Dr Thomas Stuttaford, writing in The Times, agues that single malt is less fattening than real ale.

"The tot of whisky or gin is about 75 calories, the recent EU measure a little higher. A modest calorie score compared with a pint of real ale." He adds though,  that if a mixer is added to the spirit it can easily double the calories." A gin and tonic or gin and orange or bitter lemon, contrasts badly with gin and bitters or whisky and water."

"Even a dry martini has more calories than a whisky and water", he added.

He  used  to persuade  beer drinkers, even if moderate consumers who were grossly overweight, to convert to malt whisky and water. 

Of course it depends on how large the 'tot' is...