The problem is just to keep from getting fatter. The energy balance model does not really offer us guidance in doing that. Its focus on calories and calories-in versus calories-out fails to get to the underlying issue, which is body composition. Moreover, calories in foods are not the same as they are in a bomb calorimeter.
A person might remain in energy balance and still become fatter while staying at the same weight by losing lean body mass, including muscle, organ and brain mass. Lean body wasting leads to sarcopenix obesity which tips us into a dynamic cascade descending into metabolic syndrom, inflammatory insulin resistance, systemic inflammation, cell damage and dysfunction, altered gene expression, immune dysfunction, and diabetes to the rest point solution of the dynamics, which is death. To me, it is all about the dynamics.
What about the dynamics?
First, fast dynamics of weight differ from slow dynamics. Fast dynamics are there to keep your brain alive in face of energy variations. Variations of energy intake and expenditure are a feature of living, but they balance over short time scales and have little to do with your weight. By the end of a month, these variations are approximately balanced. Short time scales have little to do with long-term weight gain.
You gain weight on a long time scale, which is on a scale of years. Yet, nearly all diet studies are on short time scales of hours or days. Most of these studies last no more than a few weeks and at most go for a year, and they drop the drop outs or make an attribution of weight gain or loss to them based on, well nothing. I think the time scale problems make short-term, and they are all short-term based on the time scale of the dynamics, of little use.
Macro compostion studies are no better, if you look at the attractors of the dynamics. The macronutrient partition models can be divided into two classes with either a single fixed point body weight or a manifold of body weights. A manifold contains an infinity of body weights and balanced dietary intake and expenditures, with no single fixed point. The empirical diet studies fail to identify which of these possbilities is the rest point or points of the energy dynamics. In short, you can be in energy balance at a single fixed point or an infinity of fixed points of weight and energy balance. The empirical diet study data cannot distinguish between these possibilities on long or short time scales.
In short, body composition and body mass are not determined by diet energy content or macro-nutrient compostion or energy expenditure through activity. The approach to a fixed point, if a unique one even exists, is on such a long time scale (as long as a decade) that you would never know that your weight would settle at that fixed point from the results of a diet study.
Just a couple of points more.
There is an iatrogenic factor to consider. The experimental intervention may make things worse. It is obvious and many studies indicate that diets predispose to weight gain once the energy restriction ends. Almost all diet iterventions result in weight gain and an altered body composition that is worse for long-term health.
Then there is the uncertainty principle. If you focus on weight gain or loss, you cannot detect the other changes that take place with precision. The more precise is the focus on energy intake and expenditure, the less precise and often neglected are the measurements of other health outcomes.
Double blind experiments can mislead because human subjects are not blind willingly. They often guess or share medications or simply ignore instructions. Would you willingly submit to an experiment where you are equally likely to do or take something that may be a placebo? Not me. They are doing it because they are paid to take part in the clinical trials. Some do it for the money, others take part out of desperation. To my knowledge, there are no studies that take up that issue. I can say that a colleague who is a distinguished mathematical psychologist told me that experimental psychology experiments fail to treat the subjects as intelligent humans. He said, humans in experiments are not humans in the real world.
In the end, we are all ongoing experiments of n=1. If we regard ourselves as such, then we will PAY ATTENTION. Paying attention to what you eat and do and how you function is the only way your brain will engage the subject. What you pay attention to is almost the whole thing. I pay attention to my body composition, my posture, and my functional capacity to do the things I want to do. Except that I should add, I pay attention to my wife.