My fiance has gained 40 kg in less than a year. What could be the reason?

Hello doctor,

I am concerned about excessive weight gain by my fiance. He is a 29 year old male, whose height is approximately 6 feet, and he weighs 150 kg. Over the last two years, my fiance had lost around 40 kg using the Banting diet, common in our country. It is based on the principles of no carbohydrates, starches or sugars and higher protein, but does allow the odd cheat meal. Since then, in the last eight months, he has had two attempts at quitting smoking and was put on Pendine 5 and Zartan CO for high blood pressure. He has a family history of hypertension. As a result, he has gained weight at quite a quick pace despite sticking to his Banting diet. The meal sizes have not changed, and he has an active lifestyle. We hike or do vigorous walks of 5 to 8 km on most days.

At this stage, he has almost gained the full 40 kg back in less than a year, which seems very excessive and way above normal for quitting smoking. I was wondering if perhaps he has some thyroid issues, as his mother has hypothyroidism. Or could it be a side effect of the medication? We need some advice. We are at a loss at what to do. I would like to add that he struggled with weight issues since childhood. Also, we are currently not in his country, so visiting a doctor may be difficult.