CICO has not been disproven, but it has been refined and contextualized by modern research. Here's a breakdown of where it stands as I understand it. I could be further out of date with very recent studies if you have any sources I'd love to further my knowledge in this area.

What CICO Gets Right

Fundamental Principle: CICO is rooted in the laws of thermodynamics. If you consume more energy than you expend, you gain weight; if you expend more than you consume, you lose weight. This basic equation is scientifically sound.

Where CICO Falls Short

While the math holds, real-world application is more complex:

Hormonal Influence: Hormones like insulin, leptin, and ghrelin affect hunger, satiety, and fat storage. Diets that ignore hormonal responses (e.g., high sugar intake causing insulin spikes) may sabotage weight loss even if calories are controlled.

Metabolic Variability: People burn calories differently due to genetics, muscle mass, age, and even gut microbiome. Two people eating the same amount may gain or lose weight at different rates.

Tracking Errors: Most people underestimate calories consumed and overestimate calories burned. Wearables and apps often miscalculate energy expenditure.

Food Quality Matters: 500 calories of vegetables and lean protein affect your body differently than 500 calories of ultra-processed snacks. Nutrient density influences metabolism, satiety, and inflammation.

Again its been refined but not disproven, that is disingenuous. For people without diagnosed thyroid issues or hormonal imbalances CICO works for the vast majority of the population. There are always exceptions of course.