Inflammation is always present in the body to some extent.
It is expressed by the Cox-2 family of cytokines. These may become overly produced due to neglect of Omega-3 intake of essential fats, which are Cox-1 favorable, and keep the inflammatory ones down.

There are markers for inflammation;
Sed rate, and C-reactive protein are two of them.
These however only show disease elevations.

In general if aspirin and/or NSAIDs help with symptoms, that indicates inflammation of some sort. It is a hint as to triggers or cause.

There are specific diets to keep inflammation down.. One is the Zone Diet, and also Dr. Wahl's mitochondrial diet, and some others.

example:
http://www.drweil.com/drw/u/ART02012...lammatory-diet

Diets of this type are very popular now. They focus on good fats, (olive oil, and Omega-3's), vegetables, fruit, lean protein and fish, nuts. They limit or remove carbs from pastas, bread as a rule. They also limit and discourage saturated fats.

Some of these diets are called "pain" diets, because they help reduce inflammatory pain. Some people with specific food intolerances may find pain increased when using a triggering food. Citrus for example, is implicated in joint pain. Some people cannot tolerate nightshade veggies.(myself included).
Gluten, dairy, are also commonly reported for some.