The term “fast food” generally refers to food that people intend to consume quickly, either on- or off-site. There is plenty of well-researched evidence demonstrating the various negative health effects of eating and overeating fast food, in both the short- and long-term.

Many fast food establishments now list the number of calories each item contains. However, this is only part of the consideration of whether it is healthy or not.

Fast food is typically poor in terms of nutrition. According to a 2015 review, fast food tends to contain various substances that are generally unhealthy. It is high in sugar, salt, saturated or trans fats, and many processed preservatives and ingredients. It also lacks some beneficial nutrients.

However, not all fast food has negative impacts, and a person can make an informed choice by researching the nutritional content of particular fast food items. People can find this information on the websites of most major restaurants.

That said, even the more healthy fast food items are generally high in sugar, salt, saturated fats, and trans fats. The Office of Disease Prevention and Health Promotion notes that the typical person in the United States consumes too much of these food components.

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Fast food is typically high in sugar, salt, and saturated or trans fats. The body’s reaction to these nutrients results in a range of short-term impacts when a person eats fast food.

Spike in blood sugar

Fast food breaks down quickly, causing a rapid spike in blood sugar because of the refined carbohydrates and added sugar. In turn, this causes an abnormally large insulin surge, resulting in a drop in blood sugar. This can cause people to feel tired. Insulin promotes further hunger within a short time after the meal.

Blood pressure

A small 2016 study found that consuming high levels of salt could immediately impact the proper functioning of a person’s blood vessels. Excess sodium intake also has links to fluid retention.

Increased inflammation

A single serving of fast food could increase inflammation throughout the body. A 2015 study found that one fast food meal high in saturated fat increased airway inflammation in individuals with asthma. This inflammation acts as a trigger for asthma attacks.

Affects nutrient intake

Fast food does not typically contain fresh fruit and vegetables. If an individual eats fast food frequently, they may find it challenging to reach their recommended daily intake of at least 5 servings of fruit and vegetables. They may also have difficulties reaching their ideal fiber intake, which according to the Food and Drug Administration is 28 grams per day.

Binge eating

Fast food is highly palatable, meaning the body breaks it down quickly in the mouth, and it does not need much chewing. Therefore, it activates the reward centers in the brain rapidly.

This combination trains the palate to prefer these highly processed, highly stimulating foods and reduces someone’s desire for whole, fresh foods.

Research from 2018 and other previous studies have suggested a link between fast food consumption and the incidence of food addiction for these low-nutrient items.

A small 2017 study of 15 adults found that a single day of high-fat overeating damaged insulin sensitivity. This can then trigger a cycle of binge eating or binge eating disorders.

There is plenty of well-researched evidence showing that regularly eating fast food can harm a person’s health.

A 2015 study identified the sometimes irreparable effects of eating fast food. Such risks include obesity, insulin resistance, type 2 diabetes, and various cardiovascular conditions.

This is because most fast food is high in sugar, salt, saturated fat, trans fats, processed ingredients, and calories. It is also generally low in antioxidants, fiber, and many other nutrients.

Digestive system

Many fast food meals are extremely low in fiber. Doctors associate low-fiber diets with a higher risk of digestive conditions such as constipation and diverticular disease, as well as reductions in healthy gut bacteria.

Immunity and inflammation

A 2019 review examined the effects of a Western diet on a person’s immune system. This diet consists of high amounts of sugar, salt, and saturated fat from only a few sources.

The authors noted that a Western diet could lead to higher inflammation, lower control of infection, higher cancer rates, and a higher risk of allergic and autoinflammatory disease.

Memory and learning

A 2020 paper suggests a link between unbalanced diets high in saturated fat and simple carbohydrates, typical of fast food, and a lower capacity for memory and learning. This sort of diet may also raise the risk of Alzheimer’s disease and Parkinson’s disease.

Allergies

In a 2018 review, the authors established a link between fast food consumption and an increase in asthma, rhinoconjunctivitis, and eczema.

Heart disease

The FDA suggests that a diet high in salt often increases a person’s blood pressure, making a person more prone to heart attacks, stroke, kidney disease, or heart disease.

The FDA also notes that a diet high in trans fats raises the amount of low-density lipoprotein or “bad” cholesterol and lowers the amount of high-density lipoprotein or “good” cholesterol. This means that a person is more likely to develop heart disease.

Obesity

The United States Department of Agriculture points out that typical fast food contains a very high number of calories. If a person eats more calories than they burn each day, they gain weight, which may lead to obesity.

According to the Centers for Disease Control and Prevention (CDC), obesity increases a person’s risk of developing a range of serious health conditions.

Education

Another consequence of younger people regularly eating fast food is their unintentional lack of understanding of basic meal preparation, cooking, and healthy eating.

Over time, this perpetuates dependence on fast food, and people may not learn how to prepare healthy, balanced food in the home. Consuming healthy meals can support a person’s long-term health throughout their lifespan.

Eating lots of fast food could also impact an individual’s mental health and make them more prone to depression and anxiety.

A 2021 study compared data from 322 males and 322 females age 30 or older. They found an association between healthy food such as leafy greens, nuts, and fish and positive mood, while the opposite was true of fast food. In addition, women reported significantly more negative associations with fast food than men.

Fast food tends to be high in salt, sugar, saturated fats, trans fats, calories, and processed preservatives and ingredients. A wealth of well-conducted research has proven the negative health effects of consuming too much of these food components.

In the short term, fast food impacts blood sugar and blood pressure, increases inflammation, and may mean an individual does not eat enough necessary nutrients. In the long term, a diet rich in fast food could lead to issues with digestion, immunity, inflammation, heart health, obesity, and more.

Not all fast food is bad, however. Certain menu items might be lower in these substances than others, while some fast food outlets might focus on providing more healthy options.

To preserve health, a person should try to identify fast food items that contain less salt, fat, sugar, and total carbohydrates, and generally try to limit the amount of fast food they consume.