Why many people believe that consuming lots of fruits can make you gain weight?

Why many people believe that consuming lots of fruits can make you gain weight?
I know people that they dont consume fruits or veggies a lot as they have this notion that those can make you gain weight if you eat them very often. Im aware that frutis have their natural sweetener and that sugar is not bad but what about if you consume that sugar very often? Will it really make you gain weight? The same applies with starchy veggies (potatoe, yucca, yams, sweet potatoes, etc)

I have a brother who believes in that idea like other people, he is not thin he has soem extra pounds but he is alreayd 47 years old. He has this notion that he is not loosing weight due to consume fruits every day and he beleives that the furits are making him have this extra extra pounds. My brother does not work out.

He told me that now is harder for him to loose weight as many years ago. Well I told him that weel he is much older now and probably his metabolism and body is becoming slower as well. He also added that many years ago without any professional guidance he was able to loose weight even if he never had worked out or do any kind of exercise and that is true many years ago he was thinner than now and he never went to a nutritionist or anything. But he did manage to get rid of some foods he was consuming at home that made him gain weight. SO now he is all worried and does not know why he can't loose weight as before on his own. He believes the fruits is the reason and the rice as well but also he says he is not eating dinner like in a way to loose weight.
Why many people believe that consuming lots of fruits can make you gain weight?
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