@R.O.S.S.I There's a few other elements to dropping so low in cals.
Downsides:
- Harder to sustain - mentally not just physically, food is not only important for physical activity but for cognitive function as well.
- Impact on activity levels reduce even further due to less available energy coming in
- Detrimental to your metabolic health, ie if you sustain a low calorie intake over a period of time your body will adapt and lower its requirements
- Actually difficult to hit base levels of required nutrients to sustain normal healthy function, as an example most suggest at a very very minimum 30g of fats per day, and thats 270 cals, over a 1/4 of your target, in extremely low volume, low satiating food.
- No room for manoeuvre once you plateau
- Doesn't teach a healthy respect for food, or give you an understanding of how your body reacts to different levels of calories.
Upsides:
It gets you quick wins. In my view thats pretty much it.
Studies over and over again have shown that crash diets work temporarily and in the vast majority of cases the weight just gets put back on. Due to any combination of the above mentioned downsides.
It might be good to get some more information regarding what your goals are, and so a more sustainable approach can be suggested, also an expectation of how long you should take to do what you want to do. Why crash diet for 6-8 weeks of utter hell, to potentially hit your goal, to then rebound in the following months, when you can hit your target over 6 months where you are only actually in a deficit for 3-4 of those, for example?