I trust mayoclinic.com and they tell you that you should not fall below 1200
calories in a day if you're a woman, and not to fall below 1800
calories a day if you are a man. An average individual needs 1200 to keep just their basic organs going. If you don't have enough
calories to keep those happy, well then you are straining your heart and your other very important organs to survive. This can lead to problems as you may have suspected.
Sweetpea may be on to something about the bulkiness of your food. Just incorporate more veggies and less meats etc. I have zero problem getting my 1500 cals in and I eat a variety of foods.