Long Term -
Eating a poor quality diet high in junk food is linked to a higher risk of obesity, depression, digestive issues, heart disease and stroke, type 2 diabetes, cancer, and early death. And as you might expect, frequency matters when it comes to the impact of junk food on your health.
A review of studies on fast food and heart health found having fast food more than once a week was linked to a higher risk of obesity, while eating fast food more than twice a week was associated with a higher risk of metabolic syndrome, type 2 diabetes and death from coronary heart disease.
Short term -
Just a few days of junk food could change your metabolism. A small study of 12 healthy young men found eating junk food for just five days led to a reduced ability of their muscles to turn glucose into energy, even though they didn't eat more calories as part of the study. Over the long term, this change could lead to insulin resistance and eventually type 2 diabetes.
Another effect of just a couple of days of junk food is poor digestion. Because junk food lacks fiber, eating too much of it could lead to constipation.
(read more: http://www.chicagotribune.com/lifestyles/health/ct-nutrition-fast-food-20180301-story.html )