This is one of those posts where the answer is complex and can't be typed out in a few minutes.
He will have to normalize his digestion and detox the body. Which can also include toning up which ever organs are weak, but first a detox must be preformed while adjusting the diet to match his digestive powers.
And this of course involves a willingness to change.
It would take a few months to start to see progress but it can be done.
It is normal for your waste products to smell bad, but when its over powering, and exudes out of the skin and breath its a sign there is an overload of toxins.
There is a putrid flesh smell that some people emit when there is liver toxicity. Specifically the Ayurvedic type called "Pitta" or fire can exhibit a rotting flesh smell when they are toxic.
All of this of course can be improved with a few changes.
Remember that no one detox will work for everyone, an individualized approach is needed.