Elderly Father wants to gain weight

Elderly father needs to gain weight per his doctor. He is diabetic. My question is what can he add to his two daily shakes to increase calories without affecting the amount of sugar he must balance for his diabetes? Thanks in advance!

This is best to work out with a registered dietitian. Fat is the most calorie dense macronutrient, but you don’t want too much. Protein is great but also quite filling.

Natural Peanut butter (no added sugars), blended into chocolate or vanilla Huel shakes tastes good and can definitely be used for gaining weight. Low glycemic index and is a whole food (albiet blended).

Another option is applesauce (with no added sugar). Apples have been shown to help with type 2 diabetes and have a low glycemic index.