Comparison of a carbohydrate-rich diet and diets rich in stearic or palmitic acid in NIDDM patients. Effects on lipids, glycemic control, and diurnal blood pressure

Dietary stearic acid and palmitic acid do not differently affect ABCA1-mediated cholesterol efflux capacity in healthy men and postmenopausal women: A randomized controlled trial

BACKGROUND

The saturated fatty acid stearic acid (C18:0) lowers HDL cholesterol compared with palmitic acid (C16:0). However, the ability of HDL particles to promote cholesterol efflux from macrophages (cholesterol efflux capacity; CEC) may better predict coronary heart disease (CHD) risk than HDL cholesterol concentrations.

OBJECTIVE

We examined effects of exchanging dietary palmitic acid for stearic acid on ATP-binding cassette transporter A1 (ABCA1)-mediated CEC, and other conventional and emerging cardiometabolic risk makers.

DESIGN

In a double-blind, randomized, crossover study with two 4-week isocaloric intervention periods, 34 healthy men and postmenopausal women (61.5 ± 5.7 years, BMI: 25.4 ± 2.5 kg/m²) followed diets rich in palmitic acids or stearic acids. Difference in intakes was 6% of daily energy. ABCA1-mediated CEC was measured from J774 macrophages to apolipoprotein (apo)B-depleted serum.

RESULTS

Compared with the palmitic-acid diet, the stearic-acid diet lowered serum LDL cholesterol (-0.14 mmol/L; p = 0.010), HDL cholesterol (-0.09 mmol/L; p=<0.001), and apoA1 (-0.05 g/L; p < 0.001). ABCA1-mediated CEC did not differ between diets (p = 0.280). Cholesteryl ester transfer protein (CETP) mass was higher on stearic acid (0.11 mg/L; p = 0.003), but CETP activity was comparable. ApoB100 did not differ, but triacylglycerol concentrations tended to be higher on stearic acid (p = 0.100). Glucose concentrations were comparable. Effects on insulin and C-peptide were sex-dependent. In women, the stearic-acid diet increased insulin concentrations (1.57 μU/mL; p = 0.002), while in men, C-peptide concentrations were lower (-0.15 ng/mL; p = 0.037). Interleukin 6 (0.15 pg/mL; p = 0.039) and tumor necrosis factor alpha (0.18 pg/mL; p = 0.005), but not high-sensitivity C-reactive protein, were higher on stearic acid. Soluble intracellular adhesion molecule (9 ng/mL; p = 0.033), but not soluble vascular cell adhesion molecule and endothelial-selectin concentrations decreased after stearic-acid consumption.

CONCLUSIONS

As expected, stearic-acid intake lowered LDL cholesterol, HDL cholesterol, and apoA1. Insulin sensitivity in women and low-grade inflammation might be unfavorably affected by stearic-acid intake. However, palmitic-acid and stearic-acid intakes did not differently affect ABCA1-mediated CEC.

CLINICAL TRIAL REGISTRY

This trial was registered at clinicaltrials.gov as NCT02835651.

Association Between Nutrient Patterns and Hypertension Among Adults in the United States: A Population-Based Survey

INTRODUCTION

Hypertension (HTN) is a common medical condition associated with many adverse health outcomes. Diet plays a crucial role in the pathology, prevention, and management of HTN.

AIM

To identify nutrient patterns (NPs) and to investigate their association with the risk of HTN among adults in the United States (US).

METHODS

This cross-sectional study used data from the US community-based National Health and Nutrition Examination Survey (NHANES). Participants with data on dietary intake and blood pressure were analyzed. NPs were determined by principal components analysis (PCA). In all the analyses (analysis of covariance and multivariate logistic regression), we accounted for the survey design and sample weights.

RESULTS

Overall, 22,184 (4002 hypertensive and 18,182 normotensive) individuals were included. We identified three NPs which explained 50.8% of the variance of the dietary nutrient consumption. There was a graded decrease in the odds of association with HTN by quartiles of mono-unsaturated fatty acids (MUFA) dietary pattern where the 4th quartile was associated with a 28% (odds ratio [OR] 0.72, 95% confidence interval [CI] 0.63-0.82; p < 0.001) lower odds of HTN compared with the first quartile. The second NP "high in micronutrients and vitamins" presented a decreasing trend in the odds of association with HTN with the 4th quartile having a 20% [OR 0.80, 95% CI 0.63-0.97; p < 0.001] lower odds of HTN compared with the 1st quartile.

CONCLUSION

Our findings provide further evidence on the inverse association between a high intake of minerals, vitamins, and MUFA and the risk of HTN. Further observational studies and clinical trials are needed to better understand the influence of MUFA, vitamins, and mineral consumption on HTN.

Fatty acid regio-specificity of triacylglycerol molecules may affect plasma lipid responses to dietary fats-a randomised controlled cross-over trial

BACKGROUND/OBJECTIVES

Hypercholesterolaemic effects of saturated fatty acids (SFA) may be influenced not only by the chain length, but also by their specific location within the triacylglycerol (TAG) molecule. We examined the hypothesis that dietary fats rich in SFA, but containing mostly unsaturated fatty acids in the sn-2 position with most SFA in sn-1 and -3 (palm olein [PO] and cocoa butter [CB]) will have similar serum lipid outcomes to unsaturated olive oil (OO).

SUBJECTS/METHODS

Thirty-eight participants (20-40 yr, 18.5- ≤ 27.5 kg/m2) completed a 4-week randomised 3 × 3 crossover feeding intervention, preceded by 2-week run-in and separated by 2-week washout periods. Background diet contained 35 percentage of total energy (%E) fat, 18%E protein, 48%E carbohydrates, differing in test fats only (palm olein (PO), CB, OO; 20%E). Total cholesterol (TC)/high density lipoprotein cholesterol (HDL-C) ratio and related variables; TC, HDL-C, low density lipoprotein cholesterol (LDL-C), TAG, apoA1, ApoB, ApoA1 (apolipoprotein A1)/ApoB (apolipoprotein B), lipoprotein (a) (Lp(a)), NEFA, LDL sub-fractions, were assessed pre- and post-intervention. Data were analysed using mixed effects longitudinal models with a P-value < 0.05 considered significant.

RESULTS

Changes in plasma fatty acids (P < 0.05) confirmed compliance; C18:1 increased with OO compared to PO and CB; C16:0 decreased with OO and C18:0 increased following CB. No differences were seen for TC/HDL-C (mean [95%CI] change for PO, 0.08[0.00, 0.15] mmol/L; CB, 0.06 [-0.05, 0.16] mmol/L; and OO, -0.01 [-0.15, 0.13] mmol/L; P = 0.53] or any other parameter including LDL sub-fractions. OO decreased IDL-A compared to PO (-2.2 [-4.31, -0.21] mg/dL, P = 0.03).

CONCLUSION

In healthy young participants, plasma lipid responses to PO and CB, enriched in SFA but having primarily unsaturated fatty acid in the sn-2 position of TAG, did not differ from OO.

Comparison of diets enriched in stearic, oleic, and palmitic acids on inflammation, immune response, cardiometabolic risk factors, and fecal bile acid concentrations in mildly hypercholesterolemic postmenopausal women-randomized crossover trial

BACKGROUND

Direct comparisons between SFAs varying in chain length, specifically palmitic acid (16:0) and stearic acid (18:0), relative to the latter's metabolic product, oleic acid (18:1), on cardiometabolic risk factors are limited.

OBJECTIVE

The aim of this study was to determine the relative comparability of diets enriched in palmitic acid, stearic acid, and oleic acid on inflammation and coagulation markers, T lymphocyte proliferation/ex-vivo cytokine secretion, plasma cardiometabolic risk factors, and fecal bile acid concentrations.

METHODS

Hypercholesterolemic postmenopausal women (n = 20, mean ± SD age 64 ± 7 y, BMI 26.4 ± 3.4 kg/m2, LDL cholesterol ≥ 2.8 mmol/L) were provided with each of 3 diets [55% energy (%E) carbohydrate, 15%E protein, 30%E fat, with ∼50% fat contributed by palmitic acid, stearic acid, or oleic acid in each diet; 5 wk/diet phase] using a randomized crossover design with 2-wk washouts between phases. Outcome measures were assessed at the end of each phase.

RESULTS

Fasting LDL-cholesterol and non-HDL-cholesterol concentrations were lower after the stearic acid and oleic acid diets than the palmitic acid diet (all P < 0.01). Fasting HDL-cholesterol concentrations were lower after the stearic acid diet than the palmitic acid and oleic acid diets (P < 0.01). The stearic acid diet resulted in lower lithocholic acid (P = 0.01) and total secondary bile acid (SBA) concentrations (P = 0.04) than the oleic acid diet. All other outcome measures were similar between diets. Lithocholic acid concentrations were positively correlated with fasting LDL-cholesterol concentrations (r = 0.33; P = 0.011). Total SBA, lithocholic acid, and deoxycholic acid concentrations were negatively correlated with fasting HDL cholesterol (r = -0.51 to -0.44; P < 0.01) concentrations and positively correlated with LDL cholesterol:HDL cholesterol (r = 0.37-0.54; P < 0.01) ratios.

CONCLUSIONS

Dietary stearic acid and oleic acid had similar effects on fasting LDL-cholesterol and non-HDL-cholesterol concentrations and more favorable ones than palmitic acid. Unlike oleic acid, the hypocholesterolemic effect of stearic acid may be mediated by inhibition of intestinal hydrophobic SBA synthesis. These findings add to the data suggesting there should be a reassessment of current SFA dietary guidance and Nutrient Facts panel labeling.This trial was registered at clinicaltrials.gov as NCT02145936.

Palm oil and blood lipid-related markers of cardiovascular disease: a systematic review and meta-analysis of dietary intervention trials

BACKGROUND

Palm oil (PO) may be an unhealthy fat because of its high saturated fatty acid content.

OBJECTIVE

The objective was to assess the effect of substituting PO for other primary dietary fats on blood lipid-related markers of coronary heart disease (CHD) and cardiovascular disease (CVD).

DESIGN

We performed a systematic review and meta-analysis of dietary intervention trials. Studies were eligible if they included original data comparing PO-rich diets with other fat-rich diets and analyzed at least one of the following CHD/CVD biomarkers: total cholesterol (TC), low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, TC/HDL cholesterol, LDL cholesterol/HDL cholesterol, triacylglycerols, apolipoprotein A-I and B, very-low-density lipoprotein cholesterol, and lipoprotein(a).

RESULTS

Fifty-one studies were included. Intervention times ranged from 2 to 16 wk, and different fat substitutions ranged from 4% to 43%. Comparison of PO diets with diets rich in stearic acid, monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs) showed significantly higher TC, LDL cholesterol, apolipoprotein B, HDL cholesterol, and apolipoprotein A-I, whereas most of the same biomarkers were significantly lower when compared with diets rich in myristic/lauric acid. Comparison of PO-rich diets with diets rich in trans fatty acids showed significantly higher concentrations of HDL cholesterol and apolipoprotein A-I and significantly lower apolipoprotein B, triacylglycerols, and TC/HDL cholesterol. Stratified and meta-regression analyses showed that the higher concentrations of TC and LDL cholesterol, when PO was substituted for MUFAs and PUFAs, were not significant in young people and in subjects with diets with a lower percentage of energy from fat.

CONCLUSIONS

Both favorable and unfavorable changes in CHD/CVD risk markers occurred when PO was substituted for the primary dietary fats, whereas only favorable changes occurred when PO was substituted for trans fatty acids. Additional studies are needed to provide guidance for policymaking.

The evidence for medical nutrition therapy for type 1 and type 2 diabetes in adults

This article reviews the evidence and nutrition practice recommendations from the American Dietetic Association's nutrition practice guidelines for type 1 and type 2 diabetes in adults. The research literature was reviewed to answer nutrition practice questions and resulted in 29 recommendations. Here, we present the recommendations and provide a comprehensive and systematic review of the evidence associated with their development. Major nutrition therapy factors reviewed are carbohydrate (intake, sucrose, non-nutritive sweeteners, glycemic index, and fiber), protein intake, cardiovascular disease, and weight management. Contributing factors to nutrition therapy reviewed are physical activity and glucose monitoring. Based on individualized nutrition therapy client/patient goals and lifestyle changes the client/patient is willing and able to make, registered dietitians can select appropriate interventions based on key recommendations that include consistency in day-to-day carbohydrate intake, adjusting insulin doses to match carbohydrate intake, substitution of sucrose-containing foods, usual protein intake, cardioprotective nutrition interventions, weight management strategies, regular physical activity, and use of self-monitored blood glucose data. The evidence is strong that medical nutrition therapy provided by registered dietitians is an effective and essential therapy in the management of diabetes.

Saturated fat and cardiometabolic risk factors, coronary heart disease, stroke, and diabetes: a fresh look at the evidence

Dietary and policy recommendations frequently focus on reducing saturated fatty acid consumption for improving cardiometabolic health, based largely on ecologic and animal studies. Recent advances in nutritional science now allow assessment of critical questions about health effects of saturated fatty acids (SFA). We reviewed the evidence from randomized controlled trials (RCTs) of lipid and non-lipid risk factors, prospective cohort studies of disease endpoints, and RCTs of disease endpoints for cardiometabolic effects of SFA consumption in humans, including whether effects vary depending on specific SFA chain-length; on the replacement nutrient; or on disease outcomes evaluated. Compared with carbohydrate, the TC:HDL-C ratio is nonsignificantly affected by consumption of myristic or palmitic acid, is nonsignificantly decreased by stearic acid, and is significantly decreased by lauric acid. However, insufficient evidence exists for different chain-length-specific effects on other risk pathways or, more importantly, disease endpoints. Based on consistent evidence from human studies, replacing SFA with polyunsaturated fat modestly lowers coronary heart disease risk, with ~10% risk reduction for a 5% energy substitution; whereas replacing SFA with carbohydrate has no benefit and replacing SFA with monounsaturated fat has uncertain effects. Evidence for the effects of SFA consumption on vascular function, insulin resistance, diabetes, and stroke is mixed, with many studies showing no clear effects, highlighting a need for further investigation of these endpoints. Public health emphasis on reducing SFA consumption without considering the replacement nutrient or, more importantly, the many other food-based risk factors for cardiometabolic disease is unlikely to produce substantial intended benefits.

Dietary fat modifications and blood pressure in subjects with the metabolic syndrome in the LIPGENE dietary intervention study

Hypertension is a key feature of the metabolic syndrome. Lifestyle and dietary changes may affect blood pressure (BP), but the knowledge of the effects of dietary fat modification in subjects with the metabolic syndrome is limited. The objective of the present study was to investigate the effect of an isoenergetic change in the quantity and quality of dietary fat on BP in subjects with the metabolic syndrome. In a 12-week European multi-centre, parallel, randomised controlled dietary intervention trial (LIPGENE), 486 subjects were assigned to one of the four diets distinct in fat quantity and quality: two high-fat diets rich in saturated fat or monounsaturated fat and two low-fat, high-complex carbohydrate diets with or without 1·2 g/d of very long-chain n-3 PUFA supplementation. There were no overall differences in systolic BP (SBP), diastolic BP or pulse pressure (PP) between the dietary groups after the intervention. The high-fat diet rich in saturated fat had minor unfavourable effects on SBP and PP in males.

Influence of fat and carbohydrate proportions on the metabolic profile in patients with type 2 diabetes: a meta-analysis

OBJECTIVE

The effects of dietary macronutrient composition on metabolic profiles in patients with type 2 diabetes have been inconsistent. This meta-analysis aimed to elucidate the effect of replacing dietary fat with carbohydrate on glucose and lipid parameters in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

We searched for randomized trials that investigated the effects of two kinds of prescribed diets (a low-fat, high-carbohydrate [LFHC] diet and a high-fat, low-carbohydrate [HFLC] diet); in these studies, energy and protein intake did not differ significantly between the two dietary groups. Nineteen studies that included 306 patients met our inclusion criteria. Median diet composition of carbohydrate/fat in the LFHC and HFLC diets was 58%/24% and 40%/40%, respectively.

RESULTS

Changes in values for A1C, fasting plasma glucose (FPG), and total and LDL cholesterol did not differ significantly between the LFHC and HFLC groups. However, the LFHC diet significantly increased fasting insulin and triglycerides by 8% (P = 0.02) and 13% (P < 0.001), respectively, and lowered HDL cholesterol by 6% (P < 0.001) compared with the HFLC diet. There were positive associations among the magnitude of changes in FPG, fasting insulin, and triglycerides for the diets analyzed. However, stratified analysis indicated that the increase in triglycerides was insignificant when accompanied by energy intake restriction.

CONCLUSIONS

Our findings suggested that replacing fat with carbohydrate could deteriorate insulin resistance while the adverse effect on triglycerides from the LFHC diet could be avoided by restricting energy intake to a degree sufficient for the attainment of weight reduction.

Dietary saturated and unsaturated fats as determinants of blood pressure and vascular function

The amount and type of dietary fat have long been associated with the risk of CVD. Arterial stiffness and endothelial dysfunction are important risk factors in the aetiology of CHD. A range of methods exists to assess vascular function that may be used in nutritional science, including clinic and ambulatory blood pressure monitoring, pulse wave analysis, pulse wave velocity, flow-mediated dilatation and venous occlusion plethysmography. The present review focuses on the quantity and type of dietary fat and effects on blood pressure, arterial compliance and endothelial function. Concerning fat quantity, the amount of dietary fat consumed habitually appears to have little influence on vascular function independent of fatty acid composition, although single high-fat meals postprandially impair endothelial function compared with low-fat meals. The mechanism is related to increased circulating lipoproteins and NEFA which may induce pro-inflammatory pathways and increase oxidative stress. Regarding the type of fat, cross-sectional data suggest that saturated fat adversely affects vascular function whereas polyunsaturated fat (mainly linoleic acid (18 : 2n-6) and n-3 PUFA) are beneficial. EPA (20 : 5n-3) and DHA (22 : 6n-3) can reduce blood pressure, improve arterial compliance in type 2 diabetics and dyslipidaemics, and augment endothelium-dependent vasodilation. The mechanisms for this vascular protection, and the nature of the separate physiological effects induced by EPA and DHA, are priorities for future research. Since good-quality observational or interventional data on dietary fatty acid composition and vascular function are scarce, no further recommendations can be suggested in addition to current guidelines at the present time.

Detrimental Impact of Trans Fats on Human Health: Stearic Acid-Rich Fats as Possible Substitutes

  Strong evidence demonstrated the negative effect of trans fatty acid (TFA) intake on cardiovascular diseases (CVD), diabetes, systemic inflammation, and hemostasis. As a consequence, different regulatory actions have been developed around the world, aiming to reduce human consumption of TFA. Replacement for TFA functionality requires incorporation of plastic and stable saturated fats; the present options are palm or fully hydrogenated oils. Palm oil has been described as responsible for negative biological effects on serum cholesterol levels and CVD risk. Different epidemiological and clinical studies recommend reduction of saturated fatty acid (SFA) intake, mainly myristic and palmitic acids. Experimental evidence strongly suggests that stearic acid is a wholesome substitute for TFAs and other SFAs in food manufacturing. In this article, biological effects of stearic acid on human health are reviewed in comparison to TFAs, SFAs, and unsaturated fatty acids. Current revised understanding on dietary intake, digestion, and absorption is also covered.

The effect of palm oil, lard, and puff-pastry margarine on postprandial lipid and hormone responses in normal-weight and obese young women

Only a few studies have been published on the postprandial effects of different fatty acids in obese subjects. Therefore, the present study investigated the effects of three test meals containing palm oil (PO), lard (LD), or puff-pastry margarine (PPM), all normal dietary ingredients, on postprandial lipid and hormone responses in normal-weight and obese young women. The study was performed as a randomized, crossover design. The fats differed in the content of palmitic acid, stearic acid, andtransmonounsaturated fatty acids allowing a dietary comparison of different ‘solid’ fatty acids. The obese women had significantly higher fasting concentrations and postprandial responses of plasma total triacylglycerol (TAG), chylomicron-TAG, and insulin compared with the normal-weight women but there was no significant difference in the postprandial responses between the three test meals. The obese women had fasting concentrations of leptin four times greater than the normal-weight women. There were no postprandial changes in the concentrations of leptin. The fasting concentrations of HDL-cholesterol were significantly lower in the obese women than in the normal-weight women, whereas there was no significant difference between the two groups in the concentrations of total cholesterol or LDL-cholesterol. These results provide evidence that obese women have exaggerated lipid and hormone responses compared with normal-weight women but the different contents of saturated andtransmonounsaturated fatty acids provided by PO, LD, and PPM have no effect in either group.

Effects of dietary saturated, monounsaturated, and n-3 fatty acids on blood pressure in healthy subjects

BACKGROUND

The quantity and quality of fats consumed in the diet influence the risk of cardiovascular disease (CVD). Although the effect of diet on plasma lipids and lipoproteins is well documented, less information exists on the role of fats on blood pressure (BP).

OBJECTIVE

The objective was to evaluate the effects of different types of dietary fat on BP in healthy subjects.

DESIGN

Healthy subjects (n = 162) were randomly assigned for 3 mo to follow 1 of 2 isoenergetic diets: 1 rich in monounsaturated fatty acids (MUFA diet) and the other rich in saturated fatty acids (SFA diet). Each group was further randomly assigned to receive supplementation with fish oil (3.6 g n-3 fatty acids/d) or placebo.

RESULTS

Systolic BP (SBP) and diastolic BP (DBP) decreased with the MUFA diet [-2.2% (P = 0.009) and -3.8% (P = 0.0001), respectively] but did not change with the SFA diet [-1.0% (P = 0.2084) and -1.1% (P = 0.2116)]. The MUFA diet caused a significantly lower DBP than did the SFA diet (P = 0.0475). Interestingly, the favorable effects of MUFA on DBP disappeared at a total fat intake above the median (>37% of energy). The addition of n-3 fatty acids influenced neither SBP nor DBP.

CONCLUSIONS

Changing the proportions of dietary fat by decreasing SFAs and increasing MUFAs decreased diastolic BP. Interestingly, the beneficial effect on BP induced by fat quality was negated by the consumption of a high total fat intake. The addition of n-3 fatty acids to the diet had no significant effect on BP.

Chocolate and prevention of cardiovascular disease: a systematic review

Background

Consumption of chocolate has been often hypothesized to reduce the risk of cardiovascular disease (CVD) due to chocolate's high levels of stearic acid and antioxidant flavonoids. However, debate still lingers regarding the true long term beneficial cardiovascular effects of chocolate overall.

Methods

We reviewed English-language MEDLINE publications from 1966 through January 2005 for experimental, observational, and clinical studies of relations between cocoa, cacao, chocolate, stearic acid, flavonoids (including flavonols, flavanols, catechins, epicatechins, and procynadins) and the risk of cardiovascular disease (coronary heart disease (CHD), stroke). A total of 136 publications were selected based on relevance, and quality of design and methods. An updated meta-analysis of flavonoid intake and CHD mortality was also conducted.

Results

The body of short-term randomized feeding trials suggests cocoa and chocolate may exert beneficial effects on cardiovascular risk via effects on lowering blood pressure, anti-inflammation, anti-platelet function, higher HDL, decreased LDL oxidation. Additionally, a large body of trials of stearic acid suggests it is indeed cholesterol-neutral. However, epidemiologic studies of serum and dietary stearic acid are inconclusive due to many methodologic limitations. Meanwhile, the large body of prospective studies of flavonoids suggests the flavonoid content of chocolate may reduce risk of cardiovascular mortality. Our updated meta-analysis indicates that intake of flavonoids may lower risk of CHD mortality, RR = 0.81 (95% CI: 0.71–0.92) comparing highest and lowest tertiles.

Conclusion

Multiple lines of evidence from laboratory experiments and randomized trials suggest stearic acid may be neutral, while flavonoids are likely protective against CHD mortality. The highest priority now is to conduct larger randomized trials to definitively investigate the impact of chocolate consumption on long-term cardiovascular outcomes.

Dietary stearic acid and risk of cardiovascular disease: Intake, sources, digestion, and absorption

Individual FA have diverse biological effects, some of which affect the risk of cardiovascular disease (CVD). In the context of food-based dietary guidance designed to reduce CVD risk, fat and FA recommendations focus on reducing saturated FA (SFA) and trans FA (TFA), and ensuring an adequate intake of unsaturated FA. Because stearic acid shares many physical properties with the other long-chain SFA but has different physiological effects, it is being evaluated as a substitute for TFA in food manufacturing. For stearic acid to become the primary replacement for TFA, it is essential that its physical properties and biological effects be well understood.

Analysis of variance (ANOVA) models in lower extremity wounds

Consider a study in which 2 new treatments are being compared with a control group. One way to compare outcomes would simply be to compare the 2 treatments with the control and the 2 treatments against each using 3 Student t tests (t test). If we were to compare 4 treatment groups, then we would need to use 6 t tests. The difficulty with using multiple t tests is that as the number of groups increases, so will the likelihood of finding a difference between any pair of groups simply by change when no real difference exists by definition a Type I error. If we were to perform 3 separate t tests each at alpha = .05, the experimental error rate increases to .14. As the number of multiple t tests increases, the experiment-wise error rate increases rather rapidly. The solution to the experimental error rate problem is to use analysis of variance (ANOVA) methods. Three basic ANOVA designs are reviewed that give hypothetical examples drawn from the literature to illustrate single-factor ANOVA, repeated measures ANOVA, and randomized block ANOVA. "No frills" SPSS or SAS code for each of these designs and examples used are available from the author on request.

Nutritional fats and the risk of type 2 diabetes and cancer

Dietary factors are important predictors for the risk of diabetes type 2. Increased consumption of fibre-rich foods, fruits and vegetables as well as limited amounts of total and saturated fats are essential elements in the prevention of diabetes type 2. The association between these dietary factors and the appearance of diabetes was not only present in cohort studies but were also major elements in the dietary part of the two large diabetes prevention trials (Finnish Diabetes Prevention Study, Diabetes Prevention Program). There is also strong evidence for a relation between obesity and total fat intake and the incidence of certain types of cancers. There is a significant correlation between total fat intake and the risk of cancer; however, it is much weaker than that of the effect of red meat. Recommendations to decrease red meat intake, particularly processed meat, may decrease the risk of colorectal and prostate cancer and may have beneficial effects on breast cancer as well, although this evidence is less compelling. Overall, recommendations focused on controlling or reducing body weight by regular physical activity and avoidance of excessive energy intake from all sources, particularly from fat and saturated fats, by increasing consumption of fibre-rich carbohydrates, vegetables and fruits are effective in decreasing the risk for type 2 diabetes by more than 50% in high-risk individuals. Similar dietary patterns are likely to diminish the manifestation of certain forms of cancers. These conclusions are in agreement with current recommendations for cancer prevention as propagated by the American Cancer Society.

Arabinoxylan fibre improves metabolic control in people with Type II diabetes

OBJECTIVE

To determine whether diet supplementation with arabinoxylan-rich (AX)-fibre from wheat improves glycaemic control in Type II diabetes.

DESIGN

Randomized, crossover intervention trial.

SETTING

Monash Medical Centre.

SUBJECTS

A total of 15 subjects with Type II diabetes.

INTERVENTIONS

Over two 5-week periods, subjects supplemented their usual diet with control bread and muffins (50% whole wheat, 50% white flour) (control diet) or with AX-bread and muffins (50% whole wheat, 36% white flour, 14% AX fibre) (AX diet). Subjects completed a 7-day food diary. At 0 and 5 weeks, venous blood was collected for determination of fasting and 2 h glucose, insulin, fructosamine and blood lipids. Blood pressure, body weight and body fat were also determined. A 24 h faecal sample, from 12 subjects, was weighed and analysed for faecal polysaccharide as a marker for dietary compliance.

RESULTS

Control and AX diets were similar except the AX diet supplied an additional 15.1 (12.0-18.5) (mean (95% confidence intervals)) g/day dietary fibre (P=0.000). Consumption of the AX diet increased faecal output by 61.5 (0.2-122.8) g/day (P=0.05) on a wet weight basis and significantly lowered fasting and 2 h plasma glucose, 2 h insulin and serum fructosamine (P=0.002, 0.000, 0.015, and 0.02, respectively). Blood lipids, body weight, fat mass and blood pressure remained unchanged.

CONCLUSION

A supplement of 15 g/day of AX-rich fibre can significantly improve glycaemic control in people with Type II diabetes.

Palmitic and stearic acids similarly affect plasma lipoprotein metabolism in cynomolgus monkeys fed diets with adequate levels of linoleic acid

This study was designed to evaluate whether the exchange of specific saturated fatty acids [SFA; palmitic acid (16:0) for stearic acid (18:0)] would differentially affect plasma lipids and lipoproteins, when diets contained the currently recommended levels of total SFA, monounsaturated fatty acids and polyunsaturated fatty acids (PUFA). Ten male cynomolgus monkeys were fed one of two purified diets (using a cross-over design) enriched either in 16:0 (palmitic acid diet) or 18:0 (stearic acid diet). Both diets provided 30% of energy as fat (SFA/monounsaturated fatty acid/PUFA: 1/1/1). The palmitic acid and stearic acid diets were based on palm oil or cocoa butter (59% and 50% of the total fat, respectively). By adding different amounts of sunflower, safflower and olive oils, an effective exchange of 16:0 for 18:0 of approximately 5% of energy was achieved with all other fatty acids being held constant. Monkeys were rotated through two 10-wk feeding periods, during which time plasma lipids and in vivo lipoprotein metabolism (following the simultaneous injection of (131)I-LDL and (125)I- HDL were evaluated). Plasma triacyglycerol (0.40 +/- 0.03 vs. 0.37 +/- 0.03 mmol/L), plasma total cholesterol (3.59 +/- 0.18 vs. 3.39 +/- 0.23 mmol/L), HDL cholesterol (1.60 +/- 0.16 vs 1.53 +/- 0.16 mmol/L) and non-HDL cholesterol (2.02 +/- 0.26 vs. 1.86 +/- 0.23 mmol/L) concentrations did not differ when monkeys consumed the palmitic acid and stearic acid diets, respectively. Plasma lipoprotein compositional analyses revealed a higher cholesteryl ester content in the VLDL fraction isolated after consumption of the stearic acid diet (P < 0.10), as well as a larger VLDL particle diameter (16.3 +/- 1.7 nm vs. 13.8 +/- 3.6 nm; P < 0.05). Kinetic analyses revealed no significant differences in LDL or HDL transport parameters. These data suggest that when incorporated into diets following current guidelines, containing adequate PUFA, an exchange of 16:0 for 18:0, representing approximately 11 g/(d.10.46 mJ) [ approximately 11 g/(d.2500 kcal)] does not affect the plasma lipid profile and has minor effects on lipoprotein composition. Whether a similar effect would occur in humans under comparable dietary conditions remains to be established.

Relationship of dietary fat to glucose metabolism

The relationship between dietary fat and glucose metabolism has been recognized for at least 60 years. In experimental animals, high fat diets result in impaired glucose tolerance. This impairment is associated with decreased basal and insulin-stimulated glucose metabolism. Impaired insulin binding and/or glucose transporters has been related to changes in the fatty acid composition of the membrane induced by dietary fat modification. In humans, high-fat diets, independent of fatty acid profile, have been reported to result in decreased insulin sensitivity. Saturated fat, relative to monounsaturated and polyunsaturated fat, appears to be more deleterious with respect to fat-induced insulin insensitivity. Some of the adverse effects induced by fat feeding can be ameliorated with omega-3 fatty acid. Epidemiological data in humans suggest that subjects with higher intakes of fat are more prone to develop disturbances in glucose metabolism, type 2 diabetes or impaired glucose tolerance, than subjects with lower intakes of fat. Inconsistencies in the data may be attributable to clustering of high intakes of dietary fat (especially animal fat) with obesity and inactivity. Metabolic studies suggest that higher-fat diets containing a higher proportion of unsaturated fat result in better measures of glucose metabolism than high-carbohydrate diet. Clearly, the area of dietary fat and glucose metabolism has yet to be fully elucidated.

Diet, blood pressure and hypertension

Prevention of hypertension, and control of blood pressure in patients with hypertension, are necessary for the reduction of cardiovascular morbidity and mortality. Lifestyle modifications are one of the most important tools for effective lowering of blood pressure. Most randomized controlled studies have shown that even a modest weight loss of 3-9% is associated with a significant reduction in systolic and diastolic blood pressure of roughly 3 mm Hg in overweight people. Limitation of sodium chloride in food has historically been considered the critical change for reducing blood pressure. Changes in sodium intake do affect blood pressure in older persons and in patients with hypertension and diabetes, whereas its role in population blood pressure has proven controversial. Recent meta-analyses indicate that adequate intake of minerals, e.g. potassium and probably calcium, rather than restriction of sodium, should be the focus of dietary recommendations. Although epidemiological data point to a direct relation between the intake of saturated fat, starch and alcohol, as well as an inverse relationship to the intake of omega-3 fatty acids and protein, our knowledge about macronutrients and blood pressure is scanty. It may well prove more productive to look at food instead of placing emphasis on single nutrients. Thus the Dietary Approaches to Stop Hypertension (DASH) demonstrates that a diet rich in fruits, vegetables, low-fat dairy products, fibre and minerals (calcium, potassium and magnesium) produces a potent antihypertensive effect. Such a diet is not very restrictive and should not produce compliance problems. Further high-quality research on the influence of macronutrients and food will yield data for updated recommendations, enabling better prevention and control of the blood pressure problem.