Does Fast Food Cause Obesity?

Does fast food cause obesity? In short… yes. While it is certainly not the only cause, in conjunction with other factors, fast food restaurants are a big part of the obesity problem.


In fact, how frequently individuals visit fast food restaurants is directly correlated with their weight. According to a 15-year study of 3,000 adults, people who visited fast food restaurants more than twice per week gained roughly 9 to 11 pounds (4 to 5 kg) more than people who visited them less than once per week (1).

The “common sense” reasoning behind the weight gain is that fast food is less healthy than other food, but this assumption is only partially correct.

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Does fast food cause obesity?

Fast food causes obesity for 4 reasons…

Unhealthy Ingredients
Contains More Fat, More Sugar, & More Carbs And Less Vitamins & Minerals

Unhealthy Ingredients: Contains More Fat, More Sugar, & More Carbs And Less Vitamins & Minerals

There are many types of fast food restaurants – from burgers to pizza to chicken to tacos, but despite their unique menus, the underlying content of their food is the same. Most fast food ingredients contain more energy, total fat, saturated fat, carbohydrates and added sugars than healthier food of the same weight. As a result of these less healthy ingredients, eating fast food has been found to be directly associated with both being overweight and exceeding the recommended levels of fat and sugar (2) (3).

In addition, most fast foods contain substantially fewer vitamins and minerals such as vitamin A, carotene, vitamin C, vitamin E, calcium, magnesium and zinc. Numerous studies have shown that eating healthier foods that contain more of these vitamins and minerals (i.e fruits and vegetables) makes people feel full on less food, leading to more effective weight management (4).

Last and possibly most importantly, most fast food menu items contain a high amount of sugar, often in the form of high fructose corn syrup. Evidence is (re)emerging that suggests sugar could be the true cause of the obesity epidemic and many of the obesity-related health problems.

The following video breaks down what happens to your body when you eat too much fast food:

Larger Portions
As Average Weight Has Grown So Have Portion Sizes

Larger Portions: As Average Weight Has Grown So Have Portion Sizes

As popularized by the 2004 documentary Super Size Me (if you haven’t seen it, you can watch it for free here), the problem with the ingredients of fast food is further compounded by fast foods’ growing portion sizes. It’s no coincidence that portion sizes have grown in parallel with the average person’s body weight from the 1970’s through today (5).

Research has proven that when given larger portion sizes, the average person will still eat their entire meal regardless of whether or not they feel full (6).

Low Cost
2,000- Calorie Diet Of Junk Food Costs 10x Less Than Same Calories Of Healthy Food

Low Cost: 2,000- Calorie Diet Of Junk Food Costs 10x Less Than Same Calories Of Healthy Food

Researchers at the University of Washington found that a 2,000-calorie diet of junk food costs 10 times less than a 2,000 calorie healthy diet (7). This low cost of fast food encourages people to choose it over more expensive healthier food, which is a big reason that lower-income individuals are more likely to be obese (8).

To make things worse, the researchers also found that healthier foods are more likely to increase in cost over time. During their 2-year study, the cost of healthy food went up by 19.5% while the cost of unhealthy food dropped by 1.8%.

Fast Food Restaurants Extremely Prevalent

Convenience: Fast Food Restaurants Extremely Prevalent

The final factor that makes fast food cause obesity is its convenience, or more specifically, how close fast food restaurants are to your home, job or school.

For instance, children that have a fast food restaurant within 0.10 miles of their school have a 5.2% greater chance of being obese. For pregnant women, the same distance to fast food restaurants increases their obesity odds by 2.5%. No other restaurant types have any correlation with obesity rates (9).



  • Mark A Pereira PhD, et al. Fast-food habits, weight gain, and insulin resistance (the CARDIA study): 15-year prospective analysis. The Lancet, Volume 365, Issue 9453, Pages 36 – 42, 1 January 2005.
  • Bowman, S.A., Vinyard, B.T. 2004. Fast food consumers vs non-fast food consumers: a comparison of their energy intakes, diet quality, and overweight status. Journal Of American College Of Nutrition. v. 23(2). p. 163-168.
  • Press Release: Study Links Fast Food to Overall Poor Nutrition and Obesity Risk. Children’s Hospital Boston. Jan 2004. Available at:
  • Ello-Martin JA, Ledikwe JH, Rolls BJ. The influence of food portion size and energy density on energy intake: implications for weight management. Am J Clin Nutr. 2005 Jul;82(1 Suppl):236S-241S.
  • Lisa R. Young, PhD, RD and Marion Nestle, PhD, MPH. The Contribution of Expanding Portion Sizes to the US Obesity Epidemic. February 2002, Vol 92, No. 2 | American Journal of Public Health 246-249
  • Parker-Pope, Tara. A High Price for Healthy Food. New York Times. Dec 2007. Available at: Accessed Mar 2010.
  • Jennifer L Black, James Macinko (2008). Neighborhoods and obesity. Nutrition Reviews 66 (1), 2–20.  doi:10.1111/j.1753-4887.2007.00001.x
  • Janet Currie, Stefano DellaVigna, Enrico Moretti, Vikram Pathania. The Effect of Fast Food Restaurants on Obesity and Weight Gain. Feb 2009. The National Bureau of Economic Research. NBER Working Paper No. 14721*

[ Last editorial review/modification of this page : 04/16/2018]

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