Weight lose, and gain, is very simple:
- You cannot gain weight without a calorie surplus
- You cannot lose weight without a calorie deficit
Period. Nothing more, nothing less. But, you’re saying to yourself, I’ve trimmed 500-1000 calories out of my diet, and I’m still not losing weight!!! I measure it all!!! I’ll explain!
Here is an expansion on that point, breaking down the science of thermodynamics, the psychology of eating, and the common pitfalls that create the illusion that the laws of physics have stopped applying to your body.
1. The Undeniable Physics: Thermodynamics
The statement rests on the First Law of Thermodynamics, also known as the Law of Conservation of Energy. It states that energy cannot be created or destroyed, only transferred or changed from one form to another.
In the context of the human body:
Mass (Fat/Muscle) constitutes stored energy.
Calories are the unit of measurement for that energy.
If you consume 2,500 units of energy but your body only burns 2,000 units to stay alive and move around, that extra 500 units must go somewhere. It cannot vanish. It is stored as mass (fat or muscle). Conversely, if you burn 2,500 but eat 2,000, your body must find 500 units of energy to keep the lights on. It harvests this from your stored mass.
Biologically, it is impossible—0% probability—to generate fat tissue in a calorie deficit.
2. The Paradox: “I’m in a deficit, but I’m not losing weight”
When someone claims, “I have cut 1,000 calories and the scale hasn’t moved,” they are essentially claiming that their body has mutated to violate the laws of physics. Since that isn’t happening, the reality is much more mundane, yet frustrating.
If you are not losing weight, you are not in a calorie deficit.
Here is the explanation for where the math is going wrong.
A. The “Input” Error (Underestimation)
Most humans are terrible at estimating portion sizes. Studies consistently show that people—even dietitians—underestimate their calorie intake by anywhere from 20% to 50%. The “Zero” Calorie Traps: Cooking oils, sprays, dashes of creamer, and “just a bite” of someone else’s meal often go untracked. One tablespoon of olive oil used to sauté vegetables adds 120 calories. Do that three times a day, and you’ve erased a 360-calorie deficit while thinking you ate “clean.” Eyeballing vs. Weighing: A “cup” of oatmeal or a “tablespoon” of peanut butter varies wildly depending on how it is scooped. Without a food scale, you are guessing, and usually guessing low. Label Inaccuracy: FDA regulations allow food labels a margin of error of up to 20%. If you are eating highly processed foods, you may be consuming 20% more than the box claims.
B. The “Output” Error (Overestimation)
People tend to vastly overestimate how many calories they burn. The Wearable Lie: Fitness trackers and cardio machines are notorious for inflating calorie burns by 20% to 90%. Looking at your watch and seeing “500 calories burned” usually means you burned closer to 250 or 300. The Reward Mechanism: Subconsciously, people often think, “I worked out hard, I earned this treat.” If you burn 300 calories running but eat back 400 calories in a post-workout snack, you are in a surplus.
C. The Moving Target (Metabolic Adaptation)
This is the most “valid” reason for a stall, though it still adheres to CICO (Calories In, Calories Out). TDEE Drops: As you lose weight, your body becomes smaller. A smaller body requires less energy to exist. A deficit for a 200lb person is maintenance for a 170lb person. NEAT Reduction: NEAT (Non-Exercise Activity Thermogenesis) refers to fidgeting, walking to the car, and standing upright. When you restrict calories, your brain subconsciously tries to save energy by making you move less throughout the day. You might sit more often or fidget less.
The Result: You were in a deficit, but due to weight loss and reduced movement, your maintenance level has dropped. Your “diet” intake is now your “maintenance” intake.
D. The Masking Agent (Water Retention)
Sometimes, you are losing fat, but the scale isn’t moving because water is filling the void. Cortisol: A steep calorie deficit mimics stress. This spikes cortisol, which increases water retention. * The “Whoosh” Effect: Fat cells can fill with water after releasing triglycerides. Eventually, the body releases this water (often overnight), resulting in a sudden drop in weight. If you are truly in a deficit, stick with it. The physics will catch up.
Summary
The equation works 100% of the time. If the outcome isn’t what you expect, one of the variables in your equation is wrong.
You are either:
- Eating more than you think.
- Burning less than you think.
- Retaining water that masks the fat loss.
If you are not losing weight, you must lower the intake or increase the output. Math does not care about your feelings, but it also never lies.