Should You Try Fasted Exercise?

Picure from Boycemode

I rode to Kukup, a small fishing village in Johor, Malaysia on Good Friday. My bicycle speedometer showed (pictured below) that I rode 160 km when I got home. I had to lie down on the floor after setting my bike aside. I was super tired and was cramping everywhere. Took me quite a while before I could shower.

160 km

There must have been about 40 riders in that group. We stopped for a drink at a small coffee shop in Kukup and I overhead another rider saying he fasted for the ride. I don't know how he did that.

Fasted training means one abstains from consumption of food for 8-12 hours in advance of a training session. Most people do an overnight fast so training is done in the morning before breakfast. It has become popular among people interested in fat loss, metabolic health and for performance or adaptation reasons (especially endurance athletes).

Why would anyone do fasted training? There are lots of videos and reels online suggesting that when you train in a fasted state, your insulin levels are lower, so your body is more likely to use your fat stores for fuel (lipolysis) and better fat utilization.

There are endurance athletes who use fasted training to encourage adaptations like increased mitochondrial density. This is to allow their cells to make more new mitochondria and increase existing mitchondria.  Our cells often increase mitchondria biogenesis in response to increased energy demands triggered by physical activity. With more mitochondria in our cells we become stronger.

With fasted training, endurance athletes are training for better fat utilization to spare their glycogen stores so they can have better endurance. This may work if you're exercising at lower intensities, not when you are going fast at higher intensities since carbohydrate/ glycogen is still very much needed. With fasted training, there will be a severe restriction on the ability to do anaerobic work.

Moreover, over the course of a day, the net fat loss may not be that much different from fed training.

Fasted training may improve insulin sensitivity and glucose tolerance especially in sedentary or overweight individuals.

I also know people who feel better when  they exercise or train on an empty stomach and most find it logistically easier to exercise right after waking up.

Although fasted training can help metabolic adaptations described above, it can also potentially lead to a deficit in total daily calorie intake and this has been shown in active males.

If this reduction in daily calorie intake is not the intended outcome of fasted training it can potentially lead to a state of low energy availability, which when repeated frequently may lead to stress fractures and poor bone health (Raleigh et al, 2024). 

The incidence of bone injury was 1.61 times higher in those who currently use fasted training compared to those who never used it.

Fasted training is not ideal for everyone since you may feel sluggish, lift less (if you're weight training) and perform worse in high intensity workouts. In prolonged fasted states, there is a higher chance that your muscles will be broken down to be used for fuel with intense workouts.

In summary, weigh the pros and cons of fasted training, be aware of how your body responds to it and ensure that it works for your body in the long run.

References

Raleigh C, Madigan S, Sinnott-O'Connor C et al (2024).Prevalence Of Reducing Carbohydrate Intake And Fasted Training In Elite Endurance Athletes And association With Bone Injury. Eur J Sp Sci. 24(9): 1341-1349. DOI: 10.1002/ejsc.12170

Zouhal H, Saedi A, Salhi A et al (2020). Exercise Training And Fasting: Current Insights. Open Access J Sp Med. 21(11): 1-28. DOI: 10.2147/OAJSM.S224919

Her Coach Asked Her to Skip Breakfast

I wrote about the ketogenic diet the week before and a runner I treated two days ago was advised to skip breakfast before her runs to get into the "ketogenic zone" so that she can burn more fat.

I was fairly skeptical as I doubt you can be ketogenic and start burning ketones just by skipping breakfast despite not eating from dinner time the night before.

Anyway, I told her an article I'd just read on a similar topic while doing research writing the earlier ketogenic diet article.

British researchers studied elite cyclists who were habitual breakfast eaters on two occasions. One one occasion, they arrived at the laboratory in an overnight fasted state and ate breakfast. On the other occasion the did not eat breakfast (like my patient).

Researchers found that elite cyclists had a 4.5% drop in a 30 minutes time trial race in the evening after skipping breakfast. This is even after allowing the cyclists to eat as much as they want for lunch.

Due to our busy schedules, we may not be able to exercise in the mornings. While rushing to work, we may even skip breakfast.

The results showed that skipping breakfast may only be effective in reducing calories for people who eat breakfast regularly (and this helps to lose weight) in the short term.

However exercise performance may be compromised through out the whole day if you skip breakfast. Not great at all if you're exercising or training again later in the day. This will be worse if you're competing later in the day.

Don't skip breakfast.


Reference

Clayton DJ, Barutcu A et al (2015). Effect Of Breakfast Omission On Energy Intake And Evening Exercise Performance. Med Sci Sp Ex. 47(12): 2645-2652. DOI: 10-1249/MSS.0000000000000702.

Have a look at this article where a high-carb diet trounces low-carb one for endurance athletes.

Can The Ketogenic Diet Help With Weight Loss And Sporting Performance?

Picture from The Star

I couldn't believe my eyes when I saw two of my patients two days ago (both husband and wife are in their 50's). Both had lost 12-15 kg while on a ketogenic diet supplemented by going to the gym occasionally in less than three months. The husband even showed me a six-pack for his abdominal muscles. He said that he hadn't had them since his teenage years. I was shocked to say the least.

It seems like the ketogenic diet (eliminating carbohydrates) is all the rage in the fitness world nowadays. The ketogenic diet is similar to the caveman diet I've written about way back in 2009. It is probably time for me to revisit that low carb, high fat diet since I get questions on whether it is a good to be on a keto diet? Whether it helps to lose weight and most importantly whether it makes you stronger or faster as an athlete?

Those on the ketogenic diet follow a strict guideline to consume 80 percent of their calories from fat, 15 percent from protein and just 5 percent from carbohydrates.

After you eliminate carbs from your diet, your body goes into a state of ketosis where it uses fat for fuel. It uses the available fatty acids to produce ketones such that when your body is in ketosis, eating more fat will enable you to burn more fat.

While it is clear that you can definitely lose weight (or fat) while on the ketogenic diet, I am more interested if it helps sporting performance.

Previously I had questioned if carbohydrate loading was still relevant? The 1983 article quoted in that post is frequently quoted in the ketogenic community. The cyclists in that study underwent a 4 week ketogenic diet showed they used significantly more fat compared to a high carbohydrate diet.

Yes, fat burning was significantly ramped up (since they had 4 weeks to get used to the diet), time trialing ability remained unchanged but high intensity power was affected. There was a severe restriction on the ability of the cyclists to do anaerobic work.

Sports scientists around the world subsequently experimented with various fat adaptation protocols and kept coming up with same problem. The ability to sustain race pace was not a problem but sprint ability was always compromised.

Louise Burke, head of Sports Nutrition at the Australian Institute of Sport got together 19 elite 50 km race walkers preparing for the 2016 Rio Olympics over two training camps. They spent 3 weeks adapting to a low carb, high fat diet as the 1983 Phinney study had prescribed. Results confirmed that these elite walkers became super efficient at fat burning. The bad news was these fat adapted walkers became less efficient, requiring more oxygen to sustain their pace. This is a big liability while racing.

Consider an elite runner in the Boston marathon when a fellow runner surges on Heartbreak hill and he/ she cannot follow, the race may then be lost. Or for a cyclist (who on a low carb, high fat  diet) competing in the Tour De France on daily stages where breakaways or sprints to break up a pack is the norm and he cannot sprint to keep up then he definitely has no chance for a stage victory.

This is because high fat diets don't just ramp up fat burning, they actually decrease carbohydrate usage by decreasing the activity of a key enzyme called pyruvate dehydrogenase or PDH.

However, if you are doing ultra distance racing then the loss of sprint power isn't a big deal at all since you are more interested in completing the distance under a certain time rather than outsprinting a fellow runner. Especially when a bigger challenge for an ultra runner is refueling. Those of you who have done ultras will know what I mean when you are so sick of eating a sports gel or a banana after 12 hours without needing to go to the toilet.

It will be so much better and easier for your participation if you can rely less on external carbs while drawing on your fat reserves.

Take home message is that the low carb, high fat diet is effective for losing weight (but long term effects are not known).

If you're on the keto diet and exercising and/ or racing at 60% of your V02 max then your exercise efficiency should remain the same once you have gotten use to the diet. This mean that for moderate efforts no problemo, performance is not affected.

However if you're exercising/ racing over 70% V02 max, i.e. when you're going faster, charging uphills, it will not be the best diet plan for you.


References

Burke LM, Ross ML et al (2016). Low Carbohydrate, High Fat Diet Impairs Exercise Economy And Negates The Performance Benefit From Intensified Training In Elite Race Walkers. J Physiolo. DOI: 10.1113/JP273230

Phinney SD et al (1983). The Human Metabolic Response To Chronic Ketosis Without Caloric Restriction: Preservation Of Submaximal exercise Capability With Reduced Carbohydrate Oxidation. Metabolism. Aug 32(8): 768-776.


Thank you for reading this long article.

*Olympic 50 km race walkers were chosen for Louise Burke's experiment as the event is among the longest in the Olympics, with the winning time just under 4 hours. Also for the rules of sport that forbid race walkers from breaking into an all out sprint, making the loss of high end power less of a problem. Burke published a very famous article called "Fat adaptation for athletic performance: The nail in the coffin?" in 2006.

She, however softened her stance in 2015 with another article "Re-examining high-fat diets for sports performance: Did we call the nail in the coffin too soon?".

Also note that Kenyan runners get 76.5% of their calories from carbohydrates (including 23% from ugali, a sticky and stomach filling cornmeal starch) and 20% from loads of sugar in their tea and porridge.

Ethiopian runners get 64.3% of their calories from carbohydrates (biggest contribution from injera, a sourdour flat bread made from an Ethiopian grain called teff).

If there's a better alternative diet than carbs for better endurance performance, the Kenyans and Ehtopian runners certainly are not following that.