I didn't do domestic science at school because it occupied the same time in the senior school timetable as Latin.
When I left school after my Highers, I went to a finishing-school that taught domestic science as part of the accomplishments young ladies were deemed to need in 1968.
I agree the quantities in most recipes were smaller, but for dinner two courses were served every day, either soup followed by a main dish of meat or fish with potatoes and at least one vegetable, sometimes two. Or a meat or fish course followed by dessert, so I doubt the size of the portions were the reason that there were fewer obese people, or sufferers from diabetes 2 at comparitvely young ages.
If you read older cookery books ,you will see that there is less sugar in desserts and cakes, and usually no sugar in savoury dishes. We were taught the importance of a well-balanced diet, and taught that a certain amount of physical excercise was necessary for those who had a sedentary occupation and,or mainly travelled by car.
Comparitively more adults rode bikes (talking about Denmark here) or walked to work, or used public transport. Using public transport you were unlikely to be able to travel from door to door, so a certain amount of walking would be necessary.
Women too were only just starting to use labour-saving devices in the home, apart from vacuum cleaners. The first flat I lived in, we did our washing in a communal wash-house that only had a washing-machine of the vintage that washed clothes in cold water. You had to rinse them by hand, transfer heavy wet washing into a spin-dryer and from there into a laundry basket, and cart it into the adjacent cellar where the clothes-lines were and hang it up, or outside to a drying-green if the weather was suitable for drying clothes outdoors.
In blocks of flats the householders washed the staircases (front and back stairs) once a week from their own door down to the floor below.
This kind of housework was one very good reason why relatively few women were overweight, and till around 1980, you might manage to persuade your husband to dry dishes or vacuum the sitting-room floor once a week(!), but men proudly asserted that they knew nothing about doing washing or washing floors and most of them had the sense to keep it that way!