According to the article it's not the mental exertion that causes the weight loss, it's the stress and anxiety players experience for extended periods of time,

According to the article it's not the mental exertion that causes the weight loss, it's the stress and anxiety players experience for extended periods of time, quote from the article: "Grandmasters sustain elevated blood pressure for hours in the range found in competitive marathon runners". So it's unlikely extended periods of mental exertion would have the same effect without having additional stress or pressure.