Gym Protein for Diabetes patient ?

Your friend needs to learn a few things about nutrition. The body needs forty nutrients and eight of them are called "complete protein". Their are other kinds of proteins too. Nutrition is the youngest science and not fully studied. Doctors have no training, but some of them think they do. It turns out they are trained in dietetics and they don't know the difference. So your friend has to learn the subject himself.

Protein shakes are made of powdered milk, soy flour, sugar, and flavor. They cost about $1.25 for the amount of protein you get in a quarter's worth of milk. Your body needs 4/10 gram of complete protein per pound of weight, about 65 grams for a female and 80 grams for a male. You do not need more because you exercise or less because you loaf. For convenience you only count 6 grams per egg, 12 grams per glass of milk, and 24 grams per quarter pound of meat. If you eat more than the body needs, the excess is burned as ordinary but expensive calories. If you really think you need more protein, get powdered milk and mix it into your food. Or eat more eggs.

People who run gyms assume that all their customers want to be alone, so they offer no coaching. So your friend has to learn that business too. (I did gymnastics for four years in high school and did not even learn why warming up was important.) There are different exercises for building muscle and maintaining tone. You have to know all the muscles and specific exercises for each one. To build a muscle you work it to exhaustion and then let it rest about two weeks while you exercise other muscles. So you make a schedule, muscle by muscle.

Learn the business:
www.amazon.com/Adelle-Davis/e/B001J3RULO
www.adelledavis.org/
cronometer.com/ (I haven't tried the software.)
charlesatlas.com/ An exercise plan that has been successful for over 80 years and requires no equipment