Low‐carbohydrate ketogenic diets in body weight control: A recurrent plaguing issue of fad diets?

The most appropriate type of diets to maintain or lose body weight over the medium to long term has been a matter of controversy and debates for more than half a century. Both voluntarily and coercive food restriction, resulting in negative energy and macronutrient balance and hence weight loss, have not been designed to be maintained for the long term. By contrast, when a classical and traditional type of alimentation is consumed in ad lib conditions (e.g., the Mediterranean “diet”), it generally provides an appropriate nutritional density of essential macronutrients and micronutrients; it is hence appropriate for long‐term use, and it provides several benefits for health if the compliance of the individuals is maintained over time. In this short review, we focus on four specific aspects: first, the need to agree on a clear definition of what is “low” versus “high” in terms of total carbohydrate intake and total fat intakes, both generally inversely related, in a representative individual with a certain lifestyle and a certain body morphology; second, the importance of discussing the duration over which it could be prescribed, that is, acute versus chronic conditions, focusing on the comparison between the fashion and often ephemeral low‐carbohydrate diet (acute) with the well‐recognized traditional Mediterranean type of alimentation (chronic), which includes lifestyle changes; third, the particular metabolic characteristics induced by the low‐carbohydrate (high fat) diet, namely, the scramble up of ketone bodies production. The recent debate on ketogenic diets concern whether or not, in iso‐energetic conditions, low‐carbohydrate diets would significantly enhance energy expenditure. This is an issue that is more “academic” than practical, on the ground that the putative difference of 100–150 kcal/day or so (in the recent studies) is not negligible but within the inherent error of the methodology used to track total energy expenditure in free living conditions by the doubly labeled water technique. Fourth, the potential medical risks and shortcomings of ingesting (over the long term) low‐carbohydrate ketogenic diets could exacerbate underlying renal dysfunction, consecutive to the joint combination of high‐fat, high‐protein diets, particularly in individuals with obesity. This particular diet promotes metabolic acidosis and renal hyperfiltration, which ultimately may contribute to a significant reduction in life expectancy in middle‐age people.