I have recently been on a mission to lose weight and have successfully managed to lose 20 kgs in 4 and a half months via circuit training thrice a week and 8K runs twice a week. I have gone down from 105 kgs to 85 kgs. I have recently started playing tennis again, which I used to do years ago before I was unfit. I have started noticing that along with my diet, in which I try to contain my calorie intake to under 1700 cals per day, I am starting to feel extremely light headed and very fatigued during tennis games. I understand that compared to my normal workout in the last four months ( 45 minute circuit training or an 8K run which lasts the same amount of time ), my tennis games can last anywhere between 1.5 hours to 3 hours. I seem to notice an above normal reduction in weight since I started playing tennis ( 1.5 kgs in a week over the past couple of weeks). I am worried that I am burning more muscle now that fat and was wondering what is the best way to ensure that I can continue to play tennis while maintaining the same weight loss rate. Would I need to ensure a slightly higher calorie consumption on days that I play tennis. Today, I have just had 160g of ice cream which constitute around 400 to 600 calories one hour before a game and feel extremely guilty about doing so as I normally have tried to stay away from sweets/high cal foods). Any advice is greatly appreciated.
You should eat a normal diet with a normal amount of calories. The weight loss toward an ideal weight should come from gains in physical fitness. Suppose in the future you weigh 70 kg, you are eating 2500 Kcal/day and you are physically very fit. If you then have equilibrium between consumed energy and energy expenditure at 2500 Kcal/day, then why can't such an equilibrium be reached now? So, clearly, you should be able to eat a lot more and yet stay at your present way or even lose some weight.
You don't want too large of a calorie deficit, especially for intense cardio training. I don't know about tennis, but for long distance running, you want a combination of simple and complex carbohydrates before a long workout. Avoid too much fiber. Refuel afterwards with protein-carb ratio (chocolate milk is the standard example).
You have mentioned that your games last anywhere from 1.5 to 3 hours. During such long games, it is not enough to hydrate yourself with water... You need to replenish the electrolytes that your body needs to go on, thus explaining the light headed feeling. I would recommend gatorade for such intense matches.
Pre-workout food must be eaten atleast before 45 minutes to your workout. And should be something that digests quickly like simple carbs. Dont over eat and keep in mind that your body has glycogen stored before any Pre-workout snack. Post-workout recovery is the most important aspect for you to perform so have some protein and carb rich food in 30 minutes after workout. And dont compromise on the hydration. Drink gatorade or orange juice(natural source of electrolytes). Best if luck and keep training!