Figure 1 shows total perirenal fat as a function of body weight in rats fed low fat reference diet (Control), obesity inducing high fat diet (HF) and obesity inducing high fat diet containing 1.5 % by weight of the oil composition of the present invention, CO (Copepod Oil) (HF + 1.5% CO) (n=10).
Figure 2 shows glucose oxidation capacity (as μmol/min/g dry weight) of heart muscle tissue of rats fed low fat reference diet (Control), obesity inducing high fat diet (HF) and obesity inducing high fat diet containing 1.5 % by weight of the oil composition of the present invention (HF +1.5 % CO). Values are mean ± 95 % C.I. (n = 8, 6 and 6 for Control, HF and HF + 1.5 % CO, respectively).
Figure 3 (A) shows the blood glucose levels during intraperitoneal glucose tolerance test in mice given the control diet (Control), high fat diet (HF) and high fat diet containing 1.5% by weight of the oil composition of the present invention (HF + 1.5% CO), respectively.
Figure 3 (B) shows the area under the curve of blood glucose levels during intraperitoneal glucose tolerance test in mice of the same groups shown in Figure 3 (A). Data are expressed as mean ± S.E. *P < 0.05 for HF vs. Control; #P < 0.05 for HF + 1.5% CO vs. HF.
DETAILED DESCRIPTION OF THE INVENTION
The following term shall herein have the meaning as indicated below unless otherwise specifically stated:
Wax esters: Wax esters are esters of long-chain or very long-chain acids (fatty acids) and long-chain or very long-chain alcohols (fatty alcohols). Long-chain in this context means from 14 to 22 carbons, whereas very long-chain refers to 24 or more carbon atoms. Wax esters are important component in waxes. Usually, the term "wax" refers to a wide class of lipids characterized by being solids at room temperature, e.g. when it looks like honeycomb material or bees-wax. However, waxes may be both solid and liquid. They are produced by animals (beeswax, wool wax (lanolin), sperm whale wax and orange roughy oil) and plants (candelilla, carnauba, rice-bran, sugar cane (policosanol) and jojoba. All leaf surfaces and many vegetables and fruits are covered by a microcrystalline layer of wax. Waxes are used in the food, pharmaceutical and cosmetic industries for the protection of surfaces.
Wax esters of the present invention are monoesters of long-chain unsaturated fatty alcohols and long-chain unsaturated fatty acids, notably omega-3 fatty acids, and the oil composition of the present invention is completely soluble and free-flowing at room temperature.
It has been shown that the oil composition of the present invention, used as a minor supplement in a high- fat, obesity inducing Western type of diet, specifically inhibits visceral fat accumulation induced by such a diet. Moreover, it has been shown that the oil composition of the present invention can counteract impairment of heart function induced by such a diet. The oil composition of the present invention can in other words be used to counteract the most harmful effects of obesity inducing Western diets.
The oil composition of the present invention has been obtained from the marine copepod Calanus finmarchicus. The chemical composition of this oil differs markedly from that of other oils, and it was investigated if it would differ also regarding the possible biomedical responses it may elicit. However, there is nothing in the prior art that would lead a person skilled in the art to consider it likely that inclusion of as little as 1.5 % (w/w) of the present oil composition in an obesity inducing high-fat (24 % w/w) Western type of diet would result in a statistically highly significant reduction of visceral fat accumulation in rats, without affecting growth or deposition of fat in other adipose tissues. Moreover, and equally unexpected, the present oil composition reduced the visceral fat accumulation in rats fed on this high-fat diet to the same level as in rats fed on the low-fat (4 % w/w) diet used as the reference diet, not inducing obesity. It is also evident that the present oil composition may counteract deterioration of healthy heart function typically seen in obesity induced type 2 diabetes, as demonstrated by high cardiac glucose metabolism even after long time feeding on an obesity inducing high-fat diet.
The n-6/n-3 proportion of fatty acids in dietary lipids affects the pattern of fat accumulation in the body. Diets in which this proportion is high (e.g. > 5/1), as in high- fat Western diets, have a stronger tendency to induce central obesity and accumulation of visceral fat than diets with a lower n-6/n-3 ratio. For comparison, since the oil composition of the present invention constituted only a minor fraction of an obesity inducing high-fat Western type of diet, the n-6/n-3 fatty acid ratio was still as high as 5/1 in our experimental diet.
The oil composition of the present invention contains the n-3 fatty acids EPA (eicosapentaenoic acid = C20:5n-3) and DHA (docosahexaenoic acid = C22:6n-3), like other marine oils. However, the level of EPA and DHA is somewhat lower than in fish oil and krill oil (Table 1), whereas it is rich in stearidonic acid (SDA = C18:4n-3). Nevertheless, it might be argued that the observed inhibition of diet induced visceral obesity could be due to the presence of EPA and DHA. However, it should be borne in mind that wax esters, including marine wax esters, are digested very slowly compared to triglycerides and phospholipids and that EPA and DHA in the wax ester is not readily available for absorption as free acid. In fact, it is a common understanding among the skilled in the field that wax esters are not digestible, and that a marine wax ester rich oil like that from Calanus finmarchicus therefore is a poor source of EPA and DHA. Moreover, in the experiments of Belzung et al. (1993) described above, the amount of omega-3 consumed by the animals was in the range of 0.7 -1.4 grams daily. By comparison, the oil composition of the present invention contributed with only 0.06 gram omega-3 daily to rats feeding on the obesity inducing high-fat diet. Accordingly, it can be concluded that the inhibition of visceral fat accumulation shown in the present invention neither can be ascribed to omega-3 as in the experiments of Belzung et ah, nor can it be due to change in the ratio of n-6/n-3 fatty acids in a more healthy direction.
The oil composition according to the present invention can be derived from marine copepods, preferably a copepod of the genus Calanus, such as Calanus finmarchicus. Freshly harvested, frozen/thawed or dehydrated raw material can be used as the raw material for obtaining the oil compositions, using any method known by the skilled in the art, such as but not limited to, conventional fish oil production technology, biotechnological methods, organic solvents or supercritical fluid extraction, and cold pressing. Independent of the procedure of obtaining the oil and the yield of oil, the typical gross composition will be as shown in Table 1.
Table 1. Typical chemical composition of three different marine oils: (A) Copepod oil from Calanus finmarchicus caught in Norwegian waters, (B) cod liver oil from Atlantic cod Gadus morhua, and (C) krill oil from Euphausia superba caught in the Southern ocean, given in mg/g oil.