Can a healthy diet lower my cholesterol?

Dietary Recommendations

The third National Cholesterol Education Program (NCEP) reaffirmed its position that the primary target of cholesterol-lowering therapy should be low-density lipoprotein cholesterol (LDL-C), the major cause of coronary heart disease (CHD).¹ Therapeutic lifestyle changes that can lower LDL-C include weight loss, increased physical activity, and dietary modifications (e.g., reduced intake of saturated fats).

There is limited evidence that reducing dietary intake of cholesterol directly improves serum cholesterol levels, however what is important is reducing cardiovascular risk overall. The most recent 2018 cholesterol guidelines by the American College of Cardiology (ACC) and American Heart Association (AHA) point to the importance of lifestyle choices, particularly for the nearly one-third of the US population that has metabolic syndrome because of their elevated risk of atherosclerotic cardiovascular disease (ASCVD).² People with metabolic syndrome have three of five of the following risk factors: elevated waist circumference, elevated serum triglycerides, reduced HDL-C, elevated blood pressure, and elevated fasting glucose. Lifestyle modifications, including healthy dietary choices, seek to improve all parameters of risk, including high LDL-C.

Dietary choices that maximize cardiovascular health in these guidelines advise that the majority of individuals’ diets should be composed of vegetables, fruits, whole grains, legumes, healthy protein (low-fat dairy and poultry, seafood, and nuts), and non-tropical vegetable oils. Intake of sweets, sugar-sweetened drinks, and red meats should be limited.² It is recommended that this dietary pattern should be modified to consider other medical conditions (such as diabetes), personal and cultural preferences, and appropriate calorie requirements to avoid weight gain or restrictions to promote weight loss.

Relationship between Diet and Cholesterol Levels

More research is needed to determine the relationship between dietary intake and plasma cholesterol levels and their effect on cardiovascular disease risk (CVD).³ Dietary guidelines once recommended that dietary cholesterol contributed to cardiovascular risk. But newer evidence suggests that as dietary cholesterol increases, endogenous cholesterol production decreases, achieving serum cholesterol homeostasis.⁴ Similarly, as dietary cholesterol decreases, endogenous cholesterol production may increase, potentially neutralizing any benefit of cutting cholesterol from the diet.

Berger et al. conducted a systematic review and meta-analysis of 19 randomized controlled trials (n=632) comparing healthy people consuming high levels of dietary cholesterol (501 mg/day to 1415 mg/day) with controls (consuming less than 415 mg/day).⁵ Elevated cholesterol in the diet resulted in a significant increase of both HDL-C and LDL-C, with the net LDL/HDL ratio remaining constant. Dietary cholesterol was not statistically significantly associated with cardiovascular disease risk.

Experts now feel that the relationship between dietary cholesterol and cardiovascular risk was previously overstated. In light of these findings, the 2015-2020 Dietary Guidelines for Americans⁶ modified its recommendations, removing the maximum intake limit of 300 mg/day cholesterol.

However, there is a large body of literature that correlates the consumption of foods that are high in saturated fats with cardiovascular risk.^7,8 Further, the consumption of trans-fatty acids used in processed baked goods, margarine, and other products has been shown to increase cardiovascular risk.⁹ An advisory statement by the AHA in 2017 recommended replacing saturated fats with polyunsaturated fats to decrease cardiovascular risk consistent with 2015-2020 Dietary Guidelines for Americans.¹⁰ In its report, the AHA stated that randomized controlled trials that replaced saturated fats with polyunsaturated vegetable oil reduced the risk of cardiovascular disease by 30%.

Stefanik et al. conducted a randomized controlled trial to study the effect of diet and exercise in 180 postmenopausal women (ages 45 – 64) and 197 men (ages 30 – 64) with moderately elevated LDL-C (>125 mg/dL but <210 mg/dL in women; >125 mg/dL but <190 mg/dL in men) and low HDL-C levels (≤59 mg/dL in women; ≤44 mg/dL in men).¹¹ The participants were randomized to aerobic exercise, the NCEP Step 2 diet (a reduced fat diet), diet-plus-exercise, or to a control group. Although the degree of weight change was not significantly different between the diet group and the diet-plus-exercise group, only the diet-plus-exercise group found significant reductions in the LDL-C compared to controls. For women, LDL-C decreased 14.5 ± 22.2 mg/dL in the diet-plus-exercise group compared to 2.5 ± 16.6 mg/dL (p<0.05) in the diet group; for men LDL-C decreased 20.0 ± 17.3 mg/dL vs 4.6 ± 21.1 mg/dL (p<0.001), respectively. Participants assigned to either the exercise only or the diet only group showed no statistically significant reductions in LDL or total cholesterol levels compared to those assigned to the control group. This finding highlights the combined effect of low fat diet and exercise in improving lipid profile even in the absence of additional weight loss from exercise.

Hooper et al. conducted a systematic review for the Cochrane database assessing the effect of reducing saturated fat intake on mortality and cardiovascular morbidity.⁷ They chose this analysis rather than an analysis of the effect of diet on lipid levels, noting that any single dietary change might positively impact one cardiovascular risk factor but simultaneously impact another risk factor negatively. This 2015 Cochrane review of 15 randomized controlled trials with approximately 59,000 participants reported that reducing dietary saturated fat decreased the risk of cardiovascular events by 17% (risk ratio 0.83, 95% confidence interval [0.72 – 0.96]).

References:

1. Executive summary of the third report of the National Cholesterol Education Program (NCEP) expert panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III). JAMA 2001; 285 (19): 2486-2497.
2. Grundy S, Stone N, Beam C, Birtcher KK, Harm PD. 2018 AHA/ACC/AACVPR/AAPA/ ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA guideline on the management of blood cholesterol. J Am Coll Cardiol 2019; 73 (24): e285-e350.
3. Soliman G. Dietary cholesterol and the lack of evidence in cardiovascular disease. Nutrients 2018; 10 (780): 1-14.
4. Jones PJH. Dietary cholesterol and the risk of cardiovascular disease in patients: a review of the Harvard Egg Study and other data. Int J Clin Pr Suppl 2009; Oct (163): 1-8,28-36.
5. Berger S, Raman G, Vishwanathan R, Jacques PF, Johnson EJ. Dietary cholesterol and cardiovascular disease: a systematic review and meta-analysis. Am J Clin Nutr 2015; 102 (2): 276-294.
6. 2015 – 2020 Dietary Guidelines for Americans. 8 ed: U.S. Department of Health and Human Services and U.S. Department of Agriculture; 2015. https://health.gov/dietaryguidelines/2015/. Accessed 10/23/2019.
7. Hooper L, Martin N, Abdelhamid A, Davey Smith G. Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev 2015;(6): CD011737.
8. Yu E, Hu FB. Dairy products, dairy fatty acids, and the prevention of cardiometabolic disease: a review of recent evidence. Curr Atheroscler Rep 2018; 20 (5): 24.
9. Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ, Willett WC. Trans fatty acids and cardiovascular disease. N Engl J Med 2006; 354 (15): 1601-1613.
10. Sacks FM, Lichtenstein AH, Wu JHY, et al. Dietary fats and cardiovascular disease: a presidential advisory from the American Heart Association. Circulation 2017; 136 (3): e1-e23.
11. Stefanick ML, Mackey S, Sheehan M, Ellsworth N, Haskell WL, Wood PD. Effects of diet and exercise in men and postmenopausal women with low levels of HDL cholesterol and high levels of LDL cholesterol. N Engl J Med 1998; 339 (1): 12-20.