4 years ago i tried losing weight with 1400 calories a day (+exercise) and after one week had lost one half pound and was the walking dead.

The next week i ate 1700 calories a day (+exercise) low carb ketogenic and lost 6 pounds with great energy once through the transition but even in the first 5 days had better energy than the first week diet.

Third week stayed keto and lost another 3 pounds and now weight what i did when graduating high school.

Calorie type matters!