The effect of mulberry leaf and white kidney bean extract mixture on postprandial glucose control in prediabetic patients

Relation

Liu Y, Zhang J, Guo H, et al. Effects of a mixture of mulberry leaves and white kidney bean extract on postprandial glycemic control in prediabetic subjects aged 45–65 years: a randomized controlled trial.J Funct Foods. 2020;73:104117.

Study objective

To determine the acute and chronic effects of 2 plants—mulberry leaf and white kidney bean—with different antihyperglycemic components on glucose control in patients with prediabetes

Draft

A randomized, single-blind control trial at the Department of Nutrition and Food Hygiene, School of Public Health, in Beijing

Participant

The study included 66 participants aged 45 to 65, all with prediabetes. One person was excluded because he or she was unable to participate in part of the study. Researchers recruited participants through flyers, posters and the internet and selected them during a one-month period between July and August 2018.

Researchers examined participants using 2 criteria methods: a questionnaire and laboratory tests.

The researchers adopted the American Diabetes Association (ADA) prediabetes diagnostic criteria: glycohemoglobin (i.e., hemoglobin A_1C) between 5.7% and 6.4%; Fasting plasma glucose (FPG) from 100 mg/dL to 125 mg/dL; or an oral glucose tolerance test (OGTT) result in the range of 140 mg/dL to 199 mg/dL.

Subjects were excluded if they had any of the 5 following criteria:

• Bestehende Diagnose einer Krankheit, die den Glukosestoffwechsel beeinflussen könnte. Dazu gehörten Diabetes, Verdauungsstörungen, Schilddrüsenprobleme, Nierenerkrankungen, Lebererkrankungen oder Krebs
• Langzeitanwendung von Nahrungsergänzungsmitteln oder Arzneimitteln, die den Glukosestoffwechsel beeinflussen
• Allergische Reaktionen auf Studienprodukte
• Unfähigkeit zur Teilnahme am Vorstellungsgespräch aufgrund von Problemen im Zusammenhang mit Seh-, Hör- oder geistiger Behinderung
• Schwangerschaft oder Stillzeit

Study parameters assessed

The researchers conducted the laboratory tests 2 weeks before the start of the study, including fasting blood glucose and hemoglobin A tests_1C(HbA_1c).

Participants were divided into 2 groups of 33 participants each, with one acting as a control group and the other as an intervention group.

Researchers used 3 steps to evaluate the acute and chronic effects of the mulberry leaf and white kidney bean extract mixture on post-meal glucose control.

Level 1 (Baseline)

Level 1 is the baseline for the study. The researchers took a fasting venous blood sample and asked participants to eat 100 grams of white bread and drink 200 ml of water within 10 minutes. Blood was collected 30, 60 and 120 minutes after consumption.

Stage 2 (acute impact test)

One week after the basic blood sample, both the test group and the control group consumed another 100 grams of white bread and 200 ml of water within 10 minutes. The test group also received a mixture of mulberry leaf and white kidney bean extract (1.5 grams) with this test meal. The control group received nothing additional. Again, blood was taken 30, 60 and 120 minutes after consumption.

Stage 3 (chronic impact test)

After stage 2, the test group consumed 1.5 grams of mulberry leaves and white kidney bean extracteveryonemeal, 3 times daily with their normal diet for a period of 4 weeks. Therefore, participants in the test group received a total of 4.5 grams of the dietary supplement every day. The control group received no nutritional supplements and also ate their normal diet.

Researchers contacted participants three times a week to help them adhere to study protocols. Twice during Phase 3 (on Day 15 and Day 29), participants were given a meal containing 100 grams of white bread and 200 ml of plain water to consume in 10 minutes, and their blood glucose levels were checked 30, 60, and 120 minutes after they started eating.

Using both substances together is believed to have greater potential for lowering postprandial glucose levels by combining active antiglycemic agents in each plant.

Throughout the study, participants were asked to avoid mulberry leaves, white kidney beans, and any substances containing mulberry leaves or white kidney beans, as well as anything that might alter their glucose metabolism. Participants were asked to maintain their normal exercise and dietary habits.

Two days before each blood collection visit, participants received instructions to avoid strenuous exercise, heavy meals, caffeine, alcohol, and tobacco; eating the same meal every time before going for blood work; and fasting for 10 to 14 hours before coming in. They were asked to come in before 9:00 a.m. on the morning of the blood draw and given instructions on the testing process.

Primary outcome measures

Level 2 (Acute Effects)

• Die postprandialen Glukosespiegel waren nach 30 Minuten gegenüber dem Ausgangswert erniedrigt (P<0,001) und nach 60 Minuten (P=0,006).
• Die postprandialen Insulinspiegel waren nach 30 Minuten gegenüber dem Ausgangswert erniedrigt (P=0,002) und nach 60 Minuten (P=0,010).
• Die postprandialen C-Peptid-Spiegel waren nach 30 Minuten gegenüber dem Ausgangswert erniedrigt (P=0,010) und nach 60 Minuten (P=0,002).

The final measurement looked at the area under the curve representing 120 minutes after ingestion of the mulberry leaf and white kidney bean extract mixture and showed significant decreases from baseline for glucose, insulin and C-peptide.

Level 3 (chronic effects)

Supplementation with a mixture of mulberry leaves and white kidney bean extract resulted in no significant changes as measured by the area under the curve (120 minutes) for glucose, insulin, or C-peptide levels on days 15 and 29.

The Homeostatic Model Assessment - Insulin Resistance (HOMA-IR), the Hemoglobin A_1cand serum glycated proteins (GSP) showed no significant change on days 15 and 29.

Key insights

For Phase 1, the baseline phase of the study, there was no significant difference between the test group and the control group, even after adjusting for body mass index (BMI).

However, in the acute phase of the study, the test group had significantly lower postprandial glucose, postprandial insulin and postprandial C-peptide levels in the 30-minute and 60-minute periods. These measures were also lower after adjusting for BMI. In the 120-minute time frame, the percent change in the intervention group for postprandial glucose, postprandial insulin, and postprandial C-peptide was more significant (from baseline) than in the 30- and 60-minute time frames.

In the chronic phase of the study, the test group showed no significant effects.

Practice implications

This is the first study to examine the combination of mulberry leaves and white kidney bean extract to reduce glucose levels.

Using both substances together is believed to have greater potential for lowering postprandial glucose levels by combining active antiglycemic agents in each plant. White kidney beans contain an active α-amylase inhibitor, and the 1-deoxynojirimycin (DNJ) found in mulberry leaves also blocks α-amylase activity. The flavonoids and polysaccharides in the mixed extract also show alpha-glucosidase inhibitory activities.

Alpha-amylase and α-glucosidase are two brush border enzymes responsible for starch metabolism in the proximal small intestine. By blocking enzymes that break down carbohydrates, the carbohydrates remain intact and are too large to be absorbed. This has implications for pre-diabetic and diabetic populations as lower absorption is a key factor in lowering blood sugar levels and may affect HbA levels in the longer term_1clevels.¹

Adding foods high in α-amylase inhibitors may be indicated for prediabetic patients to include in their diet plans to reduce postprandial glucose levels. Alpha-amylase inhibitors are found in many common beans in addition to white kidney beans, particularly red kidney beans and black kidney beans.²Eating foods that limit starch digestion and absorption can be a good way to gently modify blood sugar levels, and further research should give us better guidance in learning the best food combinations for controlling glucose levels.