Tania P. Markovic

The Determinants of Glycemic Responses to Diet Restriction and Weight Loss in Obesity and NIDDM

OBJECTIVE To examine the mechanisms by which weight loss improves glycemic control in overweight subjects with NIDDM, particularly the relationships between energy restriction, improvement in insulin sensitivity, andregional and overall adipose tissue loss. RESEARCH DESIGN AND METHODS Hyperinsulinemic glucose clamps wereperformed in 20 subjects (BMI = 32.0 ± 0.5 [SEM] kg/m2, age = 48.4 ± 2.7 years) with normal glucose tolerance (NGT) (n = 10) or mild NIDDM (n = 10) before and on the 4th (d4) and 28th (d28) days of a reduced-energy (1,100 ± 250 [SD] kcal/day) formula diet. Body composition changes were assessed by dual energy x-ray absorptiometry and insulin secretory changes were measured by insulin response to intravenous glucose before and after weight loss. RESULTS In both groups, energy restriction (d4) reduced fasting plasma glucose (FPG) (ΔFPG: NGT = −0.4 ± 0.2 mmol/1 and NIDDM = −1.1 ± 0.03 mmol/1, P = 0.002), which was independently related to reduced carbohydrate intake (partial r = 0.64, P = 0.003). There was a marked d4 increase in percent of insulin suppression of hepatic glucose output(HGO) in both groups (ΔHGO suppression: NGT = 28 ± 15% and NIDDM = 32 ± 8%, P = 0.002). By d28, with 6.3 ± 0.4 kg weight loss, FPG was further reduced (d4 vs. d28) in NIDDM only (P = 0.05), and insulin sensitivity increased in both groups (P = 0.02). Only loss of abdominal fat related to improvements in FPG (r = 0.51, P = 0.03) and insulin sensitivity afterweight loss (r = 0.48, P = 0.05). In contrast to insulin action, there were only small changes in insulin secretion. CONCLUSIONS Both energy restriction and weight loss have beneficial effects on insulin action and glycemic control in obesity and mild NIDDM. The effect of energy restriction is related to changes in individual macronutrients, whereas weight loss effects relate to changes in abdominal fat.

A Randomized Controlled Trial Investigating the Effects of a Low-Glycemic Index Diet on Pregnancy Outcomes in Gestational Diabetes Mellitus

OBJECTIVE The prevalence of gestational diabetes mellitus (GDM) is rising. There is little evidence to demonstrate the effectiveness of one dietary therapy over another. We aimed to investigate the effect of a low–glycemic index (LGI) versus a conventional high-fiber diet on pregnancy outcomes, neonatal anthropometry, and maternal metabolic profile in GDM. RESEARCH DESIGN AND METHODS Ninety-nine women (age 26–42 years; mean ± SD prepregnancy BMI 24 ± 5 kg/m2) diagnosed with GDM at 20–32 weeks’ gestation were randomized to follow either an LGI (n = 50; target glycemic index [GI] ~50) or a high-fiber moderate-GI diet (HF) (n = 49; target GI ~60). Dietary intake was assessed by 3-day food records. Pregnancy outcomes were collected from medical records. RESULTS The LGI group achieved a modestly lower GI than the HF group (mean ± SEM 47 ± 1 vs. 53 ± 1; P < 0.001). At birth, there was no significant difference in birth weight (LGI 3.3 ± 0.1 kg vs. HF 3.3 ± 0.1 kg; P = 0.619), birth weight centile (LGI 52.5 ± 4.3 vs. HF 52.2 ± 4.0; P = 0.969), prevalence of macrosomia (LGI 2.1% vs. HF 6.7%; P = 0.157), insulin treatment (LGI 53% vs. HF 65%; P = 0.251), or adverse pregnancy outcomes. CONCLUSIONS In intensively monitored women with GDM, an LGI diet and a conventional HF diet produce similar pregnancy outcomes.

Glycemic index and pregnancy: a systematic literature review.

Background/Aim. Dietary glycemic index (GI) has received considerable research interest over the past 25 years although its application to pregnancy outcomes is more recent. This paper critically evaluates the current evidence regarding the effect of dietary GI on maternal and fetal nutrition. Methods. A systematic literature search using MEDLINE, EMBASE, CINAHL, Cochrane Library, SCOPUS, and ISI Web of Science, from 1980 through September 2010, was conducted. Results. Eight studies were included in the systematic review. Two interventional studies suggest that a low-GI diet can reduce the risk of large-for-gestational-age (LGA) infants in healthy pregnancies, but one epidemiological study reported an increase in small-for-gestational-age (SGA) infants. Evidence in pregnancies complicated by gestational diabetes mellitus (GDM), though limited (n = 3), consistently supports the advantages of a low-GI diet. Conclusion. There is insufficient evidence to recommend a low-GI diet during normal pregnancy. In pregnancy complicated by GDM, a low-GI diet may reduce the need for insulin without adverse effects on pregnancy outcomes. Until larger-scale intervention trials are completed, a low-GI diet should not replace the current recommended pregnancy diets from government and health agencies. Further research regarding the optimal time to start a low-GI diet for maximum protection against adverse pregnancy outcomes is warranted.

Beneficial effect on average lipid levels from energy restriction and fat loss in obese individuals with or without type 2 diabetes.

OBJECTIVE The risk of cardiovascular disease in type 2 diabetes is greater than is accounted for by conventional risk factors. We investigated whether energy restriction or modest fat loss improved the lipid profile in obese subjects with and without type 2 diabetes. The relationship of site of adipose tissue loss to lipid changes was also examined. RESEARCH DESIGN AND METHODS Lipid levels were measured in 18 subjects with normal glucose tolerance (NGT) (n = 9, BM1 = 31.5 ± 0.8 [SEM] kg/m2) or type 2 diabetes (n = 9, BMI = 31.8 ± 0.7) before and on the 4th (d4) and 28th (d28) days of a hypocaloric formula diet. Body composition was assessed with dual energy X-ray absorptiometry on dO and d28. RESULTSL:— Mean daily energy intake during the diet was 1,100 ± 60 kcal (33% protein, 38% carbohydrate, and 29% fat). Mean weight loss was 6.2 ± 0.4 kg. Initial lipid profiles were similar in subjects with or without diabetes, and diabetes did not affect the responses. Dietary intervention resulted in early (d4) and late (d28) changes. Energy restriction(d4) reduced VLDL cholesterol and total triglyceride (TG) concentrations andincreased LDL particle size. With fat loss (d28), there were falls in total LDL cholesterol (free and esterified components), LDL TG, and LDL apolipoprotein B (apoB) concentrations. Reduction in central abdominal fat (but not other body fat) was correlated with a less atherogenic lipid profile: Δ abdominal fat versus Δ LDL free cholesterol, r = 0.65, P = 0.006 and versus Δ apoB, r = 0.64, P = 0.008. CONCLUSIONS Even in obese subjects with an average lipid profile, modest weight loss reduces atherogenicity, independently of type 2 diabetes, and abdominal fat loss is specifically related to such improvements.

Do ketogenic diets really suppress appetite? A systematic review and meta-analysis.

Very‐low‐energy diets (VLEDs) and ketogenic low‐carbohydrate diets (KLCDs) are two dietary strategies that have been associated with a suppression of appetite. However, the results of clinical trials investigating the effect of ketogenic diets on appetite are inconsistent. To evaluate quantitatively the effect of ketogenic diets on subjective appetite ratings, we conducted a systematic literature search and meta‐analysis of studies that assessed appetite with visual analogue scales before (in energy balance) and during (while in ketosis) adherence to VLED or KLCD. Individuals were less hungry and exhibited greater fullness/satiety while adhering to VLED, and individuals adhering to KLCD were less hungry and had a reduced desire to eat. Although these absolute changes in appetite were small, they occurred within the context of energy restriction, which is known to increase appetite in obese people. Thus, the clinical benefit of a ketogenic diet is in preventing an increase in appetite, despite weight loss, although individuals may indeed feel slightly less hungry (or more full or satisfied). Ketosis appears to provide a plausible explanation for this suppression of appetite. Future studies should investigate the minimum level of ketosis required to achieve appetite suppression during ketogenic weight loss diets, as this could enable inclusion of a greater variety of healthy carbohydrate‐containing foods into the diet.

The effect of a high-egg diet on cardiovascular risk factors in people with type 2 diabetes: the Diabetes and Egg (DIABEGG) study—a 3-mo randomized controlled trial

BACKGROUND Previously published research that examined the effects of high egg consumption in people with type 2 diabetes (T2D) produced conflicting results leading to recommendations to limit egg intake. However, people with T2D may benefit from egg consumption because eggs are a nutritious and convenient way of improving protein and micronutrient contents of the diet, which have importance for satiety and weight management. OBJECTIVE In this randomized controlled study, we aimed to determine whether a high-egg diet (2 eggs/d for 6 d/wk) compared with a low-egg diet (<2 eggs/wk) affected circulating lipid profiles, in particular high-density lipoprotein (HDL) cholesterol, in overweight or obese people with prediabetes or T2D. DESIGN A total of 140 participants were randomly assigned to one of the 2 diets as part of a 3-mo weight maintenance study. Participants attended the clinic monthly and were instructed on the specific types of foods and quantities to be consumed. RESULTS There was no significant difference in the change in HDL cholesterol from screening to 3 mo between groups; the mean difference (95% CI) between high- and low-egg groups was +0.02 mmol/L (-0.03, 0.08 mmol/L; P = 0.38). No between-group differences were shown for total cholesterol, low-density lipoprotein cholesterol, triglycerides, or glycemic control. Both groups were matched for protein intake, but the high-egg group reported less hunger and greater satiety postbreakfast. Polyunsaturated fatty acid (PUFA) and monounsaturated fatty acid (MUFA) intakes significantly increased from baseline in both groups. CONCLUSIONS High egg consumption did not have an adverse effect on the lipid profile of people with T2D in the context of increased MUFA and PUFA consumption. This study suggests that a high-egg diet can be included safely as part of the dietary management of T2D, and it may provide greater satiety. This trial was registered at the Australia New Zealand Clinical Trials Registry (http://www.anzctr.org.au/) as ACTRN12612001266853.

Randomized Controlled Trial Investigating the Effects of a Low–Glycemic Index Diet on Pregnancy Outcomes in Women at High Risk of Gestational Diabetes Mellitus: The GI Baby 3 Study

OBJECTIVE Dietary interventions can improve pregnancy outcomes in women with gestational diabetes mellitus (GDM). We compared the effect of a low–glycemic index (GI) versus a conventional high-fiber (HF) diet on pregnancy outcomes, birth weight z score, and maternal metabolic profile in women at high risk of GDM. RESEARCH DESIGN AND METHODS One hundred thirty-nine women [mean (SD) age 34.7 (0.4) years and prepregnancy BMI 25.2 (0.5) kg/m2] were randomly assigned to a low-GI (LGI) diet (n = 72; target GI ∼50) or a high-fiber, moderate-GI (HF) diet (n = 67; target GI ∼60) at 14–20 weeks’ gestation. Diet was assessed by 3-day food records and infant body composition by air-displacement plethysmography, and pregnancy outcomes were assessed from medical records. RESULTS The LGI group achieved a lower GI than the HF group [mean (SD) 50 (5) vs. 58 (5); P < 0.001]. There were no differences in glycosylated hemoglobin, fructosamine, or lipids at 36 weeks or differences in birth weight [LGI 3.4 (0.4) kg vs. HF 3.4 (0.5) kg; P = 0.514], birth weight z score [LGI 0.31 (0.90) vs. HF 0.24 (1.07); P = 0.697], ponderal index [LGI 2.71 (0.22) vs. HF 2.69 (0.23) kg/m3; P = 0.672], birth weight centile [LGI 46.2 (25.4) vs. HF 41.8 (25.6); P = 0.330], % fat mass [LGI 10 (4) vs. HF 10 (4); P = 0.789], or incidence of GDM. CONCLUSIONS In intensively monitored women at risk for GDM, a low-GI diet and a healthy diet produce similar pregnancy outcomes.

Fat oxidation, body composition and insulin sensitivity in diabetic and normoglycaemic obese adults 5 years after weight loss

OBJECTIVE: To investigate whether normal glucose-tolerant and type II diabetic overweight adults differ in response to weight regain with regard to substrate oxidation and metabolic parameters.METHODS: A total of 15 overweight-obese subjects: seven normal glucose tolerant (NGT) and eight with type II diabetes (DM) were restudied 5 y after significant weight loss. Prediet, after 28 days calorie restriction and at 5 y, subjects were characterised for weight, height, waist-to-hip ratio (WHR) and body composition by dual-energy X-ray absorptiometry. Fasting glucose, insulin, leptin and lipid levels were measured and subjects underwent euglycaemic–hyperinsulinaemic clamp (insulin 0.25 U/kg/h for 150 min). Indirect calorimetry was performed resting and in the final 30 min of the clamp. Dietary assessment was by 4-day diet-diary.RESULTS: Both NGT and DM groups regained weight at 5 y and were not different to prediet. Total body fat (%) and WHR were higher at 5 y compared to prediet in both groups. Fasting glucose was increased in NGT subjects at 5 y, and fasting insulin was higher in both groups at 5 y compared to prediet. Insulin sensitivity (GIR) was similar at 5 y compared to prediet, but at 5 y DM subjects were more insulin resistant than NGT subjects. At 5 y, both DM and NGT groups had significantly reduced basal fat oxidation and no significant suppression of fat oxidation with insulin. Clamp respiratory quotient levels at 5 y were significantly higher in NGT compared to DM subjects.CONCLUSION: Reduced basal fat oxidation, and reduced variation in substrate oxidation in response to insulin develop with fat regain and fasting hyperinsulinaemia in both NGT and DM obese adults.

Egg Consumption and Human Cardio-Metabolic Health in People with and without Diabetes

The guidelines for dietary cholesterol and/or egg intake for both the general population and those at higher risk of cardiovascular disease (for example, people with type 2 diabetes mellitus (T2DM)) differ between countries, and even for different specialist societies in a country. The disparity between these guidelines is at least in part related to the conflicting evidence as to the effects of eggs in the general population and in those with T2DM. This review addresses the effect of eggs on cardiovascular disease (CVD) risk from both epidemiological research and controlled prospective studies, in people with and without cardio-metabolic disease. It also examines the nutritional qualities of eggs and whether they may offer protection against chronic disease. The evidence suggests that a diet including more eggs than is recommended (at least in some countries) may be used safely as part of a healthy diet in both the general population and for those at high risk of cardiovascular disease, those with established coronary heart disease, and those with T2DM. In conclusion, an approach focused on a person’s entire dietary intake as opposed to specific foods or nutrients should be the heart of population nutrition guidelines.

Effects of a low-glycemic index diet during pregnancy on offspring growth, body composition, and vascular health: a pilot randomized controlled trial

BACKGROUND Elevated maternal blood glucose concentrations may contribute to macrosomia, adiposity, and poorer vascular health in the offspring. OBJECTIVE The aim was to explore the effect of a low-glycemic index (low-GI) diet during pregnancy on offspring growth, adiposity, and arterial wall thickness during infancy. DESIGN This was a longitudinal follow-up study in a self-selected subgroup of mother-infant pairs (n= 59) participating in a larger randomized trial comparing the effects on perinatal outcomes of a low-GI diet and a conventional high-fiber (HF) diet during pregnancy. Infant anthropometric measurements were taken every month for 6 mo and then at 9 and 12 mo of age. Adiposity was assessed at birth and at 3 mo by air-displacement plethysmography by using the Pea Pod system (Cosmed) and at 6 and 12 mo by bioimpedance analysis (Bodystat). Aortic intima-media thickness was assessed at 12 mo by high-resolution ultrasound (Philips). RESULTS Maternal dietary GI was lower in the low-GI group than in the HF group (51 ± 1 compared with 57 ± 1;P< 0.001). No differences in neonatal outcomes were observed in the main trial. In the self-selected subsample, birth weight and length z scores were lower in the low-GI group than in the HF group (birth weight z score: 0.2 ± 0.2 compared with 0.7 ± 0.2, respectively;P= 0.04; birth length z score: 0.3 ± 0.2 compared with 0.9 ± 0.2, respectively;P= 0.04), but adiposity from birth to 12 mo of age and growth trajectories from 1 to 12 mo of age were similar. Aortic intima-media thickness was lower in the low-GI group than in the HF group (657 ±12 compared with 696 ± 12 μm, respectively;P= 0.02), which was partly mediated by differences in birth weight. CONCLUSION In women at risk of gestational diabetes mellitus, a low-GI diet influences offspring birth weight, birth length, and arterial wall thickness in early childhood, but not adiposity or growth trajectory during the first year of life. This trial was registered at anzctr.org.au as ACTRN12610000681055.