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NASHVILLE, Tenn. – New research suggests lowering carbohydrate intake in the diet. However, according to some experts, the methodology of the trial does not allow drawing conclusions.
The results of a randomized trial comparing the metabolic effects of diets with a variable carbohydrate / lipid ratio were presented on November 14th at the 2018 Obesity Week by David S. Ludwig, MD, and Cara B. Ebbeling, both of the New Balance Foundation. Center for Obesity Prevention, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts. The results were published simultaneously in BMJ.
The study found that reducing dietary carbohydrates increased energy expenditure while maintaining weight loss, especially in patients with high insulin secretion. However, the use of double-labeled water by researchers to measure energy expenditure has been questioned at the Obesity Week Symposium by Kevin Hall, Ph.D., principal investigator at the National Institute of Obesity. diabetes, digestive and renal diseases, Bethesda, Maryland.
Symposium Chair and President of the Society of Obesity, Caroline M. Apovian, said Medscape Medical Newsis: "We need to do more studies to show that this is the case, there is controversy … It could mean that we have not yet found a way to know what each person needs to eat to be healthier. "
The study tested the carbohydrate-insulin obesity model, which indicates that increasing the ratio of insulin concentrations to glucagon after eating a carbohydrate-rich meal moves away Metabolic fuels of oxidation and stores them in adipose tissue. This process is thought to increase hunger and cravings, reduce energy expenditure and predispose to weight gain, especially in people with high insulin secretion, explained Ludwig.
Previous studies had not found any difference in energy expenditure between low carb and fat diets, and consisted mainly of short-term diets – less than two weeks, he said. However, the process of adapting to one or the other diet takes longer than that, he noted.
The current study tested the effects of different diets in the carbohydrate / fat ratio on energy expenditure when maintaining weight loss for 20 weeks in 164 adults with a body mass index of 25 kg / m2 or more having lost at least 10% of their body weight during a 10-week break-in period with a diet containing 45% of total energy from carbohydrates, 30% of fat and 25% proteins.
Participants were assigned to one of three weight-based diets based on the ratio of carbohydrate / fat, all containing 20% protein: rich (60% carbohydrate, 20% fat), moderate (40% carbohydrate, 40% fat) or low (20% carbohydrate, 60% fat) for 20 weeks.
Total energy expenditure – measured with doubly labeled water – was differentiated by diet in the intent-to-treat analysis (P = 0.002), with a linear trend of 52 kcal / day for each 10% decrease in carbohydrate contribution to total energy intake.
The change in total energy expenditure was 91 kcal / day higher for participants in the moderate carbohydrate diet and 209 kcal / day higher for participants in the low carbohydrate diet compared to the high carbohydrate diet.
In the per protocol analysis, which included 120 participants, the respective differences were 131 kcal / day and 278 kcal / day.
Among participants with the highest third of insulin secretion before weight loss, the difference between high and low calorie diets was 308 kcal / day in intention-to-treat analysis and 478 kcal / day in per protocol analysis (P <0.004).
Ghrelin and leptin were both lower among those assigned to a low carbohydrate diet (vs.P <0.007 for intention-to-treat and per protocol analyzes for ghrelin and P = .06 and P = 0.005, respectively for leptin).
The methodology in question
With doubly labeled water, hydrogen and oxygen have been partially or completely replaced (labeled) with an unusual isotope for tracing purposes. Hall stated that, although it is considered the standard method for measuring energy expenditure, this method has flaws for several reasons, including the fact that it has not been validated in the framework of low carb diets.
Hall also said that doubly labeled water "requires a careful estimate of the respiratory quotient that depends on the composition of the diet, the energy imbalance and their interaction".
In addition, he noted that the method distorts the results in favor of the hypercohydrate diet of about 30 to 60 kcal / day by "the loss of deuterium isotope via de novo lipogenesis".
Finally, Hall stated that "dual differences in water expenditure must be corroborated by appropriate measures of energy intake and changes in body composition".
Ludwig refuted on several technical points and concluded "the post-hoc analyzes are highly speculative and very weak data to attack a reference method that has been used in various dietary conditions for at least three decades".
Apovian, professor of medicine and pediatrics at Boston University and director of the Boston Medical Center's Center for Nutrition and Weight Management, said Medscape Medical News"We have a study that shows that low carb diets allow you to increase your energy expenditure compared to your low fat diet.There are some limitations … The answer may lie in genetics."
When asked what doctors should tell patients who learn about the best diet, she said, "Whatever diet you think you can join, it is the best diet. Is all we know. "
BMJ. Posted on November 14, 2018. Abstract
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