New pathways to obesity prevention and metabolic health : the relationship between diet and the gut microbiome : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Science at Massey University, Tāmaki Makaurau, Aotearoa New Zealand

Background Diet is one of the key drivers of the global obesity epidemic. Based on the results of rodent experiments, the gut microbiota may play an important role in this multifaceted disease. Additionally, the microbiota is known to be influenced by the habitual diets consumed by humans. Aims and objectives The aim of this PhD research was to characterise the habitual dietary intake of two New Zealand populations (Pacific and New Zealand European (NZE) women) with different metabolic disease risk and body fat profiles (lean and obese). The first objective of the research was to explore the relationship between habitual macronutrient intake in relation to body fat content and metabolic health markers. The second objective was to characterise a posteriori dietary patterns (derived from multiple days of dietary assessment) and to explore the association with body fat content and metabolic health markers. The third objective was to explore the characteristics of microbiota composition in relation to habitual diet (dietary patterns, foods, and nutrients), body fat content and metabolic health markers. Methods Between July 2016 and September 2017, Pacific (n=126) and NZE (n=161) women, aged 18-45 years, living in Auckland, New Zealand, were recruited to a cross-sectional study, based on their body mass index (lean and obese) and stratified as having low (<35 % body fat) or high (≥35 % body fat) body fat percentage (BF%). Dietary intake was assessed using a 5-day estimated, non-consecutive, food record and a validated semi-quantitative food frequency questionnaire, which were used to calculate habitual dietary intake using the National Cancer Institute (NCI) method. Body composition and BF% were assessed by dual-energy x-ray absorptiometry. Fasting blood samples were analysed for metabolic biomarkers (lipid and glucose profiles). Bulk DNA was extracted from faecal samples and the metagenomic sequences associated with the microbiota were analysed using MetaPhlAN and QIIME2 software. Enterotypes characterising the microbiotas of the participants were predicted in R and the species that defined enterotypes were determined using STAMP software. A posteriori dietary patterns were identified using principal component analysis. Adjusted multivariate regression models were conducted to explore the association between BF% and habitual macronutrient intake and adherence to dietary patterns, as well as the association between microbiota composition and habitual diet. Results There were no significant differences in BF% between Pacific and NZE women (p=0.498). Higher energy adjusted habitual dietary fibre (DF) intake was associated with lower BF% (β= -0.35, p≤ 0.001) for both Pacific and NZE women, and this relationship became stronger after further adjustments for protein (g/day), total carbohydrate (g/day), and total fat (g/day) intake (β= -0.47, p≤ 0.001). Women in the highest tertile of DF intake were older, had lower concentrations of fasting plasma insulin, and lower socioeconomic deprivation levels. Four dietary patterns that explained 30.9 % of the observed variance in habitual diet were identified. Higher adherence to dietary patterns characterised by core foods (the “colourful vegetable, plant protein, and dairy” and “fruit, starchy vegetables, and nuts” patterns) were inversely associated with BF%. In contrast, patterns characterised by more ‘discretionary’ foods (“sweet and fat rich carbohydrate”) and less diversity of core foods (“animal meat and fat”) were positively associated with BF% for both Pacific and NZE women. Three enterotypes were identified by higher relative abundance of specific bacterial species: enterotype 1 was characterised by Pacific and NZE women (n=146) and the abundances of Faecalibacterium prausnitzii and Eubacterium rectale. Enterotype 2 (n=70) was characterised by Pacific women, Bifidobacterium adolescentis, Bifidobacterium bifidum, and Lactobacillus ruminis; and by higher BF%, visceral adipose tissue, and concentrations of fasting insulin. Enterotype 3 (n=70) was predominately found in older NZE women with lower deprivation, and characterised by Akkermansia muciniphila, Ruminococcus bromii, Subdoligranulum species, and Methanobrevibacter smithii. Adherence to the “colourful vegetables, plant protein, and dairy” dietary pattern was positively associated with enterotypes 1 and 3 and negatively with enterotype 2. Conclusion Consuming more core foods rich in dietary fibre was associated with enterotypes 1 and 3, including lower adiposity and metabolic disease risks. In contrast, consuming more discretionary foods was associated with enterotype 2, higher adiposity and metabolic disease risks. This PhD research highlights habitual diet-microbiota-host associations, which are similar for a population of women with different metabolic disease risk, body fat profiles, and deprivation levels. Whether the microbiota is a cause or consequence of metabolic health has yet to be elucidated. However, habitually consuming more core foods rich in dietary fibre is associated with microbiota composition, and lower metabolic disease risks

The fecal microbiotas of women of Pacific and New Zealand European ethnicities are characterized by distinctive enterotypes that reflect dietary intakes and fecal water content

Obesity is a complex, multifactorial condition that is an important risk factor for noncommunicable diseases including cardiovascular disease and type 2 diabetes. While prevention and management require a healthy and energy balanced diet and adequate physical activity, the taxonomic composition and functional attributes of the colonic microbiota may have a supplementary role in the development of obesity. The taxonomic composition and metabolic capacity of the fecal microbiota of 286 women, resident in Auckland New Zealand, was determined by metagenomic analysis. Associations with BMI (obese, nonobese), body fat composition, and ethnicity (Pacific, n = 125; NZ European women [NZE], n = 161) were assessed using regression analyses. The fecal microbiotas were characterized by the presence of three distinctive enterotypes, with enterotype 1 represented in both Pacific and NZE women (39 and 61%, respectively), enterotype 2 mainly in Pacific women (84 and 16%) and enterotype 3 mainly in NZE women (13 and 87%). Enterotype 1 was characterized mainly by the relative abundances of butyrate producing species, Eubacterium rectale and Faecalibacterium prausnitzii, enterotype 2 by the relative abundances of lactic acid producing species, Bifidobacterium adolescentis, Bifidobacterium bifidum, and Lactobacillus ruminis, and enterotype 3 by the relative abundances of Subdoligranulum sp., Akkermansia muciniphila, Ruminococcus bromii, and Methanobrevibacter smithii. Enterotypes were also associated with BMI, visceral fat %, and blood cholesterol. Habitual food group intake was estimated using a 5 day nonconsecutive estimated food record and a 30 day, 220 item semi-quantitative Food Frequency Questionnaire. Higher intake of 'egg' and 'dairy' products was associated with enterotype 3, whereas 'non-starchy vegetables', 'nuts and seeds' and 'plant-based fats' were positively associated with enterotype 1. In contrast, these same food groups were inversely associated with enterotype 2. Fecal water content, as a proxy for stool consistency/colonic transit time, was associated with microbiota taxonomic composition and gene pools reflective of particular bacterial biochemical pathways. The fecal microbiotas of women of Pacific and New Zealand European ethnicities are characterized by distinctive enterotypes, most likely due to differential dietary intake and fecal consistency/colonic transit time. These parameters need to be considered in future analyses of human fecal microbiotas.Peer reviewe

A cross sectional study of the behavioural differences between obesity-resistant and obesity-susceptible individuals

Background: Over the last 30 years, the prevalence of obesity has steadily increased into the global epidemic that it is today (1). The number of overweight and obese individuals has increased sharply; however, there is still a substantial sector of the population who have remained lean, despite living within an obesogenic environment. Objective: The aim of the present study was to identify potential behavioural differences between obesity-resistant individuals (ORI) and obesity-susceptible individuals (OSI). Design: The current cross-sectional study used data from the 2010 Ice Tea Study (Cohort 1) and the 2008 Born to Be Lean Study (Cohort 2). Participants from both cohorts were screened with a pre-tested tool to classify individuals who appear resistant or susceptible to obesity. Study participants were recruited through advertisements placed in the local paper, and invitations sent out to consenting participants from previous studies. Cohort 1 consisted of 117 participants (58 males and 59 females), aged between 19-55 years old, who completed the Dutch Eating Behavior Questionnaire (DEBQ) and the Intuitive Eating Scale (IES). The results from these two questionnaires were scored and analysed with STATA version 12 and were adjusted for sex and body mass index (BMI). Cohort 2 consisted of 105 participants (52 males and 53 females) aged between 19-56 years old, who completed a 60-part qualitative and quantitative pretested questionnaire (Lifestyle Questionnaire). Twenty-three questions were selected from the Lifestyle Questionnaire for analysis as they had particular relevance to behavioural and environmental influences. Statistical analyses were conducted using STATA version 12 and results were adjusted for sex and BMI. Results: Cohort 1: ORI scored significantly lower than OSI on the restrained eating scale of the DEBQ (p<0.001). There were no significant differences between ORI and OSI for the emotional (p=0.116) or external eating (p=0.881) scales of the DEBQ. Obesity-resistant individuals had significantly higher total IES scores than obesity-susceptible individuals (p<0.001). Obesity-resistant individuals also scored significantly higher than obesity-susceptible individuals for the unconditional permission to eat (p<0.001), eating for physical reasons (p=0.042) and reliance on internal hunger and satiety cues subscales (p=0.001). Cohort 2: ORI were significantly less likely than OSI to attempt weight loss (p=0.002), and significantly more likely to attempt to gain weight through dietary modification (p<0.001). Obesity-susceptible individuals were significantly more likely to recall their body weight in relation to significant life events in comparison to obesity-resistant individuals (p=0.001). In addition, obesity-resistant individuals were significantly more likely than obesity-susceptible individuals to eat when they were hungry (p=0.006) and feel energetic (p=0.019) and significantly less likely to feel tense (p=0.049) and exercise for weight control (p<0.001). Conclusions: Obesity-resistant individuals were significantly less likely than obesity-susceptible individuals to engage in restrictive eating behaviours, while also demonstrating higher intuitive eating behaviours and energy levels. Obesity-susceptible individuals were more likely than obesity-resistant individuals to restrict and modify their dietary intake to induce weight loss and report feeling tense. Cognitive behavioural interventions that incorporate intuitive eating should be recommended as part of weight management and maintenance techniques for individuals who are struggling to control their body weight

A cross sectional study of the behavioural differences between obesity-resistant and obesity-susceptible individuals

Background: Over the last 30 years, the prevalence of obesity has steadily increased into the global epidemic that it is today (1). The number of overweight and obese individuals has increased sharply; however, there is still a substantial sector of the population who have remained lean, despite living within an obesogenic environment. Objective: The aim of the present study was to identify potential behavioural differences between obesity-resistant individuals (ORI) and obesity-susceptible individuals (OSI). Design: The current cross-sectional study used data from the 2010 Ice Tea Study (Cohort 1) and the 2008 Born to Be Lean Study (Cohort 2). Participants from both cohorts were screened with a pre-tested tool to classify individuals who appear resistant or susceptible to obesity. Study participants were recruited through advertisements placed in the local paper, and invitations sent out to consenting participants from previous studies. Cohort 1 consisted of 117 participants (58 males and 59 females), aged between 19-55 years old, who completed the Dutch Eating Behavior Questionnaire (DEBQ) and the Intuitive Eating Scale (IES). The results from these two questionnaires were scored and analysed with STATA version 12 and were adjusted for sex and body mass index (BMI). Cohort 2 consisted of 105 participants (52 males and 53 females) aged between 19-56 years old, who completed a 60-part qualitative and quantitative pretested questionnaire (Lifestyle Questionnaire). Twenty-three questions were selected from the Lifestyle Questionnaire for analysis as they had particular relevance to behavioural and environmental influences. Statistical analyses were conducted using STATA version 12 and results were adjusted for sex and BMI. Results: Cohort 1: ORI scored significantly lower than OSI on the restrained eating scale of the DEBQ (p<0.001). There were no significant differences between ORI and OSI for the emotional (p=0.116) or external eating (p=0.881) scales of the DEBQ. Obesity-resistant individuals had significantly higher total IES scores than obesity-susceptible individuals (p<0.001). Obesity-resistant individuals also scored significantly higher than obesity-susceptible individuals for the unconditional permission to eat (p<0.001), eating for physical reasons (p=0.042) and reliance on internal hunger and satiety cues subscales (p=0.001). Cohort 2: ORI were significantly less likely than OSI to attempt weight loss (p=0.002), and significantly more likely to attempt to gain weight through dietary modification (p<0.001). Obesity-susceptible individuals were significantly more likely to recall their body weight in relation to significant life events in comparison to obesity-resistant individuals (p=0.001). In addition, obesity-resistant individuals were significantly more likely than obesity-susceptible individuals to eat when they were hungry (p=0.006) and feel energetic (p=0.019) and significantly less likely to feel tense (p=0.049) and exercise for weight control (p<0.001). Conclusions: Obesity-resistant individuals were significantly less likely than obesity-susceptible individuals to engage in restrictive eating behaviours, while also demonstrating higher intuitive eating behaviours and energy levels. Obesity-susceptible individuals were more likely than obesity-resistant individuals to restrict and modify their dietary intake to induce weight loss and report feeling tense. Cognitive behavioural interventions that incorporate intuitive eating should be recommended as part of weight management and maintenance techniques for individuals who are struggling to control their body weight

Dietary Intake of New Zealand European and Pacific Woman from the PROMISE Study

Background: New Zealand is culturally diverse and has one of the highest rates of obesity in theworld, especially among women. [...

Physical Activity and Metabolic Health in New Zealand European and Pacific Women from the Promise Study

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