Many people have come to believe that sugar is one of the main culprits behind weight gain but this is not necessarily true. Sugar will raise insulin levels higher than complex carbohydrates which can be useful particularly around workout time. Raising insulin levels during training will decrease muscle tissue breakdown. For health reasons complex carbs are recommended for other times of the day. Here are some excellent food choices for carbohydrates:

Low-calorie diets: It is harmful to reduce your daily calorie intake lower than 1400 calories per day, because your body adjusts to a semi-starvation state and looks for alternative sources of energy. In addition to burning fat, your body will eventually burn muscle tissue. Because your heart is a muscle, prolonged starvation will weaken it and interfere with its normal rhythms. Low-calorie diets don't meet the body's nutrition needs, and without nutrients your body cannot function normally.

It is possible to do more in less time — at least when it comes to your workouts. By incorporating interval training — that means bursts of high-intensity moves — you’ll give your metabolism a huge boost, says Glenn Gaesser, Ph.D., director of the Kinesiology Program at the University of Virginia and author of The Spark. If you usually jog at a consistent pace, try adding a 30-second to one-minute sprint every five minutes, or, if you’re on a treadmill, change up the incline for one-minute intervals.
That’s basically what I did. I counted calories for a while using good old spreadsheets. That made me realize that foods like pasta and rice where high calories, so I should watch with that. Now I haven’t counted calories and years, and watch out with carbs. That’s how I’ve been able to keep my weight stable and visible abs over the past 10 years or so.
Gastrointestinal disorders are another common cause of unexplained weight loss – in fact they are the most common non-cancerous cause of idiopathic weight loss.[citation needed] Possible gastrointestinal etiologies of unexplained weight loss include: celiac disease, peptic ulcer disease, inflammatory bowel disease (crohn's disease and ulcerative colitis), pancreatitis, gastritis, diarrhea and many other GI conditions.
At its core, burning fat comes down to the process of lipolysis—the breaking down of fat lipids, explains Seedman. This happens in the mitochondria of the muscles, or the powerhouses of the cells, responsible for generating the energy our cells need to do their jobs. Exercise has been shown to improve mitochondria function, which then promotes fat breakdown, Seedman adds. Plus, working out helps regulate pretty much all the hormones that optimize fat loss.