Abstract
Objectives
As the never-ending macronutrient debate for weight loss continues, conflicting evidence persist. Per the carbohydrate-insulin hypothesis, a low-carbohydrate diet (LC) should produce a greater weight/fat loss compared to a low-fat/calorie diet (LF) by releasing less of the anabolic hormone insulin. However, from a ‘calories in, calories out’ perspective, does restricting calories on a LC diet produce a greater weight/fat loss compared to a LF diet?
Methods
A systematic review and meta-analysis of LC vs LF trials for weight loss was conducted and data were collected from 53 studies. Weight loss data were converted to kcals (1 kg = 3500 kcals) and a ratio was produced for each individual diet (ID-Ratio: weight loss in kcals/restricted dietary kcals) where a ratio of 1 indicates that one dietary kcal restriction equals one kcal of weight loss. Next, to compare the two diets, a comparison ratio (DC-Ratio: LC ID-Ration/LF ID-Ratio) was produced where a ratio greater than 1 indicates greater weight loss per dietary calorie restricted with LC diet. These calculations were repeated for body fat loss for full duration (n = 30 trials) and time of greatest weight loss (TGWL; Weight Loss: n = 19 trials; Fat Mass Loss: n = 4 trials).
Results
LC diets produced a greater weight loss (Full Duration: 6.10 kg vs 4.86 kg; n = 53 trials; P = 0.024; TGWL: 6.29 kg vs 4.34 kg; n = 19 trials; P = 0.024), however no difference was found for the amount of restricted calories or fat mass loss for either duration. No difference was found for the LC and LF ID-Ratios for weight or fat mass loss for either duration. The mean weight loss DC-Ratio was greater than 1 (Full Duration Mean: 1.61, SD: 1.71, n = 53 studies, P = 0.004; TGWL Mean: 1.74, SD: 1.0, n = 19 trails, P = 0.010) indicating a greater weight loss per calorie restricted with a LC diet. However, the fat loss DC-Ratio was not different from 1 (Full Duration Mean: 1.74, SD: 1.09, n = 30 trials, P = 0.552; TGWL Mean: 1.25, SD: 0.53, n = 4 trials, P = 0.428).
Conclusions
From a ‘calories in, calories out’ perspective, restricting calories on a LC diet produced a greater weight loss for the full duration of the trails and at the time of greatest weight loss compared to a LF diet. As no effect was seen on LC diets and fat mass loss, these results do not support the carbohydrate-insulin hypothesis of obesity.
Funding Sources
School of Life Sciences, Arizona State University.
Increased Consumption of Dairy Foods and Protein during Diet- and Exercise-Induced Weight Loss Promotes Fat Mass Loss and Lean Mass Gain in Overweight and Obese Premenopausal Women
