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Questions for the Sports Dietitian: Fasted Cardio

Updated: Mar 18, 2020

Here are a few questions I was presented with for an article for Reebok's Lifestyle website: 1. What exactly is the point of doing cardio on an empty stomach? Simply, there isn't a reason you need to do it. The more complete question is likely, why would someone want to do it? I have heard it from past clients and athletes, two things, it's either too early in the morning and they aren't hungry or they are doing it to optimize fat loss and essentially lose unwanted weight. A meta-analysis from the British Journal of Nutrition in 2016 showed higher fat oxidation while performing cardio exercise during a period of fasting while also comparing glucose and insulin levels, however overall effects were minimal and not significant. The Journal of the International Society of Sports Nutrition in 2014 compared women who performed steady state cardio in a calorie deficit, in a fed or fasted state, three days per week for one hour. Results showed overall weight loss and body fat loss though there was no significant difference between the two groups of women. Based on these two studies and many others that have crossed my desk, there is no significant advantage to performing cardio exercise in a fasted state. 2. Can fasted cardio be harmful to the body at all?

I work with a very athletic population and whether some individuals want to define themselves as an athlete or not - they should be fueling like an athlete to benefit their performance. The special needs of an athlete include: higher carbohydrate as it's their main fuel source, higher protein needs for optimal maintenance and recovery of lean body mass, higher overall caloric needs due to training and higher amounts of muscle mass, and lastly more specific recovery needs to refuel and repair their muscle. With that said a 20-30 minute workout may not require a comprehensive pre and post workout nutrition strategy as the body has enough stored energy and as long as someone is eating adequately throughout the day they will largely remain healthy. However, if activity becomes higher heart rate over 45 to 60 to 90 minutes not only will performance suffer, but you may begin to compromise lean muscle mass, muscle mass, and they last thing you want to do in nutrition is do anything to compromise muscle mass. 3. If participating in fasted cardio, what should one eat after this session? What should a recovery meal look like? If someone has decided to perform higher heart rate, cardio based activity fasted for an extended period of time they should focus on the R's of recovery: Refuel - consume carbohydrate to replenish stored energy in the muscles, which is even more necessary for people pulling a two-a-day or looking to remain focused and attentive mentally during work they rest of the day. A 2:1 or at least 1:1 ratio of carb to protein can be followed post workout; if you need 30 grams of protein post workout you should plan for 30-60 grams of carb. Repair - consume adequate protein to maintain and repair muscle that has been stressed during activity. About 0.2 grams of protein per pound is a solid rule. Rehydrate - replace fluid stores that were lost from sweat during the activity. 16 ounces for every pound lost during activity, which tends to fall around 16-32 ounces post workout. Urine should be close to clear or hay colored within two hours post workout.

Keep it simple: chocolate milk may be the easiest and most optimal recovery option as it provides quick hydration along with the essential electrolytes that need to be replaced. There is also the all important carb to protein ratio within this simple option as well. You can also utilize a more specific post workout ready to drink beverage like Fairlife Core Power along with a carbohydrate source like tart cherry juice to support reduced inflammation or a simple piece of fruit.

Keep it easy: Nuked Sweet Potato: 1 medium sweet potato, microwaved 1/2 cup low fat Greek yogurt and cinnamon Recovery Smoothie: 1 cup strawberries, 1/2 banana, 1 TB chia seeds, 6oz low fat Greek yogurt water, and ice Pretzels & Hummus: 1/4 cup hummus, handful pretzels, 1 hard boiled egg Handful dry roasted edamame (about 1/2 cup) and 3 clementines or another piece of fruit

Keep it within your usual lifestyle: eating a meal and drinking water within two hours can simply provide you with all you need as well

Burrito bowl with chicken or steak, brown rice and black beans, choose one additional fat option in either the guacamole or cheese

Build you own salad with dark green leaf base, choose at least three other colorful non-starchy, hearty vegetable (broccoli, roasted Brussels sprouts, carrots, asparagus, artichoke hearts), add starch like black beans or chickpeas and maybe even some quinoa if available, choose your beneficial fat option in avocado, olive oil based dressing, or nuts/seeds. Make sure to top it off with protein like tofu, tuna, or salmon. 4. I’ve heard that performance can suffer when one is doing fasted cardio—is that true? And if so, is this more of a tool to be used for those looking to loose weight?

Yes, as mentioned fasted cardio can definitely compromise performance and lean body mass. One interesting area to understand is perceived exertion. While an individual who's fasted before activity may be able to perform and complete the same cardio activity in the same amount of time as an individual in a fed state - the fasted individual may perceive the activity to have been more challenging. This can have a cumulative effect on the mind and deter an individual from wanting to continue finding themselves in middle of a challenging workout multiple times in a week. This is were sports psychology can come in because people can begin to doubt their abilities. If someone is looking to lose weight and reduce body fat remember that the differences between groups of women following a general calorie deficit or performing fasted cardio showed no significant advantage either way. Whatever is more sustainable over time is the more important decision to make. 5. Is fasted cardio a sustainable option? Why or why not?

That's relative to each persons current lifestyle habits, preferences, and personal accountability. A majority of the time, no. Periods of fasting or even lower calorie intake can definitely be sustainable, however that may become more challenging over time as perceived exertion remains high and possible muscle losses along with injuries accrue. Not to mention celebrations, holidays, and social occasions usually begin to accumulate in someones life and it's more challenging to remain consistent without external accountability. 6. How would you like to be attributed in this article?

Ryan Turner, RD, CSSD, CDN

Director, Sports Nutrition at Tone House Owner and Founder of Food is Fuel NYC

Listen to the The Breakdown podcast on Spotify or iTunes, co-developed with trainer Joe Rodonis, where we talk with other thought leaders in the fitness and nutrition industry to bring you no BS advice to benefit your training and health.

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