Linda C Tapsell

Substituting dietary saturated for monounsaturated fat impairs insulin sensitivity in healthy men and women: The KANWU study

Aims/hypothesis. The amount and quality of fat in the diet could be of importance for development of insulin resistance and related metabolic disorders. Our aim was to determine whether a change in dietary fat quality alone could alter insulin action in humans. Methods. The KANWU study included 162 healthy subjects chosen at random to receive a controlled, isoenergetic diet for 3 months containing either a high proportion of saturated (SAFA diet) or monounsaturated (MUFA diet) fatty acids. Within each group there was a second assignment at random to supplements with fish oil (3.6 g n-3 fatty acids/d) or placebo. Results. Insulin sensitivity was significantly impaired on the saturated fatty acid diet (-10 %, p = 0.03) but did not change on the monounsaturated fatty acid diet ( + 2 %, NS) (p = 0.05 for difference between diets). Insulin secretion was not affected. The addition of n-3 fatty acids influenced neither insulin sensitivity nor insulin secretion. The favourable effects of substituting a monounsaturated fatty acid diet for a saturated fatty acid diet on insulin sensitivity were only seen at a total fat intake below median (37E %). Here, insulin sensitivity was 12.5 % lower and 8.8 % higher on the saturated fatty acid diet and monounsaturated fatty acid diet respectively (p = 0.03). Low density lipoprotein cholesterol (LDL) increased on the saturated fatty acid diet ( + 4.1 %, p < 0.01) but decreased on the monounsaturated fatty acid diet (MUFA) (–5.2, p < 0.001), whereas lipoprotein (a) [Lp(a)] increased on a monounsaturated fatty acid diet by 12 % (p < 0.001). Conclusions/interpretation. A change of the proportions of dietary fatty acids, decreasing saturated fatty acid and increasing monounsaturated fatty acid, improves insulin sensitivity but has no effect on insulin secretion. A beneficial impact of the fat quality on insulin sensitivity is not seen in individuals with a high fat intake ( > 37E %). [Diabetologia (2001) 44: 312–319]

Oat β-glucan increases postprandial cholecystokinin levels, decreases insulin response and extends subjective satiety in overweight subjects

This study recorded acute biochemical and subjective measures of satiety, followed by energy intake from a subsequent meal, after varying doses of beta-glucan in extruded breakfast cereals. Molecular weight, solubility and viscosity of beta-glucan products were determined. Seven male and seven female subjects (BMI 25-36 kg/m) consumed five breakfasts (different doses of beta-glucan sourced from two different technological processes) and dietary intake was measured after four hours. Blood was collected to measure glucose, insulin, ghrelin and cholecystokinin, and visual analogue scales measured subjective satiety. Molecular weight, solubility and viscosity indicated products were likely to increase luminal viscosity. beta-Glucan was found to decrease insulin secretion over 2 h (RMANOVA, p = 0.011) in a dose responsive manner from 2.16 to 5.68 g per serving (p = 0.007). Cholecystokinin levels increased linearly over the same range of beta-glucan concentrations (p = 0.002) in women. Subjective satiety was increased at a beta-glucan dose of 2.2 g (p = 0.039). Subsequent meal intake decreased by greater than 400 kJ with higher beta-glucan dose (>5 g). beta-Glucan improves satiety and release of cholecystokinin is likely to be part of the mechanism. Products with different sources of beta-glucan provide similar benefits but each product requires individual testing.

Long-term effects of increased dietary polyunsaturated fat from walnuts on metabolic parameters in type II diabetes.

Background/Objectives:Most dietary interventions have metabolic effects in the short term, but long-term effects may require dietary fat changes to influence body composition and insulin action. This study assessed the effect of sustained high polyunsaturated fatty acids (PUFA) intake through walnut consumption on metabolic outcomes in type II diabetes.Subjects/Methods:Fifty overweight adults with non-insulin-treated diabetes (mean age 54±8.7 years) were randomized to receive low-fat dietary advice ±30 g per day walnuts targeting weight maintenance (around 2000 kcal, 30% fat) for 1 year. Differences between groups were assessed by changes in anthropometric values (body weight, body fat, visceral adipose tissue) and clinical indicators of diabetes over treatment time using the general linear model.Results:The walnut group consumed significantly more PUFA than the control (P=0.035), an outcome attributed to walnut consumption (contributing 67% dietary PUFA at 12 months). Most of the effects were seen in the first 3 months. Despite being on weight maintenance diets, both groups sustained a 1–2 kg weight loss, with no difference between groups (P=0.680). Both groups showed improvements in all clinical parameters with significant time effects (P<0.004), bar triacylglycerol levels, but these were just above normal to begin with. The walnut group produced significantly greater reductions in fasting insulin levels (P=0.046), an effect seen largely in the first 3 months.Conclusions:Dietary fat can be manipulated with whole foods such as walnuts, producing reductions in fasting insulin levels. Long-term effects are also apparent but subject to fluctuations in dietary intake if not of the disease process.

Impact of foods enriched with n-3 long-chain polyunsaturated fatty acids on erythrocyte n-3 levels and cardiovascular risk factors

Consumption of fish or fish oils rich in the n-3 long chain PUFA EPA and DHA may improve multiple risk factors for CVD. The objective of this study was to determine whether regular consumption of foods enriched with n-3 long-chain PUFA can improve n-3 long-chain PUFA status (erythrocytes) and cardiovascular health. Overweight volunteers with high levels of triacylglycerols (TG; >1.6 mmol/l) were enrolled in a 6-month dietary intervention trial conducted in Adelaide (n 47) and Perth (n 39), and randomised to consume control foods or n-3-enriched foods to achieve an EPA + DHA intake of 1 g/d. Test foods were substituted for equivalent foods in their regular diet. Erythrocyte fatty acids, plasma TG and other CVD risk factors were monitored at 0, 3 and 6 months. There were no significant differences between groups for blood pressure, arterial compliance, glucose, insulin, lipids, C-reactive protein (CRP) or urinary 11-dehydro-thromboxane B2 (TXB2) over 6 months, even though regular consumption of n-3-enriched foods increased EPA + DHA intake from 0.2 to 1.0 g/d. However, the n-3 long-chain PUFA content of erythrocytes increased by 35 and 53 % at 3 and 6 months, respectively, in subjects consuming the n-3-enriched foods. These increases were positively associated with measures of arterial compliance and negatively associated with serum CRP and urinary 11-dehydro-TXB2 excretion. Sustainable increases in dietary intakes and erythrocyte levels of n-3 long-chain PUFA can be achieved through regular consumption of suitably enriched processed foods. Such increases may be associated with reduced CV risk.

Nuts and Berries for Heart Health

Nuts are nutrient-dense foods with complex matrices rich in unsaturated fatty acids and other bioactive compounds, such as L-arginine, fiber, minerals, tocopherols, phytosterols, and polyphenols. By virtue of their unique composition, nuts are likely to beneficially impact heart health. Epidemiologic studies have associated nut consumption with a reduced incidence of coronary heart disease in both genders and diabetes in women. Limited evidence also suggests beneficial effects on hypertension and inflammation. Interventional studies consistently show that nut intake has a cholesterol-lowering effect and there is emerging evidence of beneficial effects on oxidative stress, inflammation, and vascular reactivity. Blood pressure, visceral adiposity, and glycemic control also appear to be positively influenced by frequent nut consumption without evidence of undue weight gain. Berries are another plant food rich in bioactive phytochemicals, particularly flavonoids, for which there is increasing evidence of benefits on cardiometabolic risk that are linked to their potent antioxidant power.

Low plasma vitamin E levels in major depression: diet or disease?

Objective: Levels of vitamin E have been reported to be lower in patients suffering major depression, but whether this is due to inadequate dietary intake or the pathophysiology of depression is not known, and was the subject of the present study.Setting: Wollongong, Australia.Methods: Plasma vitamin E (α-tocopherol) was measured in 49 adults with major depression, age (mean±s.d.): 47±12 y. In a subset (n=19) usual dietary intake of vitamin E was determined by diet history.Results: Subjects had significantly lower plasma α-tocopherol (4.71±0.13 μmol/mmol cholesterol) than has previously been reported for healthy Australians, and plasma α-tocopherol was inversely related to depression score (by Beck Depression Inventory) (r=−0.367, P<0.009). Diet analysis indicated that 89% of subjects met or exceeded the recommended intake for vitamin E, and dietary intake was not related to plasma α-tocopherol level in this subset.Conclusion: These findings suggest that plasma levels of α-tocopherol are lower in depression, but this is not likely to be the result of inability to meet recommended dietary intake.Sponsorship: This study was supported in part by the Clover Corporation and the Australian Research Council.

The recurrence of gestational diabetes: Could dietary differences in fat intake be an explanation?

OBJECTIVE To present the results of a comprehensive dietary review of a group of women with a recurrence of gestational diabetes mellitus (GDM), compared with a group of women with no recurrence of GDM during a subsequent pregnancy. RESEARCH DESIGN AND METHODS The dietary intake of 14 women with a recurrence of GDM was compared with 21 women with no recurrence of GDM. Women with GDM in one pregnancy have a recurrence rate of only 30–50%. While the reasons for this have not been determined, dietary factors have been considered probable. RESULTS The women with a recurrence of GDM consumed 38.4 (by diet history) and 41.4% (by food record) of their total energy intake as fats, compared with 34.1 (P <0.01) and 33.1% (P <0.001), respectively, for women with no recurrence. The percentage intake of polyunsaturated, monounsaturated, and saturated fatty acids was similar in both groups. There was a proportionate reduction in carbohydrate intake as a percentage of total energy and in fiber intake in grams for the women with a recurrence of GDM. CONCLUSIONS When the relationship between saturated fat intake and insulin resistance is considered, the possibility exists that dietary modification of fat intake before and during pregnancy may reduce the recurrence rate of GDM.

Limited Lipid-lowering effects of regular consumption of whole soybean foods

Aim: To examine cardiovascular health benefits of foods containing a whole soybean extract. Methods: The study design was a randomized, placebo-controlled crossover trial of consuming soy-based milk and yoghurt (treatment) or equivalent dairy products (control) for 5 weeks each. Twenty-six mildly hypercholesterolaemic and/or hypertensive volunteers were recruited from the community as study volunteers, of which 23 completed. Main outcome measures included clinic and ambulatory blood pressure, arterial compliance, lipids, fatty acids and isoflavones in fasted blood and 24-hour urinary isoflavone excretion. Nutrient intakes were assessed initially and after each 5-week period. Multiple regression analyses were used to determine predictor variables in statistical models; order effects were tested by repeated measures ANOVA. Changes in Lp(a) were determined by Wilcoxon signed ranks tests; other differences between treatment and control were assessed by t tests. Results: Plasma and urinary isoflavones were markedly increased by whole soy supplementation but there were no overall differences in plasma lipids, blood pressure or arterial compliance between the soy and dairy diets. However, in 8 equol-positive subjects (equol detected in either plasma or urine), retrospective analysis revealed significant reductions in total cholesterol (8.5%), LDL cholesterol (10%), LDL:HDL ratio (13.5%), plasma triglycerides (21%) and lipoprotein(a) (11%) with the soy diet. These reductions were independent of changes in polyunsaturated fat and other macronutrient intakes. Conclusions: Regular consumption of whole soybean milk and yogurt products had no effect on plasma lipids, blood pressure or arterial compliance in at-risk subjects, despite substantially increasing isoflavone levels in blood and urine. Retrospective analysis suggests that improvement of plasma lipids may have been limited to equol-positive subjects.

Dietary Patterns and Blood Pressure in Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Hypertension is a major risk factor for developing cardiovascular disease, stroke, and kidney disease. To lower blood pressure (BP), several lifestyle changes are recommended such as weight loss, exercise, and following a healthy diet. Investigating the effect of single nutrients may have positive results, but food is consumed as part of a whole diet, resulting in nutrient interactions. The aim of this systematic review and meta-analysis was to assess the effect of dietary patterns on BP in adults. Studies that were published between January 1999 and June 2014 were retrieved using Scopus, Web of Science, and the MEDLINE database. Seventeen randomized controlled trials were included in the meta-analysis. The results suggest that healthy dietary patterns such as the Dietary Approaches to Stop Hypertension diet, Nordic diet, and Mediterranean diet significantly lowered systolic BP and diastolic BP by 4.26 mm Hg and 2.38 mm Hg, respectively. These diets are rich in fruit, vegetables, whole grains, legumes, seeds, nuts, fish, and dairy and low in meat, sweets, and alcohol. Lifestyle factors such as exercise and weight loss in combination with dietary changes may also reduce BP. Further research is needed to establish the effect of dietary patterns on BP in different cultures other than those identified in this review. The review was registered on PROSPERO (International prospective register of systematic reviews) as CRD42015016272.

Relative validity of a diet history interview in an intervention trial manipulating dietary fat in the management of Type II diabetes mellitus

BACKGROUND This study assesses the relative validity of a diet history interview in 56 free-living individuals with Type II diabetes mellitus. METHODS The diet history interview was compared to a 3-day food record in a 1-year dietary intervention trial. The plausibility of energy intake data was examined throughout the trial. Paired data were compared for differences and the presence of systematic error was determined by Bland Altman analysis. Changes in accuracy and responsiveness were assessed over time. RESULTS The proportion of underreporters was larger in the diet history at baseline. Underrecording with the food record was more common in subjects with BMIs > 30 kg/m(2). There was no difference between paired dietary data from the two methods; however, data on fatty acids failed to correlate. These correlations improved when outliers were removed. There was no evidence of a relationship between bias and mean intake of dietary variables. Accuracy of diet history measurement did not change during the trial for energy or macronutrients, but data on protein and monounsaturated fat were both affected by BMI. The diet history was more responsive than the food record to changes in monounsaturated fatty acid intake after 3 months, but this changed at the end of the trial. CONCLUSION The diet history provided good estimates of energy and macronutrient intakes in a sample group with Type II diabetes mellitus. However, energy intake data revealed a high prevalence of underreporting especially in people with higher BMIs.