This video interview with Toronto nephrologist Dr. Jason Fung presents his research indicating that no, they're not. Calories aren't equally fattening: WHEN we eat has a big impact on how fattening calories will be.
He's one of the intermittent fasting gurus: and yes, most days I practice gentle IF (along with the IE, intuitive eating) by creating at least a 14-15 hour window between my last meal of the day and my first meal of the next day. At previous points in my life I've fasted for up to 7 days: but this moderate IF routine is working well for me at the moment.
Fung came to IF from his kidney specialty. Many of his patients in kidney failure are diabetics. And many diabetics are obese. And, he reasons, widespread (no pun intended) obesity is really associated with the low fat craze of the 70s through 90s. There was a scientific misconception that eating fat makes us fat and increases blood cholesterol too.
When people didn't eat enough fat, they got hungrier faster: fat, so often associated with protein, is a partnership key to satiety. So instead of eating 3 meals a day which included fat, they responded to hunger with continuous grazing . . . typically, 3 meals and 3 snacks (or more) a day.
That meant the body was always relying upon incoming fuel and never depleting stored fuel: fat. And without depletion of stored fuel, obesity and diabetes and kidney failure exploded. Fung found that treating kidney failure with dialysis didn't deal with the underlying causes of the kidney failure, the diabetes and the obesity. And of course seeking to control obesity with traditional dieting (calorie counting, calorie restriction) is notoriously unsuccessful in the long run.
Fung believes that we don't eat too much necessarily but that we eat too continuously. Human beings evolved to fast: "breakfast" meant something. Human beings throughout most of our evolutionary history seldom ate oftener than once a day Our hunter ancestors quite frequently experienced days with no meals at all.
And so 800 or 1,000 calories twice a day over an 8-10 hour period has a very different impact on the body than the same 1,600 or 2,000 calories a day on pretty much continuous intake over a 16-18 hour period.