Yep, it was called "Fat Head." The exercise regime wasn't even that strict, it was basically continuing the regular walking the documentarian already did. However, the food intake was strictly limited to 1800 calories and less then 100g of carbs per day. The goal being to show fast food isn't inherently unhealthy, it was the quantity (as already noted above) being eaten in Super Size Me that was unhealthy. In that regard, Fat Head succeeded as the documentarian's health metrics all improved (lot weight, lower blood pressure, better cholesterol measurements).