© iStock

First restaurant - The first modern fast food chain was called White Castle and was opened in the United States in 1921. The chain sold hamburgers, hot dogs and eggs.

© iStock

Chewing - This type of food takes less time to chew and consequently to reach the stomach. This means the body is not satiated and ends up wanting more food.

© iStock

Fast food - What's more, the body doesn't recognize when you're actually full and people end up consuming more in order to feel satisfied.

© iStock

Attractive colors - The colors used by fast food chains are usually red and yellow, because they're bright and attractive colors. This is a way to grab the consumer's attention and entice them into the restaurants.

© iStock

Frozen hamburgers - The hamburgers are prepared in large factories and then frozen. This allows restaurants to serve food faster and not waste too much time grilling them to serve to the customer.

© iStock

Grill marks - In addition, the black grill marks we often see on the hamburgers are actually artificial. They're created with smoke flavorings to give the impression of being grilled on the spot.

© iStock

Curiosities - Oysters were one of the first foods to be marketed as a fast food in the United States.

© iStock

Salads - The salads sold in fast food chains may not be the best option as they often contain many additives and can have lots of calories.

© iStock

Same food - It doesn't matter if it's beef, pork, or chicken, because the food served in these restaurants has pretty much the same flavor. Companies try to keep the flavor the same in order to please as many people as possible.

© iStock

Eggs - The eggs in fast food chains are not the same as the ones we buy in supermarkets. They have a different composition and contain glycerin and other food additives.

© iStock

Soda - Fast food chains usually offer you a larger soda for a small amount, but the truth is that the medium one is almost the same size as a large one. They just want you to buy the most expensive one.

© iStock

Eating hours - The best time to eat at a fast food restaurant is between 12 a.m. and 1 p.m. and between 7 p.m. and 8 p.m., as this is when the food is freshest.

© iStock

Smell - The smell of food is another method to persuade you to consume. Many fast food restaurants even keep their doors open in an attempt to attract customers inside with the smell.

© iStock

Hand food - In almost every fast food restaurant there's no cutlery, which is no accident. Some say that eating with your hands is more pleasurable than eating with a knife and fork, and the fast food chains have thought of that as well.

© iStock

Fries - This is one of the foods that customers crave the most. In fact, french fries often have about 19 ingredients in their composition, including flavor enhancers, additives and other chemicals.

© iStock

Bacteria in the machines? - Soda machines are rarely cleaned in most fast food chains since it's very difficult to do so.

© iStock

Milkshake - Milkshakes served at fast food restaurants have 2 times more sugar than is recommended for one serving. This might explain why many people love this type of sweet drink.

© iStock

Beware of the coffee - Coffee has also been subject to changes in its composition. Some coffees served at these restaurants have a chemical that acts on the nervous system and can even cause depression.

© iStock

Promotions - One way to get the customer to consume fast food is by offering promotions and cheap meal deals. People often end up choosing full or multi-item meal deals.

© iStock

Takeaway - If you choose to take away your food, remember that the food will lose its taste after just 5 minutes, as they are prepared for immediate consumption.

© iStock

Healthy food? - Healthy food options such as salads, soups or chicken are used to try to persuade people who are not regular fast food consumers. However, much of this food may contain even more calories than a plain burger.

© iStock

More calories - Fast food has more calories now than it had in the past. This can be explained by the greater variety of products available nowadays and also by the addition of some chemicals and extra sugars.

© iStock

Toys - Obviously, there's a reason why toys and gifts are put on children's menus. These fast food chains use them as a form of advertising to capture children's attention and interest.

© iStock

Ready-made burgers - The hamburgers served in fast food chains take only 30 seconds to 1 minute to be served, precisely because they've already been seasoned and frozen.

© iStock

Unsalted fries - To save time, many of these restaurants don't cook products on the spot and the ones that have already been cooked end up sitting there for a while. A good idea can be to order some unsalted fries because they will prepare some specially for you.

© iStock

'Old' foods - Many fast food chains don't put leftovers in the garbage. This means some foods are reused and later served to customers.

© iStock

Beef burgers - Processed hamburger meat can contain several pieces of beef in a single serving. Can you imagine how many cows die for just one burger?

© iStock

Chicken - Grilled chicken breast can be a healthy option, though they are often rubbed with butter to prevent them from sticking to the grill.

© iStock

Addiction - Some substances found in fast foods can be addictive and lead customers to consume more. Chemicals and sugar are the biggest culprit.

© iStock

Chemical residue - Grills and other kitchen items are cleaned with super-concentrated chemicals. This means that early morning customers can get these products mixed in their food or drink.

© iStock