Intermittent Fasting: Is 16/8 or 5:2 better?

Intermittent Fasting is a big player in the nutrition space - with many athletes wondering if it’s the next best thing to achieve results. Just like most dietary approaches, there are various types or versions of Intermittent Fasting - so which type is best for athletes?

In this blog post, we explore the two main types of fasting - 16/8 and the 5:2 diet. You’ll learn about what each involves and I’ll share some insights to help answer which one is better. Read on to learn if Intermittent Fasting should be on your next agenda and game plan. 

Intermittent fasting has quickly become one of the most popular topics in the nutrition space. I regularly get asked by clients on what do I think about fasting and whether they should try it themselves. Today you will learn which I would recommend to athletes if I had to make a recommendation for beginners. 

Two Things You Need To Understand

The first thing you have to understand about intermittent fasting is that it’s a diet style not actually a diet per se. It doesn’t dictate what you eat, it simply dictates when you eat. The second thing to know is that it comes in many different forms. In other words, there are different ways of doing it. The two types that come up most often are the 16/8 regimen and the 5:2 diet. 

The 16/8 Regimen

The 16/8 approach to intermittent fasting is when you fast for 16 hours and you only eat within an 8-hour window.  It’s a regimen that more naturally replicates our normal eating patterns and is relatively mild compared to more severe forms of fasting seen in the nutrition space.

For example, you could start eating at noon and finish at 8 pm. Rinse and repeat. 

The premise is that it helps you avoid eating more calories at the beginning and the end of the day and help improve satiety with your diet but limiting the hours of eating. This can work for many people as eating XYZ calories within a smaller window of opportunity is generally more filling than spreading the intake across the day.

5:2 Diet

The 5:2 diet, on the other hand, is quite different. The diet involves eating relatively normal for 4-5 days of the week but then the other 2 days you're fasting and eating a lot fewer calories. On the 2 fasting days, participants will generally eat between 500-800 calories - so clearly a very low caloric intake. Alternating 5 days of normal eating with 2 days of low-level calories can hypothetically help create an overall deficit for the week. 

Example of the diet in action: let’s say you need 2000 calories per day to lose weight (14,000 calories for the week). With a 5:2 approach, you could eat 2480 calories Monday to Friday by only eating 800 calories on both Saturday and Sunday. 

The big issue is that restricting calories to such a low level repeatedly for 2 days is neither fun nor necessarily healthy. Oh, and it’s also not technically necessary as you saw in the example that calorie control is clearly the basis of it all. In a nutshell, very seldom will it be sustainable. 

The Similarities

Both approaches primarily depend on controlling calorie intake and suppressing appetite. Also, most people decide to do intermittent fasting for the purpose of weight loss. Very rarely will I have someone ask me about fasting for a goal such as muscle gain or performance. It’s almost always seen as a “weight loss diet” - which can be an issue when the need for a lifestyle plan is not appreciated by the athlete. 

It’s not hard to see why fasting is seen as a weight-loss tool. Fasting windows suppress the opportunities to eat and when you avoid eating at certain times, it can help minimise excessive snacking and grazing that may make it hard to control calories. So all types of fasting have these things in common - but the differences in how each achieves this can not be underestimated.  

When it doesn’t work

The reality is that the premise behind intermittent fasting and its effectiveness relies on calorie control. Calories in, calories out still dictates the result so if you believed some gurus that fasting is the magic solution, you would be mistaken. While fasting can be effective for some athletes and help minimise calorie intake or help make a calorie deficit easier to manage, it’s not “foolproof”. It’s very possible to still overeat calories in an eating window (whether it’s 6, 8, 10 hours).

For example, if you need to eat 2000 calories to be in a mild calorie deficit, you can still eat 2500 calories in an 8-hour eating window and won’t lose weight. Again, it’s a tool to help, not a bulletproof weight loss plan. 

For Athletes - Key Considerations/Limitations

As an athlete, you need to look beyond the basics of the diets and tools that you are considering using. There are different considerations due to the unique nature of Sports Nutrition and the demands of your sport. You require a different personalised plan to help you still perform at an adequate level while achieving your goal. 

So without further ado, here are key Intermittent Fasting considerations for athletes:

1. Fasting regimens diminish the potential for repair and recovery nutrition due to the restricted windows of opportunity for fuelling and the strict times that may not align with training and sport. 
   
2. Intermittent fasting is not great for optimising protein muscle synthesis so if you want to build muscle, then understand it’s not ideal for this goal. 
   
3. Athletes who compete regularly may not be able to optimise their glycogen stores and repair muscle adequately to maintain performance levels. 
   
4. You are at increased risk of significantly undereating calories as an athlete doing fasting as you have increased demands which vary across the seasons. 
   

Should You Do It?

Nutrition individualization is key for success with any dietary approach and intermittent fasting is no different. Choosing whether or not you should do Intermittent Fasting depends largely on your own preferences so you need to ask yourself questions first. 

At the end of the day, some athletes enjoy fasting while others completely hate it. Choose your path based on your preference and your lifestyle. If a diet is not sustainable then it doesn’t matter how good it is on paper. You need to be able to do it consistently and maintain it over time and only you can truly determine if fasting fits into your lifestyle.

Here are questions to ask yourself first:

1. Why am I considering it?
   
2. Do I see myself sustaining it?
   
3. Will I enjoy doing it at least to some degree?
   
4. How does it align with my sporting demands?
   
5. Do I have a Sports Dietitian to help guide me?
   

These questions are not exhaustive but are important starting points and help address the main concerns an athlete considering fasting should have. Don’t jump into it blindly or you may find yourself struggling. 

So...16/8 or 5:2?

So now that we've covered all the background information and considerations for fasting, you want to know the answer to the question of which version of Intermittent Fasting I recommend as a Sports Dietitian.

In my personal experience working with clients, I generally recommend the 16:8 method. The reason is that it replicates a normal eating pattern and isn't too restrictive. Plus it’s easier to follow and understand while being more flexible (win-win in my books!). The fasting window isn't as severe as some other fasting styles - especially things like 5:2 and OMAD (One Meal A Day Diet). 

However, remember that you aren’t my client (unless you are already and reading this, then hello), so this is NOT nutrition coaching advice (it’s general info for your consideration). 

If you truly want to be assessed and provided individualised advice that is right for you and considers your goals, needs, and sport - then CLICK HERE to reach out to me and see if working with a Sports Dietitian is what you need. A Sports Dietitian will determine if fasting is a viable option for you and if it should be done in the first place. 

Conclusion

There you go, now you know about the 2 most common forms of Intermittent Fasting and whether or not you should consider it. It clear that 16/8 is a better version as it’s not as restrictive and hard to follow as the 5:2 approach - and is nutritionally more balanced.   

However, even if you deem fasting as the next step for your journey, do understand that as an athlete there are clear limitations and considerations. So choose wisely and make your choice with the understanding that “fasting is not magic and there are better approaches for performance focussed athletes out there”. 

Also, I’ve got a question for you: do you want 1:1 individualised help from a Sports Dietitian?

The reality is that you don’t get brownie points for struggling through this alone. I can help take out the guesswork, provide a calibrated plan, and most importantly provide direct coaching accountability that you need so you can keep pushing forward and getting the results in the long term with a periodised approach. 

I can actually help you bridge that gap between point A and point B and optimise your nutrition to gain your athletic and competitive edge - helping you reach your goal of becoming the athlete you want to be.

Interested? Then simply email me at: aleksa@theclimbingdietitian.com.au

P.S. I have a new 90-day nutrition program called the 90-Day Macro Sherpa program - which is a nutrition coaching experience designed to help kickstart your flexible nutrition lifestyle and show you how to harness it the right way. 

To apply, simply click here and start the process for reaching your peak potential. 

Coach Aleksa