Elaine Lewis, hbsc, ND
Monique Aucoin, bmsc, ND
Kieran Cooley, bsc, ND
The medical assessment and diagnosis of dyslipidemia involves stratifying results from a standard fasting lipid panel with cardiovascular risk, as determined by the Framingham Risk Score.3 The standard fasting lipid panel, including Total Cholesterol (TC), Low-Density Lipoprotein (LDL)-C, High-Density Lipoprotein (HDL)-C, and Triglycerides, should be assessed in accordance with the particular country’s cardiovascular risk assessment recommendations. Canadian and American guidelines vary slightly, with both prioritizing the individualization of lipid panel results according to CVD risk.2,3 LDL-C levels must be adjusted along with the categories of low, intermediate, and high risk in order to assess the marker accurately. Conventional dyslipidemia treatment centers on the use of statin medication to target LDL-C, based on data suggesting a CVD risk reduction of 25-35%.3 Non-HDL cholesterol and Apolipoprotein B are also emerging as potential targets for lipid-lowering therapy.3yslipidemia is a primary risk factor for the onset and progression of atherosclerotic cardiovascular disease, which continues to be a leading cause of death in the United States and Canada. In both countries, the prevalence of cardiovascular disease (CVD) and its economic burden are expected to increase in years to come.1,2 Canadian data suggest a decrease in mortality associated with coronary artery disease, attributed to increased management of CVD risk factors such as dyslipidemia, smoking, and blood pressure.1
Dietary and lifestyle interventions continue to be recommended as first-line therapy for dyslipidemia and cardiovascular disease prevention, given their known impact on cardiovascular risk reduction.1,3 However, specific recommendations regarding evidence-based interventions may not be well known to the average primary healthcare provider. This article will synthesize key dietary strategies supported by current literature as they relate to the treatment of dyslipidemia.
Interventions for Dyslipidemia
Portfolio Diet
The Portfolio diet, coined by Canadian researcher, Dr David Jenkins, is a therapeutic diet combining known cholesterol-reducing interventions in order to attain a synergistic and additive effect on the lipid panel. It includes dietary soy protein, plant sterols (as margarine), viscous fibers (such as oats, barley, and psyllium), and almonds as additional vegetarian protein. As a combination diet, the Portfolio diet has been shown to achieve significant reductions in LDL-C, total cholesterol (TC), and the TC/HDL ratio, with sparse impact on HDL-C.4-6 It has also been found to reduce C-reactive protein (CRP) and Apolipoprotein B, and to significantly improve overall cardiovascular risk.4 Adding monounsaturated fatty acids, in the form of sunflower oil or avocado, to the basic Portfolio diet has been shown to significantly target the elevation of HDL-C (+0.12 mmol/L) and a further reduction in TC/HDL (-0.28 mmol/L).7
Mediterranean Diet
The Mediterranean diet, as the name suggests, reflects the traditional dietary patterns of those living in countries situated within the Mediterranean region. A recent Cochrane review8 of the Mediterranean Diet and cardiovascular disease defines this diet by 7 criteria:
- High monounsaturated/saturated fat ratio
- Low-to-moderate red wine consumption
- High consumption of legumes
- High consumption of grains and cereals
- High consumption of fruits and vegetables
- Low consumption of meat and meat products, and increased consumption of fish
- Moderate consumption of milk and dairy products
The systematic review and meta-analysis reviewed 11 RCTs, including 52 044 participants, and concluded reductions in total cholesterol (-0.23 mmol/L) and LDL-C (-0.07 mmol/L), with variable impact on HDL-C and triglycerides.8
In comparing the efficacy of the Mediterranean diet with low-fat diets, a meta-analysis including 6 RCTs found the Mediterranean diet to produce improvements in total cholesterol, triglycerides, and overall cardiovascular risk after 2 years of administration, with no significant differences in LDL-C or HDL-C.9
Dietary Fat
Foods high in fat have long been questioned regarding their impact on lipids. A meta-analysis comparing dietary fatty acid to carbohydrate intake noted a higher mono- and polyunsaturated fat diet to promote significant improvements in total cholesterol, LDL-C, HDL-C, and triglycerides.10
Soy
Soy is a traditional food consumed in East Asian countries and has been extensively studied in the post-menopausal population due to its estrogen-modulating effects. Soy is also a major component of the Portfolio diet. As a singular intervention for hypercholesterolemia, dietary soy has been associated with decreases in LDL-C and TC; however, studies demonstrate inconsistent effects on triglycerides and HDL-C.11-13 Many trials studying the effects of soy compare it to a casein control, which may compromise generalizability. Beneficial effects on TC and LDL-C appear to be greater in men vs women, and in premenopausal vs postmenopausal women.14 Triglyceride elevation and post-prandial glucose elevation have both been identified as adverse effects from dietary soy, though this trend has not been sufficiently corroborated by evidence.11,12
Nuts
Nuts are a highly nutrient-dense food group, known for their cardioprotective and antioxidant properties. A systematic review and meta-analysis of 25 clinical trials with unmedicated normolipidemic and hyperlipidemic adults found improvements in TC, LDL-C, and triglycerides with a daily intake of at least 67 g of nuts. This effect was stronger in studies where nuts were compared to a nut-free diet or Western diet, vs a Mediterranean or low-fat diet.1
Beta-glucan
Beta-glucan is a highly viscous soluble fiber found in the endosperm cell wall of oats and barley. A systematic review of 22 high-quality RCTs using at least 3 g/day of oat beta-glucan observed an average reduction in TC (5%) and LDL-C (7%) compared to controls in patients with normal or elevated cholesterol.16 A meta-analysis of 11 RCTs using at least 3 g/day of barley beta-glucan demonstrated an average reduction in TC (0.30 mmol/L) and LDL-C (0.27 mmol/L) compared to controls in patients with normal or elevated cholesterol.17 Suggested mechanisms, among others, include a decrease in dietary cholesterol uptake, a decrease in bile acid reuptake, and inhibition of cholesterol synthesis.16
Glucomannan
Glucomannan is a soluble fiber from Amorphophallus konjac, which is available in supplement form. A meta-analysis of 14 RCTs using 1.2-15.1 g/day of glucomannan found an average reduction of TC (0.499 mmol/L), LDL-C (0.414 mmol/L) and triglycerides (0.125 mmol/L). Suggested mechanisms for this effect include prolonging gastric emptying time (which decreases food intake), suppression of hepatic cholesterol synthesis, and an increase in bile acid elimination.18
Psyllium
Psyllium, derived from the plant Plantago psyllium, is one of the greatest sources of soluble dietary fiber. A meta-analysis of 19 studies, including patients with mild-to-moderate hypercholesterolemia, yielded reductions in TC (0.375 mmol/L), LDL-C (0.278 mmol/L) and HDL-C (0.035 mmol/L). Participants in these studies consumed either a standard commercial psyllium product (10.2 g/day) or foods enriched with 3-15 g/day of psyllium. The impact of psyllium on cholesterol appears to be dose-dependent, with doses of 5, 10, and 15 g/day producing 5.6, 9, and 12.5% reductions in LDL-C, respectively.19
Flaxseed
Flaxseed, from the plant Linum usitatissimim, is one of the oldest crops but has gained recent attention as a medicinal food. It is a source of soluble fiber as well as alpha-linolenic acid and lignans. A meta-analysis of 10 studies found different cholesterol-lowering effects from the various flaxseed constituents. Whole flaxseeds, at a dose of 20 to 50 g/day, were found to reduce TC (0.19 mmol/L) and LDL-C (0.16 mmol/L), while lignans, at a dose of 200-600 mg/day, reduced TC
(0.28 mmol/L) and LDL-C (0.16 mmol/L). Flaxseed oil did not significantly impact cholesterol levels. Greater reductions were seen among participants with baseline TC and LDL-C greater than 5.7 and 3.4, respectively. In general, larger reductions in cholesterol were seen among female participants, particularly postmenopausal women; however, this may have been due to the baseline cholesterol levels or type of flax product used.20
Discussion
“Let food be thy medicine and medicine be thy food.” This is a familiar quote from Hippocrates, and in the management of dyslipidemia, a critical component of the treatment plan. There are a number of dietary interventions that have significant evidence to support their use in the treatment of dyslipidemia. All of the interventions reviewed in this paper positively impact total- and LDL cholesterol. While fewer interventions appear to impact triglyceride levels, nuts and glucomannan appear to produce significant reductions. The Portfolio diet has demonstrated an ability to increase HDL-C, and the Mediterranean diet has been shown to have moderate impact on LDL- and total cholesterol.
While many individual dietary changes have been reviewed, a treatment plan is likely to include a combination of functional foods and dietary modifications. The Portfolio and Mediterranean diets both include a combination of several cholesterol-balancing foods, and a variety of resources are available to help patients implement these dietary strategies. While the changes in cholesterol levels with these diets appear to be small, their impact on disease risk reduction is substantial. Several studies have established that every 1% decrease in LDL-C is associated with a 1% decrease in CVD mortality.21
Furthermore, the dietary strategies reviewed appear to have many other protective mechanisms in addition to modifying cholesterol. For example, the Mediterranean diet has been shown to decrease blood pressure, body weight, fasting plasma glucose, and high-sensitivity CRP – all risk factors for CVD.9
Very few side effects were reported for these interventions, with gastrointestinal symptoms from increased fiber intake being the most common. Trials examining the Portfolio diet uncovered minor allergies to soy and almonds that were otherwise unknown to participants.
Depending on a patient’s baseline cholesterol level, dietary interventions may be adequate for the management of dyslipidemia. In cases with more significantly elevated levels, nutritional supplements, exercise protocols, or herbal medicines may be helpful additions to the therapeutic plan (see table online).
Table 1. Effects of Diets & Dietary Constituents on Blood Lipids
| Intervention | Dose | TC | LDL-C | HDL-C | TG | |
| Larger Effect Size | Portfolio Diet | 1.45 mmol/L ¯ | 1.21 mmol/L ¯ | 0.12 mmol/L | No change | |
| Soy | 47 g dietary soy/d | 0.60 mmol/L ¯ | 0.56 mmol/L ¯ | 0.04 mmol/L | 0.15 mmol/L ¯ | |
| Glucomannan | 1.2-15.1 g/d | 0.50 mmol/L ¯ | 0.41 mmol/L ¯ | No change | 0.13 mmol/L ¯ | |
| Smaller Effect Size | Mediterranean Diet | 0.23 mmol/L ¯ | 0.07 mmol/L ¯ | No change | No change | |
| Psyllium | 10-15 g/d | 0.38 mmol/L ¯ | 0.28 mmol/L ¯ | 0.04 mmol/L ¯ | No change | |
| Beta-Glucan | 3 g/d | 0.30 mmol/L ¯ | 0.27 mmol/L ¯ | No change | No change | |
| Nuts | 67 g/d | 0.28 mmol/L ¯ | 0.26 mmol/L ¯ | No change | 0.23 mg/dL ¯ (high TG only) | |
| Flaxseed | 20-50 g/d flax seeds200-600 g/d lignans | 0.19 mmol/L ¯ seeds0.28 mmol/L ¯ lignans | 0.16 mmol/L ¯ seeds and lignans | No change | No change |
(TC = total cholesterol; LDL-C = low-density lipoprotein; HDL-C = high-density lipoprotein; TG = triglycerides)
Elaine Lewis, HBSc, ND, is a naturopathic physician and research resident, graduating from CCNM. She is a member of the Ontario and Canadian Associations of Naturopathic Doctors and is licensed by the Board of Directors of Drugless Therapy – Naturopathy. Elaine emphasizes the impact of evidence-based naturopathic medicine by using this model in her teaching and patient care. Beyond her role as the research resident, she mentors students in a variety of courses, and lectures externally to organizations and healthcare providers. Elaine practices in Mississauga at Back to Play Chiropractic and in North York at the Integrated Healthcare Centre.
Monique Aucoin, BMSc, ND, is a naturopathic physician and clinical trial coordinator at CCNM. She is currently involved in the design and implementation of studies investigating the efficacy and safety of natural health products in the treatment of IBS, depression, ADHD, and cardiometabolic disorders. In addition to her research work, Monique has a private practice in Brampton, with an emphasis in mental health and stress management. She is passionate about helping people to understand the root cause of their illness and restore balance using simple and effective treatments.
Kieran Cooley, BSc, ND, is an associate director of research and assistant professor in CCNM’s department of Research and Clinical Epidemiology. Kieran’s experience includes a broad range of clinical trials, systematic reviews, and collaborations investigating naturopathic medicine and various natural health products. This includes a recent collaboration evaluating the effectiveness of naturopathic medicine for CVD risk, published in the Canadian Medical Association Journal. A recipient of the SickKids Training Award in Complementary/Alternative Health Care, he has previously investigated behavioral disorders in children, with a focus on ADHD. Kieran is committed to fostering an evidence-based approach to naturopathic medicine and a long life of learning and sharing.
References
- Genest J, McPherson R, Frohlich J, et al. 2009 Canadian Cardiovascular Society/Canadian guidelines for the diagnosis and treatment of dyslipidemia and prevention of cardiovascular disease in the adult – 2009 recommendations. Can J Cardiol. 2009;25(10):567-579.
- Stone NJ, Robinson JG, Lichtenstein AH, et al. Treatment of blood cholesterol to reduce atherosclerotic cardiovascular disease risk in adults: synopsis of the 2013 American College of Cardiology/American Heart Association cholesterol guideline. Annals Intern Med. 2014;160(5):339-343.
- Anderson TJ, Grégoire J, Hegele RA, et al. 2012 update of the Canadian Cardiovascular Society guidelines for the diagnosis and treatment of dyslipidemia for the prevention of cardiovascular disease in the adult. Can J Cardiol. 2013;29(2):151-167.
- Jenkins DJ, Kendall CW, Faulkner D, et al. A dietary portfolio approach to cholesterol reduction: combined effects of plant sterols, vegetable proteins, and viscous fibers in hypercholesterolemia. Metabolism. 2002;51(12):1596-1604.
- Jenkins DJ, Kendall CW, Faulkner DA, et al. Assessment of the longer-term effects of a dietary portfolio of cholesterol-lowering foods in hypercholesterolemia. Am J Clin Nutr.
