dietary fiber and blood pressure

Comparison of the Atkins, Ornish, Weight Watchers,and Zone Diets for Weight Loss and Heart DiseaseRisk Reduction: A Randomized Trial

Dansinger ML, Gleason JA, Griffith JL, Selker HP, Schaefer EJ.JAMA 2005;293:43–53.

Study Question: The purpose of this study was to assessadherence rates and the effectiveness of four popular diets(Atkins, Zone, Weight Watchers, and Ornish) for weightloss and cardiac risk-factor reduction.Methods: This single-center, randomized trial of overweightor obese (body mass index: mean, 35; range, 27–42) stud-ied adults aged 22 to 72 years with known hypertension,dyslipidemia, or fasting hyperglycemia. A total of 160 par-ticipants were randomly assigned to either Atkins (carbo-hydrate restriction, n � 40), Zone (macronutrient balance,n � 40), Weight Watchers (calorie restriction, n � 40), orOrnish (fat restriction, n � 40) diet groups. After 2 monthsof maximum effort, participants selected their own levels ofdietary adherence. The primary end points were 1-yearchanges in baseline weight and cardiac risk factors, andself-selected dietary adherence rates per self-report.Results: Assuming no change for participants who discon-tinued the study, mean (SD) weight loss at 1 year was 2.1(4.8) kg for Atkins (21 [53%] of 40 participants completed,p�0.009), 3.2 (6.0) kg for Zone (26 [65%] of 40 com-pleted, p�0.002), 3.0 (4.9) kg for Weight Watchers (26[65%] of 40 completed, p�0.001), and 3.3 (7.3) kg forOrnish (20 [50%] of 40 subjects completed, p�0.007).Each diet significantly reduced the low-density lipoprotein/high-density lipoprotein (HDL) cholesterol ratio by ap-proximately 10% (all p�0.05), with no significant effectson blood pressure or glucose at 1 year. Amount of weightloss was associated with self-reported dietary adherencelevel (r�0.60; p�0.001) but not with diet type (r�0.07;p�0.40). For each diet, decreasing levels of total/HDLcholesterol, C-reactive protein, and insulin were signifi-cantly associated with weight loss (mean r�0.36, 0.37, and0.39, respectively) with no significant difference betweendiets (p�0.48, p�0.57, P�0.31, respectively).Conclusions: The researchers concluded that each populardiet modestly reduced body weight and several cardiac riskfactors at 1 year. Overall dietary adherence rates were low,although increased adherence was associated with greaterweight loss and cardiac risk-factor reductions for each dietgroup.Perspective: The present study suggests that poor sustain-ability and adherence rates resulted in only modest weightloss and cardiac risk-factor reductions for each diet group asa whole. Cardiac risk-factor reductions were associatedwith weight loss regardless of diet type, underscoring the

concept that adherence level rather than diet type was thekey determinant of clinical benefits. Further research isindicated to identify practical techniques to increase dietaryadherence, including techniques to match individuals withthe diets best suited to their food preferences, lifestyle, andmedical conditions. DM

Dietary Fiber and Blood Pressure

Streppel MT, Arends LR, van’tVeer P, et al. Arch Intern Med2005;165:150 – 6.

Study Question: Does increasing dietary fiber influence theblood pressure (BP)?Methods: A meta-analysis of randomized placebo-controlledtrials was used to estimate the effect of fiber supplementa-tion on BP overall and in population subgroups. Twenty-four original studies published between January 1, 1966,and January 1, 2003, fulfilled criteria for meta-analysis.Data were abstracted on fiber dose, fiber type, BP changes,study design features, and study population characteristics.A random-effects model was used for meta-analysis. Popu-lations were considered hypertensive if more than 50% ofpersons were taking antihypertensive drugs or the mean BPat baseline was 140/90 mm Hg or higher.Results: A total of 1404 subjects were included. Mean trialduration was 9.0 weeks, 16 trials were double-blind, and15 had BP as the primary outcome. Average baseline BP was133/82 mm Hg, and in 8 trials the participants were con-sidered hypertensive. Baseline fiber intake in 11 trialsranged from 12.8 g/d to 44 g/d (mean 24.8 g/d). Fiber dosesvaried between 3.5 and 42.6 g/d (mean 11.5 g/d). Mean netchange in weight during fiber supplementation ranged from�2.5 kg to �1.0 kg. Fiber supplementation (equally solubleand insoluble) changed systolic BP by �1.13 mm Hg (95%confidence interval: �2.49 to 0.23) and diastolic BP by�1.26 mm Hg (�2.04 to �0.48). Reductions in BP tendedto be larger in older (�40 years) and in hypertensivepopulations than in younger and in normotensive ones.Conclusions: Increasing the intake of fiber in Western pop-ulations, where intake is far below recommended levels,may contribute to the prevention of hypertension.Perspective: The reduction in diastolic BP associated withfiber supplement is modest but may be clinically relevant.Two very large cohort studies found the risk of hyperten-sion is inversely correlated with dietary fiber. It is not clearwhy fiber, either as supplements or obtained in fruits/vegetables and whole grains, is associated with less hyper-tension and lower BP. One hypothesis is the reduction inglycemic index reduces serum insulin, and fiber increasesinsulin sensitivity and endothelial function. Adults shouldconsume at least 25 g of fiber daily, which reduces choles-terol and has been shown to reduce mortality following amyocardial infarction. MR

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Preventive CardiologyAbstracts