*It's all about calories in Vs out.
Governments have been saying that since the 1970s, and yet obesity rates are rising.*
That's because people can't/don't/won't stick to it.
If people actually understood what their BMR was, stuck to a healthy, balanced diet which was in deficit, interspersed with a reasonable amount of exercise, they will, in 99% of cases, lose weight.
The problem is, they kid themselves, and kid each other on actually being in deficit. Willpower is lacking, motivation to exercise is waning, but in reality, all they do is self sabotage.
And then the serial dieters hop on the next fad. Low carb this, low fat that, high carb here, high fat there. Kid yourselves it's the type of diet making the difference if you want, the reason you are losing weight is, you are in calorie deficit.