Low-Calorie Mediterranean Diet vs. Low Carb Diet for Weight Loss

Study examines the effect of Mediterranean or low carb diet on weight, waist circumference and blood glucose in patients with obesity. 

Mediterranean diets contain low-calorie and balanced macronutrient composition. The Traditional Mediterranean diet has consisted of mainly vegetables, legumes, fruits, grains, nuts, and olive oil, with moderate consumption of fish and red wine, and low amounts of whole-fat dairy products, red meat, and processed foods. Current guidelines recommend this diet for weight loss and cardiometabolic benefits (Fernandez et al., 4). A prospective study published in 2008 found that high adherence to the Mediterranean diet was associated with an 83% relative reduction in developing diabetes (incidence rate ratio 0.17, 95% CI [ 0.04 – 0.75]) (Martinez – Gonzalez et al., 4) 

Another diet that is commonly applied for weight loss is the low-carbohydrate diet which contains high protein; a low carb diet is considered an alternative to Mediterranean diets because it reduces body weight faster and prevents weight regain. That is because a low carb diet induces satiety, suppresses hunger, reduces liver fat, increases thermogenesis, and maintains lean body mass (Foster et al., 2086). Both the low-carb diet and the Mediterranean diet have their pros and cons. Many times, patients have hard times deciding whether the low-carbohydrate diet is appropriate for their situations. To help patients better understand these diets, Dr. Tricò and colleagues conducted a study to compare the effectiveness of the Mediterranean diet and low-carbohydrate diet on weight loss and glucose homeostasis in patients with obesity and high risk of diabetes. 

This study is a parallel-arm, open, randomized clinical trial. The study recruited 36 patients between 25 – 60 years old who had obesity and were on the waiting list for bariatric surgery at the outpatients’ clinic of the University Hospital of Pisa in 2018–2019. Inclusion criteria were a BMI > 35 kg/m2, weight stable (+1%) for at least six months before the study. In addition, exclusion criteria were diabetes, CKD, heart failure, liver failure or NASH, chronic diarrhea (including IBD), endocrine diseases, current use of medications that affect body weight and glucose metabolism.  

After getting history and physical exams, participants were randomized to consume two types of diet, low carb diet and Mediterranean diet, for four weeks. The low-carb diet consisted of beef, veal, cold cuts (carpaccio, cured ham), eggs, seasoned cheese, vegetables, and fruits. Macronutrients included 30% carbohydrate, 30% protein, and 40% fat. The Mediterranean diet was mainly whole grains (pasta, bread, whole wheat), eggs, poultry, fish, vegetables, legumes, fruits, olive oil (main condiment), and low red and processed meat. Energy distribution was 55% carbohydrate, 15% protein, and 30% fat. 

The research team provided two sessions of behavioral, dietary counseling for patients. The first session was at randomization, which counseled nutrition education, common dietary errors, and recommendations for each type of diet. The second was after two weeks, whose purposes were to verify dietary adherence and to reinforce nutritional suggestions. At baseline and after four weeks of diet, participants fasted overnight then were admitted to the Clinical Research Unit the next day to provide a venous blood sample for insulin and C-peptide assessment. The research team utilized modeling plasma glucose, insulin, and C-peptide profiles during 75-g oral glucose tolerance tests (OGTT) at baseline and the end of dietary intervention. These tests were to estimate insulin secretion, insulin clearance, and the different components of β-cell function. 

Conventional bioimpedance analysis (BIA) helped determine body composition calculated from anthropometric data. Waist circumference and hip circumference were recorded. Indirect calorimetry measured Resting Energy Expenditure (REE). The homeostasis model assessment (HOMA) index and oral glucose insulin sensitivity (OGIS) index helped estimate insulin sensitivity. Van Cauter’s model of C-peptide kinetics estimated C-peptide deconvolution and Insulin Secretion Rate (ISR).  

Variables are reported as counts or percentages. Median [interquartile range] represented the skewed distribution of the variables. Mann-Whitney test or Fisher’s exact test estimated the baseline differences between groups. Multivariate analysis of variance (MANOVA) analyzed repeated measures. Counts and percentages reported the + standard deviations (SD) and nominal variables. A p-value represented the differences between diets.  

There were 32 participants; 88.9% completed the study and were included in the final analysis. Seventeen patients had a low-carb diet, and 15 patients had a Mediterranean diet. The result showed that a low-carb diet had a weight reduction 58% greater than the Mediterranean diet did. This difference is statistically significant (p-value = 0.001). Waist circumference, fat mass, and basal metabolic rate also decreased significantly in patients consuming low-carb diets. Fasting plasma glucose and glucose tolerance did not change after the dietary interventions. C-peptide deconvolution increased insulin secretion similarly at both baselines and after glucose-stimulated. 

The study had a few limitations. First, the study conclusion is not generalized for patients who have T2DM or low-grade obesity. Second, the research team only relied on self-reported dietary compliance to determine adherence to the nutritional interventions. Third, the sample size of the low-carb diet arm was smaller than the other arm. This difference may interfere with the differences in glucometabolic parameters and mislead the weight loss difference. Finally, the study only reviewed the difference after four weeks of interventions. There should be more longitudinal studies with a larger scale in the future to provide a better overview of the efficacy that these diets can provide. 

Practical Pearls: 

• Low carbohydrate / high protein can induce weight loss in a shorter time than the Mediterranean diet. 
• A low carbohydrate diet can also reduce waist circumference, fat mass, and basal metabolic rate.  
• Neither of low carbohydrate diet or the Mediterranean diet changes the fasting plasma glucose and glucose tolerance 

Fernandez, Maria Luz et al. “Highlights of Current Dietary Guidelines in Five Continents.” International journal of environmental research and public health. Mar. 20, 2021, Jun 9, 2021.  

Foster Gary et al. “A Randomized Trial of a Low-Carbohydrate Diet for Obesity”  The New England Journals of Medicine, May 22, 2003. Jun 9, 2021. 

Tricò, Domenico et al. “Effects of Low-Carbohydrate versus Mediterranean Diets on Weight Loss, Glucose Metabolism, Insulin Kinetics and β-Cell Function in Morbidly Obese Individuals.” Nutrients April 18, 2021. Jun 9, 2021. 

Martínez-González, M Á et al. “Adherence to Mediterranean diet and risk of developing diabetes: prospective cohort study” BMJ, Apr 5, 2008. Jun 9, 2021. 

Thi Vietthi Huynh, 2022 PharmD Candidate, Lake Erie College of Osteopathic Medicine – School of Pharmacy.