The study protocol was approved by the National Nutrition and Food Technology Research Institute (NNFTRI), Shahid Beheshti University of Medical Sciences (SBMU), Tehran, Iran (IR.SBMU.NNFTRI.REC.1396.187). All participants provided written informed consent prior to participating in the study.
This trial was a randomized controlled open-label clinical trial open to breast cancer patients with locally advanced or metastatic disease who were receiving chemotherapy for at least 12 weeks. The study was conducted at the medical oncology clinic at Shohada-e-Tajrish hospital, Cancer Research Center, Tehran, Iran, from July 2017 to October of 2018. Participation was open to patients 18 to 70 years of age. Exclusion criteria screened for significant cardiac, renal or neurologic comorbidities; symptoms of malnutrition, diabetes, pregnancy, and Karnofsky index less than 70. Using a block balanced randomization method, patients were assigned to the intervention (n = 40) or control (n = 40) groups. Randomization was computer-generated by a statistician who was not a member of the medical team. Blinding the participants or study personnel was not deemed feasible in this diet intervention. The project coordinator enrolled the participants and assigned them to their interventions. Both the KD and the control diet were calculated to be eucaloric using the Mifflin-St. Jeor formula. The KD consisted of 6% of calories from CHO, 19% from protein, 20% from medium-chain triglyceride (MCT) oil, and 55% from fat. A dietitian provided specific nutritional counseling to each participant in individual face-to-face meetings. Patients engaged in ongoing weekly counseling sessions via phone, WhatsApp, or Telegram and were assessed for compliance and possible adverse effects. To further enhance compliance, dietary recommendations were individualized and appropriate recipes were provided to patients in the KD group were asked to refrain from eating any grains, grain products, starchy vegetables, fruit or sugar. Dietary carbohydrates were limited to non-starchy vegetables, and dietary proteins were obtained primarily from egg, meat, poultry and fish. Small amounts of lower carbohydrate berries and nuts were allowed as long as they did not exceed the carbohydrate limit in the diet prescription. Subjects were encouraged to increase their fat intake and to select from a variety of sources, including olive oil, butter and cream cheese. Patients were asked to choose only the foods specified in the diet plan provided to them. Patients were also encouraged to use medium-chain triglyceride (MCT) oil. MCT oil, an odorless and tasteless saturated fat, does not require bile or pancreatic enzymes for digestion. It is easily converted to ketones in the liver thereby enhancing ketosis. Every 2 weeks, 500 ml of MCT oil from Nutricia (Erlangen, Germany) was provided to each subject in the KD group. For better tolerance, initial dosage of MCT was kept low and increased daily over a 6-day period until maximum tolerable dosage was achieved. Dosage was reduced in a similar stepped process.
The patients in the control group were instructed to follow a standard diet consisting of 55% CHO, 15% protein, and 30% fat. Dietary compliance was checked by assessing blood beta-hydroxybutyrate levels every 3 weeks and dietary intake at baseline and end of the study.
QoL was assessed using the EORTC QLQ-C30 (version 2) and IORTC QLQ-BR23 questionnaires developed by the European Organization for Research and Treatment of Cancer. The validity and reliability of the questionnaires has previously been evaluated in Iran [19, 20]. The questionnaires were completed at enrollment, at 6-weeks, and at the end of the intervention.
Dietary intake assessment
Hospital dietitians used a 24-h dietary recall (24HR) to obtain a total of 3 days intake (one weekend day and two workdays) through telephone and face-to-face interviews both at the beginning and end of the study. The amount of each food consumed was estimated using common household containers (bowls, cups, and glasses) and standard measuring cups and spoons as references. The mean quantity of total energy, carbohydrate, protein and fat were estimated from the 24HRDietary intake was analyzed by Nutritionist IV software (Version 3.5.2 US).
Physical activity assessment
Physical activity was measured using the IPAC (International Physical Activity) questionnaire at baseline, at 6 weeks, and at the end of the study.
Fasting blood sampling for serum Na+, K+, Ca++, P+, lactate, Mg++, LDH, albumin, ammonia, and ALP were performed at baseline, midway through the intervention (6 weeks), and at 12 weeks. T3, T4, and TSH were measured at baseline and the end of the intervention.
Considering the 80% power and α = 0.05, the sample size was calculated as 30 individuals per group. Assuming a 20% dropout during the 12 weeks of the study, the final number of participants was calculated as 40 patients in each group.
Statistical analysis was carried out according to the intention-to-treat protocol. Continuous variables were tested for normal distribution by the Kolmogorov-Smirnov test and then reported as mean ± standard deviation or median as appropriate. Student t-test or Mann–Whitney U test was used to compare the continuous variables between the two groups. Paired sample t-test or Wilcoxon was used to compare the continuous variables within the two groups. The ANCOVA test was used to eliminate the effect of confounding factors.
Pearson correlation analyses were used to estimate associations between total carbohydrate intake and serum beta-hydroxybutyrate.
Data were analyzed using the SPSS version 18.0 software (Chicago, IL, USA) and Stata version 13. P < 0.05 was considered as statistically significant.