Diabetes mellitus is a disease in which blood sugar is not properly taken up into cells. Thus, the level of glucose in the blood remains high. The uptake of glucose into the body's cells is controlled by the hormone insulin, which is produced by the pancreas. Type 1 diabetes is due to the pancreas failing to produce sufficient insulin. It is often caused by genetic factors. Non-insulin-dependent diabetes, or type 2 diabetes, occurs when the body's cells are unable to respond very efficiently to the insulin produced. It is associated with obesity, overnutrition, excess dietary fat and sugar, and other factors. Type 2 diabetes accounts for around 90% of all diabetes. Both types of diabetes are treated by the injection of insulin, which acts to reduce the blood glucose concentration by facilitating the uptake of glucose by the cells in type 1 diabetes, and by supplementing the body's insulin in type 2 diabetes.
Over 18 million adults in the U.S. have diabetes (CDC, 2006), and over 170 million people worldwide have the condition, while its incidence is rising dramatically. The World Health Organization estimates that there may be 300 million people with diabetes by 2025 (WHO and FAO, 2002). There is a pressing need to develop a range of approaches to tackle type 2 diabetes and also address the root causes of its increased incidence, such as obesity and poor diet. Improvements in diet are therefore an important strategy in combating type 2 diabetes.
Foods containing inulin are beneficial in the diet of people with diabetes mellitus. Inulins and fructooligosaccharides are not absorbed in the intestines (Rumessen et al., 1990), and therefore do not affect insulin levels, because the body does not sense a need to produce insulin. The ingestion of sucrose or glucose prompts blood sugar and insulin changes, but no corresponding effects are noted when equivalent amounts of inulin or fructooligosaccharides are ingested (Roch-Norlund et al., 1972). Therefore, consuming inulin-rich foods helps to restore normal levels of blood sugar, whereas foods containing starch and sucrose further raise blood sugar levels. Experiments during the 1980s and 1990s confirmed the beneficial role of inulin-rich foods in diabetic diets. Daily intake of fructooligosaccharides has been shown to reduce blood sugar levels in both diabetic and healthy subjects (Luo et al., 1996; Yamashita et al., 1984), for instance, while inulin reduced insulin peaks compared to diets containing other carbohydrates (Rumessen et al., 1990). An intake of around 16 to 23 g of inulin per meal has been recommended in diabetic diets (Van Loo et al., 1995).
There is a long history of inulin-containing plants being used to treat diabetes. The Greek physician Theophrastus used dandelion (Taraxacum officinale L.) to treat the condition, a plant also used as an early treatment in Eurasia. In North America, the root of elecampagne (Inula helenium L.) has historically been used to lower blood sugar levels (Tungland, 2003). In 1874, it was reported that no sugar appeared in the urine of diabetics who were given a daily inulin dose of 50 to 120 g (Külz, 1874). Jerusalem artichoke tubers are rich in inulin and fructooligosaccharides and are therefore an ideal item to include in diabetic diets. Jerusalem artichoke was fed to diabetic patients in the 1920s with promising results (e.g., Carpenter and Root, 1928). It proved beneficial when substituted for other carbohydrate foods, such as potatoes, over periods ranging from 6 days to several months. The increase in blood sugar after eating Jerusalem artichokes (0.02 to 0.07% in 3 h) was significantly lower than when consuming an equivalent amount of fructose or other carbohydrates (Root and Baker, 1925). However, gastrointestinal side effects in patients limited the extent to which the vegetable was subsequently prescribed.
Today, a moderate quantity of Jerusalem artichoke is recommended in diets aimed at countering diabetes and obesity. Eating Jerusalem artichoke daily, however, could become monotonous. Fortunately, foods incorporating tuber extracts also provide the health benefits of Jerusalem artichoke. Flour from Jerusalem artichoke, for instance, replaces wheat flour in a range of food products aimed at the weight-loss, health food, and diabetic food markets (Roberfroid and Delzenne, 1998). Jerusalem artichoke is also being added to butter, purée, drinks, and other products aimed at diabetics.
The flour made from Jerusalem artichoke tubers is a low-calorie, fat-free source of energy and fiber, which is rich in nutrients, including calcium, potassium, and iron. For the health food market, Jerusalem artichoke flour is often included in products that also contain live bacteria, especially bifidobacteria. The bacteria (probiotic) and food substrate (prebiotic) act to maintain a healthy balance of microflora in the colon (see below).
To make flour, Jerusalem artichoke tubers are macerated, heated, and spray-dried. In the process, inulin is hydrolyzed to short-chain fructooligosaccharides (Yamazaki et al., 1989). Jerusalem artichoke flour is also used to supplement animal feed. In one study, the composition of a typical Jerusalem artichoke flour was 2.1% (of dry weight) nitrogen, 16.2% insoluble fiber, 4.2% ash, and 77.5% soluble carbohydrate. The carbohydrate comprised fructans with degrees of polymerization of 1 to 2 (33.3%), 3 to 4 (46.4%), and over 5 (20.3%) (Farnworth et al., 1993).
Fructans and fructose extracts, which can potentially be obtained from Jerusalem artichoke, have become attractive to industry for a number of food and nonfood applications because of their health benefits (e.g., Fleming and GrootWassink, 1979; Fontana et al., 1993; Fuchs, 1993; Roberfroid, 2005). Short-chain fructooligosaccharides (degree of polymerization of 2 to 5), for example, are increasingly used as low-calorie sweeteners in processed foods, and their utilization is anticipated to expand significantly in the future.
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