Community Research and Development Information Service - CORDIS

FP5

GUTINTEGRITY Report Summary

Project ID: Q5RS-2000-31656
Funded under: FP5-LIFE QUALITY
Country: Sweden

Dietary vegetable lipids and nutrient uptake

Although optimal use of high energy diets can increase protein efficiency and despite the adaptive response of rainbow trout to high-fat diets through:
- Maintenance of energy intake until values of 20.5 kJ DE/g diet,

- Increased utilization of lipids for energy purposes and

- Reduction of hepatic lipogenesis, trout were still depositing to maintain the chemical composition of their whole-body and tissues. Simply stated, feeding trout high fat diets produces fatter fish, lipid deposition being primary in the visceral cavity and to a lesser extent in muscle. Since the development with age of adipose tissue is correlated with a recruitment of pre-adipocytes, increased storage capacity by dietary manipulations results from hyperplasic and hypertrophic processes in trout. Besides, the use of high fat diet depresses de novo fatty acid synthesis and increases lipid storage of dietary origin.

Therefore, a low quality dietary lipid profile may impair the nutritional value of fish flesh as human food.

A change in dietary lipids clearly effects the fatty acid composition of the polar lipids constituting the enterocyte membranes. The effect was pronounced in fish fed only vegetable oils, whereas fish fed small amounts of marine lipids retained in the fishmeal (2% of total lipids), were relatively successful in maintaining their levels of 20:5n-3 and 22:6n-3 in a similar range as the fish receiving 40% and even 100% fish oil (FO). Fish fed sunflower oil (SO) were distinguished from the other dietary groups in that these fish were not fully capable of maintaining their levels of 20:5n-3, they seem to increase their levels of 20:4n-6 in the membranes which probably is due to the ample supply of 18:2n-6 from the SO and may lead to altered membrane characteristics.

Intra-membrane proteins, like the active transporters of water soluble nutrients, glucose and amino acids, can be affected by changes the surrounding membrane lipid composition. The intestinal uptake of the non-toxic, non-essential amino acid proline was not affected by dietary vegetable oils when fed in a mixture. Using a diet containing only SO, both the proline and the essential fatty acid leucine uptake were negatively affected. Mixtures of dietary vegetable oils instead increased the uptake rate of the two essential amino acids leucine and histidine. In summary, the uptake rate of essential amino acids seems to be more sensitive to changes in dietary replacements then the non essential amino acids and a mixture of vegetable oils seems to affect the active uptake mechanisms to a lesser extend then diets containing only SO. The same pattern seems to be present for intestinal glucose uptake.

A very interesting and for aquaculture important life stage of the Atlantic salmon is the parr-smolt transformation, during which cortisol and GH, among other hormones have regulatory functions. Apart from being a developmental hormone, cortisol is also a stress related hormone and the consistently elevated plasma levels of cortisol in fish fed SO indicates that the substitution of fish oil by SO creates a situation of chronic stress. These elevated cortisol levels also affects the intestinal uptake of amino acids revealing a higher uptake rate coincident with the peak in plasma cortisol levels that is most pronounced in the fish fed SO.

A substitution of FO with vegetable oils changes the composition of fatty acids in the diets and this will probably affect the intestinal uptake rate of specific fatty acids. The uptake of selected fatty acids was indeed dependent and regulated by dietary vegetable oils. Fish fed a SO based diet, rich in the fatty acid 18:2n-3, showed a down regulation of intestinal fatty acid uptake of both 18:2n-3 and the fatty acid 16:0 whereas fish fed a linseed oil-based diet, rich in 18:3n-3, instead showed an up regulation of the intestinal uptake of 18:3n-3 and 16:0. These findings open up a new and important field of research. A better understanding of the physiological mechanisms and regulatory events of this specific intestinal uptake of fatty acids would be of great importance for the design of diets containing mixed vegetable oils. The apparent co-transport of unsaturated fatty acids with 16:0 opens up interesting question as to whether the transport of unsaturated fatty acids, including their incorporation into TAG and/or phospholipids, is dependent on a “co-uptake” of the saturated fatty acid 16:0.

Thus, even though the substitution of fish oils with vegetable oils does not affect the overall growth, performance or digestibility, this substitution, especially when using vegetable oils of just one source, may lead to changes in intestinal uptake mechanisms for both water and lipid soluble nutrients. Furthermore, an increased knowledge about the specificity and regulation of intestinal fatty acid uptake mechanisms may be valuable when designing the proportions of fatty acids constituting vegetable oil mixtures to be used for diets.

Contact

Thrandur BJORNSSON
Tel.: +46-31-7733691
E-mail
Record Number: 34042 / Last updated on: 2004-10-14
Information source: e-TIP
Collaboration sought: Further research or development support, Information exchange/Training
Stage of development: Scientific and/or technical knowledge (basic research)
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