as in the general obesity epidemic...

any thoughts/ideas?

Actually neither. Obesity is caused by cellular starvation caused by a problem with how carbs and fat are metabolized.

"Good Calories, Bad Calories" by Gary Taubes explains it all.

The short answer is neither.

Increased energy consumption and decreased energy expenditure are both effects - not causes - of the body going into fat-storage mode. The cause of fat storage is hormonal imbalance: When you eat carbs, you have sugar spikes followed by insulin spikes. Insulin tells your body to store fat. Even if your nerves and muscles are starved for energy, you will store the energy as fat instead of using it when your body is flooded with insulin. The result: hunger and fatigue, commonly misunderstood as gluttony and laziness.

National estimates of dietary fructose intake increased from 1977 to 2004 in the United States.the evidence shows that the greater increases occurred in total daily energy and carbohydrate intakes.
So the answer is reduce OMEGA 6 industrially made corn, soybean, safflower and sunflower oil, and everything that contains them to reduce energy intake and to eliminate refined carbohydrate intakes. wheat grains sugars fructose etc.

I suffer from late effects of polio. I can't exercise without making myself ill. I managed to lose nearly 3 stone without cutting calories or increasing exercise simply by changing the type of calories I consumed.
Very low carbs + loads of MCT/coconut oil fats = more calories the BMR = 2lbs weight lost each week with no extra energy expenditure.

Read Good Calories, Bad Calories and report back your opinion.

If someone is still healthy, then if they cut back their portions, they are reducing their insulin production, which will cut their weight. This is why people initially, when they are young, can lose weight by dieting. However, most diets fail over time. This is well explained in GCBC which is only $12 from Amazon.
If I try to simplify the explanation - and hopefully don't mangle the information in the book - you have fat. Nutrients go into your fat layer, and then nutrients are released to feed your body. Obesity occurs when your fat refuses to release nutrients to your body to supply its needs. Your body is now starving. As a survival mechanism, your body drives you to eat more food. As some higher food intake level, your body again begins to release nutrients to feed your body. So obesity drives eating. Over-eating calories (if you select low carb food) does not make one obese, although reducing consumption of carbs reduces insulin production. Reducing insulin reduces your weight. GCBC has many examples - if you eat a very low carb diet (which means eating a lot of meat) you can eat a lot of calories.
There are cases cited in GCBC where people were not hungry on 800 calories per day of meat, but when 400 calories of carbs were added, they became hungry. page 339-340. The bottom line is, the carbs have to go to lose weight and keep it off. The added benefit is, you will also greatly reduce the likelihood of getting many horrendous diseases of civilization from your future, as described in GCBC.

The book is published as The Diet Delusion in the UK.

I can confirm from personal experience that this is true. Before starting a VERY low carb WOE (meat & eggs & fat), I was hungry at 1500 calories, 1800 calories, even 2200+ calories. Since switching to M&E 5 weeks ago, I find I am eating in the neighborhood of 1500 calories but sometimes MUCH less--I need to watch this, I know--and not getting hungry. I eat twice a day and NEVER have cravings or hunger pangs. This has been a true revelation for me and just facinating to actually experience.