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Updated: Dec 4, 2021

Increases in strength and muscle mass are interdependent processes. This means, the stronger we are, the better we are at building muscle - and the higher our muscle mass, the more weight we can lift.

Both processes are determined by energy availability (i.e. how many calories we ingest throughout the day), macronutrient intake, as well as parameters like sleep, stress management, as well as genetic factors.

The current analysis (1) aims to determine whether a calorie deficit affects lean mass and strength gains during a resistance training period.

The paper is a meta-analysis, which looks at a given scientific question with a birds-eye view. In short: it is an “analysis of analyses”.

This what the researchers found:

Picture A depicts the relationship between a calorie deficit and its effects on lean body mass.

As we can see on the left hand side of the vertical line, all interventions were in favour of NOT being in a calorie deficit – that is: either at maintenance or “bulking” calories.

Muscle protein synthesis is a process which requires sufficient energy to be available through the ingestion of food. In order to “lay down more material”, we need to ingest “more material”. Operating in a caloric surplus of ~300-500 is a solid approach to gain lean muscle mass in the presence of strength training.

The current analysis shows that being in a caloric deficit of ~500 calories per day impaired subjects’ ability to gain lean muscle mass.

This is quite a significant deficit, and we can conclude that the further we drift into a caloric deficit, the greater our ability to build muscle is impaired.

Picture B shows the relationship between low energy availability and strength gains.

We can see that there is an all but 50:50 distribution between studies showing no impact of a caloric deficit on strength gains vs studies showin that there WAS a negative effect.

Taking a closer look, we find that the dotted studies on the left side of the vertical bar are showing a greater effect size (i.e. a value determining “How strong was the effect?”), which means that overall it resulted in a slight favour FOR eating at maintenance or surplus calories and against an energy deficit for building strength.

My interpretation and experience tell me that strength gains ARE possible in caloric deficit.

However, several nuances need to be addressed:


Long-term exposure to a caloric deficit prevents the body from building muscle tissue efficiently, or at least we find it impossible to reach a significant level. The duration of the studies included in the current meta-analysis had a maximum duration of five months. As such, we cannot conclude how results would look like if subjects had been exposed to a caloric deficit over a longer period of time.

I am inclined to conclude that the rate of strength progress is slowed down when combined with a caloric deficit - least not considering the fact that increases in muscle mass are essential for increases in strength in the long run.


Is the person new to strength training? If yes, then almost ANY intervention will make the person stronger and improve their body composition. I very much doubt that for anyone with a strength training experience of greater than one or two years, being chronically in a caloric deficit will maximize their improvements. The body would simply be in a non-anabolic environment for too long for its hormonal and structural processes to fully flourish and bring about significant changes..


If the person has sound sleep all week, good energy and stress management, as well as a strong drive to improve performance, that person is more likely to be successful at gaining strength in a caloric deficit, at least in the short term. If the person is challenged with poor sleep, low energy levels, and low drive, I doubt that being in a deficit will lead to increases in strength in in the long run, never mind being able to maintain it.

Concludingly, the present meta-analysis (1) demonstrates that in order to build muscle mass efficiently, a caloric surplus and/or at maintenance outmuscles being in a caloric deficit for such gains. To increase strength in a caloric deficit, other lifestyle factors would have to fall into place in order to keep progressing in the long run.

The bottom line: for anyone wanting to maximise their strength and muscle gains, being in a caloric surplus combined with periods of maintenance is essential.

As there is never a “black or white” in field of strength training and fitness, we need to ask “What is good, better, and best - and for whom”?

The answer to this question you will have figured out.

In best health.

Oliver Sifkovits

Reference (1): Murphy & Koehler, 2021: Energy deficiency impairs resistance training gains in lean mass but not strength: A meta-analysis and meta-regression. Scan J Med Sci Sports. PMID: 34623696

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