Diabetes And Berries
Nutrition therapy is an important part of diabetes management. The presence of complex carbohydrates and bioactive compounds in berries helps manage high glucose levels and reduce diabetes-associated risks such as heart disease and inflammation.  Berries are also known to reduce the risk of diabetes in prediabetics.
According to the Health and Nutrition Examination Survey, berries make for the 10 per cent of all the fruits consumption in the US. They are low in calories and high in antioxidants such as vitamin C and folic acid; micronutrients such as potassium, vitamin K, fibre, manganese and copper and polyphenolic flavonoids such as tannins, flavonols and anthocyanins.
Flavonoids In Different Berries Forms
Anthocyanins are the most predominant flavonoids in berries and its content is minimally affected by processing. Raw strawberries, raspberries or blueberries contain around 42 per cent more anthocyanins compared to frozen forms.
Similarly, puree forms of this fruit contain 60 per cent less while juice forms contain 78 per cent reduced anthocyanins levels. 
Storing temperature, heat treatment and duration degrade the levels of flavonoids. A freeze-drying method is considered the most effective as it tends to keep the levels of anthocyanins intact.
Seasons also play a vital role in determining the content in berries. Berries cultivated in summer tend to have more phenolic compounds compared to those cultivated during winters. Other factors like different geographical regions and agricultural practises are also considered.
Effects Of Berries On Glucose Levels In Healthy Adults
Berries are known to manage glucose response after a meal, which sharply increases after the food intake. In a study, it was found that berries modulate gastrointestinal hormones that control satiety, hunger and metabolic response.
When a person consumes food, a peptide hormone called glucagon stimulates the secretion of insulin, that further controls the sudden spike of glucose in the body. It also helps provide satiety to prevent excess consumption of food. 
Resveratrol in berries also helps in counteracting leptin resistance, a condition when a person is obese but the brain is unable to identify it and still gives the signal for the consumption of more food. Overall, a diet enriched with berries helps prevent obesity, insulin resistance and glucose tolerance. 
Effects Of Berries On Glucose Levels In Obese Adults
Obesity is linked to insulin resistance and high cholesterol, factors that may cause diabetes and heart diseases. Berries like cranberries, blackberries and blueberries have shown improvement in insulin resistance in people who are overweight or obese.
In a study carried out in obese people, it was found that when berries were consumed with breakfast, lower glucose concentration in the blood up to several hours. 
Anti-Diabetic Effect Of Blueberries
In a study, it was found that blueberry reduces the risk of heart diseases associated with diabetes. Blueberries are high in anthocyanins which can alter the functioning of receptor proteins that contribute to glucose regulation, lipid homeostasis and decrease in inflammation.
Blueberries reduce fats in the abdominal area and increase skeletal muscles by reducing fasting insulin, triglycerides and insulin resistance. 
Anti-Diabetic Effect Of Blackberries
According to a study, blackberries increases fat oxidation when consumed during physical activities and also provides high energy to carry out the workout for a longer period. Additionally, blackberries promote the build-up of skeletal muscle and lower adipose tissues, contributing to weight loss, which in turn, reduces the risk of diabetes. 
Anti-Diabetic Effect Of Cranberries
In a study carried out on abdominally obese men, it was found that intake of cranberries (around 500 mL day) in a form of fruit or juice reduces inflammatory biomarkers, lipoprotein and glucose levels. This shows that cranberries are effective in reducing the risk of diabetes and also in managing the symptoms in diabetics. 
Berries are regarded as a superfood in the prevention and control of diabetes. Though many researches highlights the importance of different berries in diabetes, the area needs more research.