KEY POINTS
■ Inflammation may be associated with chronic diseases, specifically diabetes mellitus (DM) and coronary artery disease.
■ Serum levels of inflammatory biomarkers, especially C-reactive protein, can predict risk of cardiac events and development of DM.
■ Foods that increase inflammation include refined grains, red and processed meats, fried foods, and sugar.
■ Foods that decrease inflammation include whole grains, fish and poultry, fruits and vegetables, legumes, nuts, and olive oil.
The past few decades have been filled with fad diets and ever-changing dietary advice. From low-fat/high-carbohydrate to high-fat/no-carbohydrate options, the possibilities can be confusing and overwhelming. A review of recent research finds that specific dietary patterns in addition to certain foods and nutrients can have a significant impact on the health of patients. These patterns and foods can be correlated with inflammatory markers to determine the effect of diet on the chronic disease state and associated risks. Although some of the advice may seem obvious, a look at the overall data identifies specific recommendations that could have a considerable effect on inflammatory status and overall health.
INFLAMMATION AND CHRONIC DISEASE
There has been an abundance of recent evidence about inflammatory markers and their relationship to various diseases, especially coronary artery disease (CAD) and diabetes mellitus (DM), both among the top 10 causes of mortality in the United States.1 Atherosclerosis, along with its most feared complication, MI, is primarily a disease of lipid accumulation and inflammation. Atherosclerotic lesions are caused by specific cellular and molecular responses that are part of the inflammatory response. Inflammatory biomarkers can be used to determine the possibility of future cardiac complications. One of these biomarkers, C-reactive protein (CRP), is produced primarily in the liver in response to interleukin-6 (IL-6) during times of acute infection and inflammation. CRP is also found in the endothelium of atherosclerotic plaques and is produced by the arterial tissue itself. In a basic laboratory test, the level of CRP must be greater than 10 mg/L to be detected. For levels less than 10 mg/L, such as those produced by atherosclerotic lesions, measurements of high-sensitivity CRP (hsCRP) are believed to predict the risk of future cardiac events. Although CRP is the most commonly used biomarker, additional markers of inflammation and endothelial dysfunction are often included in analyses of the inflammatory effect. These include IL-6, E-selectin, soluble intercellular adhesion molecule 1 (sICAM-1), soluble vascular cell
adhesion molecule 1 (sVCAM-1), and soluble tumor necrosis factor alpha receptor 2 (sTNFR2).
Risk and development of DM is also associated with increased levels of CRP independent of obesity, BP, and cholesterol.2 Findings indicate that hsCRP levels are driven by insulin resistance. The reason for the association is still unknown, although hypotheses include the effect of cytokines on insulin resistance, oxidative stress, or the innate immune system.2 Some authors have theorized that inflammatory biomarkers are linked with other chronic diseases, including cancer and autoimmune diseases, but there is no current consensus on this.
Many studies have been conducted on the effect of dietary factors on inflammation, specifically by measuring plasma levels of CRP and other biomarkers. These studies allow us to glean new information about dietary patterns and specific foods that may decrease inflammation in the body and reduce the risk of chronic diseases, specifically CAD and DM.
DIETARY PATTERNS AND THEIR EFFECT ON
INFLAMMATORY BIOMARKERS
Much of the evidence looks at dietary patterns versus specific foods or food groups. Using a food frequency questionnaire, participants record foods they have eaten and the number of times they were eaten over a certain period of time. This common dietary assessment tool enables researchers to determine patterns in the participants' diets.
One pattern that seems to be linked to an increased level of inflammatory markers is the Western pattern. This pattern is characterized by dietary content that is high in red and processed meats, sweets, desserts, french fries, and refined grains. In a study by Lopez-Garcia and colleagues, participants with an increased consumption of the Western pattern had higher levels of CRP (P < .001), IL-6 (P = .006), E-selectin (P < .001), sICAM-1 (P < .001), and sVCAM-1 (P = .008) after adjusting for age, body mass index (BMI), physical activity, smoking status, and alcohol consumption.3 Subjects with an increased consumption of the Western pattern had a higher BMI and were more likely to smoke and less likely to exercise. They also had a higher intake of saturated and trans fats and a lower intake of fiber and folate. In contrast, a "prudent" dietary pattern was associated with decreased levels of inflammatory markers, specifically CRP (P = .02) and E-selectin (P = .001), even after adjustment for confounding factors. This pattern is characterized by an increased intake of fruit, vegetables, legumes, fish, poultry, and whole grains. The subjects with the highest consumption of the prudent pattern were more physically active and smoked less, and they had a lower intake of saturated and trans fats and a higher intake of polyunsaturated fat, folate, and fiber.
In another study, a statistical method identified a dietary pattern that correlates with an increase in all inflammatory biomarkers, including CRP, IL-6, E-selectin, sICAM-1, sVCAM-1, and sTNFR2 (P < .001 for all).4 This pattern is also strongly linked to an increased risk of diabetes. It is high in sugar-sweetened soft drinks, refined grains, and processed meats and low in wine, coffee, and cruciferous vegetables. The association holds true even after adjusting for BMI and other characteristics.