in’ with the ‘calories out’:
- Weight Maintenance: If you consume the same number of calories as you burn, your weight remains stable.
- Weight Loss: If you burn more calories than you consume, you’ll lose weight. This is often referred to as a calorie deficit.
- Weight Gain: Conversely, if you consume more calories than you burn, the surplus energy is stored, leading to weight gain.
Common Myths About Calories In, Calories Out
“CICO is outdated and doesn’t work anymore”
You’ll often hear people say that the idea of calories in versus calories out is too basic or no longer relevant. The truth is, it still holds up. Every fat loss method, whether it’s keto, fasting or tracking macros, works by creating a calorie gap. The method might vary, but the principle doesn’t.
“It ignores hormones and metabolism”
CICO doesn’t ignore these things. It just doesn’t explain them all in one go. Hormones, metabolism and even sleep affect how many calories your body burns and how hungry you feel. They influence the numbers, but they don’t erase them. You can still apply the principle while recognising that your body is complex.
“You have to track everything to make it work”
Some people think CICO means weighing every meal and logging every bite forever. That’s not true. You can create a calorie gap without tracking at all. It might take more time and awareness, but small changes to portion sizes, food choices and movement can still lead to results.
“It means calories are all that matter”
CICO explains why fat loss happens, but it doesn’t mean you should ignore nutrition. What you eat still matters for your energy, mood, and overall health. Focusing only on numbers and ignoring things like protein, fibre and food quality can leave you feeling tired or hungry, even if you are in a calorie deficit.
Real-Life Examples of How People Misjudge Calories
Underestimating portion sizes
It’s easy to think you’re having “just a spoonful” of peanut butter or “a splash” of oil, but those little extras add up quickly. A tablespoon of oil has around 120 calories, and that handful of nuts might be closer to a small meal than a snack. Many people eat more than they realise simply because portions aren’t as small as they seem.
Forgetting about drinks
Lattes, fruit juices, energy drinks and alcohol can quietly push your intake up. One or two drinks a day might not seem like much, but over a week, they can add hundreds of extra calories. Even “healthy” smoothies or protein shakes can be more than you need if you’re already eating enough.
Eating more because you exercised
After a workout, it’s common to feel hungrier or to think you’ve “earned” a treat. But many workouts don’t burn as many calories as people expect. A 30-minute jog might use 250 calories, while a takeaway afterwards can easily top 1,000. The result is a calorie surplus even though you’ve trained.
Snacking out of habit, not hunger
It’s easy to grab a snack while watching TV, working, or just because it’s a certain time of day. These automatic habits can be hard to spot, especially if you’re not physically hungry. Over time, they can tip you into eating more than your body actually needs.
Relying on food labels or fitness trackers
Calories listed on food packaging or burned during exercise are only estimates. Your body might absorb more calories than the label suggests, and your watch might be overestimating how active you’ve been. These tools are useful, but they’re not always spot-on.
So, How Do You Use CICO Effectively?
- Awareness: Begin by getting a rough idea of how many calories you consume daily. Tools like food diaries or smartphone apps can be handy still.
- Know Your Burn: While it’s challenging to get a precise number, various online calculators can provide an estimate of your daily calorie expenditure based on factors like age, gender, weight, and activity level.
- Set Your Goal: If you’re looking to lose weight, aim for a calorie deficit, which often falls in the range of 500-1000 calories less than your daily expenditure for a safe weight loss of about 0.5 to 1kg per week. 500 less calories is, for most people, more sustainable but it may vary of course. Everyone is different.
- Quality Matters: Remember, while CICO focuses on calorie quantity, the quality of your diet matters too. 500 calories of vegetables, lean protein, and whole grains are nutritionally superior and more filling than 500 calories of sugary snacks.
CICO Recap
- Long-term success comes from creating a sustainable calorie gap, not a perfect one.
- Calories in vs. calories out still forms the foundation of fat loss.
- It explains what happens – not always why it feels easy or hard.
- Hormones, hunger, energy, mood, and movement all affect how CICO plays out.
- You don’t need to obsess over numbers – but you do need awareness.
The “Calories In, Calories Out” principle is a fundamental concept for weight management. While it provides a foundational understanding of how weight changes occur, remember that individual needs can vary, and factors like hormone levels, sleep, exercise type, and stress can all play roles. Always consult with a healthcare or nutrition professional (such as a weight loss coach) before making significant changes to your diet or lifestyle.
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