Inappropriately high levels of inflammation contribute to many of the chronic diseases of the modern world. Inflammation plays an important role in the development of atherosclerotic plaque, and inflammatory mediators have been shown to fuel tumor growth.  Certain characteristics of the Western diet are known to have pro-inflammatory effects – the high content of omega-6 fatty acids, for example, due to excessive oil and animal products, leads to overproduction of inflammatory molecules. Also, obesity is associated with chronic inflammation. Fat tissue produces a great number of both hormones and inflammatory molecules, and obesity-associated inflammation is said to be the link between excess body fat and chronic disease. 
Eating more plant foods and fewer animal products and oils is advisable to avoid these pro-inflammatory effects. Omega-3 fatty acids, in contrast to omega-6 fatty acids, are known to have anti-inflammatory effects. Fruits and vegetables are known to be protective against chronic disease due to their low calorie density and high quantity of micronutrients and antioxidants, and have been associated with reduced circulating inflammatory molecules. A recent study showed that fruit and vegetable consumption alters circulating levels of inflammatory molecules by affecting gene expression in circulating white blood cells, limiting the production of inflammatory molecules by these cells.
Young adults reported their usual food intake, and the researchers correlated this to a number of inflammatory markers in blood, as well as expression of a number of pro-inflammatory genes in white blood cells. The subjects were divided into groups based on their quantity of fruit and vegetable consumption, and inflammatory markers (C-reactive protein, homocysteine, and TNFα) were 40% lower in the group with the highest (vs. lowest) fruit and vegetable consumption. Moreover, expression of four pro-inflammatory genes (ICAM1, ILR1, TNFα, and NF-κB1) were significantly lower in the circulating white blood cells of the high fruit and vegetable consumers.  C-reactive protein and plasma homocysteine are known risk factors for heart disease, and NF-κB is a key promoter of atherosclerosis development.
This data suggests that plant foods have anti-inflammatory effects that have not yet been discovered.
We cannot underestimate the importance of high-nutrient foods. Our genes are inherited, but the expression of those genes is modified by our environment. Food components interact with our genes to affect the state of our health, and this study suggests that high-nutrient foods drive gene expression patterns that reduce inflammation and therefore risk of chronic disease.
1. Sgambato, A. and A. Cittadini, Inflammation and cancer: a multifaceted link. Eur Rev Med Pharmacol Sci, 2010. 14(4): p. 263-8.
2. Hajer, G.R., T.W. van Haeften, and F.L. Visseren, Adipose tissue dysfunction in obesity, diabetes, and vascular diseases. Eur Heart J, 2008. 29(24): p. 2959-71.
3. Hermsdorff, H.H., et al., Fruit and vegetable consumption and proinflammatory gene expression from peripheral blood mononuclear cells in young adults: a translational study. Nutr Metab (Lond), 2010. 7: p. 42.
4. Kutuk, O. and H. Basaga, Inflammation meets oxidation: NF-kappaB as a mediator of initial lesion development in atherosclerosis. Trends Mol Med, 2003. 9(12): p. 549-57.