What is Intermittent Fasting?
Intermittent Fasting (IF) is a way of scheduling your diet so that all of your calories are ingested within a set window of time. The theoretical premise behind IF is an increase in the amount of stored body fat a person uses, called fat oxidation, during the period of time in a fasted state. There are other potential benefits as well, such as improved insulin function, potential reductions in oxidative stress, and maintenance of lean tissue (muscle mass) during periods of significant caloric restriction.
The set feeding window is typically a 4-6 hour chunk of time during the day, leaving a period of about 18-20 hours in a “fasted” state. So if you typically eat 3 meals per day spread out over 10-12 hours, you would now have 1-3 meals in a window of 4-6 hours. There are many other “schedules” that fall within the realm of IF, such as 24-hour fasting, alternate day fasting, and other set windows of feeding and fasting. This article will not go into which schedule I think is best, simply because I have not tried them all, nor do I think everyone should adopt one specific method of scheduled eating. What works well for some, may be disastrous for others, so this article is really to give you the information to determine whether, and when, IF is appropriate for you, as an athlete.
As an athlete, what are my dietary priorities?
This is where things can get a little tricky. I remember a few years ago when some of the best athletes in the NBA switched to a “paleo” diet, and everyone and their mother thought that in order to play like LeBron, they should eat like a caveman. How long did that last? Most people do not prioritize the major aspects of their diet correctly, so they could not maintain this type of eating. For some people, the paleo diet is just not practical or sustainable with their training demands, performance goals, and lifestyle.
When I was in grad school, the concept of nutrient timing (the strategy of ingesting specific macronutrients/micronutrients/supplements at specific times to improve performance or recovery) was the biggest thing in the sport nutrition community. I’ll admit it, I dove in head first and told every athlete I knew that their main focus should be the timing of the food they ate. I forgot to prioritize the important things first. Don’t get me wrong, nutrient timing is important; however, from a big picture perspective, setting an alarm so that you ingest your pre-workout meal at exactly the right time before training is pretty pointless if you are not ingesting enough calories on a daily basis to support your training day after day. It is for this reason that I consider your eating schedule (whether IF or not) to be a part of nutrient timing.
I have to give credit to Eric Helms, who wrote a very solid book about dietary priorities, and thereby reminded many of us in the sport nutrition industry that when your priorities are correct, you get better results. The way I prioritize aspects of eating is a little different from Eric Helms, but only because I like to place more emphasis on how the macronutrients should be prioritized for my athletes, which can vary significantly depending on the sport demands. So here is how I break things down for my clients and athletes:
How many calories do you need to ingest on a daily basis to support the energy demands of training as well as maintain weight and body composition?
How many grams of protein do you need to ingest on a daily basis to promote the synthesis of muscle protein, prevent excessive muscle catabolism (breakdown) and maintain/improve body composition?
How many grams of carbohydrate do you need to ingest on a daily basis to fuel your training, promote proper immune and nervous system function, and promote a state of refueling, growth, and repair?
How many grams of fat do you need to ingest on a daily basis to maintain healthy hormone and cellular function?
- Micronutrient Goals
Are you varying your dietary choices enough so that you are ingesting the appropriate amounts of vitamins and minerals that are necessary for optimal bodily processes and functions?
- Nutrient Timing
Are you scheduling your meals/snacks so that you go into training as physiologically prepared as possible? Are you scheduling your meals/snacks so that you repair and recover as optimally as possible in between training and competition? Are you eating and drinking at specific times to get the most benefit from your diet.
Are you ingesting supplements that will increase your training intensity, training duration, training volume, decrease recovery time, and promote training-induced changes in strength, power, speed, and endurance?
You’ll notice that nutrient timing is 6th on my list, and therefore, in my opinion, should only be addressed once you are able to consistently hit your total calories for the day, are able to hit your macronutrient goals (protein, carbs, fats), and are getting enough variety in your diet to get the vitamins and minerals (micronutrients) you need. If your goal is to maximize your athletic performance and recovery, then doing things in this order is the best way to set up your dietary schedule around your sport, training, and lifestyle.
Fat-loss and Performance are NOT the same thing!
I want to be very clear that IF for weight loss and fat loss is a whole different monster than IF for athletic performance and recovery. It is difficult, though not impossible, for an athlete to ingest ALL their calories for the day in a restricted window of 4-6 hours. If you are prone to skip breakfast and not eat anything until lunch or late afternoon, then IF may be your best dietary scheduling option, as long as you get enough calories and hit your macro/micro goals in that feeding window. Keep in mind that as of today, there have been a few studies looking into the effects of IF on weight-loss and markers of metabolism and gene expression; however, there have yet to be any studies looking into the effects of IF on performance outcomes in athletes.
So what is the takeaway?
In conclusion, there is nothing inherently special about IF that makes it better, or worse, than any other way of dietary scheduling. The magic of dietary scheduling and nutrient timing comes when you find the set up that allows you to be the most consistent and practical with your dietary priorities. IF may be a very good way for some people to schedule their diet, but any way of dietary scheduling should be developed based on the list of dietary priorities (Calories, Protein, Carbs, Fat, Micronutrients, Nutrient Timing, Supplements).
Experimenting with your diet (I do not recommend this right before competition) is necessary to determine the best possible performance and recovery outcomes. Keep in mind that any dietary scheduling change can take a few weeks for the body to really get used to, so give yourself the time to adjust to the changes. There is no perfect dietary schedule for everyone. Find a few that interest you and take them for a “test-drive.” Keep track of how you train, perform, and recover, and then stick with the schedule that works best for you.
About Kevin Kuhn:
Kevin Kuhn, M.S.Ed., CSCS, MFS is a Kinesiologist and Sport Nutrition Coach in Dallas, Texas, as well as the Vice President of Research and Development for Classified Nutrition (ClassifiedNutrition.com). Before moving to Dallas in 2012, Kevin was the head strength & conditioning coach for the Indiana Invaders professional running club in Indianapolis, Indiana. Kevin specializes in athletic performance with great interest and experience in running-specific strength & conditioning, corrective exercise, and exercise and sport nutrition. Kevin has been certified by the National Strength & Conditioning Association as a Certified Strength and Conditioning Specialist (CSCS) and as a Master Fitness Specialist by the Cooper Institute.
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