You're stuck in the mindset that fat makes you "fat". This is the whole point of ketosis, and a rethinking of wrong dietary guidelines that have persisted for decades.
The butter in the coffee supplies fat for fuel / energy, suppresses appetite, and does not contribute to weight gain or more specifically an increase in adipose fat tissue.
Simply cutting all calories is futile. Your body needs energy to sustain itself. The point of keto diet is replacing carbs with a significant increase in fat (~70% give or take) as a percentage of calories consumed.
But it is crucial to actually consume a lot of fat, not just try to cut overall calories.
The butter in the coffee supplies fat for fuel / energy, suppresses appetite, and does not contribute to weight gain or more specifically an increase in adipose fat tissue.
Simply cutting all calories is futile. Your body needs energy to sustain itself. The point of keto diet is replacing carbs with a significant increase in fat (~70% give or take) as a percentage of calories consumed.
But it is crucial to actually consume a lot of fat, not just try to cut overall calories.