Current safety precautions are enough to protect humans against mad cow disease, according to BSE experts.
The French research was based on studies of monkeys
Banning brain, spinal tissue and older cattle from the food chain has worked, the French team told the Lancet.
By studying monkeys, they estimated how much infected tissue a human would have to eat to be at risk and said it would be more than anyone could consume.
UK experts said the exact quantity remained an enigma and recommended continued surveillance.
The Commissariat à l'Energie Atomique scientists estimate that a person would have to eat at least 1·5kg of neural (brain and spinal) tissue to be at risk of developing variant Creutzfeldt-Jakob disease (vCJD).
This applies to cattle that screen negative for disease when they are slaughtered but harbour low levels of infection.
Lead researcher Dr Jean-Philippe Deslys said this meant even if the UK switched to screening cattle older than 30 months for BSE, as is done in other parts of Europe, rather than banning sale of this produce, food would still be safe to eat.
Based on his team's tests on two monkeys and previous primate research, he also believes that transmission between cows and primates/humans is far less likely than it is between cattle.
"The efficiency of infection from cow to primate could be seven to 20 times lower than that of intraspecies infection for cattle," he said.
The incubation period for BSE transmission from cattle to human could be more than a third longer than that of human-to-human transmission, he added.
Although the present data does not provide a definitive minimum infective dose for transmission of cattle BSE to primates, Dr Deslys said it did give enough information to know that existing measures to protect our food supplies were adequate.
"To become infected you would need to eat an enormous amount of brain, which is not possible.
"The measures taken now really give a guarantee of food safety and future crises can be avoided."
Professor James Ironside, of the National CJD Surveillance Unit, at the University of Edinburgh, said the small size of the study and the fact it was carried out in monkeys meant the minimum amount of BSE-infected tissue a person would need to eat before contracting vCJD remained unknown.
In the meantime, he said it would be wrong to assume that we were seeing the beginning of the end of vCJD simply because the number of new infections was going down.
"The declining numbers of clinical cases might instead represent the end of the beginning of vCJD, and that continued surveillance will be required for a considerable time before any firm conclusions can be drawn on the likely demise of this tragic condition," he told the Lancet.