I'm not an old timer, but here are my thoughts...

Short answer: Eat Clean, Eat Less
Long answer:

Okay, so that's 13lbs in 3 weeks - that's 4.3 lbs per week. If you want to lose real weight -just do the numbers...

3500 calories is a pound, times 4.3 pounds.........you would need to burn (or cut back) 15,050 calories less than what your body needs for maintenance each week.....that's 2,150 calories a day.... I don't know what your maintenance calories are, but I imagine this doesn't leave you with much....and calories are also what can give you the energy to train and prepare for a fight....

13 lbs in 3 weeks can be done a lot easier if you "cheat" (or cut weight that isn't actual fat, but water/toxins, etc in your body). Cheat maybe isn't the right word - it just depends on your goals. Anyway, this would be sitting in the sauna for hours at a time, doing tons of cardio, working out covered in plastic wrap, taking laxatives, etc. I'm sure you could google ways to drop weight fast, but be careful - as well as being unsafe for your health, a lot of these ways are going to leave you drained, and the last thing you want to be right before a fight is drained.

I'm usually within 7 or 8 pounds of fighting weight at all times, and I can typically drop that in 3 or 4 days by eating clean and eating less. Different bodies will respond differently.

Good luck!

i lost 20 lbs in one week cutting cals back to around 800 cutting back on water to a min. saunaed a couple of times and did 2-4 hrs of cardio a day

When I cut weight, I keep my strength training routine the same and simply cut the calories. I don't agree with cutting back here unless it is a few days before the fight and you want to avoid any muscle soreness. Keeping the strength training up will help you retain muscle mass. I added a fasted run in the morning 2x a week with some green tea beforehand.

I also don't cut back on my carbohydrates. The last cut I did, actually, I raised my carb ratio and worked really hard to get them from fruits and veggies as opposed to anything with an ingredients list.

I had to cut last minute for my first fight and did the dehydration thing. I won't do that again - completely drains your energy.

Good luck dude. I'm no expert, and I'm sure any of this can be debated.

13 lbs is about 6kg. I am lighter than you and can dehydrate off 3-4kg over 4 days to make a weigh in. So if your weigh in goal is 190, then you only need to drop about 5lbs of body mass and you can make the weigh in fairly easily by reducing your fluid intake and hitting a sauna before you weigh in. This will give you a heavier fighting weight which is normally an advantage. If on the other hand you want to lose the full 13 lbs just to be in a more trim fighting shape, then follow some of the other advice in this thread on cutting. Basically just reduce calories (maintain your minimum amount of protein and essential fats, the rest can be carbs) while keeping your training as is.

Break a leg. Preferably his...

If I am within 10 lbs of goal weight, I have used the following method starting about 5 days out from a BJJ tournament with a gi/kimono. (Note: I am 5'4" and walk around at 135-138 lbs, but compete <129.9 lbs. My calorie defecit/goals will be different, so my meals will be different. THIS IS JUST AN EXAMPLE.) My comments with asterisks are the light exercises done in those days to avoid injuries or over-training the body during the calorie restriction. Crunch the number and develop your own regimen. Here it goes:

MONDAY: 1340 CALORIE GOAL. No solids after training. No food after 9pm.
Breakfast - Apple
*Elliptical*
1st Break - Coffee & Cereal
*Mid-Day Roll w/ rashguard under gi*
Lunch - Turkey Wrap & Veggie Straws
2nd break - Dry Cereal
Dinner - Salad with Chicken
*Evening Session 1 Roll w/ rashguard under gi*
*Evening Session 2 Judo*
Late Snack - Almond Milk

TUESDAY: 1340 CALORIE GOAL. No solids after 5pm. No food after 7pm.
Breakfast - Apple
1st Break – Coffee & Dry Cereal
Lunch - Turkey Wrap & Veggie Straws
2nd Break – Pickles
Dinner - Cereal / Almond Milk
*3- to 5-minute intervals / 1-minute rest:*
*Burpees*
*Mountain Climbers*
*Superman Punch Sprawls*
*½ Burpeees*
*Planks*

WEDNESDAY: No solids after 5pm. No food after 7pm.
Breakfast - Apple
1st Break– Coffee
*Mid-Day Roll w/ rashguard under gi*
Lunch - Salad with Tuna
2nd Break - Cereal
Dinner - Salad with Chicken
*Evening Roll w/ rashguard under gi*
Late Snack - Almond Milk

THURSDAY: Minimize liquids. No solids after 5pm. No food after 7pm.
Breakfast - Apple
1st Break - Coffee
Lunch – Salad with Tuna
2nd Break - Dry Cereal
Dinner - Salad with Chicken
*Evening Roll w/ rashguard under gi*
Late Snack - Almond Milk

FRIDAY: Weigh-In Day
*No Water*
Breakfast - ½ cup cereal
Lunch - 3 Turkey Slices
2nd Break - ½ cup cereal & 2 pickles
*(Sweat / Liquid Waste / Solid Waste)*
*WEIGH IN*
Dinner – Electrolytes + Water / Carb load + Protein + Vegetables & Fruit
Late Snack - Water

SATURDAY:
Breakfast - Apple / ½ PBJ / ½ Monster
*COMPETE NO-GI*
Lunch - ½ Turkey Sandwich / Granola / ½ Monster
*COMPETE GI*

This should place the body into calorie deficit, in addition to a training regimen. Protein is obtained from the tuna / chicken / turkey meals and almond milk; Carbohydrates from the wraps, cereal, and sugar; Fiber from the apples and salads. By Friday, the minimal waste from Wednesday and Thursday should be passed. Food is rationed to minimize food/waste weight during weigh-in.

For water weight, there are a few techniques that different coaches use to dehydrate/rehydrate, but I do not endorse dehydration as a safe way to shed pounds. One method (used for day-prior weighing but not day-of weighing) is: Increased water and sodium intake 4 days out, maintaining increased water but normal sodium intake 3 days out, followed by rapid decreased water and elimination of sodium intake 2 days out, and then no water intake 1 day out. The influx of sodium and water in the beginning tells the body to pass that water in more amounts and more frequently. With the rapid cut back of the water and sodium, urination will continue at that rate for a short amount of time, which should coincide with the weigh-in. More water will be passed in addition to sweat during training, with none being taken in. After weigh-ins, rehydration is mandatory. Again, that is how it has been done, but I feel one should be near goal weight prior to weigh-ins with minimal impact to eating and drinking routines.

Thanks for posting the info...question-what kind of cereal are you eating during those 5 days?