Here are 10 points. Remember to frame them properly with the use of connectives. Go in more detail on each topic if you want for your essay.

-trans fat and excess fat cause obesity problems;
-trans fat and excess fat cause other health problems, like high blood pressure, and in extreme cases, Cardiac Arrest(Heart Attack);
-medical problems cost money to fix, causing poverty in some cases;
-in cases of non-veg junk food, animals are needed to be killed and often have bad living conditions, animal cruelty occurs;
-these animals contribute to global warming and methane pollution, and the bad points associated with it;
-they are not nutritional, and by eating them you lose "space" and appetite for more nutritional healthy food, thus decreasing the amount of useful nutrients you get;
-pollution occurs in order to make the junk food usually, due to the fuel needed to cook it, and thus contributes to global warming;
-it makes you tired and lazy often, as energy is needed for digestion, decreasing your concentration and productivity
-if the wrappers used to make the food are non-biodegradable, they could cause land and water pollution, possibly killing wildlife, if not properly disposed
-nitrogen is used to fill sealed packs of many junk foods, and its extraction causes pollution