What should your calorie deficit be to lose fat as quickly as possible without losing muscle?
Perhaps you remember this famous study: Garthe and his colleagues, in 2011, compared two groups with, for one, a deficit of 19% (~ 500 kcal) and for the other a deficit of 30 % (~ 750 kcal). Both groups lost around 5.5% of their body weight, but even though the 19% deficit group lost weight at a slower rate, the candidates lost more body fat than the other group while muscle mass gainer. This means that there is an optimal calorie deficit with which you can lose fat while maintaining (or gaining) muscle mass.
Recently, Murphy and colleagues (2018) published a study that gives us a better appreciation of the phenomenon. They compiled data from hundreds of military training participants (16 independent studies) to determine how a specific calorie deficit (ranging from -59 kcal / day to -3143 kcal / day) affected power and strength. This is insightful because a decrease tells us something about muscle wasting.
Candidates with a calorie deficit of 58 to 126 kcal per day retained their power and strength, or even increased them. On the other hand, those who followed a deficit of 1237 calories (total loss of 16% of body weight) saw their strength decline more quickly. For these subjects, the threshold seemed to be around 300 kcal. Having a larger deficit was clearly detrimental to strength, power and therefore muscle mass.
Note that these participants did “military training” and did not follow an optimal strength training program, which could have less impacted their performance.
Candidates likely had average body fat levels in men (10-16%). The results show that it may be beneficial for people with the same fat level to cut calories harder (deficit of more than 600 kcal) and to sacrifice muscle mass to be able to start their muscle-building phase earlier. . They could then easily regain their muscle mass and, after a year, gain more muscle altogether, instead of taking the slow route.
Also note that people with higher fat counts can afford greater deficits without affecting muscle mass: they have a lot of stored fuel (fat) to “fill the gap”, so to speak. Someone with 25% body fat could practice a deficit of 900 kcal / day while a person with 8% could find themselves in big trouble with the same approach.
If you want to figure out your optimal personal deficit to maintain muscle, keep an eye on your heavy workout performance while trying to push your deficit further and further. If you’re losing strength on an exercise that is very clearly related to muscle mass, like the bench press, you may have gone too far.
Do you prefer to cut calories very sharply to end the cut quickly so you can start building muscle earlier, or take the slower route and keep all your muscles during the cut?
