I'm a specialist personal trainer in the uk mate, I would agree with everyone here who is saying not to give up completely even just once a week will keep you in the Jiu jitsu game, I can imagine it to be frustrating tho!
If I was to offer some simple tips on weightless it would be these
1. Only eat natural foods, only eat things that walk, swim or grow
2. Drink at least 2 litres of water a day, if you can, make this the only thing you drink
3. Eat 4-6 SMALL meals throughout the day, make sure you eat breakfast, the goal is never to be hungry and never to be full
4. Avoid all refined sugars and trans fats, read ingredients labels, if you see ingredients that wouldn't have been available to a caveman don't eat it, use herbs and spices to flavour your food.
5. Portion control, All meals should be balanced with a small amount of lean protein, a small amount of whole grain carbs and a good amount of veg, with some healthy fats, omegas, MCTs etc
6. Resistance training should be done 3 times per week focusing on large compound movements, squats, bench, row, press and dead lifts
7. Cardio should be done on an interval format, so high intensity for say 30 sec and then rest for 30 sec then repeat, no longer than 20 mins
8. Kettlebells are great as they work both of those areas, find some good KB workouts that get your heart rate up and use a heavy enough bell that it will help you build muscle
9. Make sure you take rest days, this is when your body changes not when you are actually training
10. Nutrition is key, make sure you stick to it religiously, if you are struggling to stick to it, use 1 cheat day every 7 days, that has to be strict though, start your week on a Monday and plan which day will be your cheat day, like for instance if you know you are seeing friends etc, on a cheat day you are allowed to eat anything you want guilt free, BUT it can only be on that day, the other 6 have to strictly sticking to the guidelines or it won't work!
I tried to keep it simple but it is so deep that I could go on all week about it
Any questions let me know man