The ancient yoga text Hatha Yoga Pradipika, by Swami Swatmarama, says yoga sadhana is destroyed by six causes. Amongst these he lists over-eating. Having listed the problems he also cites ways to overcome them. This shows yoga as an extremely practical tool.
However, yoga is not a judgmental science. It accepts that hunger is not just a biological urge but is also intrinsically linked to our emotional shortfalls. Even before modern day dieticians saw a link between emotions and binge eating, yoga had inferred that. This is why the navel center or manipura chakra, is associated with fear and anger which need to be overcome on our spiritual ladder. These two emotions can be held guilty for being a major sub-conscious triggers behind over-eating.
The Hatha Yoga Pradipika says yogic success is indicated by a `thin, glowing body' and increased digestive power (Verse 19 and 20, Chapter 2). In the Srimad Bhagwatam Lord Krishna explains how the body which is no longer `plagued by hunger and thirst' gains various siddhis, including the power to die at one's will and tolerate anything (pain, cold or heat) due to yogic concentration. Patanjali's Yoga Sutras observes how the yogic dhyana on the vishuddi chakra (throat center) can destroy hunger.
All this does not mean we must fast on our path to yogic tapas. Loss of hunger is a natural by-product of sustained yogic practice. This happens for easily understandable, biological reasons. First, the body becomes super-efficient, like an engine which does not guzzle excess fuel. I would like to stress this point as also the one which differentiates a yoga practitioner from a gym freak. The latter is usually ravenous after a hectic session. An advanced yoga practitioner does not feel hunger after the sadhana.
Gym instructors are famous for saying how they can eat like a horse. A yoga instructor would not be caught dead saying this, for the simple reason a good sadhana deflates hunger. Would you rather buy a machine which over-uses fuel or one which is fuel-efficient? Ultimately, the usage of fuel is not just about the money spent on gas. It also comments indirectly but loudly about the health of the entire machine. If you apply this logic to human fitness, it becomes clear yoga is a far superior form of fitness because it restores your natural metabolic ability to eat only what and when you need instead of over-eating or eating for the heck of it!