The effects of self-directed low carbohydrate diets on metabolic biomarker profiles and disease risk among New Zealand adults - the LOCA study : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics, Massey University, Albany, New Zealand

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Background: Low carbohydrate (LCHO) diets are dietary trends often adopted for fast weight loss. Concerns regarding their safety and effects on cardiovascular disease (CVD), kidney disease and diabetes risk have been raised. Aim: To investigate the associations between dietary intake and metabolic and inflammation biomarkers of self-reported LCHO diet consumers (men and women aged 20 to 45 years) in Auckland, New Zealand. Methods: This cross-sectional study recruited men and women aged 20 to 45 years following an LCHO diet for a minimum of 4-months. Four-day weighed food record, anthropometric measurements, and fasting venous blood samples were collected from participants. Participants were divided into three groups: very low carbohydrate (VLCHO) (<50g), LCHO (50-100g) and moderately low carbohydrate (MLCHO) (>100 - <150g) carbohydrate groups. Dietary intake, metabolic biomarkers and anthropometric measurements were examined in those three intake groups. Results: A total of 74 men and women participated in the LOCA study with a mean age of 35 years. The median intake of carbohydrates in this group was 14 [11.4, 26.7]% of total energy (%TE), while fat intake was 58.1% [49.1-66.0] and protein intake was 24.4% [22.9, 25.9]. Based on their carbohydrate intakes, participants in the VLCHO, LCHO and MLCHO groups, experienced elevated total cholesterol (94.7%, 89.5% and 88.9%, respectively), LDLC (94.6%, 100% and 88.9%, respectively) and HDLC (92.1%, 94.7% and 100%, respectively) concentrations. The majority of the participants experienced low estimated glomerular filtration rates (VLCHO: 89.5%, LCHO: 89.5%, and MLCHO: 88.9%). Carbohydrate intakes (grams and %TE) negatively correlated with total cholesterol (TC) (r= -0.353, P= 0.003 and r= -0.403, P= 0.001), and low-density lipoprotein cholesterol (LDLC) (r= -0.329, P= 0.007 and r= -0.335, P= 0.006). Total cholesterol concentrations were significantly associated with carbohydrate, total fat and saturated fat (SFA) intakes as %TE. Only total fat intake (%TE) significantly associated with LDLC concentrations. Conclusions: Our findings suggest LCHO diets followers predominantly replaced carbohydrate with protein and fat. High fat and SFA intakes (%TE) due to carbohydrate restrictions were accompanied by high TC, LDLC and HDLC concentrations. It is crucial to weigh the benefits and harms of LCHO diets on CVD risk.