Q: “Does fasted training burn more body fat?”

A: It’s a hotly debated topic that gets massive air play in the fat loss world and the allure of its promise has gained traction in the sports performance world.

Simply put, the answer is NO.

Now, I could leave it there.

Trust me when I sat down to write this I almost did.

This is a BIG subject.

Problem is the question is too narrow and in my mind just a bit flawed.

You see, fasted cardio on a isocaloric diet (when you hit your daily maintenance BMR/budget needs) won’t budge a bit of body fat.


A: Whether calories come from fat, carbohydrates or protein it doesn’t matter,

go over your budget and you’ll put on body fat,

go under and you’ll lose body fat.

Stick at maintenance and you won’t lose anything.

Because calories matter when it comes to losing body fat.

Q: “But what about Keto or high fat diets don’t they make you lose more body fat?”


I’ll say it again; fat loss comes from calorie restriction period.

Q: “But what about fat adaption doesn’t that promise to burn more body fat?”

A => N.O.P.E

But I see where you’re coming from, so let’s ask a different question.

“Does fasted cardio prioritise the burning of intra muscular fat and utilise blood lipids as a fuel source teaching our muscle to spare glycogen?” <= Geeky stuff right there

A: Well, YES it does.

Fasted, high fat, low carb diets increase the blood and intra muscular lipid availability. The fact that you are low on carbs means your body upregulates DIETARY and intra muscular fats as a fuel source.

Q: Is this a good approach in racing?

A: Dietary and intra muscular fat is limited and will eventually run out just like your carbohydrate stores. Liberating body fat cells takes time, too much time. Think about it. It’s why people BONK. They simply run out of stored fuel and dietary fuel.

Of course, in the real world we fuel our training and races so that doesn’t happen.

Q: “But can we really increase our ability to spare muscle glycogen and does it really give us a BIG performance advantage?”

A: Now that’s a massive question.

The answer to this is multi-faceted. The science is developing and is starting to show that working in a fat adapted state, purely focused on fat as a fuel substrate gives few advantages.

In fact, being fat adapted on a constant low carb diet has serious negative repercussions to an athlete’s ability to deliver all out power.

Now, you may think so what if you’re a long distance athlete or Ironman. But what I want you to consider is that a great training plan has sessions that are tough and glycolytic. If you want to get faster, they have to be in the plan.

Doesn’t matter which way you look at it. You need carbohydrates to supply the instant energy to produce that kind of power in those kind of sessions. Fat as fuel just doesn’t cut it in that area.

But let’s not shun low carb, high fat diets or fasted training just yet though.

Science is also starting to confirm that training at low intensity in a low carb, higher fat fed or fasted state improves the biogenesis (geeky word for developing) of muscle mitochondria (power cell of muscles).

Excitingly, it’s showing that it can almost double mitochondrial content. That, by the way, is great news. Because an increase in mitochondrial density and function = quicker clearance of lactate = ability to race at faster speeds without fatiguing.

High fat, low carb also has health benefits. It can help reduce inflammation and improve blood sugar biomarkers, but it’s not a panacea for great health especially metabolic health.

Problem is that us humans love taking things to the max, we like to work in absolutes. There is a trend with fat adaption advocates to go BIG on fat. Take the fat black coffee craze. Coffee with a large dollop of grass fed butter and or maybe cream.

My issue here is that it’s too high in fat and has little nutrient value except energy.

Overly high good saturated fat diets have also been shown to increase LDL cholesterol (the bad kind) levels. Now whether that’s because people are neglecting their overall nutrition and NOT getting the broad spectrum of nutrients needed to level that out is unclear. But it’s worth being mindful of.

It’s also fashionable at the moment to say that once you are fat adapted you can survive on fewer calories.

Thing is, your thyroid is very sensitive to caloric restriction. Drop calories down and it will downgrade to suit. Drop carbohydrates down too low and it has a double whammy affect and kick starts a series of hormonal earthquakes that causes muscle wastage, low mood, low sex drive, loss of energy, decreased immunity, shuts off female monthly cycle, funds poor sleep patterns and ruins performance in training and racing.

Which I’m guessing you don’t want?

For us at Tri Force we want your training to be meaningful, we also want you to be healthy physically, metabolically, energised and as lean as you can be.

So here’s our answer.

Periodise your nutrition around and to suit your training so that you become metabolically flexible, keep your caloric ceiling as high as you can so that you maintain great performance and be as lean as you can.

So let’s go back to the original question, as a recap.

Q: “Does fasted cardio burn more body fat?”

A: NO, total Caloric intake is the CRUCIAL factor for that.

Perhaps the question should be, does fasted cardio promote greater weight loss? (rather than fat loss)

That folks is a can of worms I’ll answer another time.

Written by

Simon de Burgh

2 X Winner of Gym Based PT

Level 2 British Triathlon Coach

Performance & Nutrition Director


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