CARBOHYDRATES, LIPIDS AND BIOMARKERS OF TRADITIONAL AND EMERGING CARDIOMETABOLIC RISK FACTORS

Aim of this PhD thesis was to investigate whether carbohydrates (CHO) or fats, and in particular saturated fats (SFA) have differential effects on cardiometabolic (CM) risk by examining potential links between these macronutrients and surrogate markers of CM risk. This broad aim was approached by two studies. The first study undertook a secondary analysis of the National Diet and Nutrition Survey Rolling Programme 2008-2014 dataset, a cross-sectional survey. The second study built on the findings from Study 1 and was a randomised parallel pilot feasibility study. Data were collected at three time points over the course of eight weeks, at baseline, at interim point and at endpoint. In the secondary analysis of study 1 (chapter 2), undertaken using the complex samples module in SPSS 25, data (n=2217) was stratified by gender, age group and BMI group. Data was initially analysed for differences in dietary intake of carbohydrates and fats between those that did or did not present with metabolic syndrome (MetS) using General Linear Models. There were very few significant differences between groups. When those with and without MetS were divided into quartiles of intake of carbohydrates (total CHO, starch and sugar) and fat (total, SFA), in most strata (analysed via Logistic Regression) there were increased odds of presenting with MetS in those consuming the highest amount of CHO or the lowest amount of SFA (all p<.05). The second study (chapter 3) was designed to focus more on these apparent links by randomising participants (n=10; 80% male) to either a diet with the aim to increase their CHO intake to ≥50% total energy (the Eatwell Guide (EWG)), or to drastically reduced their CHO intake to ≤50g/d by following a low-carbohydrate, high-fat diet (LCHF). Participants were supplied with guidelines for their allocated diet and given two-week sample meal plans and recipes tailored to their personal preferences were feasible within the remit of their diet. In addition to examining risk markers that are commonly included in such interventions, the trial also investigated the impact on adiposity proxies, food cravings, moderate-to-vigorous physical activity and a number of biomarkers that have emerged as potential CM risk markers in recent years. This included the hepatokine fibrogen growth factor 21 (FGF21). Furthermore, the second study scrutinised the food-groups, carbohydrates and subtypes of SFA that contributed to participants’ intake. The findings showed that for some markers, such as sdLDL-C the impact was unambiguous; all participants in the LCHF group presented with significantly decreased sdLDL-C concentrations (up to -34%) and 80% of participants in the EWG group with increased concentrations (up to +15%) (p=.008 for diet*time). Overall, insulin concentrations decreased by 45% in the LCHF and 12% in the EWG group 3 and all LCHF participants presented with reduced insulin concentrations by up to 59% at endpoint but only some EWG did so (by up to 35%) (p=.002 for diet*time). For FGF21 only the effect of time was significant (p=.044) and overall concentrations declined in the LCHF and increased in the EWG group. In some LCHF participants concentrations of significant CM risk markers were at their lowest with maximum SFA intake with the majority of SFA derived from meat & meat products and dairy. Overall, the two studies showed that there is scope for further research to investigate the differential effects of different food groups that are either rich in CHO or fats/SFA under consideration of the food matrix. Furthermore, the mechanisms and causes behind the interindividual responses warrant further investigation to give more tailored and personalised nutrition advice for primary and secondary prevention of CM diseases in the future