A diet rich in calories and carbohydrates was seen to slow progression of the lethal, degenerative Lou Gehrig's disease, in a small-scale study reported in The Lancet.
Formally called amyotrophic lateral sclerosis (ALS) or motor neuron disease, the disorder affects nerve cells that control muscle movement.
Patients become tired and weak and lose the power to move and eventually breathe; they die three years on average after being diagnosed.
The new study follows up on suspicions that ALS patients may be placed at even greater risk if they lose weight. They find it hard to eat and swallow, and eventually have to be fed with a tube directly into the stomach.
Experiments on mice genetically engineered to display ALS symptoms have found that those given a high-calorie diet rich in fat survived longer.
Building on this work, researchers in the United States tested 20 volunteers with advanced ALS who were at the stage of being tube-fed.
The patients were divided into three groups.
One was a "control" group which received a nutritional formula designed to keep their weight stable, while the other two received 125 percent of the calories they needed to maintain their weight.
Of these two groups, one received a high-calorie diet rich in carbohydrates, and the other a high-calorie diet rich in fats.
The diets lasted for four months, and patients were followed for a further five months afterwards.
Patients on the diet that was high in calories and carbs did far better than counterparts in the two other groups, the researchers found.
They experienced fewer "adverse events" - health problems ranging from pneumonia to muscular pains or rashes.
They also gained more weight, picking up 390 grammes (0.8 pounds) per month on average, compared to a gain of 110g (0.24 pounds) in the control group and a loss of 460g (1.01 pounds) in the high-calorie high-fat diet group.
During the five-month followup, no deaths occurred among the high-calorie, high-carbohydrate group, compared with one in the high-fat group and three in the control group, said the study.
The experiment was only conducted on a small scale and its chief goal had been to see whether ALS patients could safely change diet, rather than testing how effective the switch might be.
"This pilot study demonstrates the safety of a novel, simple, low-cost treatment for a devastating disease where currently very few treatment options are available," said lead researcher Anne-Marie Wills at the Massachusetts General Hospital in Boston.
"The adverse outcomes that we feared might result from weight gain, such as diabetes or heart disease, were not observed in our study period."
The team called for larger trials among patients at an earlier stage of ALS, to see whether these optimistic but cautious findings hold true.