TUESDAY, July 20 (HealthDayNews) -- Animal studies are pointing to problems with mitochondria, the energy factories of human cells, as an important element in Lou Gehrig's disease, the relentlessly fatal wasting-away condition.

There is "growing evidence" that mitochondrial malfunction, not only in nerve cells but also in skeletal muscle cells, may play a crucial role in the disease, says a report in this week's issue of the Proceedings of the National Academy of Sciences. The French study was led by Jean-Philippe Loeffler, research director at the National Center for Scientific Research in Paris.

Bolstering this theory is research indicating that mice bred to develop Lou Gehrig's disease, formally called amyotrophic lateral sclerosis (ALS), survived longer when fed a high-energy diet.

"What the exact molecular mechanism is, we don't know," Loeffler said. "We are working on it."

The researchers found what they call "a metabolic deficit" in mice with ALS -- a failure to effectively turn food into energy in both nerve and muscle cells. This results in an increased but inefficient expenditure of energy to keep cells functioning.

"There are two important things in the paper," said Lucie Bruijn, science director of the ALS Association, which helped fund Loeffler's work. "One is to reinforce the fact that mitochondria are likely to play an important role in ALS."

Researchers at the University of California, San Diego, recently reported an animal study that also implicated mitochondrial malfunction in ALS, she added.

"The involvement of muscle cells is also very interesting." Bruijn said. "Until now we have thought of ALS as a neuron [nerve cell] disease. The idea that the muscle cell itself might be involved is clearly important."

Much more research is needed to clarify the issue, Bruijn said. "We can't say yet whether the muscles are involved first and then the neurons," she said.

One potentially important aspect of the study was that feeding the mice a fat-enriched, high-energy diet appeared to have a beneficial effect. Loss of nerve cells decreased in mice fed the diet, and their overall survival time was 20 percent longer than that of mice fed a normal diet.

But both Loeffler and Bruijn said it is much to early to try such a diet on humans with ALS because more basic work is needed.

"It is a line of research we would pursue," Loeffler said.

"This was a laboratory study using a mouse model," Bruijn said. "We have to be very careful before we make a diet change in people. It could be harmful, because in many patients a careful balance is needed."