Can you outrun a fast food diet with high intensity exercise?

fast food HIIT exercise

Can you outrun a fast food diet with high intensity exercise?

Fast Food + High Intensity Exercise = ??

In our society, we’ve equated good health with good looks. Great athletes are supposed to be the healthiest people. There is however, much more to health than a six pack (though some don’t seem to care).

Unhealthy habits do not necessarily cause unsightly looks, or at least not right away. Does that mean we can get away with embracing these less than optimal lifestyles as long as we exercise?

Fast Food and Exercise

Most people recognize fast food is an unhealthy choice. There is research into the effects of fast food on health with and without exercise. One study found that just one week of eating more than 4,000 calories per day, combined with little physical activity, resulted in decreased insulin sensitivity in otherwise healthy young men. This decreased insulin sensitivity was avoided with a daily 45 minute treadmill running workout at 70% of VO2 max1. A decreased insulin sensitivity is a bad sign of overall health, especially in individuals who were healthy a week prior2!

High intensity exercise is thought to have a much higher ability than moderate exercise to reduce cardiometabolic risk factors such as high blood pressure, high cholesterol levels, and insulin resistance3. While high intensity exercise improves overall health, is it good enough to counteract the negative effects of a fast food diet? Turns out, researchers found some (most likely, extremely willing) participants to test this question.

The Research on Fast Food Diets and High Intensity Exercise – High Intensity Exercise: Can It Protect You from A Fast Food Diet3?

Subjects and Measurements

Sixteen subjects participated in this study. All subjects were male, between the ages of 18-30, BMIs of 18.5-29.9, physically active, and non-smokers. During the study, multiple measurements of fitness, overall health, and nutrition were taken. They included:

  • fitness band – energy expenditure data
  • blood samples – cholesterol, glucose, and other health markers
  • body composition – body weight, body fat percentage, lean mass
  • blood pressure

Fast Food Diet

For two weeks, subjects only ate at a fast food chain. Breakfast consisted of a sandwich such as an Egg or Sausage McMuffin, hash browns, and a small fruit juice or coffee. Lunch and dinner consisted of a sandwich such as a BigMac, McChicken, or Quarter Pounder with cheese, medium fries, and a medium non-diet soft drink.

According to the McDonald’s Nutrition Calculator, depending on the subjects’ sandwich choices, breakfast was approximately 700 calories, lunch and dinner were approximately 1,100 calories. Subjects also had the option of eating a muffin as a snack. At the end of the study, the average intake for all of the subjects was 3,400 calories per day.

High Intensity Interval Training (HIIT) Exercise Routine

All subjects performed a HIIT program for 14 days in a row. Each session was:

  • 5 minute warm up
  • (60 second sprints followed by 60 seconds of walking) x 15
  • 5 minute cool down


Interesting before and afters:

  • average body weight among all subjects
    • before: 167.1 lbs
    • after: 167.3 lbs
  • average waist circumference among all subjects
    • before: 32.04 inches
    • after: 32.16 inches
  • average body fat percentage among all subjects
    • before: 13.5%
    • after 13.1%
  • average fat mass among all subjects
    • before: 22.92 lbs
    • after 22.49 lbs
  • average lean body mass among all subjects
    • before: 136.69 lbs
    • after 137.57
  • average VO2 max among all subjects
    • before: 55.8 mL/kg/min
    • after 57.5 mL/kg/min

A few of the cardiometabolic measurements improved after 14 days of fast food and HIIT:

  • fasting glucose
  • total cholesterol
  • LDL (bad kind) cholesterol

One measurements was significantly worse:

  • HDL (good kind) cholesterol

What does this research mean? Can you eat unhealthy foods if you exercise a lot?

The results of this study looks great for the ‘eat like crap but exercise heavily’ crowd. Researchers do note their small sample size of subjects was made up of healthy, physically active, young men. Results for more sedentary or older populations may differ. In this study however, the results did seem to show that a bad diet could be “outrun” by  high intensity exercise.

Most measures of health and physical characteristics improved in this study. On average, subjects gained some body weight & muscle mass while losing body fat (the holy grail of gains). The subjects significantly increased their VO2 max (a measure of how fit you are) and improved most markers of overall health with the exception of HDL cholesterol levels.

Before you go out and binge on fast food in hopes of emulating these results, keep in mind the results could have been even better had the subjects been on a healthier diet. Also, the subjects’ average daily intake was about 3,400 calories. Their average energy expenditure was around 3,500 calories. Even with the poor food choices, they still created a slight calorie deficit.

Practical Takeaways

Calorie Deficits Matter

The subjects in this study created a calorie deficit: they burned more calories than they consumed. This is the most important requirement in losing weight, decreasing body fat, and improving overall health. If you want to enjoy some of the benefits from this study, burning more energy than you consume is a must.

Create your own calorie deficit using the calorie calculator.

Small Calorie Deficits Work Great

The average deficit among the subjects was only about 100 calories per day. Creating a huge calorie deficit is counterproductive. It’s hard to maintain over a long period of time and the results aren’t the best. When creating a calorie deficit, start small. Focus on increasing physical activity while MODERATELY decreasing calorie intake.

The Bottom Line – Can I eat McDonald’s everyday if I also exercise a lot?

The answer is probably no. This study only lasted 14 days and it was done on otherwise healthy, young subjects. These results surely would have turned out differently if the group was older, had any preexisting conditions, or weren’t as physically active. The activity level in this study was also not easy. For two weeks straight, subjects performed 30 minutes of very intense exercise that not many can emulate.

Yes the overall results were good, however, they could have been even better had they practiced the basic rules of good nutrition: less saturated fat, sugar, and salt, more unsaturated fat, fiber, fruits, vegetables, and lean sources of protein.


  1. Walhin, J., & Richardson, J. D. (2013). Exercise counteracts the effects of short-term overfeeding and reduced physical activity independent of energy imbalance in healthy young men. The Journal of Physiology, 591(24), 6231-6243. doi:10.1113/jphysiol.2013.262709
  2. Understanding Insulin Sensitivity and Diabetes. (2015, July 02). Retrieved from
  3. Ramos, J. S., & Dalleck, L. C. (2015). The Impact of High-Intensity Interval Training Versus Moderate-Intensity Continuous Training on Vascular Function: A Systematic Review and Meta-Analysis. Sports Medicine, 45(5), 679-692. doi:10.1007/s40279-015-0321-z
  4. McDonald’s Nutrition Calculator (n.d.). Retrieved from

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