In mice that exercise, cutting carbs way down to just 1% of their diet turns down genes that help muscles use sugar, but a 10% carb diet doesn’t — so super-low carbs seem to be needed to make this change happen.

What we've found so far is that a very low-carb diet may reduce the activity of genes involved in glucose metabolism in the muscles of exercise-trained mice. The evidence we’ve reviewed leans toward this effect occurring only at extremely low carbohydrate levels. Our analysis of the available research shows that when mice who exercise are given a diet with just 1% of calories from carbohydrates, the genes that help muscles take up and use glucose become less active [1]. This change isn’t seen when mice eat a slightly higher, though still low, amount of carbs—like 10% of their diet—suggesting there may be a threshold below which carbohydrate intake starts to affect these genes [1]. We don’t know from this evidence whether this gene change affects actual muscle performance or long-term health, only that the gene activity shifts under extreme carb restriction. Based on what we’ve reviewed so far, the effect appears specific to very low carbohydrate intake in mice that are already physically active. We have not found any studies that contradict this finding, but only one assertion was available for analysis, so our current view is limited. This means that in lab mice that run regularly, cutting carbs to extremely low levels might alter how their muscles prepare to use sugar for energy. But we don’t yet know what this means for physical performance, recovery, or metabolic health over time. Takeaway: In exercise-trained mice, dropping carbs to 1% of the diet—much lower than typical low-carb diets—may dial down sugar-metabolizing genes in muscle. We don’t know if this matters for fitness or health, but it suggests extreme carb restriction changes how muscles handle glucose at the genetic level.