OK, this turned into more typing than I intended - hope it doesn't get too many TLDR comments
I think one of the biggest problems with putting weight on is that it happens so slowly that you get used to being big, and it's easy to convince yourself that it's not so bad that you actually have to so something about it. It's also easy to convince yourself that your weight isn't affecting your health or quality of life and longevity. Or that your family and friends aren't just being polite...
In my late 40s I'd topped 100kg and was very unfit and suffering with acid reflux and backache. It was the blood pressure going in the wrong direction that finally gave me the kick I needed.
Everyone is different, and what worked for me obviously won't work for everyone, but these are the main things I'd have suggested to myself 10 years ago:
1. Learn about calories in foods and drinks. Get to understand how many calories are in what foods/drinks by calorie counting until you get a feel for it - e.g. how many calories in a pint of beer, this lump of cheese, this massive bowl of cereal?
2. Learn about how your body expends calories just existing (BMR) and with exercise. Discover how depressingly few calories a swim or walk burns and realise that a calorie deficit is going to be mostly about eating less.
3. Find some exercise that you enjoy doing and can make a hobby / habit. Anything that gets your heart rate up will tend to burn more calories and provide some endorphins as a reward. It might not burn as many calories as you'd like, but you'll feel better and it's also hard to eat while exercising. Ease yourself into anything strenuous (and speak to your GP if appropriate) - you don't want to overdo it or injure yourself.
4. Work out a calorie intake based on your activity level and target weight loss. E.g. a 500 calorie deficit per day should give nearly 0.5kg/week. Treat it as a marathon, and not a sprint - don't start off with a crazy low calorie target and then give up when you find it's too hard. You're trying to find a system that works for the long term, so change the target as you see how things go. If it takes 6 months longer to reach a weight target then does it really matter as long as you get there?
5. Keep eating sensibly / healthily and what you enjoy - it's got to be sustainable.
6. Weigh yourself at the same time each day (or few days), but don't get hung-up on any individual reading as your weight can vary a surprising amount. Use a rolling average over a few days to see how it's going.
7. If you're going to have 'days off' or backing off because of a virus, don't let yourself go mad and undo the good work for the past week.
8. Don't con yourself into thinking "I've done this exercise, so can eat what I want for the rest of the day" - sadly that's not true for normal levels of activity. Similarly, don't think you need to pre-load or eat lots after moderate exercise - your body has a substantial glycogen energy store and you'll know if you run out (bonking in cycling parlance) as it feels unpleasantly different from hunger.
9. Try to work out your weakensses (e.g. nibbling in the evening as you get tired and willpower fades) and find distractions or other ways to moderate them. E.g. exercise in the evenings instead of sitting watching TV, have less junk food in the cupboards. Maybe avoid reading this thread while you're hungry in case someone posts about eating pizzas.
10. Learn to distingush the 'not full' feeling from the 'proper hungry' feeling. Try to associate the feeling of not being full with "it means it's working"; you won't really starve or feel weak if losing weight at a sensible rate.
11. Do it with others if you can for encouragement and motivation.
It took me a couple of years to lose the weight. It's mostly a mental thing, and it got easier once I'd been at it for a couple of months - partly because you get used to it, but also because you run out of excuses that it's not achievable.
For exercise, I got back into swimming, and was challenging myself to swim faster / further. I got myself a Garmin smart watch which got me interested in metrics and seeing the effects of training. (As a bit of an aside, seeing the effects of illness and alcohol on heart rate / heart rate variability is interesting, and I drink less now). When the pools closed due to covid, as an alternative I started doing more on a second hand exercise bike, which led to buying a proper smart indoor trainer bike and riding / racing on Zwift about 6 days/week. I seem to have turned into an exercise junkie that can make people's eyes glaze over with talk of VO2max, FTP and power curves. Apart from enjoying it, I'm feeling happier and fitter, with no backache and untroubled by acid reflux. I still tend to over-eat and on holiday can put on a kg or two, but knowing what I need to do, and probably more importantly knowing that I can do it, makes it far easier to cut back for a week or two.
I'm sure I've missed a few things, but that's basically what has worked for me and hope it's of some interest. Good luck!
