Anti-inflammatory effects of plant-source antioxidants seen as key to their benefits
Type-2 or “adult-onset” diabetes is the leading cause of premature deaths in the United States.
Nearly 100 million American adults have either type-2 diabetes or pre-diabetes — and the “adult-onset” label is now misleading, given the rising rates of diabetes in teens and older children.
Earlier research on dietary approaches to diabetes prevention tended to focus on specific foods or food groups, rather than eating patterns (diets).
To remedy that knowledge gap, several recent studies instead focused on the links between a diet’s “antioxidant capacity” and its influence on the risk for diabetes.
We address the role of a diet’s antioxidant capacity in “Diets’ abundant antioxidants key to their anti-diabetes effects”, below.
But first, let’s review the results of an international study that looked for links between five “high-quality” diets and the risk for diabetes.
Singapore study links five high-quality diets to reduced diabetes risk
The newest findings flow from an analysis of data from the Singapore Chinese Health Study.
That analysis was performed by a team of scientists from the Harvard School of Public Health and universities in Singapore and China.
Their goal was to see whether and to what extent each of five high-quality diets might significantly reduce the risk for diabetes (Chen GC et al. 2019).
The five diets chosen for the analysis are considered high quality because they’ve previously been linked to reduced risks for heart disease and/or diabetes.
All five diets resemble the traditional Mediterranean diet but vary significantly in their adherence to its characteristic features:
- Moderate amounts of fish and other seafood.
- Large amounts of vegetables, fruits, legumes (e.g., beans and lentils), nuts, grains (mostly whole/unrefined), and extra-virgin olive oil.
- Low-to-moderate amounts of cultured dairy foods (e.g., cheese or yogurt) and red wine (drunk during meals).
- Small amounts of red meat, poultry, and non-cultured dairy foods (e.g., milk and butter).
Compared with the standard American diet, all five of the high-quality diets are relatively low in red meat, processed foods, and fried foods and exclude sugar-sweetened foods or beverages:
- The aMED (alternate Mediterranean) diet most closely resembles the traditional Mediterranean diet, but it eliminates dairy and includes only whole grains (i.e., no white bread, pasta, or rice).
- The AHEI-2010 (Alternate Healthy Eating Index 2010) diet closely resembles the traditional Mediterranean diet and likewise features foods and nutrients that may reduce the risks for heart disease, diabetes, and other major health conditions.
- The DASH (Dietary Approaches to Stop Hypertension) diet resembles the Mediterranean diet but is lower in sodium, to help control blood pressure*. And, compared with the aMED and AHEI-2010 diets, it places less emphasis on olive oil, fish, and red wine, while allowing more red meat. (Recent findings challenge the universality and strength of the link between dietary sodium and hypertension: see How Fake are Our Salt Fears?, Salt Intake Set by the Brain, and Salty American Diet Displays More Harmful Effects.)
- The PDI (plant-based diet index) resembles the Mediterranean diet but features plant foods and few animal foods.
- The hPDI (healthful plant-based diet index) also resembles the Mediterranean diet but, like the PDI, is dominated by plant foods.
For their analysis, the team used data from 45,411 middle-aged and older participants who were not diabetic at the start of the study.
Then, based on their self-reported intake of 165 foods, each participant received a score based on how closely their diets matched each of the five high-quality diets described above.
The volunteers were then followed for an average of 11 years, during which time more than one in 10 participants (5,027) developed diabetes.
Encouragingly, the international team’s analysis linked all five high-quality diets to significantly lower risks for developing diabetes.
Specifically — compared to those whose diets didn’t resemble any of the five diets — the participants whose diets most closely matched any of the five high-quality diets were 16–29% less likely to develop diabetes.
Here’s how the study’s senior author — Professor Rob van Dam of Harvard and the National University of Singapore — summarized their findings: “Our results are consistent with studies in other populations that a high-quality diet defined by an abundance of minimally processed plant foods such as whole grains, vegetables, fruit, nuts and legumes, but restricted intake of red and processed meat, and sweetened beverages were significantly associated with lower risk of diabetes.”
A prior study from members of the same international team looked for links between white rice the risk for developing diabetes (Seah JYH et al. 2018).
Their analysis suggested that replacing one serving of rice with a single serving of whole-grain bread reduced diabetes risk by 18%.
In contrast, their analysis revealed that replacing a serving of white rice with a serving of red meat or poultry raised the risk of diabetes by up to 40%.
Antioxidants may be key to the five diets' anti-diabetes benefits
What accounts for the apparent anti-diabetes effects of the five high-quality diets examined in the Singapore study?
It’s likely that the key factors are aspects of those diets previously linked to protection of metabolic health: omega-3 fatty acids from fish, walnuts, and greens, fiber from fruits, vegetables, beans, and whole grains, and friendly bacteria from cultured foods (e.g. yogurt and fermented/pickled foods).
And the results of several recent studies underline the importance of the antioxidants that abound in whole plant foods — such as polyphenols, carotenoids (e.g., beta-carotene), vitamins C and E, and selenium, which is an essential component in enzymes critical to the body’s own antioxidant capacity.
For example, epidemiological studies from England, Greece, China, and Mexico strongly linked antioxidant-rich diets to significantly reduced risks for diabetes (Li Y et al. 2013; Koloverou E et al. 2015; McGeoghegan L et al. 2015; Denova-Gutiérrez E et al. 2018).
And in 2014, Italian researchers reported that a polyphenol-rich diet (but not an omega-3-rich diet) exerted significant positive effects on blood sugar control — see Antioxidant-Rich Foods & Drinks May Deter Diabetes — findings that echo a similar Greek trial published in 2010: see Antioxidant-Rich Diets Linked to Lower Diabetes Risk.
(There’s significant evidence that omega-3-rich diets reduce bodily markers for diabetes risk and — over long periods of time — may reduce the risk for diabetes. For more on that, see Fish & Omega-3s May Help Deter Diabetes.)
The most recent evidence comes from an epidemiological study conducted by researchers at three French universities, who analyzed data from 64,223 French women (average age 52) who were followed from 1990-93 to 2008 (Mancini FR et al. 2018).
At the outset of the study, none of the women had heart disease or diabetes and each woman completed a diet survey designed to determine their average intakes of more than 200 different foods.
Based on the known antioxidant content of the 200 foods covered in the survey, the researchers calculated an “antioxidant score” for each person’s diet.
The French team then compared the participants’ antioxidant scores to their health status at the end of the study — and adjusted the results to account for the influence of other known diabetes risk factors such as smoking, education level, hypertension, high cholesterol levels, family history of diabetes and body mass index (BMI).
After making those adjustments, their analysis linked higher levels of antioxidants to lower diabetes risk.
Specifically, compared to the women with the lowest dietary antioxidant scores, the women with the highest antioxidant scores were 27% less likely to have developed diabetes.
The French team calculated that higher intakes of fruits, vegetables, tea, and (moderate quantities of) red wine were the dietary items most responsible for raising a participant’s antioxidant scores.
Interestingly, authors of the 2016 Greek study calculated that higher intakes of whole grain foods, fruits, and beans were the best predictors of reduced diabetes risk.
The takeaway from this research seems clear.
In addition to maintaining a healthy weight, it's very smart to follow a diet that resembles the traditional Mediterranean eating pattern — or the traditional Japanese pattern: see Mystery of the Japanese Miracle.
- Chen GC, Koh WP, Neelakantan N, Yuan JM, Qin LQ, van Dam RM. Diet Quality Indices and Risk of Type 2 Diabetes Mellitus: The Singapore Chinese Health Study. Am J Epidemiol. 2018 Dec 1;187(12):2651-2661. doi: 10.1093/aje/kwy183. PubMed PMID: 30165478.
- Denova-Gutiérrez E, Muñoz-Aguirre P, Shivappa N, Hébert JR, Tolentino-Mayo L, Batis C, Barquera S. Dietary Inflammatory Index and Type 2 Diabetes Mellitus in Adults: The Diabetes Mellitus Survey of Mexico City. Nutrients. 2018 Mar 21;10(4). pii: E385. doi: 10.3390/nu10040385.
- Koloverou E, Panagiotakos DB, Pitsavos C, Chrysohoou C, Georgousopoulou EN, Grekas A, Christou A, Chatzigeorgiou M, Skoumas I, Tousoulis D, Stefanadis C; ATTICA Study Group. Adherence to Mediterranean diet and 10-year incidence (2002-2012) of diabetes: correlations with inflammatory and oxidative stress biomarkers in the ATTICA cohort study. Diabetes Metab Res Rev. 2016 Jan;32(1):73-81. doi: 10.1002/dmrr.2672. Epub 2015 Jul 27.
- Li Y, Guo H, Wu M, Liu M. Serum and dietary antioxidant status is associated with lower prevalence of the metabolic syndrome in a study in Shanghai, China. Asia Pac J Clin Nutr. 2013;22(1):60-8. doi: 10.6133/apjcn.2013.22.1.06.
- Mancini FR, Affret A, Dow C, Balkau B, Bonnet F, Boutron-Ruault MC, Fagherazzi G. Dietary antioxidant capacity and risk of type 2 diabetes in the large prospective E3N-EPIC cohort. Diabetologia. 2018 Feb;61(2):308-316. doi: 10.1007/s00125-017-4489-7. Epub 2017 Nov 9. PubMed PMID: 29119242.
- McGeoghegan L, Muirhead CR, Almoosawi S. Association between an anti-inflammatory and anti-oxidant dietary pattern and diabetes in British adults: results from the national diet and nutrition survey rolling programme years 1-4. Int J Food Sci Nutr. 2015 Aug;67(5):553-61. doi: 10.1080/09637486.2016.1179268. Epub 2016 May 4.
- Seah JYH, Koh WP, Yuan JM, van Dam RM. Rice intake and risk of type 2 diabetes: the Singapore Chinese Health Study. Eur J Nutr. 2018 Dec 10. doi: 10.1007/s00394-018-1879-7. [Epub ahead of print] PubMed PMID: 30535795.