Fasting without the guidance of a priest can be dangerous both physically and spiritually. The purpose of Lent is the preparation for Pascha (Easter), the 40 days symbolize a) the 40 days Christ spent fasting in the wilderness, b) the 40 years Israel spent wandering in the desert, and c) the 40 days the Earth was covered in the waters (or rather these last two Old Testament events were a foreshadowing of the fast of our Lord). As with any fast it is more important to focus on prayer, alms-giving, and abstaining from sin (most especially sins like sniping, gossiping, and in-fighting) than to worry too much over food consumed. As a Protestant you would probably do well just to focus on those three than food, but try to avoid over-eating.
Once you are ready to begin converting to Orthodoxy and have access to a priest he will guide you in the best way to get into form for fasting. Generally speaking Orthodox Christians will abstain from meat and dairy products, fish, wine and olive oil (with the latter three being allowed if certain feasts fall during the Great Fast).