Hi, I was doing OMAD and fasting sometimes 48 hours when I started HRT.

What I found is that you get hungrier when you start estrogen, and even if I kept with OMAD I was binge eating in the evening to get enough calories.

In general I recommend letting yourself eat when you start HRT. I gained something like 15 lbs over a few months, and my breast growth and body shape honestly benefited from it. However, it's also important to lose the male-distributed fat, and it's not great to stay too overweight if you are obese like I am.

I guess I like to think my approach is somewhat like "fat cycling" where I am mostly trending towards weight-loss, but I let myself overeat when I get hungry and I have weeks where I semi-intentionally put on a little extra weight to force a plateau before continuing to lose weight.

Since fasting wasn't working anymore (and my doctor even recommended I stop fasting so long, which was the main way I was losing weight), I do recommend like others do to use calories in / calories out (CICO) as a method of weight loss instead.

There were a few things that finally unlocked weight loss on HRT for me:

1. recognizing that fasting was actually playing a role in getting too hungry and binge eating, and that even if you just eat a little bit (like, I started to just drink a couple tablespoons of ground flax seeds in water and a spoonful of peanut butter to break my fast around noon), it helped me not overeat as much later, so I learned to curb binge eating with strategic timing and not over fasting.

2. I had tried and failed CICO in the past because I was moralizing and rigidly strict about it. Keeping a food log put me in a weird obsessive mindspace that was unhealthy, and I perfectionistically tried to weigh and calculate every single calorie I ate, which was exhausting labor. Instead, what I learned is that you don't have to track everything - tomatoes and lettuce just don't have that many calories. Track your carbs, oils & fats, etc. And more importantly: be comfortable with rough estimating and as long as you are keeping track of calories roughly, that's what matters. HRT actually helped me be less rigid, so this is a bit of a chicken and egg situation, mental health improvements then made it easier to adhere to tracking macros, which helped me lose weight, which then helped my mental health.

Other aspects that were important for me, but which came naturally:

I didn't set any calorie goal or even explicit intention about how much to eat or not eat, but merely writing down what I was eating and how many calories I was eating (very roughly), was enough to cause a feedback loop that naturally led to weight loss for me. That is, my eating behavior changed just by observing it. Overnight it went from struggling with eating too much and controlling my eating to actually struggling to make sure I ate enough. (This was genuinely surreal for me.)

"Just observing" means I didn't form moralistic standards or goals that I could fail - all I did was observe, and I let myself overeat and didn't worry about it. I still do, when I feel really hungry. Now a lot of times I try to evaluate and judge my hunger based on the patterns I am observing, and it helps me be aware when I'm eating out of boredom vs hunger. Also helped me see how eating (i.e. eating regular and sufficient meals) is important to not over eating (i.e. compensating for eating too little one day by over-eating the next day, or not eating all day and then over-eating in a short window in the evening).

I realized with CICO that what I was eating didn't really matter as much as I had thought before, and I started to relax about the moralizing and negative self-talk I was doing with my diet (which was a broken attempt at forcing myself to lose weight with shame). Before I would feel guilty for eating sweets or certain foods, and with tracking I was watching myself lose weight eating cake, etc.

What you eat just doesn't matter as much as the calories you eat.

Anyway, we are all different, so not everything here will help you, and you have to figure out what works for you. I just recommend being gentle and loving with yourself, and being careful about any kind of rigid or demanding method of weight-loss (I think our society promotes a lot of toxicity on the topic, we are quick to blame people for being overweight, and quick to hate ourselves for meeting our basic needs by eating).

Stress reduction, getting enough hydration and sleep, etc. are also important in shaping your appetite - when possible take care of yourself and alter your conditions to support you, and things that seemed impossible before can become easy.