I've been diagnosed with it. My doctor advised a lower carbohydrate plan, but not too low, as he also prescribed metformin, which helps control blood sugar.
Basically, I'm still learning to find the "right" level of carbs that mazimizes weight loss while minimizing discomfort, and conducive to exercising comfortably. Too few and I get light headed, dizzy, fatigues, and irritable (and contrary to some low carber advice, extra fat doesn't help). Too many carbs and the weight doesn't move unless I drop calories to the point that I'm still light headed, fatigued and irritable (but not dizzy, thankfully), and its harder to keep calories that low, because carbs, even "good ones" trigger more hunger for me.
Very low carb, the weight comes off at an almost reasonable pace, but I can't function on that style of eating for long.
So, unfortunately there isn't a simple answer. Just like everyone else trial and error is the only way, but reducing carbs, especially processed ones is a great trial to start. Before going low carb, or even dropping below 150 g of carbs per day, though he should talk to his doctor, or better yet, a dietician or diabetic counselor.
I recommend the diabetic counselor, because my metabolic syndrome is often a precursor to diabetes. My husband is type II diabetic, and a visit with his diabetic counselor was as helpful to me as it was to him. Some insurances will cover it for only diabetics, but many will cover it if their doctor recommends it. Though often for fewer sessions, sometimes only once, while for diabetics it may cover a certain number of sessions every year.