Effects of Low-Carbohydrate and Low-Fat Diets

AbstractObjectiveTo examine objective versus self-reported energy intake changes (ΔEI) during a 12-month diet intervention.MethodsWe calculated ΔEI in subjects who participated in a 1-year randomized low-carbohydrate versus low-fat diet trial using repeated body weight measurements as inputs to an objective mathematical model (ΔEIModel) and compared these values with self-reported energy intake changes assessed by repeated 24-hr recalls (ΔEI24hrRecall).ResultsΔEI24hrRecall indicated a relatively persistent state of calorie restriction ≥500 kcal/d throughout the year with no significant differences between diets. ΔEIModel demonstrated large early decreases in calorie intake >800 kcal/d followed by an exponential return to approximately 100 kcal/d below baseline at the end of the year. The low-carbohydrate diet resulted in ΔEIModel that was 162±53 kcal/d lower than the low-fat diet over the first 3 months (p=0.002), but no significant diet differences were found at later times. Weight loss at 12 months was significantly related to ΔEIModel at all time intervals for both diets (p<0.0001).ConclusionsSelf-reported measurements of ΔEI were inaccurate. Model-based calculations of ΔEI found that instructions to follow the low-carbohydrate diet resulted in greater calorie restriction than the low-fat diet in the early phases of the intervention, but these diet differences were not sustained.What is already known about this subject?Diet assessments that rely on self-report, such as 24hr dietary recall, are known to underestimate actual energy intake as measured by doubly labeled water. However, it is possible that repeated self-reported measurements could accurately detect changes in energy intake over time if the absolute bias of self-reported of measurements is approximately constant for each subject.What this study addsWe compared energy intake changes measured using repeated 24hr dietary recall measurements collected over the course of the 1-year Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) trial versus energy intake changes calculated using repeated body weight measurements as inputs to a validated mathematical model.Whereas self-reported measurements indicated a relatively persistent state of calorie restriction, objective model-based measurements demonstrated a large early calorie restriction followed by an exponential rise in energy intake towards the pre-intervention baseline.Model-based calculations, but not self-reported measurements, found that low-carbohydrate diets led to significantly greater early decreases in energy intake compared to low-fat diets, but long-term energy intake changes were not significantly different.

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The mass balance model of obesity explains the weight loss advantage of a low-carbohydrate diet over a isocaloric low-fat diet

10.1101/2020.10.27.20220202 ◽

2020 ◽

Author(s):

Francisco Arencibia-Albite ◽

Anssi H. Manninen

Keyword(s):

Weight Loss ◽

Energy Balance ◽

Mass Balance ◽

Balance Model ◽

Mass Balance Model ◽

Low Fat ◽

Macronutrient Composition ◽

Low Carbohydrate ◽

Fat Diets ◽

Weight Stability

Currently, obesity treatment rests on the "calories-in, calories-out" (CICO) rule, formally named the energy balance theory (EBT). It maintains that body weight (BW) increases as food calories are greater than expended calories but decreases when the opposite occurs; hence, weight stability is expected at energy balance meaning that over time energy-in equals energy-out. It follows that dietary regimens with identical energy content should evoke similar amounts of weight and fat loss with only minor differences that follow from diet's macronutrient composition, e.g., diet-induced glycogen depletion and water excretion. A vast collection of evidence shows, however, that low-carbohydrate diets typically result in much greater weight and fat loss than isocaloric low-fat diets. Furthermore, our recent mathematical analysis demonstrated that weight stability coincides with a persistent energy imbalance and not otherwise. As an alternative, the mass balance model (MBM) was proposed that fitted weight loss data and explained the often superior weight loss evoked by low-carbohydrate diets versus low-fat diets. Here, we expand on these observations by computationally contrasting the predictions of both models in two scenarios described in the literature: altering the diet's macronutrient composition while energy intake is kept at weight maintenance level; and the weight loss response as diet composition is changed under untreated type 1 diabetes. Our results indicate that MBM predictions are remarkably accurate while those of the EBT are clearly erroneous. These findings may represent the beginning of a paradigm shift in obesity research.

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