Your body can run on sugar or fats. Turning protein into sugar or fat aren’t very efficient processes, so when you eat mostly protein with very low carbohydrate and fat intake you use up your sugar stores when you train and you start liberating more fat stores for energy.
If you eat 1500 cals from lean protein you’re going to find that you feel quite full and satisfied. You may still have some hunger for fats and carbs but that hunger is easier to deal with because you’re not hungry for protein.
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