Longevity is a subject that has been pursued by many since the beginning of human history. It would be an impossible scientific study to ask human volunteers to follow a strict pattern of diet or certain foods throughout their lives to prove a “magical” food that could extend people’s lifespans by X number of years. So the next best we can do is to observe people who lived long healthy lives what foods they had eaten or what lifestyles they followed. For example, we have learned that one well-known healthy long-lived population is the Okinawans in Japan and they ate purple sweet potato as their staple food.

   

    Anthocyanins are the plant pigments giving the red, blue, and purple hues of fruits and vegetables. Anthocyanins are antioxidants that had been known with many health benefits. An earlier blog (link) was on the health benefit of anthocyanins-rich purple foods for cognitive function improvement. This blog is about the benefit of anthocyanins on glucose control.

 

    The dose-effect of blackcurrant extract on postprandial glycemia was studied in 14 men and 9 postmenopausal women (age 46 ± 14 years) in a randomized, double-blind, crossover trial. Low sugar fruit drinks containing blackcurrant extract providing 150-mg (low dose), 300-mg (intermediate dose), and 600-mg (high dose) total anthocyanins or no blackcurrant extract (control) were administered immediately before a high-carbohydrate meal. Early plasma glucose response during 0-30 minutes was significantly reduced following the high blackcurrant extract dose with -0.34 mmol/l.hour (p <0.05), relative to control. There were no differences between the intermediate doses and control. Plasma insulin concentrations (0-30 minutes) were similarly reduced. Consumption of blackcurrant extract in amounts roughly equivalent to 100-gram blackcurrants reduced postprandial glucose level and insulin secretion (1).

 

    Healthy subjects (n=10) consumed one of three sorghum test drinks: sorghum with proanthocyanidins and rich in 3-deoxyanthocyanidins (3-DXAs), sorghum rich in 3-DXAs without proanthocyanidins, sorghum low in 3-DXAs and without proanthocyanidins, or a non-sorghum drink in a randomized cross-over study. 30 minutes later, the subjects drank a glucose solution (25 g glucose) for a glucose tolerance test. Intake of sorghum rich in proanthocyanidins and 3-DXAs drink before the glucose solution resulted in a significantly lowered postprandial glucose response than the other sorghum test drinks or non-sorghum control drink (2).

 

    Healthy male volunteers (n=14) were given purple-fleshed potatoes (~168 mg anthocyanins), yellow-fleshed potatoes, and bilberries with potato starch in a randomized cross-over study. The purple potato meal caused a smaller insulin increase than the yellow potato meal (insulin area under the curves at 120 minutes were 1347 and 2226, respectively, p < 0.05; and at 240 minutes were 1448 and 2403, p <0.05). The purple potato meal caused lower plasma glucose at 40 minutes postprandially compared with the yellow potato meal (p <0.05). The results of this study suggested that the anthocyanin-containing purple potato influenced the postprandial insulin positively by resulting in a decreased insulinemia and glycemia in healthy males. Since potatoes are the world's largest non-grain commodity, replacing yellow-fleshed potatoes with purple-fleshed potatoes as staple food could have a large potential in maintaining public health (3).

 

    In a randomized cross-over trial, healthy male volunteers (n=17) consumed yellow potatoes with or without purple potato extract (PPE, extracted with water/ethanol/acetic acid) rich in anthocyanins (152 mg) and other phenolics (140 mg). PPE significantly decreased the incremental area under the curve for glucose and insulin until 120 minutes after the meal and lowered levels of glucose at 20 and 40 minutes, and insulin at 20, 40 and 60 minutes after the meal. PPE affected some of the studied 90 inflammation markers after the meal, such as insulin-like hormone FGF-19 levels were elevated at 240 minutes which could be beneficial for diabetes management. These results suggested that purple potato extract could alleviate postprandial glycemia and insulinemia, and related inflammation (4).

 

    People with metabolic syndrome (n=47) were randomized to either a bilberry-enriched diet (BB; high anthocyanin intake, n = 15), a berry diet including strawberries, raspberries, and cloudberries (SRC; lower anthocyanin intake, n = 20) or a control diet (n = 12) for 8 weeks. The BB group consumed daily 200 g of bilberry purée and 40 g of dried bilberries (altogether ~ 400 g of fresh bilberries, ~1323 mg anthocyanins). The SRC group consumed 100 g of strawberry purée, 100 g fresh raspberries, and 100 g fresh cloudberries (~71 mg anthocyanins) in their daily diet. Fasting serum hippuric acid (a biomarker for fruit, vegetable, and polyphenol consumption) increased significantly (3.5-fold, p <0.05) only in the BB group and correlated with changes in fasting plasma glucose concentration (r = -0.54, p < 0.05) and insulin secretion (r = 0.59, p < 0.05). The results indicated that the consumption of anthocyanin-rich bilberries contributed to the beneficial effect of better glycemic control and β-cell function (5).

 

    Blackberry consumption (600 g of blackberries, which is ~ 4 cups) significantly increased fat oxidation and improved insulin sensitivity in overweight or obese males (n=27) fed a high-fat diet. In this randomized, placebo-controlled crossover study with two treatment periods, subjects were fed a controlled, high-fat (40% of energy from fat) diet which contained either 600 g/day blackberries (~1476 mg of flavonoids and ~361 mg of total anthocyanins daily) or a calorie and carbohydrate matched amount of gelatin (flavonoid-free control) for seven days before a meal-based glucose tolerance test in combination with a 24-hour stay in a room-sized indirect calorimeter. The blackberry treatment resulted in a significant reduction in average 24-hour respiratory quotient (RQ) (0.810 vs. 0.817, blackberry vs. control, p <0.05), indicating increased fat oxidation. During both the glucose tolerance test and a 4-hour time during dinner, RQ was both significantly reduced and fat oxidation increased with blackberry treatment. These differences in RQ corresponded to a 7% significant increase in 24-hour fat oxidation (more fat was used for 24 hours). Blackberry treatment also resulted in a significantly lowered insulin response curve during the glucose tolerance test, and significantly improved insulin resistance compared with those of control (6).

 

   Chinese adults aged 40-75 years with prediabetes or early untreated diabetes (n=160) were recruited in a 12-week randomized, double-blind, placebo-controlled study. The subjects were randomly allocated to receive either purified anthocyanins (320 mg/day from bilberry and blackcurrant, n = 80) or placebo (n = 80). Compared with placebo, anthocyanins moderately but significantly reduced glycated hemoglobin A1c (HbA1c) (-0.14%, p <0.05) and low-density lipoprotein (LDL) cholesterol. There was a significant reduction in insulin resistance within the anthocyanins group, but no change in the placebo group, suggesting the potential ability of anthocyanins to improve insulin secretion and sensitivity. Subgroup analyses suggested that anthocyanins were more effective at improving glycemic control, insulin sensitivity, and lipids among patients with prediabetes or early untreated diabetes (7).

 

    Patients with type 2 diabetes (n=58) were given 160 mg of anthocyanins twice daily or placebo (n = 29 each group) for 24 weeks in a randomized, placebo-controlled, double-blind trial. A daily intake of 320 mg anthocyanins corresponds to ~100 g of a mixture of fresh blueberries and blackcurrants. Anthocyanin supplementation significantly decreased serum LDL cholesterol (by 7.9%; p < 0.05), triglycerides (by 23.0%; p < 0.01), apolipoprotein (apo) B-48 (by 16.5%; p < 0.05), and apo C-III (by 11.0%; p < 0.01) and increased HDL cholesterol (by 19.4%; p < 0.05) compared with placebo after the 24-week intervention. Besides, patients in the anthocyanin group showed higher total radical-trapping antioxidant parameter and ferric ion reducing antioxidant power values than did patients in the placebo group (both p < 0.05). Serum concentrations of 8-iso-prostaglandin F2α, 13-hydroxyoctadecadienoic acid, and carbonylated proteins (all oxidative stress biomarkers) in patients in the anthocyanin group were significantly less than in patients in the placebo group (23.4%, 25.8%; p < 0.01 and 20%; p <0.05, respectively). Furthermore, supplementation with anthocyanin lowered fasting plasma glucose (by 8.5%; p < 0.05) and homeostasis model assessment for insulin resistance index (by 13%; p < 0.05), and elevated serum adiponectin (by 23.4%; p < 0.01) and β-hydroxybutyrate (by 42.4%; p = 0.01, a biomarker for fat oxidation) concentrations compared with placebo supplementation. These findings demonstrated that anthocyanin supplementation exerted beneficial metabolic effects in people with type 2- diabetes by improving dyslipidemia, enhancing antioxidant capacity, and preventing insulin resistance (8).

 

    All these human studies showed that anthocyanins had beneficial effects on glucose and insulin control in healthy people or people who were overweight, obese, or pre-diabetic and even had diabetes. Glycemic control is essential to prevent the manifestation of diabetes in predisposed individuals and the development of associated comorbidities. As shown in the study in the diabetic patients (8), a 320 mg anthocyanins daily intake which is equivalent to ~100 g of a mixture of blueberry and blackcurrants, could significantly shift the blood parameters into the healthy direction by reducing glucose, insulin, LDL-cholesterol and triglyceride, and increasing HDL-cholesterol. The extents of the changes of these parameters are comparable to some drugs on the markets for glycemic and lipid control.

 

    The beneficial effect on glucose and insulin is one of the many health benefits that anthocyanin-rich purple foods possess. One of the key nutrition tips for us to learn from Okinawan centenarians is to eat a lot of purple foods.

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References:

1. Castro-Acosta, M. L., Smith, L., Miller, R. J., McCarthy, D. I., Farrimond, J. A., & Hall, W. L. (2016). Drinks containing anthocyanin-rich blackcurrant extract decrease postprandial blood glucose, insulin and incretin concentrations. The Journal of Nutritional Biochemistry, 38, 154–161.

2. Anunciação, P. C., Cardoso, L. de M., Queiroz, V. A. V., de Menezes, C. B., de Carvalho, C. W. P., Pinheiro-Sant’Ana, H. M., & Alfenas, R. de C. G. (2016). Consumption of a drink containing extruded sorghum reduces glycaemic response of the subsequent meal. European Journal of Nutrition, 57(1), 251–257.

3. Linderborg, K. M., Salo, J. E., Kalpio, M., Vuorinen, A. L., Kortesniemi, M., Griinari, M., Viitanen, M., Yang, B. R., Kallio, H. (2016). Comparison of the postprandial effects of purple-fleshed and yellow-fleshed potatoes in healthy males with chemical characterization of the potato meals. International Journal of Food Sciences and Nutrition, 67(5), 581–591.

4. Jokioja, J., Linderborg, K. M., Kortesniemi, M., Nuora, A., Heinonen, J., Sainio, T., Viitanen, M., Kallio, H., Yang, B. (2019). Anthocyanin-rich extract from purple potatoes decreases postprandial glycemic response and affects inflammation markers in healthy men. Food Chemistry, 125797.

5. De Mello, V. D., Lankinen, M. A., Lindström, J., Puupponen-Pimiä, R., Laaksonen, D. E., Pihlajamäki, J., Lehtonen, M., Uusitupa, M., Tuomilehto, J., Kolehmainen, M., Törrönen, R., Hanhineva, K. (2017). Fasting serum hippuric acid is elevated after bilberry (Vaccinium myrtillus ) consumption and associates with improvement of fasting glucose levels and insulin secretion in persons at high risk of developing type 2 diabetes. Molecular Nutrition & Food Research, 61(9), 1700019.

6. Solverson, P., Rumpler, W., Leger, J., Redan, B., Ferruzzi, M., Baer, D., Castonguay, T., Novotny, J. (2018). Blackberry Feeding Increases Fat Oxidation and Improves Insulin Sensitivity in Overweight and Obese Males. Nutrients, 10(8), 1048.

7. Yang, L., Ling, W., Yang, Y., Chen, Y., Tian, Z., Du, Z., Chen, Z., Xie, Y., Liu, Z., Yang, L. (2017). Role of Purified Anthocyanins in Improving Cardiometabolic Risk Factors in Chinese Men and Women with Prediabetes or Early Untreated Diabetes—A Randomized Controlled Trial. Nutrients, 9(10), 1104.

8. Li, D., Zhang, Y., Liu, Y., Sun, R., & Xia, M. (2015). Purified Anthocyanin Supplementation Reduces Dyslipidemia, Enhances Antioxidant Capacity, and Prevents Insulin Resistance in Diabetic Patients. The Journal of Nutrition, 145(4), 742–748.