​In this article I discuss the importance of resistance training during fat loss phases and why it is important to start dieting only after subjecting your muscles to a recent training stimulus and to pause dieting if you are injured or cannot train for an extended period.

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Fat loss diets work by consuming fewer calories than our bodies use, forcing us to burn body fat as an energy source. However, an unwanted side effect is that being in a calorie deficit reduces muscle protein synthesis (production of new muscle tissue), while increasing muscle protein breakdown, reducing the rate of muscle growth from training, and potentially resulting in muscle loss.

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• Protein synthesis exceeds breakdown = Muscle is built

• Protein synthesis and breakdown are equal = Muscle stays the same

• Protein breakdown exceeds synthesis = Muscle is lost

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Please note that the amount of muscle that can be gained or lost in a single day is relatively small, approximately 5-30g total, outside extreme cases. However, it is the steady accumulation or loss of muscle over time that produces long-term outcomes. Protein synthesis and breakdown are unavoidable natural processes for repairing and replacing the cells of our body, but they are factors to optimise if we want to maximise progress.​

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Building muscle is harder during fat loss phases, because it is more difficult to maintain a positive balance of protein synthesis to breakdown.  I recommend training with the intent to build muscle, while also accepting that we may lose some muscle in the process. In my early training years, I was afraid of losing muscle and would sometimes terminate a diet if I had a couple of bad workouts or felt I was losing size.  If fat loss is truly a priority, then we must keep going, even if it means some muscle loss.  However, it is important that we maintain as much muscle as possible because this helps sustain our health, performance, strength, body shape and metabolism.

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Factors within our control that can improve our protein synthesis-to-breakdown ratio include:

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• Resistance training (providing high muscle activation and a tension stimulus to our muscle fibres)

• Degree of calorie deficit (studies have shown it is extremely difficult to gain muscle while in a deficit of 500+kcal per day)

• Protein intake (I aim for 2.2g per kg of bodyweight; higher protein intakes are not beneficial for most people)

• Sleep (both time and quality are important)

• Carbohydrate intake (if insufficient protein is ingested, carbohydrates trigger insulin release, which suppresses protein breakdown)

• Avoiding overextended fat loss phases (set a medium-term date to complete diets, before switching to maintenance calories to control hunger hormones)

• Overall health (conditions such as type 2 diabetes reduce insulin sensitivity, which increases protein breakdown)

• Avoiding excessive endurance training (this suppresses mTOR, a catalyst for the muscle growth process, and increases central nervous system fatigue, which reduces muscle activation)

• Avoiding very low body fat levels (not always possible if the goal is to get very ripped)

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Resistance training is the most important factor in this list. It creates a massive increase in protein synthesis that lasts for 48-72 hours. This creates a window where muscle loss is unlikely, assuming the variables listed above are satisfactory. After this period protein synthesis drops to normal levels, below protein breakdown, and muscle loss begins. The degree of protein synthesis from training is mainly dictated by the amount of time under tension each muscle experiences with high muscle activation, which requires high levels of intensity, effort, technique and exercise selection, without excess psychological or aerobic fatigue. Time under tension is best measured with training volume, or the number of hard sets taken close to maximum muscular effort. I have previously written about how I estimate that, for experienced lifters, four hard sets per week per muscle group is the minimum volume required to maintain muscle while in a calorie deficit.​

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Please note that this doesn’t imply that it is essential to train each muscle every 48-72 hours, although this is certainly a very effective training strategy. The most important factor is the amount of weekly volume that we perform, so we can compensate for training a muscle less frequently by performing extra hard sets during fewer sessions, although more frequent sessions often allow greater weekly training volumes.​

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Protein synthesis for muscle maintenance and growth is specific to each muscle, so all major muscles must receive a recent training stimulus to maintain muscle. If we diet without training, then we will lose muscle because we are not stimulating enough protein synthesis to counteract breakdown.

Some takeaways from this to fight against muscle loss:

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• Make sure you train every muscle consistently while in diet phases

• Only start diet phases when you have returned to training

• If you take a break from training, eat maintenance calories

• If you are injured and can’t train a muscle, eat maintenance calories

• Consider training muscles multiple times per week to increase weekly training volume

• When you deload by reducing training volume, then eat maintenance calories

• Focus on key factors that promote protein synthesis and suppress muscle breakdown, such as sleeping well and following a high protein diet

• Make sure you stay consistent with diet phases as you want to complete them to avoid spending unnecessary time suppressing muscle growth  ​