In two recent A Dietitian’s Journey posts, I wrote about the positive impact certain foods, such as apple cider vinegar, ginger and turmeric root have had on my blood sugar levels and more recently, about kombucha and kimchi. In this article I touch on the science to support the use of these foods to lower blood glucose levels.
Apple Cider Vinegar
Apple cider vinegar has long been popular as a folk remedy for high blood sugar and a 1988 study demonstrated that vinegar lowered both blood glucose levels and insulin following the eating of complex carbohydrates (starch) and simple carbohydrates (sucrose). It is now known that vinegar acts by a similar mechanism as the Diabetes medication Metformin® and increases fat burning, increases glucose movement into cells and increases insulin sensitivity. This may account for the effectiveness of vinegar in lowering blood glucose that has been know historically and has now been demonstrated in human clinical trials.
A 2004 study, looked at the effectiveness of apple cider vinegar in reducing blood glucose levels after a meal (postprandial) as well as insulin levels in subjects with varying degrees of insulin resistance. The small study included both non-Diabetic subjects and those with Type 2 Diabetes. The non-Diabetic subjects were either insulin sensitive (n=8) or insulin resistant (n = 11) and there were 10 subjects with Type 2 Diabetes.
Fasting subjects were randomly assigned to either drink (1) 20 g apple cider vinegar with 40 g water and 1 tsp saccharine to sweeten it or (2) a placebo (water) drink. After a week of testing, subjects switched groups, so if they previously drank the placebo, they now took the apple cider vinegar.
After a 2-minute delay, subjects ate a white bagel, butter and orange juice (87 g total carbohydrates) and blood samples measuring blood glucose and insulin levels were taken 30 minutes and 60 minutes after eating the test meal.
As would be anticipated, fasting blood glucose was higher in ∼55% of subjects with Type 2 Diabetes compared with the non-Diabetic insulin sensitive and non-Diabetic insulin resistant groups and fasting insulin was 95–115% higher in both the subjects with Type 2 Diabetes and the non-Diabetic insulin resistant group
Compared with the placebo, the insulin resistant subjects that drank the apple cider vinegar had 34% higher whole-body insulin sensitivity 60 minutes after the high carbohydrate test meal and the subjects with Type 2 Diabetes had 19% higher whole-body insulin sensitivity.
This study demonstrated that apple cider vinegar taken before a meal containing carbohydrate can significantly improve insulin sensitivity in insulin-resistant subjects – both those with Type 2 Diabetes and those with ‘pre-Diabetes’ (i.e. insulin resistant, non-Diabetic).
A 2015 study looked at the effect of vinegar on glucose metabolism in muscle, as it is considered the most important tissue for insulin-stimulated glucose disposal.
Subjects with Type 2 Diabetes drank either (1) 30 mL vinegar (6% acetic acid) and 20 mL water or (2) a placebo drink (water) before a mixed meal of bread, cheese, turkey ham, orange juice, butter and a cereal bar (with a total of 75 g carbohydrates, 26 g protein and 17 g fat).
Blood glucose, and insulin levels were measured in the subject’s forearm at 30 minutes and 60 minutes before the meal and 300 min after the meal was eaten and compared to placebo, vinegar increased forearm glucose uptake and decreased plasma glucose and decreased plasma insulin.
Researchers concluded that vinegar’s effect on carbohydrate metabolism may be partly accounted for by an increase in glucose uptake, demonstrating an improvement in insulin action in skeletal muscle.
NOTE: The amount of apple cider vinegar taken before meals in these two studies were 1.5 Tbsp. (20 mL) or 2 Tbsp. (30 mL).
Mechanism of Action
When taken with or just before meals, it is believed that vinegar slows gastric emptying, delays the uptake of glucose and slows the rise in blood sugar following a meal (2 hours postprandial).
Vinegar also stimulates an enzyme called AMP-activated protein kinase (AMPK) that increases fat oxidation, improves glucose uptake and insulin sensitivity and lowers glucose production (gluconeogenesis) in the liver. This is similar to how the diabetic medication Metformin works (see Zhou et al, 2001).
NOTE: This article is not proposing that foods such as vinegar are substitutes for medication prescribed by a doctor.
Activation of AMPK by vinegar has been demonstrated in the liver of vinegar fed rats and in human endothelial cells in vitro (see Kondo et al 2009, Sakakibara et al 2006, 2010, Li et al 2013) and this may account for the effectiveness of vinegar in lowering blood glucose that has been demonstrated in the human clinical trials, above.
Taking vinegar at meals has also been reported to significantly lower the glucose response after a meal (postprandial) – presumably by slowing the absorption of starch or polysaccharides (see Johnson 2009, 2010, Ostman et al 2005).
Ginger was shown to have blood glucose lowering activity in a 2004 study that found that pre-meal treatment with ginger lowered induced high blood glucose levels (hyperglycemia).
A 2015 study evaluated the effects of a ginger powder supplement on fasting blood glucose levels and hemoglobin A1c (HbA1c) in Type 2 Diabetics. To be included, subjects needed to have been diagnosed as T2D for at least 2 years, have a HbA1c level of 6-8%, as well as taking no antioxidant supplements for at least 3 months prior to the study, and no smoking and drinking. Subjects that took insulin before or during the study were excluded, as were those that had a change in the type or dose of medication, changes in diet or any illnesses during the study.
The fifty subjects of both genders were divided randomly into and experimental and control group, with 25 subjects in each and received either a ginger-containing capsule or a placebo capsule twice a day for 12 weeks. All subjects took their usual medications for T2D and were stable on their dose.
Of 50 patients that began the study, 41 subjects completed the study (22 in the ginger group and 19 in the control group).
Fasting blood glucose levels after the intervention study were 19.4% lower in the ginger supplemented group than in the placebo group and HbA1C was .77% lower in the ginger supplemented group than in the placebo group. It was concluded that a study with more subjects and a longer study period were needed for a better observation of the effects of ginger in improving blood glucose in those with Type 2 Diabetes.
Turmeric root (Curcuma longa) is a rhizome of the ginger family that gives curry powder (which is a mixture of several spices) its characteristic yellow colour. Turmeric has been used in both Ayurvedic and traditional Chinese medicine to lower blood sugar levels. The active component of turmeric, is curcumin.
An extensive literature review of studies on curcumin was conducted and published in 2013 with more than 200 publications retrieved using the search term “curcumin and diabetes” from the MEDLINE database, with the earliest being a case study from 1972 and curcumin has since been extensively studied in animal models of Diabetes and in a few clinical trials with subjects with Type 2 Diabetes. The conclusion of the literature review was that there is ample evidence in the scientific literature regarding the use of curcumin as a potential treatment for Diabetes as well as its associated complications.
Note: when using turmeric, be sure to add a few grinds of black pepper as it increases the bioavailability of the curcumin by ~2000 times.
Fermented Foods – Kombucha, Kimchi and Jun
Fermented foods, such as kombucha and kimchi are popular as probiotics for enhancing the microbiota of our intestine. Research in the field has focused on what role this complex bacterial community plays in health and disease in people, and how we can alter the microbiota through the foods and beverages we consume. The benefit of eating foods and drinking beverages with these probiotics has been demonstrated in studies and include improvement of constipation, diarrhea, irritable bowel syndrome (IBS), intestinal inflammatory conditions such as Crohn’s and colitis, as well as an improvement in immune function.
Lactic acid bacteria are the most widely used strains used to ferment foods; from sauerkraut, kosher dill pickles to kimchi, a staple of the Korean diet. For lactic acid bacteria to benefit the microbiota of the human intestines however, they first must be able to survive the hostile environment of digestion, which include extreme acidity, and digestive enzymes, and bile acids – not to mention low oxygen availability, and regulated temperature. It has been demonstrated in studies that they do.
A meta-analysis published in 2014 examined the effect of probiotics on glucose metabolism in patients with Type 2 Diabetes Mellitus of randomised-controlled studies where fasting blood glucose, glycosylated hemoglobin (HbA1c), insulin concentration or homeostasis model assessment of insulin resistance (HOMA-IR) changes were reported for the intervention and control groups.
Seven trials met the search criteria and results indicated that probiotic consumption significantly changed fasting plasma glucose by -0.9 mmol/L (-15.92 mg/dL). The duration of intervention for ≥8 weeks resulted in a significant reduction in fasting blood glucose of 1.2 mmol/dL (-20.34 mg/dl). HbA1C was significantly reduced by -0.54% compared with control groups. The results also showed that probiotic therapy significantly decreased homeostasis model assessment of insulin resistance (HOMA-IR) by -1.08 and insulin concentration by -1.35 mIU/L.
This meta-analysis suggests that eating or drinking foods containing probiotics may improve glucose metabolism with a potentially greater effect when the duration of intervention is ≥8 weeks, or multiple species of probiotics are consumed.
A meta-analysis published in 2016 examined the effect of probiotics on glucose and glycemic factors in Type 2 Diabetes of randomised-controlled studies published in English between January 2000 to June 2015. The main outcomes of interest were mean changes in glucose, HbA1c, insulin and homoeostasis model assessment-estimated insulin resistance (HOMA-IR).
A total of 11 studies with 614 subjects were included. It was found that there was a statistically significant difference between the probiotic consuming groups and the placebo-controlled groups on the reduction of blood glucose of -0.52 mmol/L (10 mg/dl).
Analysis identified that probiotics significantly reduced fasting blood glucose, HbA1c, insulin and HOMA-IR in participants with Type 2 Dabetes.
Kombucha and Jun
Kombucha is a beverage made by fermenting black tea and sugar with some “starter” from a previous batch, called the ‘mother’ or ‘SCOBY’ (symbiotic culture of bacteria and yeast). This is sometimes referred to as the ‘tea mushroom’ or ‘tea fungus’.
After ~ a week or 10 days, a second fermentation takes place with approximately 1 part fruit to about 10 parts fermented tea. This remains in sealed containers where it yields a lightly carbonated, mildly acidic and fruity flavoured beverage, which is the final product. In the photo to the left, this is my first batch.
Green tea and honey can also be used to make a fermented product using a very similar process, but using a different kind of SCOBY (one that is adapted to metabolize these substrates) and the resulting product is called Jun.
The taste of jun is considerably different than kombucha, as is the alcohol content. Kombucha is typically ~1.50% alcohol whereas Jun ranges from 3-7% alcohol.
With some investigation, I was able to determine that kombucha is essentially a symbiotic growth of acetic acid bacteria and osmophilic (water-loving) yeasts in a cellulose mat that the culture makes.
The main bacteria are (1) Acetobacter – acetic acid bacteria that are able to convert the ethanol (alcohol) that is initially produced in the fermentation process to acetic acid, in the presence of oxygen and (2) Gluconobacter – acetic acid bacteria that prefer sugar-rich environments.
This is the same species that converts the ethanol (alcohol) in apple cider, to apple cider vinegar. Hence, it seems reasonable to surmise that it is the acetic acid content of kombucha and jun, which give it its characteristic tart taste, that also provide the same glucose lowering effect as apple cider vinegar.
Some final thoughts…
Given that there is scientific evidence that apple cider vinegar, ginger root, turmeric root, kimchi, kombucha & jun play a role in lowering blood glucose and other markers, these foods should be considered – along with a low carbohydrate diet and intermittent fasting (extending the time between meals) when addressing the problem of high blood glucose levels resulting from insulin resistance.
Food, and the temporary absence of it, as medicine.
NOTE: These foods should not be consumed without first consulting with your doctor, especially if you are on medication for Type 2 Diabetes as they can have a potent blood effect on blood sugar levels.
If you would like to read well-researched, credible “Science Made Simple” articles on the use of a low carb or ketogenic diet for weight loss, as well as to significantly improve and even reverse the symptoms of Type 2 Diabetes, high cholesterol and other metabolic-related symptoms, please click here.
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