I've lost 10 lbs since this time last year, from 160 to 150 lbs. I'm 5'11" so I wasn't overweight before, just a little waistline pudge. My optimal weight as an amateur athlete in my teens and 20s was 145. I'm close to that.
I wasn't trying to lose weight. But my thyroid failed last year and I couldn't metabolize alcohol. A single drink gave me hangover like symptoms within an hour or so, which I'd never experienced before. I had to give up beer. That was hard. I love beer. I don't drink much, and didn't always keep any at home. When I did a six pack might last a week or two, sometimes a month. But I enjoyed casual group rides with friends and a beer or two afterward.
That's the main diet change. I just gave up beer.
I cut back a bit on the junk carbs like cookies, muffins, etc., and substituted protein/energy bars. If I do eat any junk snacks I do it just before or during bike rides to burn off the extra calories. But I'm not rigid about it. I'll have a chocolate malt with my burger even on rest days, or an occasional cookie or donut. But I'm careful to not make a habit of it.
Other than that I eat whatever I want. I don't worry about cholesterol. I don't do keto or any special diet.
I had surgery to remove thyroid cancer last November, half my thyroid. The other half isn't working so my energy is still low, despite the meds. In most folks I know who have low thyroid problems they tend to gain weight and blame the thyroid problems. When I've observed their diet habits the real problem was eating too much junk food -- lots of candy, sugary snacks, sodas, ice cream. Their main problem was depression and low energy, feeling worthless and unable to work or do much of anything. Perfect conditions for self-medicating through comfort food. I sympathize completely. But it's not the low thyroid alone that caused obesity -- I'm talking double their normal healthy weight, like women who should weigh 160 lbs or less but now weigh more than 300 lbs. That's not "low thyroid." That's due to compensating with junk food. Then they stop walking or doing anything because it's too difficult to lug around that much weight. Pretty soon they're using motorized wheelchair carts in Walmart. Then electric scooters at home. Everything aches so they're convinced they shouldn't do any exercise at all, ever. It becomes self defeating.
My heaviest was 205 lbs almost 20 years ago after car wreck injuries made it impossible to get much exercise for awhile. I ate way too much junk food. Never cared much for soda but did drink beer -- not too much but when you don't exercise at all any beer is junk calories.
I got down to 175 by 2015 when I resumed bicycling. The weight came off gradually after that, without any rigorous dieting.