Now we have gym memberships because we need to do exercise
And ironically, most people who go the gym probably burn off far fewer calories than people of the 1970s and previously who walked miles, did manual jobs, hung the washing out instead of using the dryer, used a twin tub etc etc.
*A finger of fudge is just enough to give your kids s treat 1970s. There were snacks and we had unlimited access to crisps break time at my school. There were no lunch box police and kids ate Jaffa cakes and buns for lunch.
Again people did drink alcohol and most people had the ‘alpine pops man’ we guzzled gallons of fizzy drink*
I'm also a child of the 70s and this comment isn't typical. Pop, crisps and sweets were in much smaller portions and treats once a week at most for most people, very far from 'daily guzzling' or 'unlimited'.
We only had fizzy pop once a week at most, in reality more like holidays, parties and occasional trip to the pub, and would share a quart bottle (slightly more than a litre) between 6 people - so we got about 200 ml each - I remember if we went out, we got a 250 ml panda pops bottle that wasn't full. People these days think nothing of drinking a whole can or 500 ml bottle to themselves.
1970s diet wasn't necessarily worse. Today's high protein, superfoods is a gold plated gilded version of a healthy diet. People can be equally healthy on simpler, higher carb food. Potatoes, rice etc are not inherently unhealthy. People used to eat a lot less meat as it was much more expensive than today, an example being the much derided Mumsnet chicken, where a chicken can quite reasonably feed a family for more than one meal, but people of today are, quite frankly too rich, spoilt and greedy to consider doing this.
And most people aren't eating in a food pyramid style anyway. The overweight people are not the ones who are eating a higher carb lower fat diet, they're the ones who are eating lots of processed food and sugary drinks and snacks.
More alcohol is drunk these days too, because people can afford it. Most people would go to the pub once or twice a month for a couple of drinks. They wouldn't have wine at home multiple times a week or go out at the weekend for cocktails or multiple pints.
Short version of the above is that people moved a lot more. I don't know if calorie consumption has dropped - the rationing diet was 3000 calories and was fairly high sugar - the sugar ration was over 200 g per person per week, WTF did people do with all that sugar? I would have been swapping mine for eggs.
Many people today will consume fewer than 3000 calories, but some will eat more - if you got a coffee and a pastry on the way to work for breakfast, a premade sandwich, crisps and drink for lunch, and had a pizza for dinner (look how many people boast about being able to eat an entire large Domino's pizza without it touching the sides and scoff at the idea of it feeding the suggested 3-4 people) that would be about 4000 calories.