Low-carbohydrate nutrition and metabolism
Eric C Westman, Richard D Feinman, John C Mavropoulos, Mary C Vernon, Jeff S Volek, James A Wortman, William S Yancy and Stephen D Phinney



Definition of low-carbohydrate diet
Much of the controversy in the study of LCDs stems from a lack of a clear definition. The rationale of carbohydrate restriction is that, in response to lower glucose availability, changes in insulin and glucagon concentrations will direct the body away from fat storage and toward fat oxidation. There is a suggestion of a threshold effect, which has led to the clinical recommendation of very low concentrations of carbohydrate (<20–50 g/d) in the early stages of popular diets. This typically leads to the presence of measurable ketones in the urine and has been referred to as a very-low-carbohydrate ketogenic diet (VLCKD) or a low-carbohydrate ketogenic diet (LCKD). Potent metabolic effects are seen with such diets but, beyond the threshold response, there appears to be a continuous response to carbohydrate reduction. The nutritional intake of <200 g carbohydrate/d has been called an LCD, but most experts would not consider that to provide the metabolic changes associated with an LCKD. We suggest that LCD refers to a carbohydrate intake in the range of 50–150 g/d, which is above the level of generation of urinary ketones for most people.
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Official recommendations
The growing number of studies examining the effects of carbohydrate restriction should provide data for organizations that advocate for patients with CVD and diabetes as they update recommendations for optimal diets. Until research has solved the problem of perfectly matching an individual to a diet, flexibility in choosing among many diets with measurement of intended outcomes in individual patients should be recommended.

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