Conventional wisdom states that to lose weight you need to eat less and exercise more. Although recent science has given us a more complex picture of what actually happens when we try to lose weight, this is still the best overall advice. There are exceptions, such as hormonal imbalances, that will complicate the situation. But the simple fact is that, for the most part, you can't fight physics.
There is one complication to this rule I have found from my own experience. During the height of the covid pandemic I was out of work for 18 months. During that time I got back into a daily walking regimen. I started out at 5 miles a day 5 days a week. Eventually I worked my way up to 20 miles at a pace of 4 miles an hour. I maintained a daily calorie intake of about 1300 calories. I am 5'9" and, at the time I started, I weighed 153. General rules of thumb are that 1 mile of walking burns about 80 calories and 1 pound of fat is 3500 calories. Within about 4 months of starting I weighed 143. This was before I got up to 20 miles.
And then something interesting occurred. I stopped losing weight. At about 6 months I was up to 20 miles and still at 1300 calories. I occasionally would weigh in at 140, but then I soon was back to 143. If the general rules of 80 calories per mile and 3500 per pound of fat were correct, I should have very quickly died of starvation. So what happened?
My experience seems to confirm what scientists call set point theory. This is the view that the body will try to maintain a specific weight that falls into a fairly narrow range. If you fall below that weight, which is what happened in my case, your body will attempt to gain weight. However, in light of the recent rise in obesity, it seems the reverse does not work nearly as well. It is much easier to gain weight well beyond the set point, than to lose weight in order to get to the set point. This is where issues of diet come into play and the picture gets very complicated very fast. A good friend of mine is really into this subject and his general view is that the principal culprit is sugar, with refined grains a close second. Both are highly addictive, calorie dense, and totally unnecessary for a healthy balanced diet.
Does this imply that exercise for weight loss doesn't work? Not at all! First, set point theory is complicated and has not been fully confirmed. While it does seem to explain what happened to me, it may not happen to everyone. There are a number of mitigating factors, the most important of which for older people is age. There is some evidence that weight gain with age is a natural occurrence. Maintaining a set weight as you age may be much more difficult than it is when younger. Second, even if it is true, it takes some time for it to kick in. If you are obese by the standard definition--BMI over 30--it will take quite awhile for you to reach your set point. While that is happening, you should see some weight loss due to exercise combined with diet. The effects of set point won't kick in until you near your ideal weight--whatever that may be.
Exercise can be difficult if you are sedentary, overweight or just haven't stayed reasonably fit. But the benefits far outweigh the gains!