Thanks for your question. If we look at the specific facts of your case I can see that you are eating three meals a day including a good balance of carbs and protein, plus plenty of fruit and veg. You feel full up and so it’s right to ask what could possibly be wrong about only getting 1000-1100 calories a day. In short, the answer is possibly nothing, but it’s not easy to tell. The danger around this sort of calorie intake is that no matter how good the quality of your diet, it can become increasingly hard to meet your nutritional need in terms of intake of micronutrients such as vitamins, minerals and calcium. On this basis I would really be happier seeing you edging up to 1200-1400 calories a day, but then it’s fair to say that there’s not really much advantage to doing this if the extra calories come from a treat food with little nutritional value! Everyone is different, so it may be that your personal needs are being met, though if you were to continue on the calorie intake you are now I would feel happier if you were to take a multivitamin and mineral tablet to err on the side of caution and safeguard any nutritional gaps you may have. The starvation adaptations your body makes in the face of severe food restriction are all designed to try to save the body from using it’s own muscle tissue as fuel (at it's worst your heart muscle can be degraded too). Large amounts of ketone bodies are formed by the liver from fatty acids and released into the blood within a few days after the onset of starvation. After several weeks of starvation, ketone bodies become the major fuel of the brain. The diminished need for glucose decreases the rate of muscle breakdown, and so the likelihood of survival is enhanced.

People on low calorie, especially low carb, diets, go into ketosis which arguably is what makes the diet so successful. But the downsides are that you can start to breakdown muscle as well as feel weak and have bad breath! In my opinion, for successful long term weight loss (at least within the context of having no close medical supervision) you should avoid ketosis and keep up your muscle mass. You don’t need to work too hard to do this - just avoid very low carb intakes, don’t ever go below 1000 cals a day and stay active. You are doing all those things, have no evidence of ketosis and should therefore be okay!