EVIDENCE-BASED ANSWER
Diets lower in fat, higher in soy protein, or higher in fiber reduce serum total cholesterol, low-density lipoprotein (LDL), and triglycerides. More restrictive low-fat diets also lower high-density lipoprotein (HDL), while soy protein increases HDL. Average decreases in LDL range from 6.96 to 25.14 mg/dL, depending on the particular intervention and participants’ baseline characteristics (strength of recommendation [SOR]: C, based on meta-analyses of randomized controlled trials [RCTs] measuring intermediate endpoints). A “portfolio diet” that includes cholesterol-lowering “functional foods” can reduce total cholesterol and LDL; a Mediterranean-type diet can lower LDL (SOR: C, based on fair-quality RCTs, measuring intermediate endpoints). We do not yet know whether the these diets will also help patients live longer and more healthy lives or just improve their lipid profiles.
CLINICAL COMMENTARY
Simple interventions, like reducing fast food and increasing fruit and vegetable intake, are a good starting place
Rade N. Pejic, MD
Department of Family Medicine, Tulane University School of Medicine, New Orleans, La
Dietary modifications are necessary for the successful long-term treatment of lipid disorders, as well as many other chronic medical conditions. Patients are often encouraged when they learn they can reverse a disease process without taking a medication. We should take every opportunity to educate our patients and promote healthy lifestyles. Simple interventions, such as eating less fast food and more fresh fruits and vegetables, are often a good starting place. Other simple interventions to reduce cholesterol levels are taking fiber supplements and substituting commercially available margarines with plant sterols for butter.
Dietary counseling or referral to a medical nutritionist should be part of our overall treatment plan for patients with lipid disorders. regularly scheduled follow-up visits help promote adherence to therapeutic lifestyle changes and encourage a therapeutic alliance.
Evidence summary
Dietary changes are recommended as first-line treatment for mild to moderate dyslipidemia. We examined evidence on 5 common dietary interventions for adults with dyslipidemia. The average effects on lipid levels are reported in the TABLE.
TABLE
Average effect of dietary interventions on serum lipid levels
| DIETARY INTERVENTION | AVERAGE CHANGE IN MG/DL OF LIPID LEVELS (% CHANGE) | ||||
|---|---|---|---|---|---|
| TOTAL CHOLESTEROL | LDL | HDL | TRIGLYCERIDES | ||
| Low fat | NCEP Step I | –24.36* (–10%) | –18.95* (–12%) | –1.55 (–1.5%) | –15.10* (–8%) |
| NCEP Step II | –31.32* (–7%) | –25.14* (–13%) | –3.48* (–16%) | –16.83* (–8%) | |
| Soy | All | –8.51* (–3.77%) | –8.12* (–5.25%) | –1.55* + (+ 3.03%) | –8.86* (–7.27%) |
| Hypercholesterolemia | –9.67* | –6.96* | + 3.87* | –7.97* | |
| Fiber (per g/d) | –1.74* | –2.20* | –0.12 | + 0.27 | |
| “Portfolio” | –58.39* (–22.34%) | –51.82* (–29.71%) | 3.09 (–6.50%) | 18.60 (9.33%) | |
| Mediterranean | –15.47 (–6.06%) | –19.34* (–11.37%) | 0 (–12.50%) | –17.71 (0%) | |
| * Statistically significant at P≤.05 | |||||
Low-fat
A meta-analysis of 37 mostly good-quality controlled trials evaluated the former National Cholesterol Education Program (NCEP) Step I and Step II diets in 11,586 participants.1 The Step I diet restricted in-take of total fat (≤30% of total calories), saturated fat (≤10% of total calories), and cholesterol (≤300 mg/d). Step II goals were lower for saturated fat (<7%) and cholesterol (<200 mg/d). Mean baseline lipid values (mg/dL) were total cholesterol, 233.57; LDL, 155.10; HDL, 47.95; and triglycerides, 147.91. Both of these low-fat diets significantly reduced total cholesterol, LDL, and triglycerides. The Step II diet also reduced HDL.
Soy
A meta-analysis of 23 good-quality controlled trials with 1381 participants reported that soy protein with naturally occurring isoflavones significantly reduced total cholesterol, LDL, and triglycerides while significantly increasing HDL.2 The amount of soy isoflavone consumed varied across studies. One subgroup analysis showed that consumption of >80 mg/d was associated with a better effect on lipids. In subjects with baseline hypercholesterolemia (total cholesterol >240 mg/dL), greater reductions in total cholesterol, and greater increases in HDL were reported, with comparable changes in LDL and triglycerides.
Soluble fiber
A meta-analysis of 67 good-quality RCTs evaluated the effects of soluble dietary fiber in 2990 subjects (mean baseline lipid values [mg/dL]: total cholesterol, 240.9; LDL, 164.4).3 Diets high in soluble fiber (average dose of 9.5 g/d) were associated with a statistically significant decrease in total cholesterol and LDL and no significant change in HDL or triglycerides. Type of fiber (oat, psyllium, or pectin) was not influential after controlling for initial lipid level.