The results, if they can be repeated in humans, indicate the potential importance of dietary protein for insulin control, suggest the authors in the British Journal of Nutrition .
"This effect is important inasmuch as it is of a magnitude similar to that afforded by the dual substitution of n-3 polyunsaturated fat for saturated fat and starch for sucrose," wrote lead author Francois Mariotti from France's Institut National de la Research Agronomique (INRA - UMR914 Nutrition physiology and ingestive behaviour).
"The quality of dietary protein may be an underestimated parameter in dietary strategies against the metabolic syndrome."
Study details The researchers used proteins from rapeseed - rich in cysteine - and tested their efficacy in rats fed a diet high in saturated fat and sucrose and including 20 per cent protein sourced from milk or rapeseed in relation to metabolic syndrome (MetS).
A third (control) group of mice consumed a diet of equal energy formulated with milk protein, polyunsaturated fat and starch.
MetS is a condition characterised by central obesity, hypertension, and disturbed glucose and insulin metabolism.
The syndrome has been linked to increased risks of both type 2 diabetes and CVD.
Fifteen per cent of adult Europeans are estimated to be affected by MetS, while the US statistic is estimated to be a whopping 32 per cent.
Obesity is established to be the main risk factor for MetS After nine weeks of feeding the animals the researchers report an increase in blood glucose, insulin and triglycerides levels in all groups, but insulin levels were significantly 34 per cent lower in the control group, and 56 per cent lower in the milk protein-saturated fat-fed group, than the rapeseed protein-supplemented group.
Moreover, the insulin peak after a glucose load was 28 to 30 per cent lower in both milk protein-fed groups than in the rapeseed protein-fed group.
"In this model, substituting rapeseed protein for milk protein had preventive effects on the early onset of insulin resistance, similar to those achieved by manipulating the types of dietary fat and carbohydrates," stated the researchers.
Additionally, glutathione levels were 30 per cent lower in the milk protein, saturated fat diet compared to the rapeseed oil diet, they reported.
Glutathione is a protein that is important in protecting the body from oxidative (free radical) damage.
Mechanism of action Mariotti and co-workers state that the favourable effects of the rapeseed protein may be due to the cysteine content or effects on glutathione levels and insulin sensitivity.
The researchers could not however identify the underlying mechanisms and called for further studies to address these.
"Further studies may interestingly, and complementarily, assess if rapeseed protein can improve insulin sensitivity in animals or human subjects that already display insulin resistance," they added.
An estimated 19 million people are affected by diabetes in the EU 25, equal to four per cent of the total population.
This figure is projected to increase to 26 million by 2030.
In the US, there are over 20 million people with diabetes, equal to seven per cent of the population.
The total costs are thought to be as much as $132 billion, with $92 billion being direct costs from medication, according to 2002 American Diabetes Association figures.
Source: British Journal of Nutrition Published online ahead of print, doi: 10.1017/S000711450896092X "Rapeseed protein prevents the initiation of insulin resistance by dietary saturated fat and sucrose in rats" Authors: F. Mariotti, D. Hermier, C. Sarrat, D. Tome, J.-F. Huneau