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.
Can a ‘carbohydrate tolerance questionnaire’ predict outcomes from diets differing in carbohydrate content? A pilot study
Journal of Holistic Performance | ISSN: 2463-7238 | Published: 5 July 2019
Cliff J. d C. Harvey,1 Grant M. Schofield,1 Caryn Zinn,1 Simon J. Thornley1
Background. Clinical trials and experience suggest that there is a wide variation in how people respond to different dietary protocols. Clinical experience suggests that there are common signs of relative carbohydrate ‘tolerance’ that might predict cardiometabolic and anthropometric outcomes resulting from differing diets and the optimal allocation of carbohydrate restriction that might be most suited to the individual.
Objective. We believed that people with a higher carbohydrate intolerance score (CIS) determined from completing a carbohydrate tolerance questionnaire (CTQ) would achieve larger changes in cardiometabolic and anthropometric measures of health from greater magnitudes of carbohydrate restriction.
Methods. Seventy-seven healthy participants were randomised to a very low carbohydrate ketogenic diet (VLCKD), low-carbohydrate diet (LCD), or moderate-low carbohydrate diet (MCD), containing 5%, 15% and 25% total energy from carbohydrate respectively, for 12-weeks. Anthropometric and metabolic health measures were taken at baseline and 12 weeks, and symptoms of carbohydrate withdrawal and mood evaluated by questionnaires. The association between CIS and changes in anthropometric and cardiometabolic markers and mood and symptoms of carbohydrate withdrawal were made by undertaking multiple linear regression. Differences between beta coefficients describing the outcome - CIS relationship by group were determined by an interaction term, testing for significance at a p-value < 0.05.
Results. Baseline carbohydrate tolerance was associated with improvement in serum triglycerides (TG) overall, (Beta = -0.025, p = 0.073) and in the VLCKD group (Beta = -0.034, p = 0.055). The only CIS-outcome relationship to vary significantly between groups was for change in body mass index (BMI); p = 0.007, with higher carbohydrate intolerance inversely associated with the change in BMI in the MCD group (Beta = -0.309, p = 0.032). Higher CIS was also associated with more severe symptoms of carbohydrate withdrawal (Beta = 0.214, p = 0.084) and increased mood disturbance (Beta = 0.044, p = 0.060). There was also a weak association between CIS and mood disturbance in the VLCKD group (Beta = 0.083, p = 0.014).
Conclusions. Our findings demonstrate that those with higher CIS are more likely to benefit from low-carbohydrate diets for the improvement of triglyceride concentrations. Subjects with higher scores are also more likely to experience mood disturbance and symptoms of carbohydrate withdrawal. The questionnaire might be useful for clinicians to allocate those with the highest CIS to a more moderately restricted plan to mitigate symptoms of carbohydrate withdrawal and effects on mood and to offer greater improvements in BMI. However, at this time and contrary to our hypothesis, due to the lack of clear between-group significance, it is unclear whether it can accurately predict the efficacy of dietary allocations for the individual.
Journal of Holistic Performance | ISSN: 2463-7238 | Published: 4 May 2018
Cliff J. d C. Harvey,1 Grant M. Schofield,1 Micalla Williden,1
Background. Very-low-carbohydrate ketogenic diets (VLCKDs) promote benefits for a range of health conditions. However, there is little research elucidating the ‘lived experience’ of individuals undertaking these diets, and the effects of keto-induction, during adaptation to these diets.
Objective. This study aimed to evaluate the subjective experiences of people following a very low carbohydrate, ketogenic diet.
Design. This paper describes the qualitative experiences of twenty-eight non-obese, non-diabetic participants, (2 males, 26 females: age ± SD: 35 ± 4 y) in a randomised controlled trial to test the effects of medium chain triglyceride (MCT) supplementation in a VLCKD on time to nutritional ketosis (NK), symptoms of keto-induction, and mood. The experience provided by the diet was rated by a free-form daily diary entry and post-study focus group. Diary entries and focus group transcription were coded inductively and grouped into common themes.
Results. Twenty-three participants completed the 3-week study. Physical effects accounted for over 28% of references. Other results were categorised as; mood, energy and cognition (23%), satiety and hunger (16%), cravings and temptation (11%), and sleep (8%). Overall, 49% of references were classified as ‘positive’ with 8% neutral, and 43% negative. Positive impressions were higher after participants had achieved nutritional ketosis and negative impressions higher during keto-induction. Negative impressions, both concerning physical symptoms and feelings of mood and well-being, tended towards improvement over the course of the study, and positive impressions improved. However, there was a large variation in responses, and several respondents reported adverse effects throughout the study.
Conclusion. Despite challenges, especially gastrointestinal effects, the overall perception of the diet was positive, and it provided benefits for wellbeing, mood, sleep, and sugar cravings which tended towards improvement over the course of the study. Negative experiences decreased as participants adapted to the VLCKD. Most participants continued post-study, using a lower-carbohydrate diet, due to these perceived benefits. Our findings suggest that the experience of a VLCKD is positive but variable. Further research on individual tolerance and response to low carbohydrate diets is warranted.
Exploring the acceptability of, and adherence to a carbohydrate-restricted diet as self-reported by women aged 40-55 years
Journal of Holistic Performance | ISSN: 2463-7238 | Published: 23 January 2018
Julia Claire McPhee1, Caryn Zinn 1, Melody Smith2
Background. It is well recognised that ageing in females is associated with a predilection for weight gain. Women with abdominal obesity are known to be at especially high risk of cardiovascular and metabolic disease, as well as associated poorer overall health outcomes. Many of these metabolic disorders, however, can be alleviated through weight loss.
Methods. This research describes an exploratory study investigating the self-reported acceptance of, and adherence to, a carbohydrate-restricted diet in women aged 40-55 years old. The 8-week weight loss dietary intervention was based on a whole food approach, which was lower in total carbohydrate and higher in dietary fat than mainstream nutrition guidelines. The two primary outcome measures of this research were barriers to and motivators for acceptance of and adherence to this way of eating. The mixed methods approach employed endorsed a multi-level intervention, integrating behaviour change models with both the medium of delivery and required dietary modifications.
Hypothesis. The hypothesis underpinning this study is that a lower carbohydrate, higher fat (LCHF) dietary approach, through its macronutrient profile, has the potential to enhance an individual’s self-reported adherence to behavioural lifestyle modifications required to reduce weight and improve metabolic health outcomes.
Results. Support by family members, in particular, spouses, was a key theme and appeared to act as both a barrier and motivator to adherence. Subsequent themes included satiety or feelings of fullness, being prepared by ensuring suitable food options were readily available, and acceptability of new food options.
Discussion. The findings from this study suggest self-reported adherence to this way of eating was achieved via improved satiety and enhanced social and spousal support. Moreover, results showed that for this population group, the intervention design was appropriate and medium of delivery was effective.