Jennifer B. Keogh

Long-term effects of a high-protein, low-carbohydrate diet on weight control and cardiovascular risk markers in obese hyperinsulinemic subjects.

OBJECTIVE: To compare the long-term compliance and effects of two low-fat diets differing in carbohydrate to protein ratio on body composition and biomarkers of cardiovascular disease risk in obese subjects with hyperinsulinemia.DESIGN: Outpatient, parallel, clinical intervention study of two groups of subjects randomly assigned to either a standard protein (SP; 15% protein, 55% carbohydrate) or high-protein (HP; 30% protein, 40% carbohydrate) diet, during 12 weeks of energy restriction (∼6.5 MJ/day) and 4 weeks of energy balance (∼8.3 MJ/day). Subsequently, subjects were asked to maintain the same dietary pattern for the succeeding 52 weeks with minimal professional support.SUBJECTS: A total of 58 obese, nondietetic subjects with hyperinsulinemia (13 males/45 females, mean age 50.2 y, mean body mass index (BMI) 34.0 kg/m2, mean fasting insulin 17.8 mU/l) participated in the study.MEASUREMENTS: Body composition, blood pressure, blood lipids, fasting glucose, insulin, CRP and sICAM-1 were measured at baseline and at weeks 16 and 68. Urinary urea/creatinine ratio was measured at baseline, week 16 and at 3 monthly intervals thereafter.RESULTS: In total, 43 subjects completed the study with similar dropouts in each group (P=0.76). At week 68, there was net weight loss (SP −2.9±3.6%, HP −4.1±5.8%; P<0.01) due entirely to fat loss (P<0.001) with no diet effect. Both diets significantly increased HDL cholesterol concentrations (P<0.001) and decreased fasting insulin, insulin resistance, sICAM-1 and CRP levels (P<0.05). Protein intake was significantly greater in HP during the initial 16 weeks (P<0.001), but decreased in HP and increased in SP during 52-week follow-up, with no difference between groups at week 68, indicating poor long-term dietary adherence behaviour to both dietary patterns.CONCLUSION: Without active ongoing dietary advice, adherence to dietary intervention is poor. Nonetheless, both dietary patterns achieved net weight loss and improvements in cardiovascular risk factors.

Long-term effects of a very-low-carbohydrate weight loss diet compared with an isocaloric low-fat diet after 12 mo

BACKGROUND Long-term weight loss and cardiometabolic effects of a very-low-carbohydrate, high-saturated-fat diet (LC) and a high-carbohydrate, low-fat diet (LF) have not been evaluated under isocaloric conditions. OBJECTIVE The objective was to compare an energy-controlled LC diet with an LF diet at 1 y. DESIGN Men and women (n = 118) with abdominal obesity and at least one additional metabolic syndrome risk factor were randomly assigned to either an energy-restricted (approximately 6-7 MJ) LC diet (4%, 35%, and 61% of energy as carbohydrate, protein, and fat, respectively) or an isocaloric LF diet (46%, 24%, and 30% of energy as carbohydrate, protein, and fat, respectively) for 1 y. Weight, body composition, and cardiometabolic risk markers were assessed. RESULTS Sixty-nine participants (59%) completed the trial: 33 in the LC group and 36 in the LF group. Both groups lost similar amounts of weight (LC: -14.5 +/- 1.7 kg; LF: -11.5 +/- 1.2 kg; P = 0.14, time x diet) and body fat (LC: -11.3 +/- 1.5 kg; LF: -9.4 +/- 1.2 kg; P = 0.30). Blood pressure, fasting glucose, insulin, insulin resistance, and C-reactive protein decreased independently of diet composition. Compared with the LF group, the LC group had greater decreases in triglycerides (-0.36 +/- 0.15 mmol/L; 95% CI: -0.67, -0.05 mmol/L; P = 0.011), increases in HDL cholesterol (0.23 +/- 0.09 mmol/L; 95% CI: 0.06, 0.40 mmol/L; P = 0.018) and LDL cholesterol (0.6 +/- 0.2 mmol/L; 95% CI: 0.2, 1.0 mmol/L; P = 0.001), and a greater but nonsignificant increase in apolipoprotein B (0.08 +/- 0.04 g/L; 95% CI: -0.004, 0.171 g/L; P = 0.17). CONCLUSIONS Under planned isoenergetic conditions, as expected, both dietary patterns resulted in similar weight loss and changes in body composition. The LC diet may offer clinical benefits to obese persons with insulin resistance. However, the increase in LDL cholesterol with the LC diet suggests that this measure should be monitored. This trial was registered with the Australian New Zealand Clinical Trials Registry at (http://www.anzctr.org.au) as ACTR 12606000203550.

Impact of gastric structuring on the lipolysis of emulsified lipids

Understanding and manipulating how emulsion structure impacts on fat digestion is an important step towards understanding the role of fat in our diet. This article reports on the nature of emulsion structuring within the digestive tract and how it affects the dynamics of fat digestion. Emulsions were designed a priori to have specific structuring behaviours (stable, coalesced, partially coalesced and fully broken) under gastrointestinal conditions, through careful emulsifier selection and control of solid fat composition. The impact these structures had on lipolysis was then assessed in vitro using a digestion model and in vivo by measuring the postprandial change in blood triglyceride concentration as a marker of fat absorption. The major factor controlling the rate of fat digestion in vitro was the droplet surface area available for lipase adsorption, which was governed by emulsion instability. The rate of fat absorption in vivo was only affected by large changes in the droplet surface area, and only if these changes remained until the droplets reached the small intestine. This was most evident in emulsions that had undergone extensive partial coalescence under gastric conditions. Partial coalescence resulted in a dramatic reduction in triglyceride absorption, in part because the network of fat crystals provided the agglomerates with an internal scaffold to resist re-dispersion as they passed through the pylorus. The differences in fat absorption profile achieved by controlling emulsion structural stability during digestion provide a basis for examining the physiological effects of food structure on lipid metabolism, which will be the subject of a follow-up clinical paper.

Flow-Mediated Dilatation Is Impaired by a High–Saturated Fat Diet but Not by a High-Carbohydrate Diet

Objective—It is unknown whether a low-fat diet, which may elevate triglycerides and lower high-density lipoprotein (HDL) cholesterol, harms the endothelium. Our aim was to determine whether a low-fat, high-carbohydrate (CARB) diet impaired endothelial vasodilation compared with high saturated fat (SFA), monounsaturated fat (MUFA), or polyunsaturated fat (PUFA) diets. Methods and Results—Forty healthy subjects were randomly crossed over to 4, 3-week isocaloric diets high in PUFA, MUFA, or SFA, containing at least 25 g of the relevant fat or a low-fat, CARB, high–glycemic load diet. Flow-mediated dilatation (FMD), fasting blood lipids, high sensitivity C-reactive protein, plasma intercellular, and vascular adhesion molecules plasma E- and P-selectin were measured after each intervention. SFA impaired FMD compared with all other diets (5.41±2.45% versus 10.80±3.69%; P=0.01). FMD did not change on CARB relative to MUFA or PUFA, despite 23% to 39% rises in triglyceride and 10% to 15% falls in HDL cholesterol. P-selectin was highest after SFA (121±52.7 ng/mL) versus MUFA (98±44.5 ng/mL; P=0.001) and PUFA (96±36.4 ng/mL; P=0.001). Conclusion—High SFA caused deterioration in FMD compared with high PUFA, MUFA, or CARB diets. Inflammatory responses may also be increased on this diet.

A High Protein Diet With Resistance Exercise Training Improves Weight Loss And Body Composition In Overweight And Obese Patients With Type 2 Diabetes

OBJECTIVE To evaluate the effects of two low-fat hypocaloric diets differing in the carbohydrate-to-protein ratio, with and without resistance exercise training (RT), on weight loss, body composition, and cardiovascular disease (CVD) risk outcomes in overweight/obese patients with type 2 diabetes. RESEARCH DESIGN AND METHODS A total of 83 men and women with type 2 diabetes (aged 56.1 ± 7.5 years, BMI 35.4 ± 4.6 kg/m2) were randomly assigned to an isocaloric, energy-restricted diet (female subjects 6 MJ/day, male subjects 7 MJ/day) of either standard carbohydrate (CON; carbohydrate:protein:fat 53:19:26) or high protein (HP; 43:33:22), with or without supervised RT (3 days/week) for 16 weeks. Body weight and composition, waist circumference (WC), and cardiometabolic risk markers were assessed. RESULTS Fifty-nine participants completed the study. There was a significant group effect (P ≤ 0.04) for body weight, fat mass, and WC with the greatest reductions occuring in HP+RT (weight [CON: −8.6 ± 4.6 kg, HP: −9.0 ± 4.8 kg, CON+RT: −10.5 ± 5.1 kg, HP+RT: −13.8 ± 6.0 kg], fat mass [CON: −6.4 ± 3.4 kg, HP: −6.7 ± 4.0 kg, CON+RT: −7.9 ± 3.7 kg, HP+RT: −11.1 ± 3.7 kg], and WC [CON: −8.2 ± 4.6 cm, HP: −8.9 ± 3.9 cm, CON+RT: −11.3 ± 4.6 cm, HP+RT: −13.7 ± 4.6 cm]). There was an overall reduction (P < 0.001) in fat-free mass (−2.0 ± 2.3 kg), blood pressure (−15/8 ± 10/6 mmHg), glucose (−2.1 ± 2.2 mmol/l), insulin (−4.7 ± 5.4 mU/l), A1C (−1.25 ± 0.94%), triglycerides (−0.47 ± 0.81 mmol/l), total cholesterol (−0.67 ± 0.69 mmol/l), and LDL cholesterol (−0.37 ± 0.53 mmol/l), with no difference between groups (P ≥ 0.17). CONCLUSIONS An energy-restricted HP diet combined with RT achieved greater weight loss and more favorable changes in body composition. All treatments had similar improvements in glycemic control and CVD risk markers.

Effects of a low-salt diet on flow-mediated dilatation in humans

BACKGROUND The effect of salt reduction on vascular function, assessed by brachial artery flow-mediated dilatation (FMD), is unknown. OBJECTIVE Our aim was to compare the effects of a low-salt (LS; 50 mmol Na/d) diet with those of a usual-salt (US; 150 mmol Na/d) diet on FMD. DESIGN This was a randomized crossover design in which 29 overweight and obese normotensive men and women followed an LS diet and a US diet for 2 wk. Both diets had similar potassium and saturated fat contents and were designed to ensure weight stability. After each intervention, FMD, pulse wave velocity, augmentation index, and blood pressure were measured. RESULTS FMD was significantly greater (P = 0.001) with the LS diet (4.89 +/- 2.42%) than with the US diet (3.37 +/- 2.10%), systolic blood pressure was significantly (P = 0.02) lower with the LS diet (112 +/- 11 mm Hg) than with the US diet (117 +/- 13 mm Hg), and 24-h sodium excretion was significantly lower (P = 0.0001) with the LS diet (64.1 +/- 41.3 mmol) than with the US diet (156.3 +/- 56.7 mmol). There was no correlation between change in FMD and change in 24-h sodium excretion or change in blood pressure. No significant changes in augmentation index or pulse wave velocity were observed. CONCLUSIONS Salt reduction improves endothelium-dependant vasodilation in normotensive subjects independently of the changes in measured resting clinic blood pressure. These findings suggest additional cardioprotective effects of salt reduction beyond blood pressure reduction. The trial is registered with the Australian and New Zealand Clinical Trials Registry (unique identifier: ANZCTR12607000381482; http://www.anzctr.org.au/trial_view.aspx?ID=82159).

Long-term effects of weight loss with a very low carbohydrate and low fat diet on vascular function in overweight and obese patients

Abstract.  Wycherley TP, Brinkworth GD, Keogh JB, Noakes M, Buckley JD, Clifton PM. (Commonwealth Scientific and Industrial Research Organization, Food and Nutritional Sciences; School of Molecular and Biomedical Science, University of Adelaide; and Nutritional Physiology Research Centre and Australian Technology Network Centre for Metabolic Fitness, Sansom Institute for Health Research, University of South Australia). Long‐term effects of weight loss with a very low carbohydrate and low fat diet on vascular function in overweight and obese patients. J Intern Med 2010; 267: 452–461.

Metabolic Effects of Weight Loss on a Very-Low-Carbohydrate Diet Compared With an Isocaloric High-Carbohydrate Diet in Abdominally Obese Subjects

OBJECTIVES This study was designed to compare the effects of an energy-reduced, isocaloric very-low-carbohydrate, high-fat (VLCHF) diet and a high-carbohydrate, low-fat (HCLF) diet on weight loss and cardiovascular disease (CVD) risk outcomes. BACKGROUND Despite the popularity of the VLCHF diet, no studies have compared the chronic effects of weight loss and metabolic change to a conventional HCLF diet under isocaloric conditions. METHODS A total of 88 abdominally obese adults were randomly assigned to either an energy-restricted (approximately 6 to 7 MJ, 30% deficit), planned isocaloric VLCHF or HCLF diet for 24 weeks in an outpatient clinical trial. Body weight, blood pressure, fasting glucose, lipids, insulin, apolipoprotein B (apoB), and C-reactive protein (CRP) were measured at weeks 0 and 24. RESULTS Weight loss was similar in both groups (VLCHF -11.9 +/- 6.3 kg, HCLF -10.1 +/- 5.7 kg; p = 0.17). Blood pressure, CRP, fasting glucose, and insulin reduced similarly with weight loss in both diets. The VLCHF diet produced greater decreases in triacylglycerols (VLCHF -0.64 +/- 0.62 mmol/l, HCLF -0.35 +/- 0.49 mmol/l; p = 0.01) and increases in high-density lipoprotein cholesterol (HDL-C) (VLCHF 0.25 +/- 0.28 mmol/l, HCLF 0.08 +/- 0.17 mmol/l; p = 0.002). Low-density lipoprotein cholesterol (LDL-C) decreased in the HCLF diet but remained unchanged in the VLCHF diet (VLCHF 0.06 +/- 0.58 mmol/l, HCLF -0.46 +/- 0.71 mmol/l; p < 0.001). However, a high degree of individual variability for the LDL response in the VLCHF diet was observed, with 24% of individuals reporting an increase of at least 10%. The apoB levels remained unchanged in both diet groups. CONCLUSIONS Under isocaloric conditions, VLCHF and HCLF diets result in similar weight loss. Overall, although both diets had similar improvements for a number of metabolic risk markers, an HCLF diet had more favorable effects on the blood lipid profile. This suggests that the potential long-term effects of the VLCHF diet for CVD risk remain a concern and that blood lipid levels should be monitored. (Long-term health effects of high and low carbohydrate, weight loss diets in obese subjects with the metabolic syndrome; http://www.anzctr.org.au; ACTR No. 12606000203550).

Comparison of isocaloric very low carbohydrate/high saturated fat and high carbohydrate/low saturated fat diets on body composition and cardiovascular risk

BackgroundIt is speculated that high saturated fat very low carbohydrate diets (VLCARB) have adverse effects on cardiovascular risk but evidence for this in controlled studies is lacking. The objective of this study was to compare, under isocaloric conditions, the effects of a VLCARB to 2 low saturated fat high carbohydrate diets on body composition and cardiovascular risk.MethodsEighty three subjects, 48 ± 8 y, total cholesterol 5.9 ± 1.0 mmol/L, BMI 33 ± 3 kg/m2 were randomly allocated to one of 3 isocaloric weight loss diets (6 MJ) for 8 weeks and on the same diets in energy balance for 4 weeks: Very Low Fat (VLF) (CHO:Fat:Protein; %SF = 70:10:20; 3%), High Unsaturated Fat (HUF) = (50:30:20; 6%), VLCARB (4:61:35; 20%)ResultsPercent fat mass loss was not different between diets VLCARB -4.5 ± 0.5, VLF-4.0 ± 0.5, HUF -4.4 ± 0.6 kg). Lean mass loss was 32-31% on VLCARB and VLF compared to HUF (21%) (P < 0.05). LDL-C increased significantly only on VLCARB by 7% (p < 0.001 compared with the other diets) but apoB was unchanged on this diet and HDL-C increased relative to the other 2 diets. Triacylglycerol was lowered by 0.73 ± 0.12 mmol/L on VLCARB compared to -0.15 ± 0.07 mmol/L on HUF and -0.06 ± 0.13 mmol/L on VLF (P < 0.001). Plasma homocysteine increased 6.6% only on VLCARB (P = 0.026). VLCARB lowered fasting insulin 33% compared to a 19% fall on HUF and no change on VLF (P < 0.001). The VLCARB meal also provoked significantly lower post prandial glucose and insulin responses than the VLF and HUF meals. All diets decreased fasting glucose, blood pressure and CRP (P < 0.05).ConclusionIsocaloric VLCARB results in similar fat loss than diets low in saturated fat, but are more effective in improving triacylglycerols, HDL-C, fasting and post prandial glucose and insulin concentrations. VLCARB may be useful in the short-term management of subjects with insulin resistance and hypertriacylglycerolemia.

Polyphenols and Glycemic Control

Growing evidence from animal studies supports the anti-diabetic properties of some dietary polyphenols, suggesting that dietary polyphenols could be one dietary therapy for the prevention and management of Type 2 diabetes. This review aims to address the potential mechanisms of action of dietary polyphenols in the regulation of glucose homeostasis and insulin sensitivity based on in vitro and in vivo studies, and to provide a comprehensive overview of the anti-diabetic effects of commonly consumed dietary polyphenols including polyphenol-rich mixed diets, tea and coffee, chocolate and cocoa, cinnamon, grape, pomegranate, red wine, berries and olive oil, with a focus on human clinical trials. Dietary polyphenols may inhibit α-amylase and α-glucosidase, inhibit glucose absorption in the intestine by sodium-dependent glucose transporter 1 (SGLT1), stimulate insulin secretion and reduce hepatic glucose output. Polyphenols may also enhance insulin-dependent glucose uptake, activate 5′ adenosine monophosphate-activated protein kinase (AMPK), modify the microbiome and have anti-inflammatory effects. However, human epidemiological and intervention studies have shown inconsistent results. Further intervention studies are essential to clarify the conflicting findings and confirm or refute the anti-diabetic effects of dietary polyphenols.