Can baseline cardiometabolic markers predict the efficacy of carbohydrate restriction in healthy adults? A pilot study
Journal of Holistic Performance | ISSN: 2463-7238 | Published: 8 October 2019
Cliff J. d C. Harvey,1 Grant M. Schofield,1 Caryn Zinn,1 Simon J. Thornley1
Background. Low-carbohydrate diets are frequently used and are effective for improving a range of health outcomes. There is some evidence to suggest that certain individuals will achieve greater results from higher- or lower-carbohydrate diets but at this time there is little evidence to indicate the relative ‘appropriateness’ of diets differing in carbohydrate content for an individual. This study explores associations between baseline and changes in blood measures of cardiometabolic health, relative to carbohydrate allocation.
Methods. Seventy-seven healthy, non-diabetic participants (25 males, 52 females [mean age: 39 years, range: 25 to 49; mean body mass index (BMI) 27 kg/m2, range: 20-39]) participated in a 12-week, randomised, clinical intervention study. Participants completed baseline testing of blood measures and basic anthropometric measures and a lead-in week to identify habitual calorie intake. Participants were assigned to one of three low-carbohydrate diet plans which advised intakes of either 5%, 15%, or 25% of energy derived from carbohydrate, individualised to the participant and standardised for protein, at 1.4 g per kg of body weight (bw) per day. For the final nine weeks of the intervention they were advised to eat ad libitum but to adhere as closely as possible to the carbohydrate energy limit for their treatment group. Participants were instructed to continue habitual exercise patterns. Blood measures of cardiometabolic health (glucose, insulin, c-peptide, total cholesterol, high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, triglycerides (TG)) and anthropometric measures (height, weight, and waist and hip girth) were measured at baseline and at the conclusion of the 12-week dietary intervention. The associations between baseline blood and anthropometric measures and the changes in these measures were made by undertaking multiple linear regression for the baseline measure and treatment group as independent variables with the change in outcome measures as dependent variables.
Results. There was a greater improvement in participants who had more adverse baseline cardiometabolic measures from a greater carbohydrate restriction, with 7 of 11 measures most benefiting from a very low carbohydrate ketogenic diet (VLCKD) intervention relative to baseline measurements. Only HDL cholesterol reached between-group significance, with every 1 mmol/L higher HDL cholesterol at baseline associated with a 0.5 and 0.2 mmol/L improvement in HDL cholesterol for the moderate-low carbohydrate diet and low-carbohydrate diet groups respectively, and a 0.4 mmol/L worsening for VLCKD (p = 0.0006).
Conclusions. Overall, there is a consistent association between baseline markers of cardiometabolic health and changes in these markers relative to the amount of carbohydrate included in the diet. However, low HDL cholesterol might be improved most by a moderate restriction of carbohydrate to ~25% of TE when compared to greater carbohydrate restriction. Because most results were not significant due to the small sample size and preliminary nature of this study, further research is required with larger cohorts to investigate this hypothesis further.