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 per cent 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 carbohydrates did far better than counterparts in the two other groups, the researchers found.

They experienced fewer "adverse events", defined as health problems ranging from pneumonia to muscular pains or rashes.

They also gained more weight, picking up 390 grams per month on average, compared to a gain of 110 grams in the control group and a loss of 460 grams in the high-calorie, high-fat diet group.

During the five-month follow-up, no deaths occurred among the high-calorie, high-carbohydrate group, compared with one in the high-fat group and three in the control group.