Less abdominal fat with fish protein hydrolysate in the diet
New research at the National Institute of Nutrition and Seafood Research (NIFES) shows that hydrolysed proteins – peptides – from fish can affect the production and distribution of bile acids and thus reduce the development of obesity in rats.
Obesity is an increasing problem, nationally and internationally, but preventive action can be taken, which includes having a balanced diet. This is an area where it is natural to include fish and other seafood. NIFES has carried out a number of studies where rats have been fed with fish proteins in hydrolysed form, i.e. broken down into shorter components called peptides. When the lactic protein in the feed is replaced by hydrolysed fish proteins, the level of bile acids in the body increases and the rats develop less fatty tissue, especially in the abdomen. Studies are now being carried out by NIFES to establish the underlying mechanisms that this involves.
"New results show that the source of the hydrolysed proteins, and their structure, can affect the production of bile acids in the body, and thus the development of obesity", said researcher Bjørn Liaset at NIFES in Bergen.
Liaset explained this as follows: Proteins are assembled from amino acids, and proteins from different sources consist of varying amounts of the different amino acids. For instance, proteins from fish and seafood are rich in taurine compared with most other protein sources (including lactic protein, also called casein and soy). In both humans and rodents (mice and rats), taurine bonds with bile acids in the digestive system. Taurine is important for the production of bile acids in the body and for the functions they have. One important function is to split the large fat globules which are deposited in the intestine into smaller droplets, and in so doing play an important role in fat digestion. Bile acids also act as a signal substance which affects fat metabolism and fat combustion.
Under a study at NIFES rates were given a feed containing hydrolysed proteins from pollack which is rich in the amino acids taurine and glycine. These rats were compared with rats which had been given a feed containing either soy or casein as a protein source. Soy and casein have a different structure of amino acids.
"The results showed that the rats which had received fish protein had a higher body content of bile acids on fasting than the other rats, as well as less abdominal fat. They also had less of the fatty acid triacylglycerol in the blood, which is a know market of cardiovascular diseases", said Liaset.
"One possible explanation is therefore that the rats which were given hydrolysed proteins from pollack increased the production of bile acids in the body which resulted in less secretion of lipoproteins from the liver, and in which we find the fatty acid triacylglycerol". Bile acids also increase fat combustion in fatty tissue, and this could play a role in counteracting obesity.
"Hydrolysed proteins are peptides in concentrated form. Whether the same effect is achieve the whole fish or other species is as yet unknown, but this is something we will be studying in the period ahead", said Liaset.
The feed study involving rats is part of the research activity conducted by NIFES which in time could help to explain how fish proteins can counteract the development of obesity.
Taurine in brief
Taurine is a free amino acid and is considered to be non-essential, which means that it is produced by the body itself. Taurine levels are significantly higher in marine creatures, and almost totally absent in the plant kingdom. Taurine accounts for 50% of the free amino acids in the heart.
Glycine in brief
Glycine is a non-essential amino acid. Hydrolysed fish proteins are often rich in glycine. In the human body, glycine also plays a role in the detoxification mechanisms of the liver.
Contact:Bjørn Liaset, Seafood and Health Research Programme