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Ketogenic low‐carbohydrate high‐fat (LCHF) diets are popular among young, healthy, normal‐weight individuals for various reasons. We aimed to investigate the effect of a ketogenic LCHF diet on low‐density lipoprotein (LDL) cholesterol (primary outcome), LDL cholesterol sub-fractions and conventional cardiovascular risk factors in the blood of healthy, young, and nor-mal‐weight women. The study was a randomized, controlled, feeding trial with crossover design. Twenty‐four women were assigned to a 4 week ketogenic LCHF diet (4% carbohydrates; 77% fat; 19% protein) followed by a 4 week National Food Agency recommended control diet (44% carbo-hydrates; 33% fat; 19% protein), or the reverse sequence due to the crossover design. Treatment periods were separated by a 15 week washout period. Seventeen women completed the study and treatment effects were evaluated using mixed models. The LCHF diet increased LDL cholesterol in every woman with a treatment effect of 1.82 mM (p < 0.001). In addition, Apolipoprotein B‐100 (ApoB), small, dense LDL cholesterol as well as large, buoyant LDL cholesterol increased (p < 0.001, p < 0.01, and p < 0.001, respectively). The data suggest that feeding healthy, young, normal‐weight women a ketogenic LCHF diet induces a deleterious blood lipid profile. The elevated LDL cholesterol should be a cause for concern in young, healthy, normal‐weight women following this kind of LCHF diet.