Browsing by Author "Smith, James"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Open Access
    Diet composition and perceptions around food in individuals with Type 2 Diabetes Mellitus following a long-term low carbohydrate high fat diet
    (2019) Murphy, Tamzyn; Smith, James; Noakes, Timothy
    Background: Type II diabetes mellitus (T2D) is described as a progressive metabolic disease, characterised by disrupted glycaemic regulation, and is associated with high rates of morbidity and mortality. Low carbohydrate high fat (LCHF) diets may be particularly effective and sustainable for the treatment of T2D and have become a popular ‘self-therapy’. This study investigates the real-world dietary composition and potential effects of a long-term LCHF diet on T2D. Materials and Methods: A multi-method descriptive study investigating the diet and related aspects in 28 adult T2D patients perceiving to follow an LCHF diet for ≥ 6 months. Data collection included a quantitative phase (general detailed health and a food frequency (FFQ) questionnaires, 24-hour diet recall (24HR), 3-day food record, anthropometry, blood pressure, blood sampling, past medical records) and a qualitative phase (semi-structured interviews). Results: LCHF (duration 2.1 ± 1.5 y) consisted of 67% fat (143.2 ± 67.9 g, mainly saturated fat from added fat, eggs, meat, poultry, seafood and full cream dairy), 10% carbohydrate (64.0 ± 27.9 g, primarily from full cream dairy, nuts and seeds), 20 % protein (96.0 ± 37.4 g, primarily animal origin) and 3% alcohol (primarily wine). Cholesterol intake (616.3 (402.8–804.2) mg) was higher, and fibre (14.7 ± 7.5 g), calcium and folate lower than recommendations. Added sugar (0.5% of energy intake) and processed foods were seldom consumed. Daily energy intake was 1946.3 ± 807.2 kcal (436.7 ± 728.3 kcal. d-1 calculated energy deficit). Intermittent fasting (≥ 16 h. d-1) was followed by 61% of the group. From pre-LCHF to the time of the study, reductions were seen in obesity prevalence (- 50 %), body weight (- 16.9 ± 11.7 %), HbA1c concentration (- 2.45 ± 2.59 %) and T2D prevalence (36 % were no longer classified as T2D based on HbA1c and T2D pharmacotherapy). Non-pharmacologically-induced changes in HbA1c concentrations showed HbA1c reductions in 75 % of the group during the time on LCHF. LCHF was generally reported as sustainable, linked to reduced hunger and cravings and improvements in overall health and health-related quality of life (HRQoL). Challenges included constipation, initial adaptation and social difficulties related to LCHF. Discussion and conclusion: These findings are the first to describe the nature and composition of a self-selected ad libitum real-world LCHF diet and coexisting health parameters. LCHF can be sustainable in T2D patients and may be linked to improvements in glycaemic control, medication reduction, hunger, health and HRQoL.
  • Thumbnail Image
    Item
    Open Access
    Endogenous glucose production and gluconeogenesis during exercise in athletes on either a low-carbohydrate or mixed diet
    (2015) Webster, Christopher Charles; Noakes, Timothy; Smith, James
    INTRODUCTION. The LCHF diet produces major changes in whole-body substrate metabolism and energy stores such as reduced muscle and liver glycogen content, increased rates of fat oxidation and decreased rates of carbohydrate (CHO) oxidation. Despite reduced CHO availability, the rate of CHO oxidation that can be sustained during exercise in LCHF athletes is surprisingly high. The most probable source of this glucose is via the process of gluconeogenesis (GNG). However, endogenous glucose production (EGP) and GNG has not been studied during exercise in athletes on a LCHF diet. Therefore, the aim of this study was to determine if there are differences in EGP, GNG and glycogenolysis (GLY) during exercise in endurance-trained athletes who habitually eat either a mixed or LCHF diet. METHODS. Fourteen (7 LCHF, 7 Mix) endurance-trained male cyclists (VO₂max 61 ± 5 ml/kg/min LCHF; 6 3 ± 8 ml/kg/min Mix), matched for age (36 ± 6 y LCHF; 32 ± 5 y Mix), body composition (BMI 23.6 ± 1.8 LCHF; 23.4 ± 2.0 Mix) and relative peak power output (4.8 ± 0.4 W/kg LCHF; 5.0 ± 0.4 W/kg Mix), were recruited. Diets were analysed using the Automated Self-Administered 24-hour Recall (ASA24) analysis software. Participants cycled for 2 h at 55% of peak power output during which EGP was measured by infusion of [6,6- ²H₂ ]glucose, and fractional gluconeogenesis was measured by ingestion of ²H₂O. Blood samples were collected at regular intervals for isotope enrichment analysis. R ESULTS. Rates of GNG were similar during exercise in both the LCHF and mixed diet groups (2.8 ± 0.4 mg/kg/min LCHF; 2.5 ± 0.3 mg/kg/min Mix). The rates of GLY during exercise were significantly higher in the mixed diet group than the LCHF group (3.2 ± 0.7 mg/kg/min LCHF; 5.3 ± 0.9 mg/kg/min Mix) which resulted in significantly higher rates of EGP in the mixed diet group (6.0 ± 0.9 mg/kg/min LCHF; 7.8 ± 1.1 mg/kg/min Mix). There were significant differences in the mean fat oxidation rates (1.2 ± 0.2 g/min LCHF; 0.5 ± 0.2 g/min Mix) and CHO oxidation rates (1.3 ± 0.5 g/min LCHF; 3.1 ± 0.5 g/min Mix). Blood beta-hydroxbutyrate (βHB) concentrations were significantly higher in the LCHF group than in the mixed diet group throughout exercise but there were no differences in plasma glucose, plasma lactate, serum insulin or serum FFA concentrations. The diets of the two groups differed only in fat and CHO intake (%Protein / %Fat / %CHO: 21/72/7 LCHF; 16/33/51 Mix). DISCUSSION. Rates of fat oxidation and CHO oxidation were not associated with the rates of GNG. Apart from βHB, the precursor, substrate and insulin concentrations were remarkably similar in both groups and may have influenced GNG similarly in both groups. We conclude that rates of GNG are relatively stable across a broad range of habitual diets that can significantly alter substrate utilisation, and that dietary CHO modulates the rates of EGP via alterations in rates of GLY, both at rest and during exercise.
  • Thumbnail Image
    Item
    Open Access
    Evaluation of a nutrition and health education program on components of metabolic health on women from under-resourced South African communities
    (2022) Guillén, Pujol-Busquets Georgina; Lambert, Estelle V; Larmuth, Kate; Smith, James; Faig, Anna Bach
    Background: Diet-related non-communicable diseases (NCDs) pose a substantial burden in terms of financial cost, morbidity, and mortality. In South Africa there is currently a double burden of infectious diseases and NCDs. Overconsumption of sugar, refined carbohydrates, and poor-quality fats, increases the risk for developing chronic diseases. Families from poor communities are often forced to eat these harmful foods due to a lack of nutrition education, or because they cannot afford or don't know how to access healthy foods. While poverty is an important barrier to health and education for both men and women, it tends to yield a higher burden in women. There is evidence that low-carbohydrate high-fat (LCHF) diets can improve metabolic health in well-controlled clinical trials where quality food is either provided or where participants have the financial and logistical means to access the foods promoted by this diet. However, one cannot assume that the same nutritional advice will translate to residents of underserved communities, who may not understand the advice nor be able to afford or access the foods promoted by this diet. Women from these communities are often the gatekeepers to healthy food choices for their families, but they are at a particular disadvantage. Eat Better South Africa (EBSA) runs nutrition education programs to teach – predominately women – how to choose affordable healthier foods that are lower in refined carbohydrates and higher in healthy fats to prevent or manage metabolic conditions. Aims: This research aims to optimise the EBSA program for women from underresourced communities and to evaluate its effectiveness for changing dietary behaviour and improving metabolic health. The objectives were: 1) to explore women's perceptions of the EBSA program and the barriers and facilitators that they faced to change their dietary habits and adhere to the EBSA recommended diet; 2) to conduct community assessments in the under-resourced communities that EBSA planned to run programs, better address women's needs and explore their willingness to participate in a nutrition and health education program; 3) to assess the effects of the EBSA program on women's metabolic health and wellbeing through mixed-methods and to explore EBSA's team perceptions of the program, and 4) to explore health practitioners' perceptions of the health and nutritional advice recommended by EBSA. Methods: The first part of this project consisted of a qualitative study through focus group discussions (FGDs) with women from previous EBSA programs (n=18) and naïve EBSA participants (n=60). The second part of the project consisted of a mixed-method evaluation (n=32) of a pilot study on an EBSA intervention to assess health status changes. These methods included qualitative methods (in-depth individual (IDIs) interviews with both EBSA participants and EBSA team members and FGDs with the EBSA participants), and quantitative methods (diet assessment, metabolic health markers and physical activity behaviour) to assess changes before and after the pilot intervention program. The last part of this project consisted of a qualitative IDI study on health practitioners' perceptions and understanding of a LCHF diet (n=16). Thematic analysis of the qualitative data was conducted using NVivo 12 software. Descriptive and statistical analysis of the quantitative data was done using Stata 16 and Jamovi. Results: The first formative study indicated that the EBSA participants' greatest facilitators and barriers revolved around understanding the educational content and on how to implement the dietary advice. The mixed methods results of the second study, the pilot, indicated that, overall, the women experienced improvements in dietary behaviours and biomarkers related to inflammation, lipids, and glycaemic profiles. Furthermore, the participants waist circumference, weight, blood pressure, triglycerides and HbA1c were significantly reduced, and those changes were sustained six months after the EBSA intervention. Women's carbohydrate intake was significantly reduced, and their health markers improved despite a slight increase in sedentary behaviour. The qualitative results found that the major reason women enrolled in the program was because they suffered from NCDs. Most women found that the EBSA diet made them feel less hungry, more energetic and they felt that their health had improved. Most women spoke of socioeconomic challenges which made it difficult for them to follow EBSA's recommendations, such as employment status, safety issues in the community, and lack of support from relatives. Women felt that some health practitioners were not supportive of the diet, but that they became more positive after observing the related health outcomes. Quantitative results converged with qualitative results except for physical activity behaviour. EBSA's team perceptions of the program and participants' challenges matched participants' experiences. The final qualitative study indicated that health practitioners' approaches to LCHF diets seemed to be supportive but not advocating. Conclusion: Although, currently, some international food guidelines endorse LCHF diets, there is still a considerable amount of confusion and lack of knowledge regarding this diet. This study provided data on the dietary intake and health risk status of women from under-resourced South African communities, and the facilitators and challenges of a LCHF education program to change their dietary behaviour. Results suggested that most participants followed EBSA's dietary recommendations and experienced health improvements as a result. Follow up data at six months suggested that those changes could be sustainable. For people with diet-related chronic diseases, LCHF diets should be supported by experienced health care professionals who can facilitate optimal nutritional intake. This is the same for any other diet; the evidence for long-term compliance and the sustainability of carbohydrate restriction is currently not yet established. In the absence of this evidence, existing data suggest that it is a legitimate and potentially effective treatment to adopt a LCHF diet as an option for patients to manage and prevent NCDs in under-resourced communities.
  • Thumbnail Image
    Item
    Open Access
    Metabolic and lifestyle profiling of overweight female runners compared to lean counterparts: exploring the implications and causes of their elevated body weight
    (2016) Leith, David; Smith, James; Kohn, Tertius; Noakes, Tim
    There appears to be an emerging phenotype of recreational runners who are overweight despite being regularly active. This conflicts with the common perception that exercise protects against weight-gain, and it may be caused by underlying insulin-resistance. Alternatively, recent research has brought attention to metabolically healthy obese (MHO) individuals, who have increased adiposity but no commonly associated metabolic abnormalities, such as insulin-resistance, hypertension, dyslipidaemia and systemic inflammation. This study aimed to determine whether overweight (OW, BMI ≥ 25 kg.m⁻²) female runners were at risk of developing metabolic pathology and compare the findings to lean (LN, BMI < 23 kg.m⁻²) counterparts. A secondary aim was to explore potential inherent or lifestyle factors that may have predisposed or contributed to weight-gain in OW runners. METHODS. Twenty (10 OW, 10 LN) female recreational runners (years of running experience 7.1 ± 4.4 OW; 8.0 ± 3.7 LN) matched for mean age (38.7 ± 4.6 OW; 37.7 ± 4.3 LN), current mileage in km.week⁻¹ (42.0 ± 10.9 OW; 44.5 ± 12.1 LN) and running calibre expressed as energy expenditure (kcal.min⁻¹) in their most recent half-marathon (9.0 ± 1.1 OW; 9.2 ± 1.1 LN) were recruited for this study. Body fat percentage (BF%) was determined using DXA. Participants completed questionnaires about health history, lifestyle and eating habits and validated questionnaires concerning recent sleep and stress. Their diet was recorded using 3-day diet records and analysed using the South African Food Data System (Medical Research Council of South Africa). Habitual sleep and physical activity were quantified using 7-day actigraphy (Actiwatch 2) and accelerometry (Actigraph GTX3+) respectively. Blood pressure and resting metabolic rate were measured after an overnight fast. Blood samples were analysed for cardio-metabolic parameters and an Oral Glucose Tolerance Test was performed for insulin-sensitivity. RESULTS. OW exhibited a greater body weight (74.4 ± 6.4 kg OW; 59.4 ± 7.8 kg LN, p < 0.001) but similar fat-free-mass (49.4 ± 5.6 kg OW; 45.4 ± 5.9 kg LN) to the LN group. OW had a higher BF% (32.1 ± 3.9 OW; 21.8 ± 3.9 LN, p < 0.0001), and systolic (118 ± 10 mmHg OW; 107 ± 5 mmHg LN, p < 0.05), but not diastolic (72 ± 6 mmHg OW; 68 ± 4 mmHg LN) blood pressure. There was no difference between groups in serum uric acid, alanine aminotransferase, % HbA1c, total cholesterol, HDL-cholesterol, triglycerides or free-fatty-acids. OW had higher levels of C-reactive protein (1.30 ± 0.97 mg.L⁻¹ OW; 0.59 ± 0.35 mg.L⁻¹ LN, p < 0.05), total cholesterol / HDL-cholesterol (2.70 ± 0.40 OW; 2.30 ± 0.42 LN, p < 0.05) and LDL-cholesterol (2.99 ± 0.65 mM OW; 2.43 ± 0.72 mM LN, p < 0.05), but these were within normal ranges. IDL-cholesterol constituted a significantly greater proportion of total cholesterol in OW compared to LN, but HDL- and LDL- cholesterol sub-fraction distributions were similar. Indices of hepatic (HOMA-IR, 1.06 ± 0.51 OW; 0.86 ± 0.24 LN), and whole-body (Matsuda, 7.84 ± 2.46 OW; 9.16 ± 2.28 LN) insulin-sensitivity were variable and similar between groups. Total area-under-the-curve of the OGTT insulin response tended to be higher in OW (p = 0.08). Two OW runners had insulin-resistance (Matsuda < 5); but no participants had the metabolic syndrome. RMR (kcal.kg FFM⁻¹.day⁻¹) was lower in OW (29.5 ± 2.1 OW; 31.6 ± 2.3 LN, p < 0.05), but there were no significant differences in lifestyle factors (diet, physical activity, sleep and stress). Total energy intake in kcal.day⁻¹ (1928 ± 354 OW; 2166 ± 489 LN) and % macronutrient composition as Protein/Fat/Carbohydrate/Alcohol (20/44/33/3 OW; 16/43/36/5 LN) were both similar between groups. OW and LN also exhibited similar activity in steps.day⁻¹ (10 742 ± 3552 OW; 12 073 ± 3273 LN) and percentage accelerometer wear-time spent in Sedentary/Light/Moderate-Vigorous physical activity (75/14/11 OW; 72/15/13 LN). Both groups attained circa 7 hours.night⁻¹ of sleep, with good sleep onset latency (7.3 ± 5.8 minutes OW; 5.8 ± 3.5 minutes LN) and sleep efficiency (91.6 ± 4.4% OW; 90.7 ± 2.8% LN), and they reported reduced to average levels of recent stress. DISCUSSION. OW runners presented with greater mean adiposity than LN counterparts, but the two groups were not as distinct as anticipated. OW runners did present with greater metabolic risk according to some traditional risk factors, including inflammation, systolic blood pressure, LDL-C and total cholesterol. However, the first three were within normal ranges and the clinical relevance of the latter is questionable. It was, therefore, concluded that on average the OW group was not at metabolic risk. Only two OW runners and no LN runners were insulin-resistant according to indices derived from the OGTT. These findings may primarily reflect the insulin-sensitising effects of regular exercise and the consequent fitness of the OW runners. Appetite-dysregulation is speculated to have played an integral role in their prior weight-gain. We did not identify any lifestyle discrepancies that could have explained this weight-gain. The cross-sectional nature of this study made it difficult to assess past behaviour during weight-gain, and inter-individual variation was considerable. In combination with the small sample size, these factors limited the generalisability of the results. Future exploration of the 'overweight-runner' phenotype is warranted to clarify the mechanisms of weight-gain in habitual runners and consequent lifestyle changes that may promote meaningful weight-loss.
  • Thumbnail Image
    Item
    Open Access
    Preliminary investigations for studying the effects of low carbohydrate high fat diets on gluconeogenesis in type 2 diabetes patients
    (2020) Webster, Christopher; Smith, James; Noakes Timothy
    Type 2 diabetes (T2D) is currently one of the major health challenges across the globe. Lifestyle changes are a key component of T2D management and there is growing interest in low carbohydrate high fat (LCHF) diets as a potential dietary strategy to improve glycaemic control, reduce T2D medication requirements, and improve body weight and lipid profiles. However, carbohydrate restriction is controversial. Results from observational studies generally do not support the food choices associated with carbohydrate restriction while results from short-term randomised controlled trials (RCTs) are more likely to show significant benefits of LCHF diets. Additionally, both study designs have limitations and opinion on LCHF diets is polarised due to ambiguities in how to interpret the available data. Chapter 1 of this thesis reviews the impact of prospective cohort studies, randomised controlled trials, and dietary policies on current opinions towards LCHF diets for the management of T2D. Uncertainty over the safety of LCHF diets remains a concern and additional observational studies and short-term RCTs of the same quality as existing research are unlikely to add any further clarity. For this reason, research focused on understanding the underlying mechanisms of carbohydrate restricted diets may be an alternative approach to alleviate or validate some of the concerns being expressed about LCHF diets. One such mechanism is the dysregulation of glucose production via gluconeogenesis, which is a key pathology of T2D but which has been incompletely studied. Indeed, the effects of LCHF eating on gluconeogenesis in T2D patients has not yet been studied, nor has gluconeogenesis been investigated in the context of T2D remission. This is an area of interest for future research and the aim of this thesis was to conduct preliminary studies to prepare the groundwork for such studies. There is large heterogeneity in the low carbohydrate diets that have been prescribed in controlled trials and the composition and characteristics of the LCHF diets that patients are finding effective in the real world is unknown. Study 1 (Chapter 2 of this thesis) aimed to better understand the LCHF diet by investigating the diet, diabetes status, and personal experiences of T2D patients who had self-selected and followed an LCHF diet of their own accord. This study was a multi-method investigation which consisted of quantitative assessments of diet and diabetes status, as well as in-depth interviews which were analysed using qualitative methods. Results from this study will be used to inform design and protocol decisions in future controlled trial studies. Study 2 (Chapter 3 of this thesis) piloted the use of stable isotope tracers for the quantification of endogenous glucose production and gluconeogenesis in the early postabsorptive state (5 hours after a meal). For methodological reasons, prior investigations have usually measured gluconeogenesis after an overnight fast and therefore, little is known about the effects of dietary composition on gluconeogenesis within the early post-absorptive state. Study 2 quantifies gluconeogenesis 5 hours after a meal and the validity of the data is discussed. Finally, Chapter 4 outlines future perspectives for research based on findings from Chapter 2 and Chapter 3.