People with amyotrophic lateral sclerosis (ALS) are known to experience changes in their metabolism after their diagnosis — for example, they burn more calories while at rest. But a new study from the Netherlands suggests these changes happen even before patients have symptoms of the disease.

However, it’s too soon to know whether these changes represent a cause or an effect of the disease, experts say.

In the study, the researchers surveyed about 670 people with ALS, also known as Lou Gehrig’s disease, shortly after their diagnosis. The patients were asked to report the foods they ate in the month before they started to experience symptoms. Their answers were compared with those of about 2,000 other people in the general population who did not develop ALS.

The researchers found that before their symptoms started, the people with ALS had a higher calorie intake—consuming an average of 2,258 calories a day—than those who didn’t develop ALS, who consumed an average of 2,119 calories per day. But despite higher calorie consumption, ALS patients had a slightly lower average body mass index (BMI) before their symptoms started, compared with those who didn’t develop ALS.

The study also found that the people who developed ALS consumed slightly more fat and cholesterol, and slightly less alcohol, than those who did not develop the disease.

Because the study was conducted at a single point in time, the researchers cannot say whether any of these aspects of people’s diets could be causes of ALS or whether they are effects of having the disease.

But the findings lend support to the idea that “altered energy metabolism may already be present in patients with pre-symptomatic ALS,” said the researchers, from the University Medical Centre Utrecht.

Dr. Robert Baloh, director of the ALS Program and Neuromuscular Medicine at Cedars-Sinai Medical Center in Los Angeles, said research like the new study is important because so little is known about how people’s diets and other environmental factors might influence their risk of ALS.

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