Eating Small Amounts Of Food.

[Barsel]

Why doesn't eating small amounts of food lead to weight loss?
A friend of mine eats very little, not because she wants to lose weight (even though she is over 13st) but because she doesn't have a good appetite.
Her son who lives with her prepares and cooks most of her meals but she only eats a small portion of the meal and sometimes barely touches it, and yet she never loses weight.
Before lockdown, she used to go to keep fit 2 or 3 times a week and although that isn't up and running yet, she does go for a walk everyday and keeps fairly active.
We are told that eating less and exercising more leads to weight loss, but that doesn't seem to be the case here.
How is this possible?

[Purist]

I eat small amounts and mainly complex carbs and vegetables and small amounts of protein, its the only way I can eat without having digestive discomfort, however I keep losing weight eating this way. I do not eat any junk/sweets/fried foods, when my weight drops too much I increase my protein intake which brings me back to normal but is not good long term as I have digestive issues with too much protein.

[Barsel]

Thanks for all you answers, the funny ones, Ken and canary and the more scientific ones. Wish I could give more than 1 BA.
So, my friend is less than 5ft and she is built heavy, legs arms etc.
I would describe her as unhealthy as she cannot walk from one room to another without getting out of breath and to be honest, I think she would benefit health wise from losing some, but I haven't been able to understand why she doesn't.
Still, she has never expressed a desire to lose weight, so although I'm a bit worried about her, I would never say so.
Now I've read some of your answers, I understand about it more.

[Barsel]

Woofy, 2 of my granddaughters are like that, but I can see why.
The slim one is on the go ALL the time, it takes her all her time to sit down to eat. Whereas her sister is very sedentary loves to sit and watch TV or play on her phone but she is also very studious so spends time reading, playing the piano and studying.