Can intermittent fasting affect workouts? the impact on muscle and performance
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Intermittent fasting (IF) has become one of the most popular approaches for weight loss, but fitness professionals caution that the practice may not be ideal for everyone — especially those who prioritise strength training and long-term health.
One of the main concerns raised about IF is its potential impact on muscle mass.
Extended fasting windows can make it harder for the body to receive a steady supply of protein throughout the day. This means that while weight loss might occur, part of that reduction could come from muscle rather than fat, undermining the very strength that exercise aims to build.
Energy levels and workout performance are another challenge.
Exercising in a fasted state often leaves people feeling drained, which can reduce stamina during endurance training or heavy lifting. Over time, this fatigue can make workouts less enjoyable and harder to sustain, leading to irregular training schedules.
Beyond physical effects, IF may also carry psychological risks.
Restricting meals to tight windows can, in some cases, encourage binge-eating patterns or heightened anxiety around food. For individuals prone to disordered eating, such cycles can be particularly damaging.
Still, intermittent fasting can be managed more safely with careful planning. You can prioritise high-quality protein in the eating window — such as eggs, fish, poultry, or plant-based sources — while ensuring it’s spread across at least two meals. Combining resistance training with adequate protein intake and sufficient overall calories helps protect lean muscle.
Another strategy is to time workouts around eating periods. For instance, exercising shortly after breaking a fast allows the body to use incoming fuel for both performance and recovery. Balanced meals with carbohydrates, protein, and healthy fats further support energy levels and reduce the risk of fatigue.
Those considering IF are encouraged to pay close attention to how it affects both body and mind. Warning signs such as constant food guilt, frequent overeating after fasting, or withdrawal from social situations may indicate that the method is doing more harm than good. In such cases, shifting to a more balanced eating routine may be a healthier, more sustainable option.