Source: Adapted from Franck, A., Br. J. Nutr, 87 (Suppl. 2), S287-S291, 2002.
Obesity represents a major global health crisis. Figures produced by the World Health Organization (WHO) in 2002 revealed that worldwide more than a billion adults were overweight and 300 million were clinically obese. In 2003, the International Association for the Study of Obesity calculated that up to 1.7 billion people in the world were overweight or obese. Organization for Economic Cooperation and Development (OECD) data published in 2002 showed that over 26% of the population of the U.S. was clinically obese, while over 20% of the populations of the U.K. and Australia were obese. Until recently, obesity was thought to be a problem only for rich countries. However, obesity is now prevalent in both developed and developing world nations; undernutrition and overnutrition coexist in many countries (Gardner and Halweil, 2000; Lang and Heasman, 2004).
Overnutrition is the root cause of the obesity epidemic. The consumption of excessive amounts of high-energy fatty and sugary foods leads to the accumulation of body fat. Obesity is defined as an excessively high amount of body fat in relation to lean body mass. The standard for obesity is usually expressed in the form of body mass index: a person's weight divided by the square of his or her height in meters (kgm-2). A body mass index of 25 to 30 is considered overweight, while an index of 30 or above is considered obese. Extreme degrees of obesity are rising at alarming rates. By 2003, over 6% of the U.S. population was morbidly obese, with a body mass index over 40. A body mass index above 25 increases the risk of premature death due to a range of degenerative diseases and health conditions, including cardiovascular disease, hypertension, stroke, osteoporosis, some cancers (endometrial, breast, and colon), and diabetes mellitus (type 2 diabetes) (CDC, 2006; Lang and Heasman, 2004).
The World Health Organization estimates that over 3 million deaths a year can be attributed to overweight and obesity, a figure that is predicted to increase (WHO, 2002). Obesity increased 74% between 1991 and 2001 in the U.S., and steep increases like this are now occurring elsewhere. The rapid rise in obesity has made it one of the greatest risks to human health worldwide. Of particular concern is the obesity rate among children, which increases disease risk throughout their lifetime.
The number of overweight children in the U.S., for instance, tripled between 1980 and 2005 (CDC, 2006), while the number of clinically obese children in secondary schools in the U.K. doubled between 1994 and 2004 (NHS, 2006). The health care costs are already enormous. In 1998, it was estimated that medical expenses arising from overweight and obesity accounted for 9.1% of the total U.S. medical expenditure. The health care costs of overweight and obesity in the U.S. probably exceeded $78.5 billion in 2005 (CDC, 2006; Lang and Heasman, 2004).
The forecasts are alarming, but obesity is largely preventable. Reduced food consumption, dietary change, and more exercise, for instance, could help stem the obesity epidemic. To facilitate dietary change, there is an urgent need for food products that satisfy hunger without contributing to obesity. Jerusalem artichoke is a bulky low-energy food that fits this profile. It has a low energy (calorie) value because enzymes in the digestive system do not degrade inulin and fructooligosac-charides, a prerequisite for absorption by the body. For this reason, inulin and fructooligosaccharides are often referred to as nondigestible oligosaccharides.
The utilization of inulins as a fermentable substrate by microflora in the colon, however, means they are broken down and absorbed to a limited extent. Inulin therefore has a small caloric value. Molis et al. (1996) calculated an energy value of 2.3 kcalg-1 (9.5 kJg-1) for fructooligosaccharides, while Livesey et al. (2000) proposed a value of 2.0 kcalg-1 (8.4 kJg-1) for all carbohydrates that undergo microbial fermentation. However, most energy values calculated for inulin and fructooli-gosaccharides in the literature have been lower than this. A calorific value of 1.5 kcalg-1 (6.3 kJg-1) was reported by Hosoya et al. (1988) and Ranhotra et al. (1993), for instance, while Roberfroid et al. (1993) gave a range between 1.0 and 1.5 kcalg-1 (4.2 and 6.3 kJg-1). The differences reported for the caloric value of inulin are effectively insignificant in nutritional terms (Roberfroid, 2005). Although there is at present no universally accepted figure, the energy value for inulin is usually given as 1.5 kcalg-1 (6.3 kJg-1) on food labels and in nutritional advice (Roberfroid, 1999). Therefore, the caloric value of Jerusalem artichoke is much less than for most other root vegetables. While 100 g of boiled potato, for example, has a caloric value of 76 kcal, the same amount of boiled Jerusalem artichoke tuber has 41 kcal (Vaughan and Geissler, 1997). Jerusalem artichoke is therefore an ideal vegetable to include in a weight-losing diet. As an ingredient (e.g., flour), Jersualem artichoke inulin can replace fat and sugar in low-calorie foods.
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