Fast 800 and muscle loss - advice needed

[GreenZebraStripes]

Background-

I did the F800 back in 2022. I had already been dieting (NHS calorie counting and lost a stone but plateaud). I then did F800 and lost another stone. I wasn't exercising (strength training) during this time at all.

At the end of it, I didn't actually like how I looked - very untoned.

Long story short, I ended up getting a personal trainer, lifting weights and building muscle mass. Fast forward six more months and I'd gained around half a stone of pure muscle - my body fat had dropped from 29% to 22%.

Superb. Did I sustain it. Did I fuck.

It's now 2025 and I think I've gone from 9st 9 to maybe 12st 7. God. I need to take action as I'm over my BMI and I also have a respiratory condition that doesn't like the extra weight. I feel tired.

I reckon on 12 weeks doing F800 I could lose 1.5 - 2 stone. However am worried about losing the muscle mass I gained and looking untoned again.

Things in my favour are:

I've got a baseline of more muscle mass - when I started F800 before I already had a history of yo-yo dieting, I had twice gained and lost 2 stone in my 30s.

I'm going to strength train while doing F800 - I could walk, lift weights, maybe swim.

I plan to do another bulk and build anyway once I've lost some of the body fat.

Downside is that I won't be able to do much cardio on F800. But reckon I could force myself to go for a swim once a week

Has anyone been in a similar position? Did you lose muscle?

Alternative is just to do a normal diet but I'm really impatient.

Have you maintained your training and just eaten too much? Or has the training mostly stopped as well as eating more? Because unless you've continued to train then you'll have lost a lot of muscle mass in that time anyway as it's not recent and can just rebuild again after.

I've not trained for 8 months. I did maintain my protein very well until maybe 2 months ago.

Just Googled and muscle comes back quite quick. I think I might just try and sort my diet out and do a slight calorie deficit and train really hard.

You have inspired me! I just found out that I'm getting nowhere near enough protein, so I bought some protein powder today and am going to start trying to get at least 80 grams per day. I'm afraid that with my fasting schedule, I'm just going to lose a lot of muscle and be in poor health. I think I'll start small with low weight dumbbells at home, and work my way up. Hope you get back in your fitness groove!

Yeah getting enough protein changed my life! I would say protein powder is okay as a supplement e.g. 10g or 20g a day, but don't rely on it as your main source, as its essentially devoid of nutrients. It's filler basically. I usually have protein powder with overnight oats for breakfast- keeps me fuller for longer. I also was eating about 80g of zero fat cottage cheese a day, it's very good for protein and really versatile. Plus usual meat and fish sources - my ferritin stores increased to really good levels when I was training, GP said it was best she had seen!

It was a long journey to Discovering weight training, I'm definitely of the generation where we taught carbs and bad and don't lift weights as you will get bulky. All nonsense I know now! I just remember after I finished Fast 800 starting to see women in their 30s on Instagram lifting weights and the light bulb went- I just thought surely if I do that I will get closer to looking fitter, and I did. Focusing just on the weight on the scale is a myth, it's also about how strong you are. I went from lifting 3kg weights to leg pressing 200kg in 6 months. Good luck!

I'm going to restart swimming in my week off. Got to start somewhere.

@GreenZebraStripes Thanks so much for your reply! Yeah I always just assumed I was getting enough protein because I eat mostly healthy foods, but I saw someone posting about protein requirements while doing intermittent fasting and it made me wonder if I was losing muscle. My mouth fell open when I saw that I should be getting 80-100 grams. I'm probably not even getting half of that on a regular basis. I'm a pescatarian and enjoy tinned fish so I will be trying to incorporate more of that, as well as tofu and beans (I tend to eat a lot of pasta and veggies, gonna start buying bean-based or high protein/high fiber pasta.) I love cottage cheese so I'll take your recommendation and start buying the large container, try to eat it as a snack more often along with edamame which I also love. I'm going to try the protein powder in oatmeal as well, that should get me off to a good start. Sending you good vibes!