I also consume all my food in a 4-hour window (for me, from 10:00am to 2:00pm). I found it surprisingly easy, and I think in part that’s because I follow a whole-food plant-based diet, which precludes eating refined foods (refined sugar and foods that contain it, fruit juice (whole fruit is fine), foods made from flour, and “product foods” manufactured from refined ingredients and sold packaged under a brand name (aka CRAP (calorie-rich and processed) foods). I don’t think the 20-hour fast would be so easy were I eating refined/processed foods, which tend to be quickly digested.

I had assumed that fat and protein extended the feeling of satiation because they were slower to digest than carbohydrates, but of course dietary fiber (a carbohydrate) is not digested at all but serves as a prebiotic to nourish one’s gut microbiome. I now suspect that it is dietary fiber (abundant in whole plant-based foods) that provides the extended feeling of fullness.

Also, I eat intact whole grain rather than grain that has been cut (steel-cut oats, pot barley) or polished (white rice, pearled barley) or smashed (rolled oats, barley flakes) or pulverized (flour and foods made from it). I cook the grain as a batch and then refrigerate it, taking a portion at each meal. Refrigerating the grain after cooking it makes the starch resistant — more slowly digested. I do the same with beans/lentils: cook a batch, drain, and refrigerate, taking a portion for each meal.

I really like the 4-hour time-restricted eating. As you note, you suddenly have more free time: my mornings and evenings are now free, with no meal preparation or eating or kitchen cleanup.

I think you’ll find this quotation from the New England Journal of Medicine interesting. From “Effects of Intermittent Fasting on Health, Aging, and Disease”:

Preclinical studies consistently show the robust disease-modifying efficacy of intermittent fasting in animal models on a wide range of chronic disorders, including obesity, diabetes, cardiovascular disease, cancers, and neurodegenerative brain diseases. Periodic flipping of the metabolic switch not only provides the ketones that are necessary to fuel cells during the fasting period but also elicits highly orchestrated systemic and cellular responses that carry over into the fed state to bolster mental and physical performance, as well as disease resistance.