A new meta-analysis has tried to settle a specific version of the keto-versus-carbs question. Many comparisons of low-carb and higher-carb diets are muddied by one side simply eating fewer calories. This review, published in Nutrients, deliberately isolated the effect of carbohydrate restriction itself by including only randomized trials where both diet groups were prescribed the same energy intake or the same targeted energy deficit. The ketogenic diets in question were defined as 50 g of carbohydrate per day or less, or no more than 10% of total energy from carbohydrate.
Seven studies met that strict bar, and six of them — comprising 259 participants — contributed to the pooled weight-loss analysis.
The result: a real but small advantage for keto. Ketogenic diets produced 1.49 kg more weight loss than higher-carbohydrate diets under matched energy conditions (mean difference -1.49 kg, 95% CI: -2.41 to -0.58, p = 0.008). The result held up across sensitivity analyses, including when the highest-risk-of-bias trial was excluded.
A secondary check narrowed things further. In the three trials that also matched protein intake between groups — removing another variable that can drive weight loss on its own — the direction of the effect stayed the same, but it was no longer statistically distinguishable from no difference at all.
The certainty of the evidence was rated low, due to risk of bias in the underlying trials and the imprecision that comes with a pooled sample of 259 people. The authors also note that most trials were short-term, actual (rather than prescribed) energy and protein intake was often uncertain, and body composition — how much of the weight lost was fat versus muscle — was not analyzed.
Bottom line. When calories are held equal, keeping carbohydrate at or below 50 g per day was linked to a modest amount of extra weight loss — about a kilogram and a half — over higher-carbohydrate eating. That is a real signal, not a transformative one, and it comes from short trials with a good deal of uncertainty still attached.
Medical note. This article is for general educational purposes and should not be considered personal medical advice.