When I was still trying to lose weight, and even after I slimmed down, I was careful to never let myself go hungry, lest I feel deprived and more likely to eat fattening foods. I wasn't afraid that undereating would slow my metabolism; my understanding is that physical activity affects metabolism more than diet does. But I didn't want to face another situation like the wedding I attended in July 2012 where I went without food for many hours, found little I could eat at the buffet, and gave in and had some mini-chocolate bars and a cupcake, which I was positive were not vegan. That was the only time since going vegan that I've intentionally eaten something that contained dairy or eggs, but I still felt guilty about it. Just packing an energy bar or some almonds and raisins would have prevented it.
While now I do usually take those nuts and fruit or other snacks with me if I'm going to be out for awhile, sometimes I forget. And I get hungry. And - that's now OK. I can be hungry. I can go without food for several hours or an entire day if I need to, without undue suffering. It's uncomfortable, but it's nowhere near the level of hunger that many people in the world experience every day. I don't feel deprived, because it's not a choice that's forced upon me, and I'm not going without food for the purpose of losing weight. I'm going without for the purpose of sticking to my principles, to the best of my ability.
These principles are not only about eating vegan food specifically. I'm continually working to make healthier choices. For example, while I believe sugar is a scapegoat for obesity and diabetes, it isn't health food, either. I haven't removed it from my diet completely and likely never will, but I've cut down a lot. Visualizing the food as a part of my body, taking the time to really look at it and think about it before eating, is making it a lot easier to avoid buying junk food like candy and soda.
One example: Those candy "orange" slices at Walgreens would often call to me from the shelf, even when I wasn't particularly hungry. But they have basically no nutritional value. Plus, they come in a plastic bag that may not be recyclable. I can spend that money on a couple of actual oranges, or a large head of kale or Romaine lettuce, or even larger quantity of whole grains or dried beans, which will keep me full a lot longer. I can now pass them by.
Another example: I was walking home from getting a haircut in the Castro yesterday. It was an hour walk each way, and despite eating shortly before I left home, I was already hungry again on the way back. It was hot out, I was getting tired, and had nothing with me but water. I passed a Jamba Juice and several other places that would have been inviting to stop at for a snack, but I pressed on, despite the fact that I was going grocery shopping along the way. Shopping at Trader Joe's while hungry would have been a recipe for disaster in the past, but this time I stuck to buying only what was on the list. I knew I had a kitchen full of food waiting for me at home, and wouldn't starve before I got there.
My willpower will certainly continue to be tested, and I will never have a "perfect" diet, if such a thing even existed. But mindfulness of the composition of my body and the possible consequences of my actions is helping me make better decisions and live a better life, day by day.