The problem is that eating white rice is low in protein, and you'll lose body tissue that's not fat. Eating just chicken you'll lose glycogen which is 80% water

The problem is that eating white rice is low in protein, and you'll lose body tissue that's not fat. Eating just chicken you'll lose glycogen which is 80% water, so you'll lose more weight, while losing the same amount of fat. So when you go into extreme diets, there is a problem with measuring exactly what is going on if all you use is a scale.