At the start of a new diet and exercise routine, it's normal to have a few slip-ups and bad days of eating junk food. While you may think that eating junk food and working out might cancel each other out, it's often a bit more complicated than that.
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Eating junk foods high in fat, sugar and refined carbohydrates (most of which are empty calories) can affect your exercise performance by draining your energy, impairing your metabolism, contributing to weight gain and raising your risk of other chronic diseases.
Effects of Fast Food
By now, it's pretty clear that the effects of fast food on your mind and body can be quite damaging. A diet of chronic junk food consumption comes with a slew of harmful health effects, ranging from an increased risk of heart disease to diabetes and obesity.
The obvious result of eating a diet filled with fast food cheeseburgers, fries, processed meats, salty snacks and sugary sweets like donuts is the higher risk of putting on pounds. It's often the first thing people notice when they're eating unhealthy, but it's not the only thing that happens to your body.
In fact, a lot of the effects of fast food are invisible until it's too late. Junk food increases belly fat, which is linked to chronic problems like inflammation and high blood pressure, according to the Mayo Clinic.
An animal study featured in the May 2016 issue of the journal Experimental Physiology found that junk food was harmful to kidneys. Unhealthy diets and fast food have even been linked to depression and mental health issues.
A study published in Environmental Health Perspectives in October 2016 showed that processed junk food can increase a person's exposure to harmful chemicals, like phthalates and bisphenol A (BPA). All of that, plus the well-established link to chronic diseases like cardiovascular disease, Type 2 diabetes and even cancer, put fast food in the box of absolute no-no's when embarking on a healthy lifestyle and exercise routine.
Junk Food Affects Your Energy
Yet surprisingly, some experts actually argue that fast food can be beneficial to elite athletes — by restoring their depleted energy and glucose stores after a workout. When you exercise or lift weights, your muscles draw on glycogen stores to provide them with energy to complete the hard work. Typically, by the end of a workout, your glycogen stores will be lower, requiring you to fuel up on healthy carbohydrates or sports drinks with electrolytes.
Fast food may seem like the very last option to restore your energy stores after a good workout. But a small study with 11 participants published in the October 2015 issue of the International Journal of Sport Nutrition and Exercise Metabolism found that the effects of consuming fast food were similar to that of isoenergetic sport supplements to restore glycogen after working out.
The takeaway from this study; however, isn't that fast food is good for you; rather, it's that sugary products like energy bars or sports drinks may not be any better for you than eating fast food after a workout. In addition, elite athletes are a small fraction of the population who might benefit from consuming fast foods high in sugar or carbohydrates after an intensive, several-hour training session.
For the rest of the average population, however, things are different. If you're sedentary or moderately exercising, about half an hour a day five days a week, junk food likely won't benefit your workouts or recovery at all. This holds true especially for people who are aiming to lose weight.
In fact, junk food may drain your energy during exercise rather than refuel it. An animal study conducted at UCLA found that eating a lot of fast food causes impaired task performance and lack of motivation, rather than the other way around.
Rats fed a junk food diet tended to gain weight and take longer to complete tasks, taking plenty of breaks in between, while rats fed a healthier diet remained lean and finished tasks sooner. The fatigue and lack of energy to exercise you may feel may have more to do with your diet than your own personal motivation.
Fast food can also impair your metabolism, according to a study published in January 2016 in the journal Health Promotion Perspectives. The study found that a poor diet was linked to abdominal fat gain, disrupted insulin and glucose homeostasis, systemic inflammation and a higher risk of metabolic syndrome. An impaired metabolism can make it harder to lose weight and can also contribute to low energy.
Empty Calories, Low Nutrition
Refueling your body with healthy, nutritious food post-workout is almost as important as the exercise itself. Lean protein and healthy, complex carbohydrates rebuild muscle, maintain blood glucose levels and keep your metabolism going to burn fat. They also give you the stable energy you need to workout again the next morning, and keep your routine going strong.
One of the biggest pitfalls of fast food is its unbalanced ratio of fat, sugar and refined carbs to its nutrient count. While sweet pastries or fast food burgers on white bread may be filling and have certain amounts of protein, the remainder are mostly empty calories.
These calories, mostly added sugars like high fructose corn syrup or saturated fats, are considered "empty" because they hold no real nutritional value. You can find loads of empty calories in foods like cookies, donuts, sodas and greasy pizzas.
Consuming enough protein or healthy complex carbohydrates (such as sweet potatoes, whole wheat breads or whole wheat oats) is critical for maintaining an exercise routine. Protein that comes from fish, lean meats or legumes takes a long time to digest and is more of a slow-burning fuel for your muscles.
Complex carbohydrates and some starches, meanwhile, provide the necessary fuel for our bodies to break them down into glycogen. Both protein and complex carbs will prevent you from feeling too tired during a workout, according to the British Nutrition Foundation.
If you're not getting enough of these nutrients in your diet, you will likely lack the energy needed to complete a successful workout. Swap the fast food for sustaining, nourishing choices like whole wheat oats with Greek yogurt, salmon with sweet potatoes and whole wheat bread instead of white bread.
Read more: 10 Ways to Make Fast Food Healthier
Healthiest Workout Foods
Physical activity can reduce your tendency to eat unhealthy, partially by reducing stress that may contribute to poor eating habits, according to a study published in the February 2018 issue of Nutrients. It can also offset some of the worst health effects of fast food. But in order to really avoid the increased risk of obesity and chronic diseases, you'll have to cut down on junk food and replace it with more nourishing options in the long term.
If you're not quite ready to cut out all the junk food, there are ways to tweak your fast food intake to make it a bit healthier. If you frequent fast food restaurants, look for the healthier options and order a side salad instead of fries along with your hamburger.
If you have a sweet tooth, mix some Greek yogurt with honey, and top it with walnuts and fresh fruit. You can go lighter on salad dressings, toppings, sauces and processed cheeses; choose vegetables over pepperoni pizza. And instead of eating junk food after a workout or everyday, cut it down to a few days per week.
Not all processed foods are entirely unhealthy either, according to Harvard Health. Canned foods like tuna, beans and salmon can actually be great protein sources if you aim for the low-sodium versions. Grab some peanut or almond butter to go along with your toast or banana if you need something more filling. And if you like your cereal in the morning, choose whole-grain options instead of sugar-packed cereals.
The healthiest workout foods, however, revolve around a balance of healthy carbohydrates, protein, vegetables and fruit. A combination of these foods will not only give your body the energy it needs but also help you lose weight. When you reach that balance, eating an occasional fast food meal or big hamburger won't actually have a negative effect on your health.
When you learn to build your routine around physical activity and healthy foods, those occasional cheeseburgers become even more satisfying.
- Experimental Physiology: "Experimental Type II Diabetes and Related Models of Impaired Glucose Metabolism Differentially Regulate Glucose Transporters at the Proximal Tubule Brush Border Membrane"
- The American Journal of Clinical Nutrition: "High Glycemic Index Diet as a Risk Factor for Depression: Analyses From the Women’s Health Initiative"
- Environmental Health Perspectives: "Recent Fast Food Consumption and Bisphenol A and Phthalates Exposures Among the U.S. Population in NHANES, 2003–2010"
- International Journal of Sport Nutrition and Exercise Metabolism: "Postexercise Glycogen Recovery and Exercise Performance Is Not Significantly Different Between Fast Food and Sport Supplements"
- UCLA: "Does a Junk Food Diet Make You Lazy? UCLA Psychology Study Offers Answer"
- Health Promotion Perspectives: "Fast Food Pattern and Cardiometabolic Disorders: A Review of Current Studies"
- Journal of the Academy of Nutrition and Dietetics: "Where Are Kids Getting Their Empty Calories? Stores, Schools, and Fast Food Restaurants Each Play an Important Role in Empty Calorie Intake Among US Children in 2009-2010"
- British Nutrition Foundation: "Nutrition for Sport and Exercise"
- Nutrients: "A Role for Exercise in Attenuating Unhealthy Food Consumption in Response to Stress"
- Mayo Clinic: "How Junk Food Wrecks Your Body"
- Harvard Health: "Not All Processed Foods Are Unhealthy"