Yes you can. Replacing the water with the same amount of skimmed milk will bring the total calories of the shake to around 200-220 calories (depending on flavour). The exact calorie count per flavour with skimmed milk can be found on the website; www.shakethatweight.co.uk/shop/ . You can use other types of non dairy milk, the best being unsweetened soya milk as this is  very close to skimmed milk in terms of nutrition and calories.