In the future, infections may be cured by diet, as well as drugs

From The Economist print edition

CONTROLLING infectious disease is an arms race. Pharmacists develop drugs against particular pathogens. Those pathogens evolve resistance. Better drugs are developed. The pathogens evolve a bit more. And so on. Time, perhaps, for some creative thinking.

One person doing such thinking is Val Smith of the University of Kansas. In a paper just published in the Journal of Integrative and Comparative Biology he argues that the future of disease control may lie not in better antibiotics but in cutting off the supply of nutrients to the pathogens by manipulating a patient's diet.

Obviously, you cannot stop feeding someone entirely when they are ill, but there might be nutrients which the patient could do without but the pathogen could not. Dr Smith scoured the university's library, looking for experiments that had studied the effect of diet on animals suffering from infectious diseases. He found three specific examples, and one more general case, where changes in diet appeared to have had beneficial effects. He suggests, therefore, that it might be worth trying the same thing in people.

The first of the specific studies was on Salmonella, a bacterium found in spoilt food. In this experiment, infected mice were fed on diets that contained variable amounts of protein, carbohydrate and fat. The amount of fat did not make any difference, but the more carbohydrate there was in a diet, the more frequently the mice died of their infection. Conversely, mice on high-protein diets were more likely to live.

A high-protein diet, though, is not always the right route to take. In the second study Dr Smith identified, rats infected with Plasmodium berghei, the rodent version of malaria, were less likely to die of the disease if fed low-protein diets.

The third study examined a specific nutrient, a sugar called fructose that is abundant in fruit. In this case a low-fructose diet kept infection with a parasitic worm called Moniliformis dubius under control in rats.

The most promising line of all, though, is to control an animal's intake of iron. Many experiments have shown a fierce competition for this element between bacterial, fungal and protozoan pathogens and their hosts. Fortunately, this is a competition where the host appears to have the advantage. In situations where iron is scarce, the bodies of mice and rats (and presumably, by extension, people) seem able to collect the nutrient more efficiently than pathogens do.

The trick, Dr Smith suggests, is to cut patients' iron intake to the minimum necessary for survival. Theoretically, that would leave nothing for pathogens to make use of, thus suppressing infection and restoring, as it were, an iron constitution.