When a food product reaches its expiration date it does not really mean that it is expired already. It means that it could be expired for the time being. Manufacturers set allowance as safety measures. There are cases where expired goods can still be eaten especially if stored inside refrigerator long before its reaches the set expiry.
However, eating expired goods is highly discouraged. The risk involve is high. Producer are not responsible for your safety when the goods exceeds its expected shelf life. Side effects may vary depending on product and kind of spoilage it might undergo.
1) Physical. A powdered biscuit can be considered as spoiled because it meant to be a flat circle. Losing its crispiness due to moisture absorption is also physical spoilage. Product adulteration with pieces of sand, metals, woods and glass is harmful. Those objects might cause wound in mouth and internal organs. Plus, it might harbor unfriendly microorganisms.
Improperly packed foods are prone to physical spoilage. However, adulteration may happen during processing – such products are considered spoiled and not safe to eat.
2) Biological. Microbial contamination and growth make the product unsafe for consumption. Listeria, Clostridium, E. coli., Salmonella and Aspergillus may proliferate on goods. Eating microbes contaminated products might result to simple illness such as diarrhea, vomiting, loss of appetite to a very serious life threatening symptoms.
Aspergillus is common in grains as aflatoxin, Salmonella in meat products, E. coli in drinking water and Clostridium in canned sardines and meat. The Lestiria can withstand extreme cold products like ice cream.
3) Chemical. Some products may undergo chemical break down like rancidity of oil. Cooking oils and foods high in fat content are prone to rancidity. Rancid products have free radicals, which cause cell damaged, cancer and cardiovascular diseases. Other form of chemical spoilage is contamination with poisonous chemicals.
eg. A cassava cake was accidentally spilled with chemical pesticide while being cooked. The cake poisoned all the student who ate it. Some of the unlucky suffered death. I think you know about this late news.