What Happens If You Eat 800 Calories a Day? (Week-by-Week)
Eating 800 calories a day can cause fast weight loss at first, but energy drops and hunger rises as your body adapts. Safer deficits work better long term.
Eating only 800 calories a day is less extreme than 500—but still very low for most people. In the first week, many people see rapid scale changes, mostly from water and reduced intake. By week two and three, fatigue and cravings often increase as the body adapts.
The biggest mistake is guessing calories and thinking you're "on track" when portions are larger than expected.
If you want a safer number, start here: