One of the reasons why ancient women were slim was that their diet had certain regularity and weight, and they could not do whatever they wanted. The ancient patriarchal society put forward many requirements for women, and the low status of women was reflected in all aspects of life. In terms of diet, women can't eat until their parents and brothers have finished eating, and the weight of what they eat is limited, so they can't eat as much as they want. It is precisely because of the influence of the ancient concept that men are superior to women that women are so slim.
The second reason why ancient women were slim was that they didn't exercise, but they also had to do needlework at home, which also consumed a lot of calories. Nowadays, women choose to do a lot of aerobic exercise to keep fit, but in ancient times, women were not allowed to stay indoors, let alone exercise. It's not that ancient women didn't exercise, but that their exercise was mental. They have to do needlework, embroidery and so on. This kind of work is meticulous and tiring.
To sum up, the reasons why ancient women were slim were the above points. One of the reasons is that they eat regularly and have a certain weight limit, which was not allowed in ancient times, just as we can eat as much as we like now. The second reason is that although ancient women never leave home, they have been wasting their physical strength, which is also an important reason for their slim figure.