Functions of Slowly Digestible Starch (SDS)

Studies of the benefits of Slowly Digestible Starch (SDS) are limited. The potential health benefits of SDS are linked to stable glucose metabolism, diabetes management, mental performance, and satiety.

Slowly Digestible Starch (SDS) and the Metabolic Response

The metabolic effects of carbohydrates, particularly glucose, are related to the rate of carbohydrate absorption after a meal. A common measurement that assesses these effects is the GI. Positive associations have been established between dietary GI and the risk of colon and breast cancer. Slowly Digestible Starch (SDS) has a medium-to-low GI and therefore reduces the glycemic load of a food product compared with that of RDS, which has a high GI.

The limited research available in humans suggests that SDS blunts the postprandial increase and subsequent decline in the plasma glucose and insulin concentrations, leading to prolonged energy availability and satiety, compared with more rapidly digestible starch.

There have been few reports of the effects of Slowly Digestible Starch (SDS) on glucose tolerance or energy expenditure. The ingestion of 35 g of available carbohydrates as cornstarch or waxy cornstarch (both SDS) resulted in a smaller and more sustained increase in plasma glucose than did maltodextrin (an RDS). In healthy young women, a meal containing slowly digestible waxy cornstarch resulted in lower peak concentrations of plasma glucose and insulin than a meal containing cooked, rapidly digestible cornstarch. In young men, the consumption of uncooked cornstarch (an SDS) blunted their plasma glucose and insulin responses. During the first 120 min after consumption, the area under the glycemic dose–response curve for the SDS was smaller than that after the consumption of glucose, whereas after 120 min, there was no difference between the two areas.

Sands et al. examined the effects of uncooked waxy cornstarch (an SDS) on postprandial plasma insulin and glucose and on the whole-body energy expenditure and appetites of men and women. The consumption of uncooked waxy cornstarch led to lower postprandial glucose and insulin concentrations but had no effect on postprandial energy expenditure or appetite compared with the consumption of cooked, rapidly digested waxy cornstarch. These findings are similar to those of Wachters, who reported that the consumption of 50 g of available carbohydrate from an SDS, uncooked cornstarch, led to smaller glucose and insulin areas than the consumption of 50 g of glucose. In conclusion, these results establish that the consumption of native waxy cornstarch blunts the postprandial glucose and insulin responses in humans, potentially providing a steadier supply and release of energy over a specific period than the RDS maltodextrin.

The digestion of alginate-entrapped starch microspheres as a source of SDS generates short-chain fatty acids in the alimentary canal, including propionic, acetic, and n-butyric acids, which help to prevent colon cancer but produce little energy.

The intake of slowly available glucose improved the metabolic profiles of obese insulin-resistant subjects, particularly reducing postprandial insulinemia and lowering the levels of circulating triacylglycerols and the apolipoproteins in triacylglycerol-rich lipoproteins. RDS and SDS also differ in their ability to stimulate the secretion of the gut incretin hormones.

Slowly Digestible Starch (SDS) and Diabetes

Postprandial hyperglycemia leads to insulin resistance and ultimate pancreatic β-cell failure. This results in noninsulin-dependent diabetes mellitus, which accounts for 90% of all diabetes cases.

The occurrence of obesity-related problems is currently increasing in response to modern lifestyles, the consumption of excessive dietary fat, and a reduction in physical activity. Obesity-related problems also lead to complications such as hyperlipidemia, nonalcoholic fatty liver disease, various cardiovascular diseases, and diabetes in humans. In general, diabetes is a form of metabolic disorder that occurs with the dietary intake of excessive carbohydrates and lipids.

Type 2 diabetes mellitus (T2DM) is a common endocrine and metabolic disease caused by an absolute or relative lack of insulin in the blood, resulting in metabolic abnormalities such as obesity, hypertension, low levels of HDL, elevated triglyceride levels, hyperglycemia, and resistance to insulin. The complications of T2DM are associated with obesity, oxidative damage, dysfunction of metabolism, and eventual organ failure.

Apart from genetic causes, the dietary pattern of an individual plays a key role in the occurrence of metabolic syndrome, which is often attributed to the increasing influence of the western diet, which contains an excessive fat content and is poor in minerals and fiber.

With the increased occurrence of diabetes in humans, current research has focused on the development of drugs to treat and control T2DM. Various drugs have been developed, but the long-term use of antidiabetic drugs can have considerable adverse effects, with symptoms of hypoglycemia and kidney or liver malfunction. Because no medication is yet effective in the treatment of T2DM, current research is concentrated on the prevention or delayed onset of diabetes by exploring the functional adjuncts responsible for it.

This increase in metabolic syndrome has challenged food scientists to develop innovative food products that combine dietary satisfaction with disease management. Therefore, reducing meal-associated hyperglycemia is one goal in the prevention of diabetes mellitus. Slowly Digestible Starch (SDS) has a beneficial metabolic effect on diabetes and is recommended for its prevention and management. Several processes are used to produce either components that remains undigested in the upper intestinal tract or intermediate starch, which is digested slowly in the small intestine. In this way, the release of glucose is slowed, which is advantageous for diabetic patients.

SDS-containing breakfast foods also improve carbohydrate metabolism and reduce the insulin requirements of insulin-treated T2DM patients. Because there is a lack of suitable sources, uncooked cornstarch is recommended as a source of SDS for those suffering from diabetes. This can improve the glycemic response at the next meal and prevent evening hypoglycemia in diabetic patients who are treated with insulin.

Slowly Digestible Starch (SDS) and Mental Performance

The consumption of foods containing high levels of sugar correlates with risk factors for cardiovascular disease, including impaired glucose metabolism, obesity, dyslipidemia, T2DM, and hypertension. Many biological pathways are involved in these adverse outcomes, including the glucose-related dysregulation of vascular biology and vascular functions. Most studies of sugar intake and cardiovascular risk have been cross-sectional and based on patients’ self-reported usual dietary habits.

A previous investigation of the effects of acute glucose ingestion on resting cardiovascular function demonstrated its potent hemodynamic effects, which are characterized by increased cardiac output, heart rate, systolic blood pressure, superior mesenteric artery flow, and reductions in diastolic blood pressure, and total peripheral resistance. These glucose-induced hemodynamic changes reflect, at least in part, the increased demand of the gut for blood to maintain its digestive activities.

Evidence suggests that the acute ingestion of glucose increases the mental challenge-induced activity of the hypothalamic–pituitary–adrenal axis and the total peripheral resistance and that prolonged challenge increases the cardiac output. The ingestion of a gelatin-based drink containing “complex carbohydrates” is associated with increases in cardiac output and systolic blood pressure, reduced total peripheral resistance at baseline, and an increased heart rate in response to mental challenges. These studies are clinically important because the elevated autonomic nervous system and cardiovascular responses to mental challenges and delayed recovery have been identified as risk factors for cardiovascular disease.

Previous studies have made mental efforts using indices of psychophysiology, particularly cardiovascular measures. Metabolic measures represent a complementary approach by which the investment in the mental effort is explicitly linked to the process of energy mobilization. Glucose provides energy for our brains. One study showed that glucose levels in the blood can influence mental performance, especially higher mental activities, and studies using glucose drinks have also demonstrated the positive effect of glucose, which tended to improve attentional performance by 8% (P < 0.07). When the specific effects of macronutrients on performance are evaluated, the effects of meals are less consistent. A limited amount of data is available on the effects of the carbohydrate absorption rate on cognitive performance.

Glucose regulation has been associated with cognitive performance in elderly subjects with normal glucose tolerance, and dietary carbohydrates enhance cognition in subjects with poor memories. A literature review that focused on the physiological effects of starches concluded that glucose may influence both memory and mood.

Slowly Digestible Starch (SDS) and Satiety

Most mammals, including humans, prefer foods and liquids rich in sugar. A preference for this macronutrient stems from both its sensory and post ingestive properties and is regulated at the brain level. Several central mechanisms underlie the drive to consume sucrose. For example, multiple studies assessing operant behavior have shown increased motivation to obtain sweet foods. Furthermore, sucrose intake, especially chronic intake, activates components of the central reward circuitry, for example, by modifying the expression of genes encoding opioid peptides and their receptors or by affecting the release of neuropeptides and neurotransmitters, such as dopamine and opioids.

Satiety is a complex phenomenon controlled by social, physiological, and psychological factors. The ability to balance energy intake and expenditure is critical to survival, and sophisticated physiological mechanisms have evolved to do this, including appetite control. Satiation and satiety are part of the body’s appetite control system and are involved in limiting energy intake. Satiation is the process that causes one to stop eating, whereas satiety is the feeling of fullness that persists after eating, suppressing further consumption, and both are important in determining the total energy intake. Satiation and satiety are controlled by a cascade of factors that is initiated when a food or drink is consumed and continues as the ingesta enters the gastrointestinal tract and is digested and absorbed. Signals of the ingestion of food energy are transmitted to specific areas of the brain that are involved in the regulation of energy intake, in response to the sensory and cognitive perceptions of the food or drink consumed and the distension of the stomach. These signals are integrated by the brain, and satiation is induced. When nutrients reach the intestine and are absorbed, a number of hormonal signals are released that are also integrated in the brain to induce satiety. In addition to these episodic signals, satiety is also induced by fluctuations in hormones, such as leptin and insulin, which indicate the level of fat stored in the body.

The concept that blood glucose levels, determined by carbohydrate intake, are the central regulator of satiety is based on the glucostatic theory of food intake regulation. This theory maintains that low blood glucose can cause high blood insulin levels, which signal satiety. Campfield and Smith reviewed our current knowledge of the complex regulatory mechanisms mediating the dynamics of blood glucose and meal initiation, which supported the proposition that transient declines in blood glucose promote hunger. A stable and low insulin response after a meal also seems to be important for the regulation of satiety, which supports the hypothesis that Slowly Digestible Starch (SDS) has a beneficial effect on satiety. A study that compared slowly digested barley kernels with a white bread control reported similar results. In terms of appetite, the ingestion of slowly digested barley kernels is reported to cause greater satiety over a 3-h period than white bread.

It can be concluded that SDS affects satiety-influencing factors, such as postprandial blood glucose and insulin levels. However, further study of the mechanisms of satiety is required, including gut hormones and meal composition.

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