For people with diabetes, sticking to a low glycaemic diet results in small but important improvements in blood sugar levels, cholesterol, weight and other risk factors, finds a study published by The BMJ today.
These improvements were seen over and above existing drug or insulin therapy, suggesting that a low glycaemic diet might be especially helpful as add-on treatment to help those with diabetes better achieve their targets, say the researchers.
The glycaemic index (GI) rates how quickly different foods affect blood sugar levels and research has shown that low-GI foods, such as vegetables, most fruits, pulses and wholegrains, can help keep blood sugar levels steady and reduce the risk of heart disease in people with diabetes.
A low GI or GL (glycaemic load) diet is therefore recommended for people with diabetes by clinical guidelines across the world.
However, the last European Association for the Study of Diabetes (EASD) guidelines were published over 15 years ago and several trials have been published since then.
So researchers set out to summarise the effect of low GI/GL dietary patterns on blood sugar control and other known risk factors in diabetes to help inform the update of the EASD guidelines for nutrition treatment.
Their results are based on 27 randomised controlled trials published up to May 2021 investigating the effect of diets with low GI/GL in diabetes for three or more weeks.
The trials involved a total of 1,617 participants with type 1 or 2 diabetes, who were predominantly middle aged, overweight or obese with moderately controlled type 2 diabetes treated with drugs or insulin.
The trials were of varying quality, but the researchers were able to assess the certainty of evidence using the recognised GRADE system.
The results show that low-GI/GL dietary patterns were associated with small but clinically meaningful reductions in blood sugar levels (HbA1c) compared with higher-GI/GL control diets.
Reductions also occurred in other risk factors including fasting glucose (blood sugar levels after a period of fasting), LDL cholesterol, body weight, and C-reactive protein (a chemical associated with inflammation), but not blood insulin levels, HDL cholesterol, waist circumference, or blood pressure.
The certainty of evidence was high for reduction in blood sugar levels and moderate for most other outcomes, suggesting the available evidence provides a good indication of the likely benefit in this population.
The researchers point to some limitations that may have affected their results, such as imprecision in the evidence for the effect of low GI/GL dietary patterns on LDL cholesterol and waist circumference, and the small number of available trial comparisons for blood pressure and inflammatory markers.
However, they say their findings show that low GI/GL dietary patterns “are considered an acceptable and safe dietary strategy that can produce small meaningful reductions in the primary target for glycaemic control in diabetes, HbA1c, fasting glucose, and other established cardiometabolic risk factors.”
The growing incidence of diabetes mellitus and its impact on mortality and morbidity have become global problems . In 2014, almost 422 million adults across the world were reported to have diabetes mellitus (DM) and the prevalence has globally risen from 4.7% in 1980 to 8.5% . In 2016, it was estimated that DM was the seventh leading cause of mortality, with approximately 1.6 million deaths directly attributed to the disease .
Type 2 diabetes (T2D) accounts for about 90% of all diabetes cases  and is characterized by hyperglycemia and insulin resistance, which are central factors in the pathogenesis of diabetic complications. More specifically, postprandial hyperglycemia appears to play a crucial role in the pathophysiology of late diabetes complications and especially in the development of cardiovascular disease (CVD).
The incidence of CVD among patients with T2D is reported as being high in many studies, and the postprandial “hyperglycemic spikes” appear to be directly related to the development and progression of CVD in T2D . Achieving good glycemic control is of utmost importance for patients with T2D because effective treatment of postprandial hyperglycemia results in greater CVD benefits  and contributes significantly in the reduction of mortality .
Nutrition is central in the management of T2D through its clear effect on weight and metabolic control. Medical nutrition therapy offers an evidence-based approach to the management of diabetes through lifestyle modifications, which are strongly recommended to be implemented prior to the commencement of pharmaceutical therapy.
This is unfortunately frequently not followed by most physicians, even though antidiabetic medications are ineffective in preventing the progression of the disease, and it is estimated that almost half of the T2D patients will start insulin therapy within 10 years of diagnosis . For this reason, it is crucial to identify and implement effective dietary strategies to treat hyperglycemia and prevent progression of T2D through diet and lifestyle modifications.
There is a consensus that the quality and quantity of carbohydrates are the main predictors of glycemic response [9,10], and low glycemic index and/or low glycemic load dietary patterns have been shown to improve glycemic control in patients with T2D. The glycemic index (GI) of a food rich in carbohydrates provides an estimation of how quickly carbohydrates break down during digestion and how rapidly they are absorbed into the bloodstream .
Carbohydrate-rich foods that are rapidly broken down and absorbed into the bloodstream are categorized as high-GI foods. High-GI foods lead to a rapid increase of blood glucose and insulin responses following food ingestion. On the contrary, low-GI foods have a slower and smaller effect on postprandial blood glucose levels and insulin response because they are slowly digested.
Several factors determine the GI of a food , including the type of carbohydrate (amylopectin-rich starch is readily digested and absorbed, whereas amylose-rich starch is more slowly absorbed), as well as the content of protein, fat, and quantity and type of fiber (water-soluble dietary fiber delays postprandial glycemia, whereas non-water-soluble fiber does not have this effect), and finally the food particle size and pH (lower pH food and drinks delay postprandial glycemia).
The GI of food is measured in vivo on the basis of the area under the curve of postprandial glucose after ingestion of a carbohydrate-rich food containing 50 g digestible carbohydrate, compared with the same curve after ingestion of 50 g glucose. GI is then expressed as the percentage of this ratio . Glycemic index does not provide information on how increased and prolonged glycemia will be when ingesting a specific amount of a carbohydrate-rich food.
A separate measure called the glycemic load (GL) does both, providing a more accurate picture of a food’s real-life impact on postprandial glycemia. Watermelon, for example, has a high glycemic index (74). However, a 100 g serving of watermelon has so little carbohydrate that its glycemic load is only 4. The term low glycemic load (GL) integrates (a) the GI of the food or diet with (b) the amount of carbohydrates in a given quantity of a food, meal, or diet. A comprehensive list of the glycemic index and glycemic load for more than 1000 foods has been published .
According to a recent review of the effect of GI on glycemia in patients with T2D , dietary management strategies aiming to improve overall glycemic control and promote weight loss in patients with T2D can depend on the use of low-GI diets. However, the outcome measures of the review were glycated hemoglobin (HbA1C) and fasting blood glucose (FBG), and not postprandial glucose.
Although glycated hemoglobin (HbA1C) is used to provide a representation of the average blood glucose levels over the preceding 3 months, postprandial glucose (PPG) is used as a measure to estimate levels of blood glucose 2 hours from the initiation of a meal . This is important because PPG is an independent risk factor for T2D complications [5,16].
Many factors can influence postprandial glucose (PPG): the GI of different foods combined in a meal; the carbohydrate content; the size of a meal; the presence and the percentage of the other three macronutrients (fat, protein, and amount and type of dietary fiber) in a meal; and also factors such as hormonal secretion, gastric emptying and the sequence of all macronutrients being ingested, and meal timing [15,17].
Strategies for managing diabetes have generally focused on optimizing overall glycemic control as assessed by glycated hemoglobin (HbA1c) and fasting plasma glucose (FPG) values. However, since 2001, the American Diabetes Association  has established postprandial glucose (PPG) as an independent contributor to both HbA1c and diabetes complications, and increasing evidence suggests that all three glycemic parameters of HbA1c, FPG, and postprandial glucose (PPG) are independently important.
Increased PPG is also followed by a rise in postprandial insulin in people who do not have diabetes. In people with type 2 diabetes, the pancreas can be sluggish about secreting insulin in response to a meal, leading to postprandial hyperglycemia .
The case is made for not focusing only on PPG but also of on employing the postprandial insulin assay as a more efficient tool to diagnose prediabetes and diabetes sooner than the current standards. By the time people are diagnosed using standard glucose testing, these individuals will likely have lost up to 50% of their beta cells. When a person is diagnosed with prediabetes (using standard glucose testing), the patient will have likely lost 25% of their beta cells.
The degree of postprandial insulin increase is measured by the insulin index. The insulin index of a food represents the elevation of the insulin concentration in the blood during the 2 h period after the food is ingested. The insulin index represents a comparison of food portions with equal overall caloric content (250 kcal or 1000 kJ).
The insulin index can provide additional information to the glycemic index or the glycemic load because certain foods, such as lean meats, cause an insulin response even though they contain very low amounts of carbohydrates. Holt et al.  have noted that the glucose and insulin scores of most foods are highly correlated, but high-protein foods and bakery products that are rich in fat and refined carbohydrates “elicit insulin responses that were disproportionately higher than their glycemic responses”. They also conclude that insulin indices may be useful for dietary management and avoidance of non-insulin-dependent diabetes mellitus and hyperlipidemia.
This review, however, provides an overall insight of the potential dietary interventions that improve postprandial glucose control in patients with T2D, given that the effective and consistent control of postprandial hyperglycemia remains one of the greatest challenges and unmet needs in diabetes management.
reference link : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7352659/
More information: Effect of low glycaemic index or load dietary patterns on glycaemic control and cardiometabolic risk factors in diabetes: systematic review and meta-analysis of randomised controlled trials, BMJ (2021). DOI: 10.1136/bmj.n1651