If people were still doing manual work in the factories, would we have so many people with obesity?

There's your answer, but it doesn't work. Those days are gone.

That isn't entirely true anyways. You can still eat more than you burn - even though that type of work is conducive to heavy labor.

It's just that, people eat too much nowadays. Fully grown adults require only a stick of biscuit and water twice a day for sustenance. For other vitamins, and minerals, they only require only a handful of vegetables, beans, and nuts. All that around 1800 calories. Most obese and fully grown adults eat 'twice' that much every day. They make their stomachs restless, and with meat and fatty foods.

There is a reason why they are so unnaturally fat.