We all know that junk food is bad for us, but how bad can it really be?
Recent studies suggest that junk food affects not just the appearance of our body, but the efficiency of our brain.
According to a study published in the journal Neurology, adults who are obese in middle age are at almost four times greater risk of developing Alzheimer's disease than those who eat a balanced diet.
Doctor Weili Xu, who headed the research, suggests that "higher body fat is associated with diabetes and vascular diseases, which are related to dementia risk".
The problem seems to be with the level of insulin produced in the body, which is responsible for glucose metabolism, as in type 2 diabetes. Here, unhealthy foods lead to cells in the body becoming resistant to the insulin they need to convert sugar into energy.
Insulin regulates the transmission of signals from one brain cell to another and is key to memory and learning.
As with type 2 diabetes, it has been suggested that high levels of fat and sugar damage the brain by interrupting its supply of insulin and therefore affecting the brain cells' health and survival.
Some scientists have gone as far as to call Alzheimer's the new type 3 diabetes.
As controversial as the research may be, it could be a step towards finding a cure for the debilitating disease, which, among other types of dementia, affects 800,000 Britons.