Background Reducing saturated fat reduces serum cholesterol, but effects on other intermediate outcomes may be less clear. Additionally, it is unclear whether the energy from saturated fats eliminated from the diet are more helpfully replaced by polyunsaturated fats, monounsaturated fats, carbohydrate or protein. Objectives To assess the effect of reducing saturated fat intake and replacing it with carbohydrate (CHO), polyunsaturated (PUFA), monounsaturated fat (MUFA) and/or protein on mortality and cardiovascular morbidity, using all available randomised clinical trials. Search methods We updated our searches of the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid) and Embase (Ovid) on 15 October 2019, and searched Clinicaltrials.gov and WHO International Clinical Trials Registry Platform (ICTRP) on 17 October 2019. Selection criteria Included trials fulfilled the following criteria: 1) randomised; 2) intention to reduce saturated fat intake OR intention to alter dietary fats and achieving a reduction in saturated fat; 3) compared with higher saturated fat intake or usual diet; 4) not multifactorial; 5) in adult humans with or without cardiovascular disease (but not acutely ill, pregnant or breastfeeding); 6) intervention duration at least 24 months; 7) mortality or cardiovascular morbidity data available. Data collection and analysis Two review authors independently assessed inclusion, extracted study data and assessed risk of bias. We performed random-effects meta-analyses, meta-regression, subgrouping, sensitivity analyses, funnel plots and GRADE assessment. Main results We included 15 randomised controlled trials (RCTs) (16 comparisons, ~59,000 participants), that used a variety of interventions from providing all food to advice on reducing saturated fat. The included long-term trials suggested that reducing dietary saturated fat reduced the risk of combined cardiovascular events by 21% (risk ratio (RR) 0.79; 95% confidence interval (CI) 0.66 to 0.93, 11 trials, 53,300 participants of whom 8% had a cardiovascular event, I² = 65%, GRADE moderate-quality evidence). Meta-regression suggested that greater reductions in saturated fat (reflected in greater reductions in serum cholesterol) resulted in greater reductions in risk of CVD events, explaining most heterogeneity between trials. The number needed to treat for an additional beneficial outcome (NNTB) was 56 in primary prevention trials, so 56 people need to reduce their saturated fat intake for ~four years for one person to avoid experiencing a CVD event. In secondary prevention trials, the NNTB was 32. Subgrouping did not suggest significant differences between replacement of saturated fat calories with polyunsaturated fat or carbohydrate, and data on replacement with monounsaturated fat and protein was very limited. We found little or no effect of reducing saturated fat on all-cause mortality (RR 0.96; 95% CI 0.90 to 1.03; 11 trials, 55,858 participants) or cardiovascular mortality (RR 0.95; 95% CI 0.80 to 1.12, 10 trials, 53,421 participants), both with GRADE moderate-quality evidence. There was little or no effect of reducing saturated fats on non-fatal myocardial infarction (RR 0.97, 95% CI 0.87 to 1.07) or CHD mortality (RR 0.97, 95% CI 0.82 to 1.16, both low-quality evidence), but effects on total (fatal or non-fatal) myocardial infarction, stroke and CHD events (fatal or non-fatal) were all unclear as the evidence was of very low quality. There was little or no effect on cancer mortality, cancer diagnoses, diabetes diagnosis, HDL cholesterol, serum triglycerides or blood pressure, and small reductions in weight, serum total cholesterol, LDL cholesterol and BMI. There was no evidence of harmful effects of reducing saturated fat intakes. Authors' conclusions The findings of this updated review suggest that reducing saturated fat intake for at least two years causes a potentially important reduction in combined cardiovascular events. Replacing the energy from saturated fat with polyunsaturated fat or carbohydrate appear to be useful strategies, while effects of replacement with monounsaturated fat are unclear. The reduction in combined cardiovascular events resulting from reducing saturated fat did not alter by study duration, sex or baseline level of cardiovascular risk, but greater reduction in saturated fat caused greater reductions in cardiovascular events.

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Reduction in saturated fat intake for cardiovascular disease

Reduction and modification of dietary fats have differing effects on cardiovascular risk factors (such as serum cholesterol), but their effects on important health outcomes are less clear.
The objective of this review is to assess the effect of reduction and/or modification of dietary fats on mortality, cardiovascular mortality, cardiovascular morbidity and individual outcomes including myocardial infarction, stroke and cancer diagnoses in randomised clinical trials of at least 6 months duration.

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Reduced or modified dietary fat for preventing cardiovascular disease

Cytokine secretion and eicosanoid production in the peripheral blood mononuclear cells of MS patients undergoing dietary supplementation with n-3 polyunsaturated fatty acids

Publisher Summary This chapter discusses fatty acids and immunity. Like all mammalian cells, lymphocytes contain a variety of fatty acids, some of which, the essential fatty acids, must be supplied to the cells because they are unable to synthesize them. Of the essential fatty acids, linoleic acid and the derivative arachidonic acid are major components of the phospholipids of lymphocyte membranes, while α-linolenic and its derivatives are only minor components. A wide variety of fatty acids produce effects on both the lymphoid and reticuloendothelial systems; the actual effects produced depend on the method of administration and the chemical nature of the fatty acid. Arachidonic acid is an immediate prostaglandin precursor and plays a central role in lymphocyte activation. Membrane phospholipid fatty-acid composition alters when lymphocytes are stimulated, either by antigen or by mitogens, such as phytohaemagglutinin or concanavalin A. Increased turnover of phospholipid fatty acids, following lymphocyte stimulation, requires a transferase to incorporate new fatty acids and a means of generating lysophosphatides and free fatty acids as substrates for this enzyme.

Fatty Acids and Immunity

Patients with clinically definite multiple sclerosis, mild to moderately severe neurological disability (entry score on the Expanded Disability Status Scale (EDSS) between 3.0 and 7.0), and a progressive course defined by an increase in the EDSS of between 1 and 3 grades in the year prior to entry were randomized to receive either cyclosporine (n = 273) or placebo (n = 274) in a 2-year, double-blinded, multicenter trial. Treatment groups at entry proved balanced for age, gender, duration of illness, and neurological disability. Cyclosporine dosage was adjusted for toxicity and a median trough whole-blood level was maintained between 310 and 430 ng/ml. The mean increase in EDSS score was 0.39 ± 1.07 grades for cyclosporine-treated patients and 0.65 ± 1.08 grades for placebo-treated patients from entry until the time of early withdrawal or completion of the study (p = 0.002). Of three primary efficacy criteria, cyclosporine delayed the time to becoming wheelchair bound (p = 0.038; relative risk, 0.765), but statistically significant effects were not observed for “time to sustained progression” or on a composite score of “activities of daily living.” Active treatment did have a favorable effect on several secondary measures of disease outcome. A large and differential withdrawal rate (44% for cyclosporine-treated patients, 32% for placebo-treated patients) complicated the analysis but did not appear to explain the observed effect of cyclosporine in delaying disease progression. Multivariate analysis did not show institutional effects but did demonstrate substantial effects of baseline neurological disability on outcome. Nephrotoxicity and hypertension were common troublesome toxicities and accounted for most of the excess loss of patients in the cyclosporine arm of the study. Thus, chronic cyclosporine therapy was associated with a statistically significant but clinically modest delay of progression of disability in a group of patients with multiple sclerosis selected for moderately severe and progressive disease. Close supervision by physicians familiar with cyclosporine is mandatory to minimize known adverse effects, particularly nephrotoxicity, when considering the use of this immunosuppressant.

Efficacy and toxicity of cyclosporine in chronic progressive multiple sclerosis: A randomized, double-blinded, placebo-controlled clinical trial

Seventy-five patients in London and Belfast with multiple sclerosis were given daily supplements of a vegetable oil mixture containing either linoleate or oleate for two years in a double-blind control trial Relapses tended to be less frequent and were significantly less severe and of shorter duration in the linoleate-supplemented group than in those receiving the oleate mixture, but clear evidence that treatment affected the overall rate of clinical deterioration was not obtained

https://www.bmj.com/content/bmj/1/5856/765.full.pdf

H. P. Wright

Papers

Double-blind trial of linoleate supplementation of the diet in multiple sclerosis.