Welma Oosthuizen

Meta-analysis of the health effects of using the glycaemic index in meal-planning

Diabetes mellitus and CVD are some of the leading causes of mortality and morbidity. Accumulating data indicate that a diet characterised by low-glycaemic index (GI) foods may improve the management of diabetes or lipid profiles. The objective of the present meta-analysis was to critically analyse the scientific evidence that low-GI diets have beneficial effects on carbohydrate and lipid metabolism compared with high-GI diets. We searched for randomised controlled trials with a crossover or parallel design published in English between 1981 and 2003, investigating the effect of low-GI v. high-GI diets on markers for carbohydrate and lipid metabolism. Unstandardised differences in mean values were examined using the random effects model. The main outcomes were fructosamine, glycated Hb (HbA1c), HDL-cholesterol, LDL-cholesterol, total cholesterol and triacylglycerol. Literature searches identified sixteen studies that met the strict inclusion criteria. Low-GI diets significantly reduced fructosamine by -0.1 (95 % CI -0.20, 0.00) mmol/l (P=0.05), HbA1c by 0.27 (95 % CI -0.5, -0.03) % (P=0.03), total cholesterol by -0.33 (95 % CI -0.47, -0.18) mmol/l (P<0.0001) and tended to reduce LDL-cholesterol in type 2 diabetic subjects by -0.15 (95 % CI -0.31, -0.00) mmol/l (P=0.06) compared with high-GI diets. No changes were observed in HDL-cholesterol and triacylglycerol concentrations. No substantial heterogeneity was detected, suggesting that the effects of low-GI diets in these studies were uniform. Results of the present meta-analysis support the use of the GI as a scientifically based tool to enable selection of carbohydrate-containing foods to reduce total cholesterol and to improve overall metabolic control of diabetes.

Phytosterols/stanols lower cholesterol concentrations in familial hypercholesterolemic subjects: a systematic review with meta-analysis

Background: To-date, reviews regarding the cholesterol lowering capacity of phytosterols/stanols have focused on normo- and hypercholesterolemic (HC) subjects. Familial hypercholestrolemia (FH) is characterized by very high low-density lipoprotein cholesterol (LDL-C) concentrations and is considered a world public health problem due to the high incidence of premature coronary heart disease (CHD) in these patients. Objective: To conduct a systematic review that investigates the efficacy of phytosterols/stanols in lowering total cholesterol (TC) and LDL-C concentrations in FH subjects. Design: Randomized controlled intervention trials with the primary objective to investigate the effects of phytosterols/stanols on lipid concentrations in FH subjects were identified through selected international journal databases and reference lists of relevant publications. Two researchers extracted data from each identified trial and only trials of sufficient quality (e.g. controlled, randomized, double-blind, good compliance, sufficient statistical power) were included in the review. The main outcome measures were differences between treatment and control groups for LDL-C, TC, high-density lipoprotein cholesterol (HDL-C) and triacylglycerol (TG). Results: Six out of 13 studies were of sufficient quality. Two were excluded from the meta-analysis because the sterols were administered in the granulate form at very high dosages (12 g/day and 24 g/day) compared to the other studies that used fat spreads as vehicle with dosages ranging from 1.6–2.8 g/day. The subjects were heterozygous, aged 2–69 years with baseline TC and LDL-C concentrations of ±7 mmol/L and ±5.4 mmol/L, respectively. The duration of the studies ranged from 4 weeks to 3 months. Fat spreads enriched with 2.3 ± 0.5 g phytosterols/stanols per day significantly reduced TC from 7 to 11% with a mean decrease of 0.65 mmol/L [95% CI −0.88, −0.42 mmol/L], p < 0.00001 and LDL-C from 10–15% with a mean decrease of 0.64 mmol/L [95% CI −0.86, −0.43 mmol/L], p < 0.00001 in 6.5 ± 1.9 weeks compared to control treatment, without any adverse effects. TG and HDL-C concentrations were not affected. Conclusion: Phytosterols/stanols may offer an effective adjunct to the cholesterol lowering treatment strategy of FH patients.

Effects of a policosanol supplement on serum lipid concentrations in hypercholesterolaemic and heterozygous familial hypercholesterolaemic subjects.

Policosanol is a mixture of higher aliphatic primary alcohols that is extracted from purified sugar cane wax or a variety of other plant sources, and has been shown to have beneficial effects on serum lipid concentrations. The objective of this study was to investigate the effects of a policosanol supplement (Octa-60) on lipid profiles of hypercholesterolaemic and heterozygous familial hypercholesterolaemic subjects. Nineteen hypercholesterolaemic and familial hypercholesterolaemic subjects completed this randomised, placebo-controlled, double-blind study. The subjects received either a daily dose of 20 mg policosanol or placebo for 12 weeks. After a wash-out period of 4 weeks, the interventions were crossed over. Lipid levels were measured at baseline and at the end of each intervention period. No significant differences in total cholesterol and LDL-cholesterol from baseline to end or between policosanol and placebo were seen in the hypercholesterolaemic or familial hypercholesterolaemic groups. There were small reductions in total cholesterol and LDL-cholesterol from baseline to end in the hypercholesterolaemic group, but these changes did not differ significantly from the changes with the placebo, indicating that the observed decrease in cholesterol in the policosanol group was not due to the specific effect of policosanol treatment. The differences in response may be ascribed to the differences in composition of the higher aliphatic primary alcohols in the previously used products, compared with the local policosanol supplement. An intake of 20 mg/d policosanol for 12 weeks had no significant effect on serum lipid levels in hypercholesterolaemic and heterozygous familial hypercholesterolaemic patients when compared with placebo intake.

Cardiovascular effects of oral supplementation of vitamin C, E and folic acid in young healthy males

Numerous observational studies showed associations of antioxidants (vitamins C and E) and folate intake with a reduced risk of cardiovascular disease, but randomized controlled clinical trials have generally not supported this hypothesis. The objective of this study was to investigate the effects of a daily dosage of 1000 mg vitamin C, 800 mg vitamin E, and 10 mg folate on markers of vascular function in 31 young healthy male adults. Cardiovascular values after a 12-week vitamin (14 subjects) or placebo (17 subjects) intervention were compared to baseline values. Cardiovascular parameters (blood pressure, stroke volume, heart rate, cardiac output, vascular resistance, arterial compliance) were measured continuously after an overnight fast under controlled circumstances with a Finometer device. Our main finding was a significant decrease (p = 0.03) in systolic blood pressure in the experimental group. No statistically significant changes were observed within other cardiovascular variables of the experimental group, but possible beneficial decreases in diastolic blood pressure and increases in arterial compliance after 12 weeks of vitamin supplementation were indicated. In conclusion, beneficial effects of antioxidants and folate were observed probably because the supplementation was used by young healthy subjects under carefully controlled conditions.

Some health benefits of low glycaemic index diets - a systematic review

Background: Controversy exists regarding practical use of the glycaemic index (GI), often with reference to the responsibility of health professionals to advise consumers only when scientific evidence supports their recommendations. There are indications that low-GI diets may improve health, but the strength of the evidence is not known.

The effect of extrusion processing on the glycaemic index of dry bean products

Background: Both wheat pasta and dry beans have low glycaemic indices (GIs). However, it has been shown that several factors, including method of processing, may influence the GI of a food. Extrusion of dry beans is a relatively new dry cooking process and provides a convenient alternative to the ingestion of dry beans.