Energy balance and tracking your intake might be the most important thing, but protein intake would probably be the next most important thing. During a fat loss phase, the amount of protein needed increases for several reasons.
First, greater levels of activity increase protein requirements and activity goes up when cardio is performed in addition to weight training during a diet. Additionally, protein is used more for fuel because less fat and carbs are available due to caloric restriction.
Finally, with less dietary carbohydrate and fat available, more glycogen and body fat are utilized; as their stores decrease, this forces the body to rely more on protein as an energy source.
Both dietary and body proteins can be used for energy in the face of this energy shortfall. Thus, to protect against body protein losses, the full-body utilization of protein becomes more efficient. However, this increase in efficiency often does not prevent losses of muscle mass, especially in lean individuals, even when weight training.
Fundamentally, whether or not you gain lean tissue is determined by the combined factors of muscle protein breakdown and muscle protein synthesis (the creation of new muscle proteins).
If breakdown surpasses synthesis, a loss of lean tissue occurs (and vice versa). A common theory is that during periods of energy deficit, muscle protein breakdown increases, outpacing synthesis, resulting in the often observed losses in lean body mass.
In cases of a caloric deficit, or even advancing age, optimal protein intake should actually increase in order to preserve the lean body mass that you might lose due to the catabolic nature of age (sarcopenia) and a caloric deficit.
While it’s difficult to determine hard numbers from current data, based on current data, it appears that adding 1.5% protein each year after age 30 is probably a safe bet.
As mentioned above during a caloric deficit, it may be wise to also increase protein by 10-20% above surplus calorie levels of protein. To make things easier, here’s a table compiling some of these parameters.
These ranges appear to be optimal. By consuming these ranges of protein, you can be confident that you’re getting more than your fair share of protein to maximize your retention of lean body mass.
Another great benefit of protein is that it is the most satiating macronutrient, meaning it keeps you fuller for longer, when calories are lower this can be a great tool to help you stay on your fat loss journey.
Protein is also harder for the digestive system to breakdown which means the body has to work harder, which means more calories are used to digest protein, another positive when trying to lose body fat.