Overweight in middle-aged populations is an increasing factor in EU health-care costs. Overweight causes a loss of self-esteem, is socially disadvantageous and increases the incidence of diabetes, dyslipidaemia and coronary heart disease. Conjugated linoleic acid (CLA) can reduce body fat. This project aims to formulate a functional food containing an active CLA-isomer that will reduce overweight and improve health. Human experiments will determine which CLA isomer is active and which form has highest bioavailability. Pure CLA isomers, stable isotope-labelled CLA and a functional food containing CLA will be fed to middle-aged people including overweight subjects with no disease and to patients with diabetes or hyperlipidaemia. Complementary studies will use an animal model.
The main objective of this project is to develop a functional food containing conjugated linoleic acid, designed to reduce overweight and the negative impact of overweight on the health of the middle-aged population. The scientific objectives of the project are: 1) to assess the impact of conjugated linoleic acid (CLA) isomers on the energy metabolism and fat partitioning in overweight humans; 2) to assess the bioavailability of CLA isomers in humans, including the absorption and the utilisation of CLA as energy fuel; 3) to determine which of the CLA isomer(s) is (are) active; 4) to assess the impact of the active CLA isomer(s) on different health parameters and to determine any possible side effects. The technological objectives are 1) to develop a functional food containing the active CLA isomer(s) and to assess the metabolic impact on humans; 2) to assess the acceptability of the functional food for the consumer, including sensory evaluation.
The bioavailability of a mixture of 2 CLA isomers present as free fatty acid, ethyl esters, and triacylglycerols was tested. The raw data indicate that the ethyl ester was less well incorporated than the other forms with little difference between the free fatty acid and the TAG. Due to palatability and possibly oxidation problems with the free fatty acid, TAG is the form to be used.
Large scale preparations of the pure CLA isomers as TAG were developed and used to produce the drinkable preparation necessary for the trials in 2001. Together with four external experts in toxicology it was decided to lower the CLA dosage and to reinforce the safety of the protocol of the human study after an external publication appeared at the end of 2000 showing potential side effects of CLA.
Two rat studies were carried out in order to determine whether exercise would enhance the effects of CLA and to obtain complementary knowledge on the effects of CLA on energy metabolism. The data suggest that CLA may induce stimulation of AT and muscle protein turnover, which increases energy expenditure and could be involved in AT mass reduction.
Oxidation of CLA isomers was determined using 14C isomers of 9c,11t- and 10t,12c-CLA. The data indicated that both CLA isomers were oxidised significantly more than linoleic acid. Moreover, less radioactivity was recovered in most tissues after CLA intake than after linoleic acid intake.