A diet that is rich in walnuts may help reduce levels of low-density lipoprotein, or "bad" cholesterol, and improve general heart health. Eating walnuts may also provide several other health benefits.
Many nuts mostly contain monounsaturated fatty acids (MUFAs), but walnuts mainly consist of polyunsaturated fatty acids (PUFAs). They also contain significant amounts of alpha-linolenic acid (ALA), the plant-based source of omega-3 fatty acid.
Walnuts are rich in other nutrients too, such as folate and vitamin E. Folate helps reduce the risk of central nervous system defects in unborn babies. Vitamin E helps to form hemoglobin, the protein that carries oxygen in the blood.
However, walnuts are also a high-calorie food, and eating too many may lead to weight gain.
In this article, we look at some of the research supporting the inclusion of walnuts in the diet, especially for people who wish to control their cholesterol levels.
According to the Centers for Disease Control and Prevention (CDC), nearly 1 in 3 people in the United States have high overall levels of cholesterol in their blood.
In 2016, scientists presenting at the Experimental Biology 2016 meeting in San Diego, CA, noted that eating walnuts every day may have a positive impact on cholesterol levels, without increasing body weight.
The researchers studied data for 514 older adults, with an average age of 69 years, who were participating in the Walnuts and Healthy Aging (WAHA) study.
Around half the participants added a handful of walnuts to their daily diet, representing 15 percent of their calorie intake each day. The other half consumed their usual daily diet without nuts.
After 1 year, the researchers found that those on the walnut diet had significantly lower levels of LDL cholesterol when compared with those who ate their usual diet.
There were no significant differences between the groups regarding changes in body weight and levels of high-density lipoprotein (HDL) or "good" cholesterol.
In 2018, after further investigation, the WAHA researchers concluded that "walnuts can be incorporated into the daily diet of healthy elders without concern for adverse effects on body weight or body composition."
Better lipid profiles
Scientists continue to find evidence to support the cardiovascular benefits of walnuts.
In 2018, a review of 26 studies, using data for more than 1,000 people, concluded that those who ate a walnut-rich diet had lower levels of:
- total cholesterol
- LDL cholesterol
- triglycerides, a type of fat in the blood
- apoprotein B, a protein science has linked to cardiovascular disease
In this study, the investigators did not find that walnuts led to an increase in body weight.
They suggested one reason for the improved levels of the above compounds could be that walnuts are rich in plant sterols. These naturally occurring compounds might help to stop the body from absorbing cholesterol.
Walnuts also contain polyphenols and tocopherol, which could encourage antioxidant and anti-inflammatory activity in the body. More studies are needed to confirm this.
The researchers concluded that, "Incorporating walnuts into the diet improved blood lipid profile without adversely affecting body weight or blood pressure."
A number of other studies have also indicated that a daily helping of walnuts can benefit cardiovascular health, including in those with or at risk of developing diabetes.
In 2015, a study appearing in BMJ Open Diabetes Research Care looked at individuals aged 25 to 75 years with a high risk of diabetes. One group of participants included 56 grams (g) of walnuts in their daily diet, while the second group ate no walnuts.
After 6 months, the team found a significant improvement in the functioning of the blood vessel wall (endothelium) in those who consumed the walnuts. LDL cholesterol levels were also lower in this group.
However, the team found no significant impact on blood pressure, blood glucose, or HDL cholesterol levels in the group that ate the walnuts.
There were also significant increases in body fat among those members of the walnut-eating group who did not receive dietary counseling on how to adjust their calorie intake.
Lipid profile and diabetes
Those who consumed the walnut oil had improved lipid profiles at the end of the study period when researchers compared them with those who took the placebo.
The scientists noted that the following compounds in walnuts and walnut oil might help to achieve their health benefits:
- l-arginine, the amino acid the body needs to make the vasodilator nitric oxide
- dietary fibers
- folic acid
The researchers suggested that "walnut oil may serve as a helpful natural remedy for hyperlipidemic patients with type 2 diabetes."
The cardiovascular system is not the only part of the body that might benefit from consuming walnut and walnut oil.
A study that appears in Biology of Reproduction linked eating walnuts with an improvement in several indicators of sperm health.
The study involved 117 healthy men who were aged 21 to 35 years old and consumed a Western-style diet. The researchers divided them into two groups.
The first group ate 75 g of walnuts a day for 12 weeks and the second group avoided walnuts.
Compared with the nut-free group, by the end of the study period, the men who had eaten walnuts had significantly higher levels of:
- sperm vitality
- sperm motility, or ability to move
- sperm morphology
However, the researchers could not say whether eating walnuts would benefit young men with fertility problems.
Research in the British Journal of Cancer took data from more than 75,000 women in the United States Nurses' Health Study.
The findings suggested a link between consuming a 28-g serving of nuts at least twice a week and a significantly lower risk of pancreatic cancer. The nuts in this study included almonds, Brazil nuts, and walnuts.
The authors said that the reduction in risk was of any risk factors for pancreatic cancer that the participants might have had, such as smoking and diabetes.
In 2014, scientists published findings in The Journal of Nutrition, Health & Aging indicating that eating walnuts may improve mental ability.
The team used data from several years of the National Health and Nutrition Examination Survey (NHANES) of U.S. adults who were 20 to 90 years old.
Those with a higher daily intake of walnuts showed better performance on six tests of mental ability, including memory, concentration, and information processing speed.
A 2014 study on mice suggested that eating walnuts might benefit brain function.
The mice that were bred to model the progression of Alzheimer's disease consumed either a walnut-rich diet or a diet without walnuts.
Those that consumed walnuts showed significant improvements in learning skills, memory, anxiety levels, and other measures of brain function when the scientists compared them with those that did not.
A previous study by the same team had suggested that walnut extract may protect against the damaging effects of amyloid-beta protein. This protein is the main constituent of amyloid plaques that form in the brains of people who develop Alzheimer's disease.
The authors proposed that walnuts might help to reduce the risk, delay the start, or slow the progression of Alzheimer's disease.
Walnuts are a nutritionally rich food, but they are also high in calories and may lead to weight gain if people eat too many of them. It is, therefore, necessary to consume walnuts in moderation, and as part of a healthful lifestyle.
Also, walnuts can cause a severe or even fatal allergic reaction in a person with a nut allergy. Anyone with a nut allergy should not eat walnuts and other types of nut.
For more on allergies and how to tell the difference between an allergy and an intolerance, see our dedicated article here.
Walnuts can be a healthful and tasty addition to the diet.
Here are some ideas for using walnuts:
- eat them alone as a snack
- serve them alongside dates, dried fruit, or low-fat cheese
- sprinkle them on muesli
- make walnut bread
- add them to a salad for extra crunch
As for walnut oil, you can add it to salads or pour a little on cooked vegetables for a nutty flavor.
Cooking the oil, however, may give it a bitter taste, so it is better to add it after cooking.
A growing body of research suggests that consuming a moderate amount of walnuts may benefit cholesterol levels, the cardiovascular system, and other aspects of health.
It is worth noting that some studies into the benefits of walnuts are supported by interested parties, such as the California Walnut Commission.
Further research is necessary to confirm the possible health benefits of walnuts.