Here is what has worked for me.
After 20 years of pursuing a low fat diet and seeing my weight, cholesterol, and blood pressure gradually increase over the years, I went on a low carbohydrate diet and lost 25 pounds in 2 months. I gradually added complex carbohydrates and my weight has stabilized at a 20 pound loss. I avoid sugar, avoid simple carbohydrates, and I don't worry about fats, except for trans fats. For a sweetener, I use stevia. Try an internet search for low carbohydrate diets and stevia.
Your sparring will improve with weight loss. When in the grocery store pick up a five pound bag of sugar in each hand; that's ten pounds. Now imagine trying to spar with that much weight strapped to your waist. A pound of fat is about 3500 calories. During a tough workout you might burn 500 calories. That's 5 workouts to burn away a pound of fat. Fours cans of soda a day is about 500 calories.
Drink four less cokes a day and you will rid yourself of as much fat as a hour of working out. You must eat properly to lose weight. Exercise helps ensure the loss is in fat, not in muscle. Some disks in my neck are degenerating so I can't run, jump rope, or do any exercises that jolt my neck. I seldom spar in class because of the pain afterward, but I hate to give it up, so I do enter tournaments two or three times year. Last month I took third in 3rd degree forms and was winning at sparring until I fouled out.