Anti-inflammatory diets are hot topics, both in research and in the media. Chronic inflammation is tied to diseases like cancer, heart disease, diabetes and more. So where do “anti-inflammatory diets” fit as you consider how doable eating choices can make a difference in your health, today and long-term?
In Part 1 of this video series, Susan Steck, PhD, MPH, RD, discusses inflammation and the variety of “anti-inflammatory diets”; in Part 2, she talks about development of an overall Dietary Inflammatory Index (DII) that pulls together inflammatory and anti-inflammatory food consumption into one score meant to represent the overall effect of someone’s eating habits. In this, the final section of our interview, Dr. Steck provides an update on research using the DII to study how diet may affect health. Dr. Steck is a registered dietitian and Associate Professor of Epidemiology and Biostatistics in the Arnold School of Public Health at the University of South Carolina in Columbia.
Following the video, read on for additional insights.
Research: Diet, Inflammation & Health
As discussed in part 1 of this series, just because a food contains one nutrient or compound that seems to fight inflammation does not mean that eating that food will give you an “anti-inflammatory diet”. The effect of your eating habits on inflammation relates to how compounds in each of the foods you eat come together.
Research so far with the DII as a picture of this overall pro- or anti-inflammatory influence of diet:
- Women with the most pro-inflammatory diets (higher DII score) were 20% more likely to develop colorectal cancer than those with the most anti-inflammatory diets over 24 years of follow-up in the Iowa Women’s Health Study. This link was seen after adjusting for differences in weight (body mass index, BMI) and total calorie consumption, as well as for diabetes, age, smoking and other cancer risk factors.
- Among women in another study, the Women’s Health Initiative (WHI), those with the most pro-inflammatory diets showed over 20% more development of colorectal cancer than those with the most anti-inflammatory diets.
- Men with the most pro-inflammatory diet score were nearly 20% more likely to develop colorectal cancer than those with most anti-inflammatory diets in the NIH-AARP study. Yet DII score of women in this study was not associated with any difference in colorectal cancer risk. Therefore, the picture is not completely clear: perhaps some components of an anti-inflammatory diet are more protective than others against colorectal cancer. Perhaps other differences between these studies will come to light.
- Association of anti-inflammatory diets with breast cancer risk is also unclear. In the WHI study above, breast cancer incidence was not linked to DII score. However, a more pro-inflammatory diet score was tied to a 29% greater incidence of one particular form of breast cancer, HER-2+ cancer. What’s more, breast cancer mortality was 30% higher in women with more pro-inflammatory diets. All these links were seen after adjusting for weight (BMI), physical activity, smoking and classic breast cancer risk factors.
- Men and women with pro-inflammatory diet scores had 34% higher overall mortality than those whose diets rated as more anti-inflammatory when they were followed for 12 to 18 years after the national NHANES III dietary survey. This included 46% higher cancer mortality (with digestive tract cancer mortality especially high), and 46% higher mortality from cardiovascular disease. These statistics reflect association seen after adjusting for other likely associations, including age, weight (BMI), physical activity, smoking, diabetes, race, poverty index and more.
- Markers of inflammation and more pro-inflammatory diet scores using an adaption of the DII rating tool linked to greater development of insulin resistance in analysis of two Dutch population studies. Insulin resistance, a condition in which the body produces extra insulin in response to reduced ability of the body to respond to insulin, is a hallmark of the pathway to type 2 diabetes, and seems to raise risk of heart disease and at least some forms of cancer.
- More pro-inflammatory diet scores were not linked to metabolic syndrome, but were linked to more than double the risk of glucose intolerance (abnormally elevated blood sugar) compared to what was seen in those with more anti-inflammatory diets, among police officers in Buffalo, NY. Metabolic syndrome, characterized by presence of at least three of five metabolic abnormalities, is linked to both heart disease and type 2 diabetes. In this study, DII score was not related to other components of metabolic syndrome: triglyceride or HDL levels, blood pressure and waist circumference.
Will an Anti-Inflammatory Diet Prevent Disease?
Although good blood sugar control is important to reduce complications of diabetes, expert sources like the American Heart Association (AHA) have emphasized for years that it is not enough to prevent diabetes-related cardiovascular disease. A study presented at a recent AHA research conference suggests that one reason may be the damage to blood vessels from chronic inflammation. Research is underway looking at other ways that inflammation may damage blood vessels and interfere with heart function.
Diseases linked to chronic low-grade inflammation — including type 2 diabetes, heart disease and cancer — develop over multiple years. That makes it difficult to test effectiveness of anti-inflammatory diets in helping to prevent these diseases. The strongest evidence probably comes from combining findings of different kinds of studies.
- Randomized controlled studies that compare diet ratings with markers of heart disease or cancer risk are scientifically strong. However, these markers of risk are good guesses, but not sure bets, of who will actually develop these diseases.
- Long-term population studies like those cited above show actual development of disease over time. Here the problem is that although researchers can statistically adjust for other factors that might influence disease development, they can’t completely rule out the possibility that diet was not the true driver behind whether someone did or did not develop heart disease or cancer.
Inflammation is More than What You Eat
Excess body fat is strongly linked with inflammation — especially “dysfunctional” fat deep within the abdomen. This visceral fat produces and secretes proteins called cytokines that circulate throughout the body promoting inflammation. As body fat increases, levels of the anti-inflammatory hormone called adiponectin typically decrease.
In a study of overweight and obese women, those who achieved at least a five percent weight loss reduced inflammatory biomarkers (hs-CRP, SAA, and IL-6) by 17% to 50% compared with women in a control group asked not to change diet or exercise habits. Inflammatory markers decreased whether the weight loss was through diet or diet + exercise. The study, Nutrition and Exercise for Women (NEW), was a 12-month, randomized controlled trial. In this study, exercise alone did not show a consistent tie to reduced inflammation, even among the few who achieved at least a five percent weight loss.
Some key points:
- Although physical activity alone did not reduce inflammatory markers in the NEW study, in another intervention trial, increased physical activity seemed to play an important role in reducing inflammation beyond what was produced with weight loss over the six month study.
- In the NEW study and others, reaching an “ideal” weight or BMI was not necessary to reduce inflammation. Depending on starting weight, a five percent weight loss among many overweight or obese women like those in NEW might be 7 to 15 pounds.
- What’s more, emerging evidence suggests that anti-inflammatory effects may start even with a decrease in excess calorie consumption or a change in the balance of calorie consumption compared to calories burned in activity. If substantiated, that would mean each day of healthier habits could bring benefits even before any weight loss.
Inflammation as One Piece of the Puzzle
As evidence mounts linking inflammation to chronic diseases like cancer, heart disease and type 2 diabetes, it also shows a gap suggesting there’s more to development of each of these diseases than inflammation alone. Healthy eating habits likely influence risk of each of these diseases through effects on inflammation and through other means.
If you focus on smart eating choices and being physically active every day, you have the chance to reduce risks in multiple ways:
- reducing exposure to carcinogens, and getting plant food compounds that laboratory evidence suggests may inhibit activation of carcinogens and promote their inactivation
- more easily creating a balance of calories in-and-out to support a healthy weight and body fat level
- reducing tendencies for insulin resistance through physical activity’s influence on insulin receptors, and nutrients and phytochemicals that may help modulate cell signaling pathways
- nutrients and phytochemicals that may work together to support healthy hormone levels, normal rates of cell growth and reproduction, and self-destruction of abnormal cells
- foods with fiber and compounds that support healthy microbiota (health-promoting gut bacteria)
- reducing build-up of blockage in blood vessels and promoting function of both heart and blood vessels
The Bottom Line
Evidence so far supports smart choices in what you eat and drink as ways to decrease inflammation. Don’t get pulled off-track by headlines suggesting that one specific nutrient, supplement or “diet” is the answer. Some eating habits, like those with excess calories coming from lots of meat, refined grains, sweets and sugary soft drinks, are linked with greater health risk. Yet multiple styles of healthful eating can reduce inflammation and promote good health through other means. So focus on choices that fit your tastes and lifestyle. Build your eating habits around a wide variety of vegetables, fruits, whole grains and beans. Limit red and processed meats, salt and alcohol. Enjoy and savor nuts and seeds, herbs and spices, and perhaps coffee and tea, for the flavor they add, even while potentially adding health benefits of their own. Use physical activity and choice of food portions and snacking to support health in its many dimensions.
Sign up to receive Smart Bytes by email so you don’t miss any of the research updates and practical how-to’s ahead (see sidebar)!
** Research results from the WHI and NIH-AARP trials discussed above and in the video interview with Dr. Steck were presented at the American Institute for Cancer Research 2014 Research Conference. The studies are in process of being submitted for publication; meanwhile you can see the slides from the AICR conference presentation here, courtesy of Dr. Steck and AICR. Additional presentations from this very exciting conference can also be accessed from the AICR website. **
Shivappa N, Prizment AE, Blair, CK, Jacobs DR Jr, Steck SE, Hébert JR. Dietary Inflammatory Index and Risk of Colorectal Cancer in the Iowa Women’s Health Study. Cancer Epidemiol Biomarkers Prev. 2014 Nov; 23(11):2383-92.
Shivappa N. Dietary Inflammatory Index and Its Relationship with Inflammation, Metabolic Biomarkers and Mortality. (Doctoral dissertation). 2014. Retrieved from http://scholarcommons.sc.edu/etd/2882
Wirth MD1, Burch J, Shivappa N, et al. Association of a dietary inflammatory index with inflammatory indices and metabolic syndrome among police officers. J Occup Environ Med. 2014 Sep;56(9):986-9.
Van Woudenbergh GJ, Theofylaktopoulou D, Kuijsten A, et al. Adapted dietary inflammatory index and its association with a summary score for low-grade inflammation and markers of glucose metabolism: the Cohort study on Diabetes and Atherosclerosis Maastricht (CODAM) and the Hoorn study. Am J Clin Nutr. 2013 Dec; 98(6):1533-42.
Imayama I, Ulrich CM, Alfano CM et al. Effects of a Caloric Restriction Weight Loss Diet and Exercise on Inflammatory Biomarkers in Overweight/Obese Postmenopausal Women: A Randomized Controlled Trial. Cancer Res. 2012 May 1;72(9):2314-26.
Ryan AS, Ge S, Blumenthal JB et al. Aerobic exercise and weight loss reduce vascular markers of inflammation and improve insulin sensitivity in obese women. J Am Geriatr Soc. 2014 Apr;62(4):607-14.