Continuing doubts about which diet is better, low-carbohydrate diets or low-fat diets, remain valid today. Low-carb diets, and especially very low-carb diets (such as ketogenic diets), have gained popularity for their effectiveness in losing weight and especially fat. However, it is not yet clear which option is best in the long term, since continuing to consume very low amounts of carbohydrates on an ongoing basis can be a problem.
With this in mind, a group of researchers from Iran have conducted a review of more than 100 studies, confirming the effectiveness of reducing carbohydrates for weight loss, but with certain important nuances. Their findings were recently published in the journal Frontiers In Nutrition.
Obesity is already considered a non-infectious pandemic worldwide and is usually associated with other chronic diseases, and an increase in mortality in the medium and long term. It is known that varying the nutritional composition of the diet, beyond just reducing caloric consumption, can be essential to achieve consistent and sustained weight loss.
Low-carbohydrate diets have become a popular approach, supported by scientific evidence: a reduction in body weight is achieved through a reduction in appetite and improved insulin sensitivity.
And there would be up to three forms of low carbohydrate diet: very low carbohydrate or ketogenic diet (less than 10% of calories in the form of carbohydrates, or 20-50 g maximum per day), low carbohydrate diets (10-26% of total calories or 50-130 g per day) and moderate carbohydrate diets (26-45% or 130-230 g per day). The question is, which is the best option?
In order to obtain an answer, the researchers responsible for the study carried out a systematic review using studies from PubMed, Scopus, Web of Science and CENTRAL, until May 2021. Randomized controlled clinical trials that examined the effect of a low diet were taken into account. in carbohydrates (below 45% of energy intake) compared to a control diet (carbohydrate intake above 45%) on body weight in overweight or obese adults. In total, 110 clinical trials that met the selection criteria were selected.
A random effects dose-response meta-analysis was performed to calculate the mean difference for each 10% decrease in carbohydrate intake after 6 months, after 12 months, and after more than 12 months.
According to the results of the study, for every 10% decrease in carbohydrate intake, a reduction in body weight of 0.64 kg was achieved at 6 months of follow-up, and of 1.15 kg at 12 months of follow-up. However, when 12 months were exceeded, a carbohydrate intake of more than 40% or less than 30% was not effective for weight loss, leading to maintenance or stagnation.
As the researchers comment, a reduction in carbohydrate intake would be effective in achieving significant weight loss in the short and medium term (6-12 months); especially if said reduction of carbohydrates in the diet is accompanied by an exercise program and an associated general calorie restriction. However, after 12 months, reducing carbohydrates excessively would even be counterproductive: the range of 30-40% carbohydrates in the diet would maintain weight loss, but consuming less or more than that range would be counterproductive. .
Until now, dietary strategies to lose weight have focused on general caloric restriction, without taking into account the percentage of macronutrients, and indifferently reducing carbohydrates or fats. Previous studies have already shown that reducing carbohydrates, in the short term, would be a better option; but in the long term both types of restriction (either carbohydrates or fats) would have a similar effect.
In fact, the reduced effect of low-carbohydrate diets in the long term is usually associated with lower adherence; The researchers also highlight that these types of dietary approaches lead to a reduced desire for sweet flavors, reduced pleasure in food, and increased dietary restriction; All of these factors together make it difficult to maintain the diet long term. However, in the short term, precisely the lowest carbohydrate diets or ketogenic diets would be the ones that would lead to the best results.
As limitations of the study, the authors comment on the high heterogeneity of the data, the lack of information regarding the dietary intervention and its effects on the degree of obesity, the effects of calorie restriction and the lack of information on the dietary sources of the macronutrients (carbohydrates in general were taken into account, without differentiating between them). Furthermore, diet quality, or dietary sources of protein, fat or micronutrients were also not taken into account in most studies.
