Can the Mediterranean diet lower my cholesterol?

The Mediterranean diet is an eating model based on the dietary patterns of countries surrounding the Mediterranean Sea.¹ Its key components are its high monounsaturated/saturated fat ratio and high intake of plant-based foods. Observational studies have found reduced rates of cardiovascular disease and mortality among people on Mediterranean diets, but evidence from high-quality randomized controlled trials is lacking with respect to the Mediterranean diet’s effect on cholesterol levels. Existing lower-quality evidence suggests the diet may be effective in lowering total cholesterol (TC) slightly, but further study is needed.^2-4 Several studies have demonstrated other improvements in lipid profiles in people on the Mediterranean diet, but confounding factors need to be further elucidated.^5-9

Rees et al. conducted a Cochrane Review of 30 randomized controlled trials (RCTs) (n=12,461) on the effectiveness of the Mediterranean diet for cardiovascular disease (CVD) prevention.² The reviewers selected studies with follow-up periods of at least three months that compared the Mediterranean diet with other dietary interventions, usual care, or no intervention for primary or secondary prevention of CVD. Overall, the Cochrane review noted reduced risk of stroke and major cardiac events among people on the Mediterranean diet. To overcome some of the heterogeneity among the included studies, the authors divided their analyses into four sub-groups based on the type of control interventions and the measured outcomes. Low-quality evidence from five primary prevention trials (n=569) showed a small reduction in TC of 6.19 mg/dL (95% CI [12.38 – 0]) for those on a Mediterranean diet compared to no intervention. There was no high-quality evidence of an effect on low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), or triglycerides.

Shai et al. conducted a two-year study in which 272 moderately obese subjects were randomly assigned to one of three diets: 1) Mediterranean, restricted-calorie diet; 2) low-carbohydrate, non-restricted calorie diet, or 3) low-fat, restricted calorie diet.⁷ The purpose was to evaluate each diet’s effectiveness with respect to weight loss and each diet’s impact on certain risk factors for CVD and diabetes. For all three diets, a maximum weight loss phase occurred between the first and sixth months, while a subsequent phase of weight maintenance occurred from the seventh to twenty-fourth month. Weight loss was significantly greater in the Mediterranean and low-carbohydrate dieters, compared to the low-fat dieters. Average HDL-C levels improved during the first six months (+2.0 mg/dL) and continued to improve during the weight maintenance phase of the study (+6.3 mg/dL) for participants on the Mediterranean diet, but these improvements, while statistically significant compared to baseline, were comparable to the change in low-fat dieters (+1.7 and +6.4 mg/dL) and not as impressive as the improvements seen among the low-carbohydrate dieters (+4.8 and 8.4 mg/dL). The analysis showed that LDL-C decreased significantly at six (-4.3 mg/dL) and twenty-four months (- 5.6 mg/dL) compared to baseline with the Mediterranean diet. While this decrease was greater than seen with the other diets, the difference was not significant. It is not possible from this data alone to determine how much weight loss factored into the changes in lipids that occurred on the different diets.

A parallel-arm RCT by Doménech et al. studied the one-year effect of the Mediterranean diet supplemented with either extra virgin olive oil (MedDiet + EVOO) or nuts (MedDiet + Nuts).⁸ The authors enrolled 235 subjects with high cardiovascular risk who were randomized from the PREDIMED study to either the MedDiet + EVOO group, MedDiet + Nuts group, or a low-fat control group. Despite no significant difference in weight loss among the three groups, compared to baseline, authors found a significant decrease in TC in the MedDiet + EVOO group of 11.3 mg/dL (95% CI [-16.8 – -5.7], p<0.05) and the MedDiet + Nuts group of 13.6 mg/dL (95% CI [-18.3 – -9.0], p<0.05). The reduction in TC for the MedDiet + Nuts group was significantly greater than the reduction for the control group. Compared to baseline, the authors also found a significant decrease in LDL-C in both the MedDiet + EVOO group of 6.5 mg/dL (95% CI [-11.5 – -1.6], p<0.05) and the MedDiet + Nuts group of 11.3 mg/dL (95% CI [-15.9 – -6.6], p<0.05). However, neither diet significantly lowered LDL-C more than the control group. There was no significant change in HDL-C for any of the diets.

The Bottom Line

The Mediterranean diet seems to lower total cholesterol and may improve high- and low-density lipoprotein cholesterol levels, but it is not yet clear if these effects are a result of the specific diet, or the weight loss associated with it. Further high quality RCTS are needed.

^References 

1. Keys A, Menotti A, Karvonen MJ et al. The diet and 15-year death rate in the seven countries study. Am J Epidemiol, 1986; 124: 903- 15.
2. Rees K, Takeda A, Martin N, et al. Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2019.
3. Nordmann AJ, Suter-Zimmermann K, Bucher HC, et al. Meta-analysis comparing Mediterranean to low-fat diets for modification of cardiovascular risk factors. Am J Med. 2011;124(9).
4. Bajerska J, Chmurzynska A, Muzsik A, et al. Weight loss and metabolic health effects from energy-restricted Mediterranean and Central-European diets in postmenopausal women: A randomized controlled trial. Sci Rep. 2018;8(1).
5. Austel A, Ranke C, Wagner N, Görge J, Ellrott T. Weight loss with a modified Mediterranean-type diet using fat modification: a randomized controlled trial. Eur J Clin Nutr. 2015;69(8):878-884.
6. Esposito K, Maiorino MI, Bellastella G, Chiodini P, Panagiotakos D, Giugliano D. A journey into a Mediterranean diet and type 2 diabetes: a systematic review with meta-analyses. BMJ Open. 2015;5(8).
7. Shai I, Schwarzfuchs D, Henkin Y, et al. Weight loss with a low-carbohydrate, mediterranean, or low-fat diet. N Engl J Med. 2008;359(3):229-241.
8. Doménech M, Roman P, Lapetra J, et al. Mediterranean diet reduces 24-hour ambulatory blood pressure, blood glucose, and lipids. Hypertension. 2014;64(1):69-76.
9. Elhayany A, Lustman A, Abel R, Attal-Singer J, Vinker S. A low carbohydrate Mediterranean diet improves cardiovascular risk factors and diabetes control among overweight patients with type 2 diabetes mellitus: a 1‐year prospective randomized intervention study. Diabetes Obes Metab. 2010;12(3):204-209.