"By refraining from food and drink and by abstaining from conjugal relations with one’s spouse, one’s fast will be deemed as sufficient according to the requirements of fiqh. But this needs to be combined with struggling against one’s desires and refraining from all sins. Without such striving the fast will be of no spiritual benefit.

The angels, by their very nature, don’t possess any urge to eat, drink or procreate, nor do they disobey Allāh ta'ala. If we want to match the angels then not only must we control our natural urges, we must also abstain from all disobedience to Allāh ta'ala.

Only then will we see the true benefits and achieve the real objectives of fasting.

Source: http://shaykh.wordpress.com/2013/07/29/complete-fast-2/