Kinect Sports

To get this you just need to beat the choclate's target within the time limit.

Don't worry if you beat this before the timer runs out and it doesn't unlock it will unlock after the timer runs down.

Tips:
You can get calories before and after an event finishes
It works on movement so wave your arms and move about a lot the more you move the more you burn.
Wave as much as possible and don't worry too much about the game itself
run from left to right while waving no matter what the event this helps
Some games you can burn calories without starting the game, I would do this a little to boost your score but not too long as you still have to wait
Having a second player take over helps on the harder foods.

If you have beaten the target and the timer goes over, don't worry it normally allows one final game before finishing.

If you have anything to add, leave a comment and I'll improve this solution.

Thanks to GlorixJim for these further tips:
- you can calculate the average kcal/min you need to beat your opponent. The running games will give you the opportunity to get way past that number (20-25 kcal/min), while the light and medium stuff sometimes nets you only 3-7 kcal/min. To beat the pizza, you must average almost 8 kcal/min.
- The second player is a great way, but you can also use your GuideButton to pause the game- time DOES stop.
- I think you will burn calories after the game, regardless of moving or waving your arms.
- for some games, waving your arms (and running left/right) seriously increases your kcal/min average.
Like the volleybal related games, you score more points/kcals running left and right, waving your arms then really trying to hit/dodge the fruit. The score while standing still and catching the fruit with your feet/hands/head is a poor 0.03 kcal/second!

The easiest way to beat any opponent is during a mini game which requires you to use only one arm (ie some of the table tennis and bowling ones). Simply wave your arms side to side, walk around, do anything besides choosing which hand to use. The game won't start until you choose a hand and you can meet your calorie goal before even starting the given match. When you do this, note that your time will go well beyond what the estimated time for each challenge is.

Best Solution if you still struggle to make it in time!

I do recommend using a big towel, it is easy that way.
Move sideways and wave the towel. Not really necessary to move sideways so much but I do think it speeds it up a bit.

When you randomly get the table tennis were you can score points between 1,2,3. Just dont serve and stand still with the towel in your hand.

You can reach your target here without ending the game as the timer never starts until you serve but your calories goes up.

I also noticed it should also work with one of the bowling events. (Not the one were they charge at you).

The achievement unlocks when you have done all the 25 minutes so you need to play it out.

IMPORTANT NOTE: If you do this trick, the in game timer will be wrong and you will go overtime and have to play many extra events so you dont really need to get all calories in one go using this trick as you for example would still have to do all that time after.