What’s In It
Toffee is a lot like caramel. It’s sugar (sometimes molasses) that has been mixed with butter, and sometimes even flour, and heated until it hardens. Butter can have a place as part of a healthy Paleo lifestyle, but sugar should be avoided as much as possible, and flour is definitely not Paleo.
The Health Effects
Concentrated sources of sugar, like toffee, wreak havoc on our bodies. They create a spike in blood sugar and a corresponding spike in insulin to digest all that sugar. It promotes the storage of nutrients as fat and prevents the breakdown of fat for nutrients. It also interferes with leptin (the hormone that regulates appetite) to keep us from feeling full. The result is a sugar crash that leaves us feeling tired and hungry.
Mark Sisson has a more comprehensive list of the negative health effects of sugar.