Glucose is a life sustaining source of energy that is used by virtually all cells in the body. In the diet it is obtained through the consumption of carbohydrates, one of three macronutrients and most of which is broken down into glucose and absorbed into the bloodstream. Human bodies are designed to manage blood glucose (blood sugar) levels within a narrow range. When this management system goes awry, it can lead to an array of inflammatory, cardiovascular, and metabolic issues.
The consequences of both low blood sugar (hypoglycemia) and high blood sugar (hyperglycemia) can be dire, so the body will either direct appropriate uptake of glucose by the cells, or direct synthesis of glucose (mostly in the liver) to maintain stable levels. This direction of either uptake or synthesis depends on the intricate interplay of hormones.
The hormone responsible for the cellular uptake of glucose is insulin. It is secreted by the beta cells of the pancreas in response to rising blood glucose levels, and it unlocks the pathway that allows glucose to enter the cells, preventing hyperglycemia. If blood glucose levels fall too low, the hypothalamus signals the release of hormones that will increase blood glucose levels, preventing hypoglycemia. Glucagon, cortisol, growth hormone and catecholamines are hormones that trigger the synthesis of glucose.1
In healthy individuals, maintaining a steady, postprandial (post-meal) blood glucose level is automatic. The above processes ensure the balance. But in certain circumstances cells can become resistant to the actions of insulin, requiring the release of increasingly higher levels to unlock the glucose pathway into the cell. And when cells fail to receive a sustained source of glucose, the liver starts to signal the release of stored glucose and the synthesis of new glucose. When the pancreas can no longer keep up with the demand for insulin, hyperglycemia results.
One primary intervention measure for hyperglycemia is to increase insulin sensitivity. Physical activity, stress reduction, and weight loss can help in this regard. Managing postprandial glucose levels is another important piece of this puzzle.
The glycemic index (GI) is a tool developed to assess how quickly a particular food raises blood sugar levels. It is based on a scale of 0 to 100 and can be used as a guide for preventing postprandial blood sugar spikes.2 Foods that are low on the glycemic index are digested and absorbed more slowly than those high on the glycemic index, resulting in a slower, steadier rise in blood sugar after consumption.
Various studies have demonstrated the benefits of a low GI diet for improving insulin sensitivity in chronic conditions.3,4 One controlled clinical trial of women with polycystic ovary syndrome (PCOS) found a low GI diet resulted in statistically significant improvements in insulin resistance and insulin sensitivity over the course of 24 weeks.5 These improvements may also be responsible for a reduction in risk factors associated with heart disease. A 2009 review study looked at the metabolic effects of a low glycemic diet, concluding that the reduction in insulin secretion associated with a low glycemic diet may reduce the risk of cardiovascular disease by decreasing the likelihood of contributing factors.6
Dietary fiber intake is another means of managing blood glucose levels after a meal. Fiber is a type of carbohydrate that bypasses intestinal digestion and is not broken down into glucose. Instead, fiber travels to the colon and is metabolized by resident gut bacteria and/or excreted. Both soluble and insoluble fiber have been strongly correlated with reducing the risk of type 2 diabetes.7 However, it is soluble fiber that has shown the best effect for improving glucose response to a meal.8 There are a few different mechanisms by which soluble fiber may modulate postprandial glucose levels, but it is the ability to delay gastric emptying via its viscous, gel-forming properties that accounts for most of its effect.9
Another class of carbohydrate with fiber-type qualities is resistant starch (RS). This type of starch is resistant to digestion and reaches the large intestine where it can be fermented by gut bacteria. When compared to starches that are easily digested, RS slows the rate of digestion and leads to a sustained and lower level of glucose release into the bloodstream.10 In addition, studies have shown RS to significantly increase postprandial fat burning, which could help decrease fat accumulation long-term.11
Green banana flour is a unique source of fiber and resistant starch that is becoming more popular due to nutritional potential and health benefits. One group of healthy volunteers consumed 5 grams of unripe banana flour (UBF) three times per week for six weeks, resulting in significantly reduced hunger and increased satiety. After intake of unripe banana starch (UBS), fasting insulin showed higher sensitivity compared to baseline and control groups.12 Another study done in an animal model showed improved insulin/glucose ratio after 28 days in groups consuming both unripe bananas themselves and unripe banana starch. In addition, insulin secretion from isolated pancreatic islets was also lower compared to controls exposed to the same glucose stimuli.13
A more commonly consumed food in the Western diet is oats. Oats are well known for their soluble fiber content, but studies indicate that their effect on glucose management may go beyond just this. Oats contain beta glucans, which are a type of soluble fiber that, along with slowing glucose absorption in the gut, have been shown to increase activation of a pathway that can increases glucose uptake by the cell, even without the action of insulin, and increase the synthesis of glycogen in the liver.14 Certain varieties of oats can also be a rich source of avenanthramides. Avenanthramides are polyphenolic, bitter compounds showing promise for modulating blood glucose levels through both their action on bitter receptors, and their phenolic interruption of starch digestion.15,16 Bitter compounds have been shown to influence postprandial blood glucose levels, possibly by altering hormone secretion in the gut15, and phenolics have been shown to decrease the activity of enzymes that break down starch – and potentially decrease the absorption of glucose.16 More study is needed to elucidate these possible effects.
The management of blood glucose levels is imperative to good health, and maintaining insulin sensitivity is key. Many diet and lifestyle factors play a role in this process, and a well-planned, low GI diet, along with the inclusion of specific foods and food components, can have a positive impact on improving and maintaining healthy postprandial blood glucose levels.