When I started back in 2000, I was sort of flailing. Walking in Chestnut Hill/Wyndmoor PA, to work if it was a work day, or just working, that in not very long got me to drop 20 lbs. (LOTS of steep hills to walk.) That's 'cause I was starting to Worry because I'd hurt my back, and a MRI scan showed that in my 30's, my disks were already compressing.
In a couple years I went with the four ingredient diet - meaning I would not eat anything with HFCS, artificial colors, artificial flavors, or partially/artificially hydrogenated fats. I didn't consider myself sensitive to those, I was simply going on the assumption that if any of those four ingredients was added, it was junk food and I was better off not eating it. That lost me another 20 or so. Still not restricting amounts, just ingredients.
Then I decided to try cutting out wheat, and that's when things really took off. My lungs improved, my wind improved, I started dropping retained fluid like gangbusters, which meant easier to run or otherwise work out, which started a cycle of vastly improved health.
Over the years I (which is to say, we - my housemates and I, and DEX reluctantly) have tried vegetarian, vegan, all raw, 70% raw, old-school Atkins, and Paleo - and I have to say the Paleo has worked best for my body, my metabolism and my activity level. I'm having energy troubles now because I've been having the same trouble with sugars and sweets that smokers have with cigs during periods of high stress. I'm quite aware I'm doing it to myself, and am trying to whap myself in the head and keep to a healthier food intake. No weight gain though, I'm just too busy.
And never the grain foods, I like breathing too much.
To start, I'd suggest to anyone who isn't under medical pressure to change to start the way I did - pick those first four ingredients, and learn to avoid them. Read labels. Anything with any of those four ingredients is not something that's going to make your day better, there are always other yummy comfort foods you can nom.