The energy density of each macro
Protein and carbohydrate each provide about 4 kcal per gram; fat provides 9. That is why a "high fat" split produces far fewer grams than its percentage suggests — 70% of calories from fat is a smaller-looking number on the plate than 55% from carbs.
Alcohol, for completeness, supplies 7 kcal per gram and no essential nutrients, which is why it is not part of any macro split.
Protein is the macro worth defending
In a calorie deficit, adequate protein is what preserves muscle while fat is lost. Research consistently supports 1.6–2.2 g per kilogram of bodyweight for people training regularly — often higher than a percentage-based split produces at low calorie targets.
If the percentage split gives you less protein than that range, raise the protein share and take the difference from carbs or fat rather than accepting the preset.
Frequently asked questions
Does the split matter more than total calories? +
For weight change, no — total calories dominate. The split matters for body composition, training performance and how full you feel, which is what makes a diet sustainable.