Every mother warns her children--eating right will make you healthy. And every pregnant mother's doctor warns her--a good diet means healthier children. But now, a study by two British scientists, finds that this age-old adage may not always be true. Sometimes, they found, a poor maternal diet can actually boost the offspring's resistance to disease.

In a study published on July 25, on the journal Proceedings of the Royal Society B, Mike Boots of the University of Exeter and Katherine Roberts of the University of Leeds, in UK, found that female Indian meal moths, Plodia interpunctella, fed with a sub-optimal diet had offspring that were better able to fend off viral infections. This finding was the reverse of what is usually expected. A poor maternal diet would translate into less robust offspring. 

"This effect is seen no matter how much resources the offspring themselves have," said Dr. Boots. "This is interesting because you may expect mothers in poor environments to have fewer resources to give their offspring."

Changes in a mother's environment have been known to be passed on to offspring. When Kittiwake gull females endure poor nutrition, for example, higher levels of antibodies are passed on to their eggs. And, when Daphnia water fleas mature in crowded, low-resource conditions, their offspring are born less prone to bacterial infections. But it's never been clear how these traits are passed on. This study creates new and fundamental questions about how resistance to disease evolves in various organisms. If a rich maternal diet does not translate into robust disease resistance, then what does? How does disease resistance come about? Surely, recommending a poor maternal diet would be far from the minds of public health officials. 

Dr. Boost and Roberts raised five different maternal populations of the Indian meal moth; each of the five groups received food of a gradually decreasing quality. The food was spiked with increasing amounts of indigestible methylcellulose, which adds bulk but does not contribute any nutritional value. The offspring of these moths were then exposed to a virus and their ability to generate an immune response was measured. 

Surprisingly, those offspring whose mothers had the poorest diet were better able to fend off the virus. In addition, the offspring's response did not appear affected by their diet. No matter how good the offspring's diet was, its ability to resist disease seemed to be dictated by its mother's diet. 

How can this happen? Dr. Boots suggests that it all comes down to the costs of resources. Every adaption is costly to an individual, putting more energy and resources into growth, for example, may be done at the expense of bolstering the immune system. "It is well established that the activation and deployment of the immune system may be costly," said Dr. Boots. "However, under poor environments each offspring may be more valuable to the mother and she may invest more overall into each offspring." 

While the study did not measure the number of offspring per mother, nor did it measure the size of each offspring, the researchers believe that their results show that poor environmental conditions make a mother's offspring more valuable, and therefore she will tend to invest more in her offspring's immunity. This would not be a conscious process, but instead a genetic and physiological one. "High population densities often lead to poor individual resource levels, and may also be correlated with high individual disease risk," Dr. Boots and Dr. Roberts wrote. "We would expect natural selection to favor individuals that invest more when there is the greatest threat of disease." 

Therefore, it is not a green light for pregnant women to start eating unhealthily. Instead, the study shows how a mother's own environmental changes can be passed down to her offspring, and has significant impacts on understanding how disease outbreaks occur. Looking at diet, including a mother's diet before the outbreak, now occupies a more prominent position on that stage.

Original article: Maternal effects in disease resistance: poor maternal environment increases offspring resistance to an insect virus