American Heart Association diet is useless. When compared head to head against other things like Mediterranean, Asian, even low carb, etc, it fails miserably for heart disease biomarkers. Start perusing Jordan's forum. Lots of useful diet stuff on there.
Yes, sprints will help. And I'd start with just adding one episode of sprints a week for at least a month until you're recovery capacity improves. If you want more, I'd just add in walking, walking on an inclined treadmill (or hills), or even with a weighted vest.