Kept it simple for my Dad.

Had my dad stay with us for 10 days. When he arrived he was complaining of not being to walk properly and had muscle fatigue that wouldn't go away...
He eats a big meal a day which is usually 3/4 meat, 1/4 potatoes, sometimes just meat. He uses a pie dish to eat his dinner in!
And then he started complaining that I was overfeeding him and he didn't come to me to get fat. I gave him brunch and dinner.

By day 3 he was still complaining that I was overfeeding him but he was rapt that he could see the veins in his feet again after not seeing any for a few years. He also said that he was having daily bms which he was also struggling with and he had not piddled so much even though he is on fluid retention tablets.
He was also starting to go for his walks again as he'd been cramping and was too scared to leave home in case he really hurt himself.
By the time he left, he acknowledged that if he was able to spend another week with me, I probably would have him out running around no worries and that he was going to take on my advice when he got home.

Really simple advice - Eat your veges Dad!

I dished up his meals on smaller plates and flipped the ratios - 3/4 veges, 1/4 meat. Needless to say the first meal I dished up was confrontational for him (a quarter chicken, garlicky mashed potato, fried cabbage, beans and peas.
I rang him a couple of days later after he got home and he was excited to tell me that he'd gone out and bought a few veges but he was upset that he'd already undone my efforts without knowing how he'd done it. We have recliners and he doesn't. I suggested an alternative.
And then he mentioned that he weighed himself. And he was shocked that he'd lost weight. Which he couldn't understand how either, considering according to him I had him eating all day.
I just chuckled as I knew it was just water weight and reminded him once again 'eat your veges'.