There are some foods that are considered to be "negative calories", although there is still debate on whether they are truly real.
I noticed a couple of years ago that I can loose a lot of weight... quickly... (well, relatively speaking) during blackberry season.
Eat as many (wild) blackberries as I can pick and eat, usually microwaved for a few seconds and sprinkled with sugar (I often get a few red ones). And, yes, at 15 calories per teaspoon, I never worry about a few teaspoons of sugar. No pies, and I've been avoiding making juice.
Picking blackberries is a good way to also get outside for some fresh air.
I will also make mini-steaks (about 3/4 of an inch cubed), often bought pre-sliced as "stew meat". I'll barbeque up a batch of these, and freeze them, and pop one, or a couple in the microwave so that I always get some good protein while dieting, but not having a huge steak.
After growing a garden, I also add in some fruit and veggies. I can't resist that.
Also a good multivitamin.
A little exercise isn't vital for loosing weight, but is probably a good idea when dieting to avoid loosing muscle.
NO SIGNIFICANT FLOUR SOURCE.
Sometimes I'll crave variety so I won't always stay on my diet. But, when on my high blackberry diet, I'LL LOOSE ABOUT A POUND A DAY, and never really be that hungry as I can always get another bowl of blackberries whenever I desire. And, they are generally satiating.
(YES, I have a sweet tooth).
It is easy to gain some of the weight back in the winter, but I'm convinced that some of the weight loss is "real", and not just the effects of short term starvation, and one can knock off more and more weight day after day (10 to 20 lbs for me during the couple of months of blackberry season).
My theory of the reason for the success of blackberries. Wild Himalayan Blackberries are mostly seed which is poorly digested, and generally passes through whole. But, it is also reasonably well tolerated, although it can have laxative effects at times. Thus one gets the satiating feel of a full stomach without the calories of a full stomach. There should be some calories in sugars in the blackberries, as well as the sugar I'm adding. But, the losses are so tremendous that I believe that the body expends energy passing them through the digestive system, with little or no gain from the berries themselves.
Yes, I realize that 10 to 20 lbs in a summer doesn't equate to a pound a day, but like I said, I don't always stay on the diet, and can rebound upwards a few pounds if I break the diet. which then resets the point one is loosing weight from. I also think it would be good to overshoot one's goal by a few pounds because of the rebound. And, my target isn't loosing that much.