June Research Extracts: Foods and LDL Cholesterol Levels, Strawberries and Cardiovascular Function
Welcome to the June 2021 edition of Research Extracts. “The Extracts” is designed to keep busy practitioners and savvy consumers up to date on the latest research on diet, nutrients, botanicals, the microbiome, the environment, and lifestyle approaches to good health. Our medical team, which includes NDs, MDs, PhDs, RDs, an MS, and an LAc, has summarized the essence of several of the most interesting recent studies.
In this issue you will find new studies on the dietary impact on cardiovascular disease risk, including: (1) specific dietary factors and LDL cholesterol, (2) strawberries and heart disease, (3) plant-based diets and blood pressure, and (4) the Mediterranean diet and coronary artery disease.
Foods that influence LDL cholesterol levels
Cardiovascular disease (CVD) remains the most common cause of death in the United States. Low-density lipoprotein (LDL) cholesterol levels are a key indicator of cardiovascular health, with elevated LDL associated with higher risk for CVD. Consequently, understanding the impact of food on LDL cholesterol is a valuable tool for supporting cardiovascular health. In a large review study, published guideline documents (n=37), systematic reviews (n=108), and randomized controlled trials (n=20) were evaluated to determine the overall degree of evidence available to correlate a variety of foods with changes in LDL cholesterol.
The study found strong evidence for the largest reductions in LDL with using oils high in polyunsaturated or monounsaturated fats and low in saturated fats, such as rapeseed or canola oils, when used as a replacement for half of the saturated fats in the diet (like the Nordic diet discussed below). Soluble dietary fiber – like psyllium, beta-glucans, or oats – provided moderate reductions in LDL when intake averaged 11 g/day, as did foods enriched with plant sterols and stanols, such as fortified yogurts, when intake averaged 2.2 g/day.
Other types of fiber had smaller lowering effects. Moderate lowering effects were also seen with avocado (about one daily in place of other fats) and turmeric (600 mg curcuminoids on average). There was some evidence that flaxseed (38 g/day), soy protein (26 g/day), and tomatoes (300 g/day) also provided small-to-moderate reductions in LDL cholesterol. Foods rich in saturated or trans fats markedly increased LDL, as did large quantities (~6 cups/day) of unfiltered coffee, although decaffeinated and filtered coffee had no effect. Evidence for other tested foods was weak or the impact on LDL levels was small or unclear.
Contributed by Sheena Smith, MS MA
- Schoeneck M, Iggman D. The effects of foods on LDL cholesterol levels: A systematic review of the accumulated evidence from systematic reviews and meta-analyses of randomized controlled trials. Nutr Metab Cardiovasc Dis 2021 May 6;31(5):1325-1338. doi: 10.1016/j.numecd.2020.12.032.
Eating strawberries daily improves cardiovascular function
Phytochemicals, a group of compounds found in plants, are found in a variety of vegetables, fruits, nuts, grains, seeds, and beans. Phytochemicals give plants their characteristic flavors, colors, and smells. Phytochemicals have a variety of known benefits for immune function, hormonal regulation, and reduction of inflammation. Polyphenols in berries have been studied for lowering blood pressure. Could this confer additional cardiovascular risk benefit?
This study assessed whether strawberry intake affects cardiometabolic risk factors and vascular endothelial function in adults with moderately high cholesterol. A randomized, controlled, double-blind, 2-arm, 2-period crossover trial was conducted with 34 adults. The average age of the participants was 53, average BMI 31, and average LDL level 133 mg/dL.
Participants were randomly assigned to one of two interventions – a prepared beverage twice daily containing either 25 g of freeze-dried strawberry powder or a placebo powder for four weeks; participants then switched to the other intervention. Fasting LDL cholesterol was measured at baseline and after four weeks of consuming the assigned beverage. Other outcomes measured include inflammation, metabolic markers, quantitative polyphenolic metabolomics, flow-mediated dilation (FMD), and blood pressure (BP). FMD and BP were also assessed at one hour and two hours after a bolus of 50 g strawberry or placebo beverage.
LDL cholesterol levels did not differ after four weeks of intervention. In addition, total cholesterol, triglycerides, glucose, insulin, C-reactive protein, FMD, and BP did not change. There was a significant intervention reaction for FMD and BP at one hour after strawberry beverage consumption compared to the control group and lowered systolic BP was noted two hours post-consumption. Certain polyphenolic metabolites increased significantly in the blood following strawberry beverage consumption while others decreased. These levels were significantly associated with increased FMD.
The study concludes that strawberries can improve the health of vascular tissue when taken in sufficient amounts, a conclusion that could be related to phenolic metabolites after consuming strawberries influencing endothelial function. This data supports the inclusion of strawberries as part of a heart healthy diet in adults with moderately high cholesterol.
Contributed by Amanda Frick, ND, LAc
- Huang L, Xiao D, Zhang X, et al. Strawberry consumption, cardiometabolic risk factors, and vascular function: a randomized controlled trial in adults with moderate hypercholesterolemia. J Nutr 2021. doi:10.1093/jn/nxab034
Do plant-based diets reduce blood pressure?
Although a strict vegetarian diet is associated with lower blood pressure, it has not yet been established whether a plant-based diet that allows some animal foods has a similar effect. A recent meta-analysis reviewed data from 41 clinical trials, evaluating the effect of several primarily plant-based diets on blood pressure. The diets included were vegan, lacto-ovo vegetarian, DASH, healthy Nordic, Mediterranean, high fiber, and high fruit and vegetable. These diets focus on fruits, vegetables, whole grains, nuts, and seeds, while allowing either no animal-based foods or restriction of most animal foods.
There was high certainty that the lacto-ovo vegetarian and DASH diets significantly reduce blood pressure, moderate certainty that the healthy Nordic and Mediterranean diets significantly reduce blood pressure, low certainty that a vegan diet significantly reduces blood pressure, and very low certainty that high fiber and high fruit and vegetable diets significantly reduce blood pressure. Although there were some study limitations, including a low number of studies that evaluated the healthy Nordic, high fiber, and high fruit and vegetable diets, one strength of the study is that it includes a comprehensive review of different plant-based diet types.
You can read more about the Mediterranean diet and DASH diet here. The Nordic diet is very similar to the Mediterranean diet, except that the Mediterranean Diet focuses on olive oil, whereas the Nordic diet emphasizes canola oil.
Contributed by Jennifer Greer, ND, MEd
- Gibbs J, Gaskin E, Ji C, et al. The effect of plant-based dietary patterns on blood pressure: a systematic review and meta-analysis of controlled intervention trials. J Hypertens 2021;39(1):23-37. doi:10.1097/HJH.0000000000002604
The Mediterranean diet is more effective than a low-fat diet for blood vessel health
Speaking of the Mediterranean diet (MedDiet), a new study looked at the diet’s impact on blood vessel health. Dysfunction of the endothelium that lines the arteries is an important aspect of coronary artery disease. One single-blind arm of a larger study – the CORonary Diet Intervention with Olive oil and cardiovascular PREVention (CORDIOPREV) study – compared the effect of a Mediterranean diet (35% fat [22% MUFAs like olive oil], less than 50% carb) to a low-fat diet (28% fat [12% MUFAs], greater than 55% carbs) on endothelial function. Of the 1,002 participants in the larger study, 805 completed an endothelial function test at baseline and after one year on one of the two diets.
After one year, the participants on the MedDiet had greater flow-mediated dilation (a measure of endothelial function) than participants on the low-fat diet (3.83% versus 1.16% in the MedDiet and low-fat diet, respectively). These differences remained after stratifying the groups to those with severe endothelial dysfunction and those with non-severe endothelial dysfunction at the beginning of the study.
Looking at biochemical parameters, participants on the MedDiet had higher HDL cholesterol and lower fasting glucose and C-reactive protein (a sign of inflammation), compared to participants on the low-fat diet. The MedDiet also decreased oxidative stress, as evidenced by decreased cellular reactive oxygen species and decreased endothelial cell senescence. The MedDiet also decreased endothelial micro-particles, which are shed from endothelial cells and represent inflammation, coagulation, and disturbed vascular function. On the flipside, endothelial progenitor cells, which are representative of endothelial cell regeneration and healing, were increased in the Mediterranean diet group.
Contributed by Kathi Head, ND
- Access full text
- Yubero-Serrano E, Fernandez-Gandara C, Garcia-Rios A, et al. Mediterranean diet and endothelial function in patients with coronary heart disease: an analysis of the CORDIOPREV randomized controlled trial. PLoS Med 2020;17(9):e1003282. doi 10.1371/journal.pmed.1003282
In case you missed them – you can keep exploring these heart health posts: