¿Las dietas bajas en carbohidratos «aceleran el metabolismo»? Nuevo metanálisis sobre gasto energético
As we have frequently seen on this blog and as I have explained in several of my books, studies show that low carbohydrate diets are effective for losing weight in the short to medium term. The mechanisms that cause this effect are still not clear and researchers continue to test the relevance of various hypotheses, such as increased satiety (study), reducing processed foods (study) or metabolic changes caused by reduced insulin levels (explanation), among other.
In the image that incorporates the work you can clearly see the results:
As can be seen, in most of the studies of less than 2.5 weeks – those at the top – energy expenditure was higher in high carbohydrate diets, which in principle is not positive for weight loss. Approximately 50 kcal daily above low carbohydrate diets.
However, in the six trials below, in which the duration of the intervention was greater than 17 days, the situation was reversed and the low diets showed greater energy expenditure, about 135 kcal more per day.
This is how the authors tell it:
«In trials of less than 2.5 weeks, low-carbohydrate diets slightly reduced energy expenditure (…). In contrast, in trials of more than 2.5 weeks, the low-carbohydrate diet substantially increased energy expenditure (by approximately 50 kcal/day for every 10% decrease in energy intake from carbohydrates) with minimal residual heterogeneity. These results suggest that shorter versus longer studies have examined different physiological states. The former consist of trials in which participants experience varying degrees of metabolic adaptation to carbohydrate reduction; the latter consist of trials of sufficient duration to allow adequate adaptation and result in a consistent result.
This result supports the carbohydrate-insulin model and suggests the existence of a mechanism by which dietary carbohydrate reduction could aid in the prevention and treatment of obesity. According to this model, the high insulin/glucagon ratio of a high glycemic load diet (…) shifts the utilization of metabolic fuels from oxidation in lean tissue to storage in adipose tissue.
If the observed effects persist long term, reducing dietary carbohydrate intake to half of 60% of energy intake (a typical level for low-fat diets) would increase energy expenditure by ~150 kcal daily, which would offset (if not offset by other factors) much of the increase in energy intake that some think is the basis of the obesity epidemic.»
Some quite interesting results, although personally I think more research is needed as to whether there really are metabolic changes after those two or three weeks, the period that proponents of this type of diet say is necessary to get the body to «adapt.» . The truth is that there is no objective and rigorous definition that defines said «adaptation», based on some type of indicator or measurement, or on the metabolic and physiological conditions that occur at that moment.
In any case, this review represents a new «push» for low-carbohydrate diets, which seem to be slowly establishing themselves as an interesting option for some circumstances and people.
Update:
