No, this is not true. In fact, raw garlic properties are much superior to those of cooked garlic since the cooking mode as well as the temperature and the length of cooking play a negative role on the effectiveness of the enzymes responsible for the production of allicin. As such, and in order to take full advantage of it, it is advisable to add crushed garlic just about 10 minutes before the end of the cooking process.
On the other hand, and to benefit the most from the virtues of garlic, that excellent superfood, it is advisable that we crush the whole raw cloves of garlic with the flat side of a knife and let them rest aside for about 10 minutes before we grind them or chop them. Indeed, this method of preparation of raw garlic is the one that allows the formation of allicin (a natural molecule known for its antibacterial properties which provides the whole of garlic’s benefits) and its powerful antioxidants. Allicin is also responsible for the strong distinctive smell of garlic.
Finally, it is advisable that you store garlic cloves in the open air, in a cool and dry place. One last piece of information: One garlic clove provides about 4 kcal.