One-quarter cup of walnuts, for instance, provides more than 100 percent of the daily recommended value of plant-based omega-3 fats, along with high amounts of copper, manganese, molybdenum, and biotin. 

Heart Health
Walnuts contain the amino acid l-arginine, which offers multiple vascular benefits to people with heart disease, or those who have increased risk for heart disease due to multiple cardiac risk factors. Walnuts also contain the plant-based omega-3 fat alpha-linolenic acid (ALA), which is anti-inflammatory and may prevent the formation of pathological blood clots. 

Eating just four walnuts a day has been shown to significantly raise blood levels of heart-healthy ALA,³ and walnut consumption supports healthful cholesterol levels.
Separate research showed that eating just one ounce of walnuts a day may decrease cardiovascular risk,⁴ 

Antioxidants are crucial to your health, as they are believed to help control how fast you age by combating free radicals, which are at the heart of age-related deterioration.

Walnuts contain antioxidants that are so powerful at free-radical scavenging that researchers called them "remarkable,"⁷ and research has shown that walnut polyphenols may help prevent chemically-induced liver damage.⁸
In another study, researchers found that nuts, especially walnuts, have potent antioxidant powers. Walnut polyphenols had the best efficacy among the nuts tested and also the highest lipoprotein-bound antioxidant activity. The researchers concluded:⁹

Weight Control
Adding healthful amounts of nuts such as walnuts to your diet can help you to maintain your ideal weight over time. In one review of 31 trials, those whose diets included extra nuts or nuts substituted for other foods lost about 1.4 extra pounds and half an inch from their waists.¹⁰ Eating walnuts is also associated with increased satiety after just three days.¹¹

Brain Health
Walnuts contain a number of neuroprotective compounds, including vitamin E, folate, melatonin, omega-3 fats, and antioxidants. Research shows walnut consumption may support brain health, including increasing inferential reasoning in young adults.¹³

One study also found that consuming high-antioxidant foods like walnuts "can decrease the enhanced vulnerability to oxidative stress that occurs in aging," "increase health span," and also "enhance cognitive and motor function in aging."¹⁴

Diabetes
 Overweight adults with type 2 diabetes who ate one-quarter cup of walnuts daily had significant reductions in fasting insulin levels compared to those who did not, and the benefit was achieved in the first three months.¹⁵