I've heard about the "starvation" effect (loosely - and most likely incorrectly) defined as the inability to loose weight when one's caloric intake is too low. For example, I would guess my "base metabolic" calorie requirements are about 1,800 to 2,000 per day; I'm actually consuming between 1,100 to 1,300 per day. I work out five nites per week, and since I've had some cardiac artery problems, I do less than 12 grams of sat. fat per day. However, I don't seem to be able to loose weight or make much inroad on my "visceral" belly fat...drives me nuts!! Any truth to the "starvation effect"?
The metabolism seems to decrease over the years, particularly when meals are skipped or calorie restrictive diets are implemented. The body adapts to this stress with a biological protective mechanism; the metabolism decreases. Once more calories are reintroduced, more body fat may be gained than was originally lost. This attributes to what is known as yo-yo dieting. The body gains back more fat that what was originally lost, ultimately with fewer calories consumed. You can calculate how many TOTAL calories is recommended for your weight and gender, see Estimated Energy Requirements.
I've worked with many individuals who seemed to be unable to lose fat until they have significantly increased their calorie intake, sometimes by 100%. This is accomplished by eating 3 meals and 2 to 3 snacks throughout the day. The type of food consumed is the key; a balanced diet with plenty of fruits, vegetables, and whole grains. Lean protein sources are needed throughout the day. Refined foods such as white flour and sugar should be consumed sparingly, if not at all. See Dietary Guidelines.
When combined with the introduction of an exercise program, fat weight typically decreases and lean body weight increases. Exercise needs to consist of both an anaerobic and aerobic type activity like weight training and brisk walking. During this transaction period, fat gain is minimal if non existent. The extra calories are utilized:
Many of these mechanisms are related. Incidentally, calorie restriction has the opposite effect.
Comparing metabolism to a camp fire has been used as an analogy. If a fire is not feed with wood regularly its heat dwindles. If a large log is placed upon it, the fire takes some time to consume it. A large log can be more readily consumed by a fire that is feed regularly.
Begin by finding someone to measure your body composition every month to monitor progress and to make corrections. Get an accurate body weight to calculate and track fat weight and lean body mass.
After the metabolism is corrected, I recommend to only deliberately decrease calories as a last resort. Make sure you are getting the most you can out of exercise program and frequent feedings before calorie restriction is reimplemented. If calories are decreased, decrease the minimum number of calorie that will elicit fat loss, (ie. 100 Kcal or 250kcal). Realize the body will again adapt to lower calories and weight loss will plateau. The more the calories are restricted, the lower the metabolism will decrease, making it harder to loss fat and maintain lean body weight.
Since I am not a registered dietitian, I can not personally recommend a regimen for you due to your medical condition. I would recommend seeking the advise of a registered dietitian who is familiar with exercise and concepts such as "Thermogenisis". Many dietitians unfortunately still use the oversimplified static model; energy in = energy out. The body is much more dynamic and adaptive.
Interestingly, abdominal fat is correlated with higher incidents of coronary artery disease and Type 2 diabetes. Also see Spot Reduction Myth.
Although your peripheral body is lean, you will have to continue to lower your overall body fat before your lose your belly. Instead of trying to plow through a brick wall, take some steps back and then jump over it. Best of luck.