OK I admit it
In 1997 I weighed 115kg @ 1.8m tall. I decided that enough was enough especially as mountain climbing was getting rather hard
I curtailed my diet to ~2300 cals per day (estimate) and began increasing my exercise. Now not everyone can do it but I live in hilly country and I worked in the country so by walking and eventually running before breakfast, walking at lunch and in the evenings I managed to exercise the equivalent of 500-2000 cals per day. It took 4 years losing some every spring/summer & gaining some over winter.
I still have the spreadsheets going back to then and I carried on until I reached ~80kg which I've maintained ever since.
The equation was actually simple (Estimated calories consumed minus required calorie intake for neutral weight gain minus exercise calories)/8000 = weight loss per day in kg.
The hard part was estimating intake, working out neutral calories for me and estimating various forms of exercise although most (running, cycling ) are available. The hard one in fact was hill walking which I do a lot. My best estimate was 60 cals/km + 100 cals per 100 metres ascent+descent. This may not be all strictly accurate but my weight loss tracked my equation almost perfectly sometimes spookily so.
The 8000 in the equation is cals/kg of fat BTW. The above equation needs to be adjusted for body weight as lowering weight decreases the numerical effects of exercise - if you want to lose 3kg it matters not but in my case it was 35kg or ~40% of my final weight. I still have no feedback when I overeat I have to rely on estimates and scales but now it's become second nature and I can keep my weight ± 2kg.
I have no pride in what I did I'm very sorry it was necessary but I think the message is for most ( probably nearly all people) too many calories need to be compensated for by starvation or preferably exercise. Many people I've discovered have the same lack of feedback to excessive intake and many people have a wildly optimistic view of the effects of exercise. ( a small Mars bar is equivalent to 3-4 miles of walking, sadly a pint needs 2 miles of walking )
Another way of looking at it ; 100 cals extra/less exercise/food every day is equivalent to losing/gaining 4.5kg in a year. That easily goes to explain this 'epidemic'