I obsessively read about health, diets, and supplements. For many years I would water fast for 24 hours once a week for longevity purposes.
If you track weight gain on charts through the 20th century, most of it is related to heavily processed foods. There are many studies done on ultra-processed foods and weight gain.
Focus on removing heavily processed foods from your diet (sugary beverages should go, if you can't live without them, add a little juice to water for flavoring),
helps a lot(
), and you might try to get your gut bacteria to help you out (this is usually referred to as the microbiome). You might want to consider homemade kefir (the store bought variety does not compare) for this purpose. If you have any questions, feel free to ask. I have read many studies for over a decade, some of them about bacteria that are quite strange.