High levels of LDL cholesterol, triglycerides - or both - in the blood plasma are one of the leading risk factors related to cardiovascular diseases. Lifestyle modifications – involving weight loss and reduced intake of saturated fats – are a recommended strategy to overcome the perils associated with high LDL cholesterol levels and to improve the lipid profile.
While a low‐fat, higher carbohydrate diet is one of the most common diet strategies to reduce the intake of saturated fat, evidence suggests that dietary programs where saturated fats are replaced with unsaturated fats rather than carbohydrate, like the Mediterranean diet, can significantly lower the risk of cardiovascular diseases. “Among persons at high cardiovascular risk, a Mediterranean diet supplemented with extra-virgin olive oil or nuts reduced the incidence of major cardiovascular events.” .
A recent 2016 study , published in the Journal of the American Heart Association, suggests a diet rich in walnuts had the most significant impact on lipid levels for the participants, especially those with insulin resistance. In order to reach this conclusion, the research team from University of California, San Diego School of Medicine enrolled 245 overweight and obese adult women in a one-year behavioural weight loss program. The participants were randomly assigned to three different dietary patterns:
- low-fat and high-carbohydrate
- low-carbohydrate and high-fat
- Walnut-rich, high-fat and low-carbohydrate diet
Similar weight loss: All the three meal plans achieved similar weight loss results.
Less impact on lipid profile with low fat diet: Low fat diets resulted in most weight loss in insulin-resistant women but didn’t influence lipid levels effectively.
Most impact on lipid levels with walnut rich diet: The meal plan rich in walnuts, containing polyunsaturated fatty acids, showed the most capacity to improve the overall cholesterol levels in comparison to both other diets.
- Greater increase in HDL levels with walnut rich diet: The participants who consumed walnut rich diet experienced significant a decrease in LDL cholesterol levels while achieving greater increase in HDL cholesterol levels as compared to participants from other diet groups. This impact is important as Cheryl Rock, the principal researcher of this study explains, "Many diets have said it is okay to eat healthy fats and emphasize olive and canola oils.…. What we found is that a diet high in healthy oils did lower lipids, but it also lowered both good and bad cholesterol."
The study authors concluded that “Results from this study provide a better understanding of lipid response to diet composition in consideration of insulin resistance status. Weight loss in the behavioural weight loss intervention was comparable across lower fat, higher carbohydrate and walnut‐rich diets. Weight loss was generally associated with an improvement in the lipid profile but was influenced by insulin resistance status and diet composition. Decreased CRP was observed in all diet groups as well as improved insulin sensitivity in insulin‐resistant women. The walnut‐rich diet resulted in the most favourable changes in lipid levels while still associated with a degree of weight loss that was comparable to the lower fat diet.”
What Makes Walnuts So Heart-healthy?
Studies have consistently shown that regular consumption of walnuts has the most beneficial effect on the heart and circulatory system . So, what makes these nuts special when it comes to cardiovascular health?
While most other nuts contain monounsaturated fatty acids, walnuts are a rich source of polyunsaturated fatty acids and in particular omega -6 fatty acid (linoleic acid), alpha-linolenic acid (ALA). In fact, walnuts are the only nuts providing high level of ALA, a plant based omega-3 fatty acid particularly known for its heart healthy and anti-inflammatory benefits. ALA is known to prevent blood clot formation, prevent fatal heart attacks, reduce inflammation and maintain brain health.
A 2013 study  published in the Journal of Nutrition showed that along with reducing LDL cholesterol levels, walnuts help cut down the risk of heart disease through other mechanisms. It showed that even one-time consumption of walnut oil has a favourable effect on vascular health. The oil found in walnuts helps to maintain the integrity and functions of endothelial cells, cells that line the inner surface of the blood vessels. The study also provided evidence that eating whole walnuts improves the function of HDL cholesterol in effectively transporting and eliminating excessive cholesterol from the body. According to the study researchers, the presence of alpha-linolenic acid, gamma-tocopherol and phytosterols in walnut oil may explain the beneficial effects in preserving endothelial cell functions.
In a nutshell (pun intended), the combination of healthy fatty acids and other bio-active compounds in walnuts helps to decrease LDL cholesterol levels, improve endothelial functions, reduce blood pressure and lower inflammatory markers   – significantly lowering the major risk factors for cardiovascular heart disease through diverse mechanisms.
Well, the evidence appears compelling enough to start eating a handful of walnuts every day. Are you ready to add some crunch to your daily diet?
- Estruch et al. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet. The New England Journal of Medicine. 2013
- Tran et al. Effects of Diet Composition and Insulin Resistance Status on Plasma Lipid Levels in a Weight Loss Intervention in Women. The Journal of American Heart Association. 2016
- Feldman EB. The scientific evidence for a beneficial health relationship between walnuts and coronary heart disease. The Journal of Nutrition. 2002 May;132(5):1062S-1101S.
- Berryman et al. Acute Consumption of Walnuts and Walnut Components Differentially Affect Postprandial Lipemia, Endothelial Function, Oxidative Stress, and Cholesterol Efflux in Humans with Mild Hypercholesterolemia. The Journal of Nutrition. 2013.
- Katz et al. Effects of walnuts on endothelial function in overweight adults with visceral obesity: a randomized, controlled, crossover trial. The Journal of American College of Nutrition. 2012 Dec;31(6):415-23.
- Penny M. Kris-Etherton. Walnuts Decrease Risk of Cardiovascular Disease: A Summary of Efficacy and Biologic Mechanisms. The Journal of Nutrition.