Fenugreek is a native of the Indian sub-continent and the Eastern region. Its high adaptability to dry climate, high yield and their ability to fix atmospheric nitrogen (N) make it an ideal for short-term crop rotation in Northern countries, such as Canada. An examination in our laboratory has revealed that the Canadian-grown fenugreek seeds and the seeds of a fenugreek variety, grown in India, are of similar appearances, color, size, shape, odor, and anatomical features. The chemical composition (e.g., crude lipids, 4-hydroxyisoleucine, saponins) of Canadian fenugreek seeds has also been found to be very similar to that of the seeds of Indian origin. The Canadian variety, however, is significantly higher in crude protein and GAL contents (unpublished data).
In rats, a high sucrose diet has been reported to result hypertriglyceridemia, hyperglycemia, and hyperinsulinemia [18
]. The diet is also known to impair insulin action, leading to hypertriglyceridemia [20
]. In the present study, an addition of 5% GAL to a high sucrose diet resulted in a marked reduction in food intake in parallel with body weight gain in rats, when fed for 4 weeks. GAL belongs to a family of seed gum; it represents polymers of galactose and mannose, and it is soluble in water [22
]. Most soluble gum fibers, such as guar gum, xanthan gum, gum acacia and locust bean gum are viscous and that this property is thought to delay gastric emptying and consequently intestinal absorption [23
]. However, the ratio of body weight gain to food intake in all 3 groups in this study was similar. These data indicated that the reduction in weight gain in the high GAL group was likely due to reduced food intake, rather than malabsorption. The fiber intake was also found to be accompanied by a decreased rise in plasma insulin, which is an important factor for appetite control [24
]. It seems probable that the reduced food intake in the presence of GAL is caused by delaying in gastric empty (due to viscosity) and promoting satiety (due to insulin inhibition) of the soluble fiber. These results are in agreement with our previous in vitro
study demonstrating reduced intestinal glucose uptake with increasing GAL concentration in lean and obese JCR rats [25
]. This inhibition was found to be associated with an increase in the viscosity of the GAL-containing test solutions.
The present study was the first to demonstrate that feeding a GAL diet for 4 weeks to normal rats, markedly reduces the size of the abdominal adipose tissues compared with the control counterpart, fed a similar diet but containing an equivalent amount of cellulose as a fiber source. This result can be explained by a decrease in insulin level leading to reduced lipogenesis. The evidence of abdominal adipose tissue histology from rats fed with 5% GAL containing diet is suggestive of a high metabolic rate in the tissue, leading to a release of FFA into the circulation.
One of the plausible mechanisms linking visceral adiposity to insulin resistance is the liberation of non-esterified fatty acids (NEFAs) from visceral depots to the liver. This NEFAs in the liver, therefore, have a particularly important role in bringing about many features of insulin resistance. Stimulation of hepatic glucose synthesis may contribute to glucose intolerance [26
]. Stimulation of hepatic VLDL-TG secretion may contribute to impaired postprandial lipid metabolism (via competition with chylomicron-TG for peripheral clearance) and the development of hypertriglyceridemia. Given these facts, the high plasma and hepatic FFA in rats fed a diet containing 5% GAL for 4 weeks, observed in the present study, do not reflect insulin resistance. These rats had lower plasma TG, while VLDL-TG levels remained unchanged compared to the controls. The OGTT in these animals also remained unaffected. These results indicate that an underlying factor for the reduction of plasma insulin level in GAL-fed rats may increase lipolysis in adipose tissue, and consequently an increased plasma FFA levels and a reduced adipocyte size. The GAL-associated decrease is also accompanied by reductions in plasma and hepatic concentrations of triglycerides, total cholesterol, and LDL-cholesterol. These findings are in agreement with others, which reported similar effects using other viscous fibers [27
]. The hypocholesterolemic effects of soluble fibers may slow glucose absorption, because of their viscosity as well as by binding bile acids in the intestinal lumen leading to a decreased enterohepatic circulation [29
]. Furthermore, viscous fibers have been shown to increase the number of LDL receptors in the liver of rats [30
]. An up-regulation of the LDL receptors, therefore, increases clearance of LDL cholesterol. The results of reduced hepatic cholesterol and plasma LDL cholesterol in the present study, thus, suggest the possibility of an increased clearance of cholesterol in the liver.
In summary, GAL at 2.5% and 5% (w/w) reduced plasma triglyceride, cholesterol and hepatic cholesterol concentrations. GAL at 5% (w/w) resulted in lower food intake, which may have enhanced the release of plasma FFA, and in turn, led to the least amount (i.e. weight) of epididymal adipose tissue. These results clearly demonstrate that GAL from Canadian-grown fenugreek, a novel source of dietary fiber, has the potential benefits in modifying both glycemic and lipidemic status as well as body weight.