Why Were We So Thin In The 70s (The Truth Will Surprise You)

In the 1970s:

Walking was the default mode of transportation
Stairs were used frequently
Daily errands required physical effort
Children spent hours in active play

People did not “work out,” yet they accumulated thousands of additional steps per day. Research shows that NEAT can vary by several hundred calories daily between active and sedentary environments—enough to explain long-term weight differences without any change in diet.
For illustrative purposes only
2. Lower Energy Density and Minimal Food Processing

Meals were primarily prepared from whole foods:

Vegetables, eggs, meat, milk, legumes, grains
Limited additives, emulsifiers, and refined sugars

From a metabolic standpoint:

Whole foods require more digestion energy (higher thermic effect of food)