A good dog. Yeah, that's right. A dog.
Five years ago (Jan 2013) I weighed 232lbs. I was also looking for a new dog as my Rottie passed away in December 2012. I was researching breeds and came across the Australian Cattle Dog (ACD or blue heeler). Sounded like a good match for me, but wow - the dog requires lots of physical activity - lots!! So I made a commitment to my new 5wk old pup Cora, that I would make sure she got her exercise. I wasn't able to commit to my own health, but I had a moral obligation to Cora if I was gonna be her new mama.
So we slowly started leash training and walking. As she got older and stronger and as I got used to the activity (remember I was a 232lb couch potato), our walks became longer and further. By April or May, we were walking 2-3 miles a day, sometimes twice daily. And I had lost about 20 lbs. So we walked some more, starting taking short hikes and played tons of Frisbee, tug-o-war and kickball. And I lost more weight.
Once I felt "good" about my body and it's abilities again, I started strength training. And got stronger and lost more weight. And I started cycling. Within 14-16 months with my new workout partner, I had lost over 50lbs, down to 184lbs.
But all good things don't last. Cora was hit by a car, breaking her tibia and fibula. She required orthopedic surgery and now has a rod and pins in her left rear leg. Recovery was slow. She gained weight and I gained weight since we were no longer "working out" together. Then I had a minor knee surgery. More weight gain. Less activity.
For the last 2 years or so, both Cora and I have been struggling with our weight. We still walk 2 miles a day, but not at the intensity pre- injury and surgery. I know Cora is arthritic in her leg as am I, but I have pain meds. She doesn't :'(. She moves slower now. But she will still amble behind me for 6-8 mile hikes. I have kept off 25 of those 50lbs and "maintained" at 205ish for far too long.
Enter Molly. I adopted her in March. A 2yo heeler mix with more energy than I've seen in a dog ever!. I know my unconscious motivation for adopting her was to get off my *kitten* and on my feet once again.
I have lost 15lbs since Molly's adoption. The three of us walk most days 2 miles at about 2.5mph. When Cora isn't feeling up to it, Molly and I get 3 miles @ 3mph. We hike every weekend now. And as soon as I get the proper gear, Molly will run alongside me when I go cycling. Molly and Cora play endless games of tug-o-war and chase with each other. Cora has lost weight and gotten much more active since Molly joined our family.
So there you have it. My secret - a couple of 4-legged workout partners.

ETA - I just got back from a routine follow-up visit with my doctor. She gave my a high-5 for my 15lb weight loss since my last visit in March. She commented on my progress on the weight loss front and what caused it. I couldn't put my finger on the motivation for my renewed efforts. Until I realized it coincided with Molly's adoption. Funny how I knew when I saw Molly at the shelter that i needed her as much as she needed me.