If you are wanting to reduce body-fat you are more than likely doing so to improve your perception of body image and self-confidence.
There may be a particular body part or group of body parts that you want to improve. Let me guess:
The ideal physique, to most anyway, isn't just lean or skinny, it has shape. Definition.
This shape, whether you are male or female, comes from the possession of increased muscle tissue.
Now there is no denying it, you will not build muscle whilst dieting or 'cutting' to lose body fat. The process of fat loss requires you to be in a negative energy balance, meaning, you must consume less energy than you are exerting.
Muscle tissue does not develop or grow in these conditions. Accept it.
As a result, your focus when dieting for fat loss should be to maintain muscle.
Some say that your strength/resistance training strategy should remain the same when attempting to reduce body fat. Most, insist on simply adding cardiovascular / aerobic type exercise in order to help place you in the negative energy balance.
Whilst aerobic exercise is certainly useful, and of course, very beneficial for general health, it may not be the most optimal strategy to help you lose fat and maintain muscle.
Well, because of the fundamental principle of specificity. Your body adapts in very specific ways to what you do. Without going too in-depth and discussing topics such as molecular signalling and motor-unit recruitment, aerobic exercise will primarily improve the efficiency of cardiorespiratory system. Using such method to help improve one's body composition is merely a simple way of exerting more energy (calories), but there are far more efficient ways of doing so in order to obtain the best looking physique.
Muscle Protein Synthesis:
To explain why, first let me explain something called muscle protein synthesis (MPS).
MPS is ultimately the driving force of developing new mass through taking nutrient-sourced proteins and placing them within the structure of muscle.
Muscle Protein Breakdown (MPB) is the opposite.
Should MPS exceed MPB we have a positive protein balance and muscles will become larger.
Conversely, if MPB exceeds MPS, muscle will be reduced.
The sum of this process will give us your net protein balance, and of course, if a better physique is your goal then we should do all we can to maintain a positive protein balance in order to develop and grow muscle tissue.
When MPS and MPB are equal, muscle is maintained. This balanced state is called proteolysis.
Unfortunately, achieving a positive protein balance is not as simple as eating more protein. As said previously, reducing your overall energy intake or dieting with the intention of reducing body fat will mean that you cannot build muscle, no matter how much protein you consume. There is a lot more to MPS than simply eating a tonne of chicken.
MPS is largely determined by the extent of muscle damage created during exercise, dietary protein intake, overall calorie consumption and your hormonal status (governed by multiple lifestyle factors).
Energy or calorie restriction (dieting) reduces MPS, but does not affect MPB.
Putting it simply, eating fewer calories in order to reduce body fat makes the development of muscle tissue almost impossible, and actually results in a greater likelihood that muscle will be broken down.
Not great if we're trying to improve body composition.
Fortunately, the reductions in muscle protein synthesis are reversed when regular strength training is used (Hector, et al., 2018). According to very recent research, this reversal only seems to occur in trained muscles.
In other words, muscle protein breakdown / muscle loss can be avoided or minimised during calorie restriction provided that the given muscle is exposed to regular strength training. Untrained muscles, however, are likely to experience loss/reduction.
The study performed by Hector, et al. (2018) was only carried out over a 15-day period and looked at scores in untrained individuals, therefore does have its limitations.
All participants performed 5 days of single leg strength training over 10-days of calorie restriction.
One group ate a low protein diet (1.2g/kg) and the other ate high protein (2.4g/kg).
Both groups were in a calorie restriction (calorie deficit).
They only trained one leg throughout the 10 day period and therefore one leg remained untrained.
Body composition testing was performed using DEXA.
Muscle protein synthesis was examined by taking biopsies of quadricep muscle tissue of both the trained and untrained leg.
What they found:
Energy restriction (calorie deficit) caused a significant decrease in bodyweight, fat mass and lean body mass with no difference between the high protein and low protein groups.
The loss of lean muscle tissue was greater in the untrained leg in both groups.
The reduction in muscle protein synthesis was greater in the untrained leg of both groups, with no change in the trained leg.
Calorie restriction reduces muscle protein synthesis but does not affect muscle protein breakdown. Reductions in muscle protein synthesis are revered by strength training. During periods of energy restriction, untrained muscles are likely to lose more lean mass than trained muscles.
Understanding that muscle can be lost during calorie deficits is nothing new.
For the development of one's physique and improvement of body composition, it is important to try and minimise the loss of muscle tissue as much as possible. Ideally, we should even attempt to maintain muscle tissue.
Strength training during energy restriction preserves muscle mass.
Muscle protein synthesis elevations post workout appear to last somewhere between 24-36 hours and therefore the frequency that a particular muscle is trained is likely to determine the likelihood of one being able to maintain the mass of that muscle.
A higher strength training frequency, therefore, may be valuable when dieting.
Next time you're thinking of prioritising cardiovascular type exercise to help lose body fat, think again. It is likely that using cardio will only lead to reductions in both fat mass and lean tissue. Use what time you have to go to the gym and perform strength training a little more frequently. Its more likely to help you maintain what muscle tissue you've worked so hard to gain.
Pronounced energy restriction with elevated protein intake results in no change in proteolysis and reductions in skeletal muscle protein synthesis that are mitigated by resistance exercise. Hector, A. J., McGlory, C., Damas, F., Mazara, N., Baker, S. K., & Phillips, S. M. (2018). The FASEB Journal, 32(1), pp. 265-275.