Research consistently shows that people who eat nuts as part of a balanced diet have lowered their LDL ( low-density lipoprotein or "bad") cholesterol levels in their blood and improved their immune system. Nuts rich in selenium like Brazil nuts and soy nuts are probably the best nuts to eat if all you are doing is focusing on boosting your immune system.  

According to our government’s DASH diet, you should have 4-5 servings per week of nuts and seeds to help you lower your blood pressure. 

Nuts are:

• Low in saturated fat
• High in fiber, protein and vitamin E
• High in phytochemicals that act as antioxidants (similar to grapes and tea)

High LDL is one of the primary causes of heart disease, so nuts' ability to lower LDL cholesterol seems to be quite beneficial.  Many nuts are also rich in omega-3 fatty acids which, combined with vitamin E, works wonders for your immune system.

Omega-3s are a healthy form of fatty acids that seem to help your heart by, among other things, preventing dangerous heart rhythms that can lead to heart attacks. Omega-3 fatty acids are also found in fish, but nuts are one of the best plant-based sources of omega-3s.

Nuts contain a lot of fat; as much as 80 percent of a nut is fat. Even though most of this fat is healthy fat, it's still a lot of calories, so make sure to consume them in moderation.  You should have at least a handful of nuts per day.  A great way to get your handful each day is to add walnuts to oatmeal, put almonds in your salad, or mix a handful of cashews with some raisins and keep the mixture at your desk for light snacking.