To tell son it’s too much and affecting his dad’s self esteem.

Or buy bikes.

Not all young people go through such a stage

If he comes round when you are still in bed start bouncing up and down on the bed and make 'noises' hopefully he'll be that mortified he'll at least quit shaming you for having a lie in!

OP , are you sure about his age 25? he sounds like a teenager who still knows everything!

Yes this - has he paid lots of money for these books, seminars, courses etc? Does he spend a lot of time on social media? Does he think he's friends with these people? If so these are known scams targeting young men for ££££. They behave like cults.

Has he ever had a girlfriend? How does he speak about women? Next he'll be on the misogynist incel seminars.

Nothing like the zeal of the convert.

If we're doing unsolicited advice, you need to work on your Main Character Syndrome.

I agree that it sounds very cult like. Also I wonder if there is some Manosphere type stuff going on, a lot of them are obsessed with fitness, pushing themselves etc to "prove" their manliness. Could well be that they assured him that women will be falling over themselves to sleep with him and it hasnt happened.

You’re missing the point though. The OP’s husband hasn’t hired a life coach or personal trainer whose advice he is now ignoring. It is unsolicited interference from a family member who had been told more than once to stop.

It won't be long before you hear about how the government use alcohol and mainstream to control the people

I was going to say this!! The total change in behaviour sounds really strange. Sounds really creepy, I'm sorry you're all going through this.

He sounds completely insufferable. Not lovely at all.

It's not his home any more so even if it suits you for him to have a set of keys, he uses them only by prior arrangement (popping round to water your plants if you go away), not to drop in. Bolt the door at night and unbolt it when you are happy to answer it. Tell him he is invited for lunch or whatever and establish a loose pattern of meetings and explain that he should ask to come round otherwise, not appear.

I would also develop your own activities you like to do with him one on one, and encourage your husband and him to do the same; for example they could go for a regular, unambitious walk in nature or go fishing or mountain biking or go to auctions or whatever it might be. Let them find common ground involving gentle physical activity rather than threaten your husband with the loss of his sedentary identity.

sorry but your DH does need to do something does he have any hobbies apart from eating and watching TV sounds unhealthy.
What about you do you exercise. How about you and DH go out for a walk or something.

I was having a glass of wine in the garden yesterday after work when Ds walked through the side gate and gave me a lecture about the negative affects of alcohol which turned into how good he feels without it in his life and how disciplined he is now because he doesn’t watch tv and he doesn’t eat this and that and doesn’t understand people who let their mind rot with tv, alcohol, caffeine etc so he’s either left those people behind or trying to change them or open their eyes to their misgivings now that he pushes himself to get up early and go for a run in the rain and convince everyone how wonderful his mindset is but it’s all he talks about, he’ll ring me and talk about nothing else but how he’s changed his life and I should read this self help book and listen to this paragraph.

He sounds insufferable.

He clearly isn’t going to stop, so you need to make it clear you’re not listening. Each and every time he starts this routine, cut him off. Talk over him if you have to. No polite pussyfooting - you’re not interested.

One of my friends had a similar issue with her DS. He completely changed when he left Uni and became overly judgy of everyone and everything. He is in his 30s now and they have unfortunately drifted apart because he would not accept that he was hurting his family. She sees him maybe twice a year.

He will unexpectedly call round early on a weekend and ask why we’re still in bed. This will be about 8:30-9 when he’s been up and been for a run already.

Respond to this with "I thought we already had the sex talk with you. Maybe turn up a bit later and we'll be up/finished" he won't do that again.

The only charitable thought I can have is that he is worried about his dad's health. Maybe sit down with him and tell him you are two grown adults and have been living independent lives without interference for years now. you know what he thinks and that's fine but you don't want incessant advice and you don't want his judgement so how about when he comes over you have a cup of coffee and a chat instead of the complaints.

I think he thinks he’s the motivational speaker now.

hahaha - he really isn't. Tell him that if he thinks he is the next Tony Robbins he has a whole massive other think coming. And to work on his "bedside manner".

Do this while smoking a joint, and drinking a pint of lard.

The insufferable prig stage is usually over by the time they are 21. Tell your “lovely” son to stop lecturing and to grow up.

Did the OP say he was in the obese category?

I may be way off base, but he sounds like someone who has had an addiction and conquered it or like a person who has 'discovered' religion and who now believes they have a mission to convert the entire world. I'm not saying he was an addict, but was he living an 'unhealthy' lifestyle or perhaps 'partying' too much when he first got out on this own? Could he possibly have a girlfriend who's a 'fitness nut' but he doesn't want her to meet you because you don't live up to her standards?

The thing is, if any of the above rings true, you will never be able to 'gently' get through to him that he is being rude and insufferable. It's probably going to take some hard words like "Son, just shut up. You are living your life the way you want so please allow us to do likewise. Your 'advice' (yes, use finger quotes) is unwanted and unhelpful". If he keeps on then either keep repeating or ask him to leave until he can be more respectful. If nothing else, tell your DH that if he will not confront your son and tell him to knock it off (not argue about it, just 'shut up' or words to that effect) he's effectively putting up with it so he needs to stop complaining to you about it.

As far as the unwanted visits you have a right to set boundaries. Tell him not to visit before 10am (or later) as you will be sleeping in and do not want to be disturbed. I don't know that I'd go so far as to change the locks right now, but I would tell him that he needs to ring before he comes over or at the very least knock & announce himself before he enters.

After we left home we never simply walked into our parents' home unless we'd called first. If we hadn't we'd ring or knock, then open the door and give a 'Hello, anyone home?" and wait for a reply. My children do the same. Of course, with my children it may have more to do with the fact that I sometimes walk around the house naked. No one wants to see that!!!

Explain to your son that no one likes unsolicited advice.

Tell him you’re still in bed at the weekends because you like a nice leisurely shag. That’ll shut him up.

Your son is going through a sanctimonious phase. Seasoned with the dunning Kruger effect. Being healthy in the body does not mean healthy in relationships and mind. His dad needs to draw a line and say, son, I’m proud of you, now leave me the hell alone in my own home. I raised you to have more respect. …

Ugh, what an absolute pill he sounds. People who talk incessantly about their diet and exercise habits are among the most annoying and boring people in the world. If they only talk about themselves, it’s bad enough. Once they start criticising others, as your son does, they tend to be truly insufferable.

He’s not a teenager discovering new ideas, he’s an adult who clearly hasn’t learned how to interact politely with his own family. I would try to talk to him about his behaviour, but if he’s unwilling to listen, I would limit the time spent with him. There’s no way I would put up with being insulted and lectured to in my own home.

OP says he is overweight - not very overweight

she says he likes to watch telly - not that he spends a lot of time in front of it

if her DS was truly concerned about his dad he would have heard what she was saying and realised he is not helping and would take a different approach.

Do you have other children living nearby? He could be worried that he may have to be the sole carer for his relatively young parents because they did not look after their health in middle age?