After Samasrayanam (Pancha Samskaram), to maintain pure thoughts, to develop Satvik qualities, one needs to abstain from Onion Garlic, Onion Garlic present food items, pungent items like Radish etc.
One needs to consume only food offered to Lord Srimannarayana as prasadam.
In case one is travelling or is outside, one can sprinkle water on the food chanting Dvaya Mantram, then offer the food to Lord present in onself as Antaryami through one’s thought (uttering Sarvam Sri Krishnarpanamasthu silently within oneself)
If water is not available or situation is not ideal, then, one can think of sprinkling water on the food chanting Dvaya Mantram, then think of offering the food to Lord present in onself as Antaryami through one’s mind (uttering Sarvam Sri Krishnarpanamasthu silently within oneself)
Based upon the love and concern we have on God it is recommended to follow strict diet restrictions. Just as how the quality of the soil is based on the food (through plants) it provides, so does the ability of our body depend on the type of food given to it.
To grow Satvik qualities, Satvik food is essential. If one does not follow it then it means he/she is not interested in Satvik qualities and thus he/she need not consider themselves a devotee at all.
Our actions speak accurately about our thoughts than our words and feelings. Hence diet plays an important role in being a real Vaishnava. (Seeing Lord in everything & everyone, with compassion & Service unto all beings as Service to God)