Consuming too few calories.

There are lots of opinions out there about starvation mode, and almost as many threads. My completely non-professional take from looking at the research is that there is a metabolic slow down if you don't eat enough. It's never enough to offset the reduced calories, but it's a real thing. You're right to strive to meet your minimum calorie goal, you'll be healthier for it in the long run.

How do you feel about peanut butter? A decent trans-fat free or natural version can pack in a lot of needed calories. I have a PB&J and a glass of soy milk for dinner or a snack fairly often to boost my calories for the day (I'm a near vegan also). You might consider taking a look at 'fake' soy meats for a vegetarian calorie boost. I like the Morningstar Farms breakfast sausage.

Do you enjoy deserts at all? I'm sure there are plenty of ways you can pack in a decent amount of calories without going overboard.

Possibly vegetarian protein bars? I don't eat them myself, but I'm sure they'd be a handy supplement to your diet.

Vegetables dipped in homous (home made is lovely, so many different flavours) nuts, seeds, avacados, organic peanut butter... All calorie dense with good fats. Google calorie dense foods...x

I don't think it is good for our bodies to eat too little, and going 1200 from time to time is fine, but on a long term basis, will harm your metabolism and your body will hang onto fat. You might lose weight but it is coming from your muscles and body organs which is never a good thing. I don't know much about vegan but I personally believe that we all need a variety of nutrients, vitamins, and minerals for our long term health. Where are you getting your healthy fats and protein from?

For me personally, I think starvation mode definitely exists, I used to limit myself to eating 1300 calories a day, over 500 calories below my BMR, at first the weight came off quickly, but it stopped coming off just as quickly, there just wasn't the energy to fuel my body, I was tired all the time, cranky, so I changed it up, and started eating more.

I eat 2000 calories a day now, and I eat back a portion of exercise calories (usually via protein shake), i've never felt better or lost weight more consistently than I currently am.

For me personally, I think starvation mode definitely exists, I used to limit myself to eating 1300 calories a day, over 500 calories below my BMR, at first the weight came off quickly, but it stopped coming off just as quickly, there just wasn't the energy to fuel my body, I was tired all the time, cranky, so I changed it up, and started eating more.

I eat 2000 calories a day now, and I eat back a portion of exercise calories (usually via protein shake), i've never felt better or lost weight more consistently than I currently am.

To eat more calories is more pleasurable, it also brings about weight loss more slowly. But there's a difference between the discomfort someone might feel on a healthy low-calorie diet and actually "starving." From what I read, the act of putting on a lot of weight is pretty darn stressful for the body.

People should do whatever works for them. If they can sustain a gradual weight loss over a few years and maintain it thereafter, that's great. But some people may backslide before getting to that point. In either case, maintenance is everything.

My diet is mainly vegetable based. With the exception of I do eat mayonnaise and use chicken bouillon in my vegetables, so I can't say I am vegan.

I am very curious as to why you are on an almost "vegan" diet but still eating chicken bullion? You still need to kill a chicken to get chicken broth just the same as you would to get chicken meat. Since you're not opposed to eating animal products, why not just consume fish and/or chicken to improve your diet? Also, if you are easing out of animal products, vegan mayo is pretty much as good as the regular stuff, IMO (although I may be biased since I'm not a mayo person).

However, it has been difficult to get in 1,200 calories on mainly vegetables, even on days when I have soy milk, vegan protein powder in my smoothies, 2 corn tortillas, avocados and yes, even mayonnaise!

It sounds like you are just not eating enough food. Avocados and mayo are the only calorie-dense foods you listed. To increase your calories, you should add more fats and include enough protein in each meal. Eat more tofu, tempeh, seitan, veggie burgers, edamame, nuts, beans, etc. Cook your protein with a bit of canola/olive oil. If you are eating protein powder, you can make smoothies with bananas or other fruit (I can make smoothies with 500+ calories). One med banana is a little over 100 calories. If you are eating a mostly vegan diet, you need to plan a bit more to get proper nutrition. If you are on a very low-cal diet (1200 cals), you also need to plan more in order to get a good balance. Combining both of those... you get the idea.

The app keeps warning me that I am eating too few calories and could run the risk of putting my body in starvation mode, which would lower my metabolism and make weight loss more difficult.

Is there much truth to this? Do I need to worry about it?

There's a lot of argument about "starvation mode" on here. Dieting in general will slow your metabolism. But you can look up "adaptive thermogenesis" to read all sorts of studies to show that if you drop your calories low, your body will adjust by burning fewer calories doing other functions. (E.g., you fidget less, are colder b/c your body's trying to conserve more energy, etc.) So in some ways, it can be counterproductive. This is something to keep in mind especially if you are exercising in addition to dieting. Many have found that when they they try to exercise on such a low cal diet, their work-outs suffer. But the biggest problem most people find that 1200 or less is just not sustainable. I think someone with A LOT of weight to lose might be okay on that for a little while, but s/he should be under the watch of a doctor and on a strict nutrition plan.

I think you just need to find what works for you. Experiment. I'm in the same sort of scenario. I'm constantly trying new things to up my calorie intake. I'm a very picky eater so it's not easy. I could easily eat complete bullsh*t and be at my calorie goal, but that's not how I want to do things.