20th June, 2013: Important Update
Q. Is there a right and a wrong time to do cardio for fat loss?
A. Yes, absolutely.
Do you use cardio regularly for fat-loss? Thinking of doing so? That’s a 2 hour investment a week or more perhaps. So it’s probably worth 3 minutes of your time to find out if you actually need it, and if so when the most effective time to do it is then right?
I’ve already written about how I think cardio is a very poor time investment for fat loss in the article Cardio vs. Diet for fat loss. Just to hammer this point home, with the exception of the athletes, the clients on the results page did not use cardio* to achieve their transformations. (*or fat burners, drugs etc.) If you’re keen to do it anyway then you may as well position it at the right time of the day.
There is a very clear nutritional hierarchy of importance for losing fat:
1. Calorie Intake vs Expenditure > 2. Macronutrient Split > … 3. Timing
…is the net calorie balance for the day. Fat, or more accurately free fatty acids, are constantly being shuttled in and out of the fat stores throughout the day. Whether you are left with more or less at the end of the day is down to your energy intake vs expenditure. You can eat less, or move more to achieve this but the net result between the two will be the same.
2. The second most important factor – the macronutrients that make up that calorie balance, as this affects the degree to which we gain/lose muscle relative to fat when bulking/dieting
3. Nutrient timing comes in a distant third. -This is why I don’t tell clients to rush home and eat “within an hour” or something like that.
The thing I want you to take away from this is that cardio timing largely doesn’t matter. It pales in comparison to the importance of having the right calorie balance for the day. There are however two points of interest: 1. Stubborn body fat removal. 2. Macronutrient partitioning.
The Short Explanation:
After eating, there is no fat burning going on. – Your body uses it’s glycogen stores (from the carbohydrates you eat) for energy
In the hours following the meal. However as time passes your body gradually switches from burning carbohydrates to using body fat for energy. After 16 hours of fasting, you are burning almost entirely fat.
Here is a simplified graph of what your body uses for fuel as time passes after a meal.
The Practical Application of Cardio for Stubborn Fat Loss
After you eat, insulin and fatty acids levels in the blood are raised. Your body is oxidizing glucose for energy.
As time passes after the meal, nutrients are absorbed, insulin levels drop, and the body starts burning the fatty acids in the blood and stored body fat.
This happens because when the body senses the insulin level drop, production of catecholamines is increased, which travel through the blood, binding to the receptors on fat cells. This activates hormone sensitive lipase (HSL), which allows the release of fat from cells into the blood stream to be burned as energy.
One way of measuring this is the Respiratory Quotient (RQ), where an RQ 1.0 denotes pure carbohydrate metabolism (“storage mode”), while RQ 0.7 denotes pure fat metabolism.
The longer the time you are without food, the more fat you burn. However the type of fat the body uses changes over time. The body’s ability to mobilize sufficient fatty acids from subcutaneous fat (the fat under the skin that makes you look fat) reaches a limit around the 10-30 hour mark. At this point the body starts to oxidize intramuscular fat. This is not the type of fat we wish to target. Continuing to fast beyond that point we also risk muscle catabolism as the rate of gluconeogenesis increases. Simply put, a point in time is reached where the consequences of continuing the fast outweigh the benefits.
Practical Concerns / Application of Cardio
So you’re going to do your cardio anyway, either because you have to for your sport or because you love it, and you acknowledge that it generally isn’t needed to get non-stage level shredded if you’re a man.
Macronutrient partitioning – Thoughts
With the goal of cutting fat it’s obvious you’re going to be in a new weekly calorie deficit. It is worth making the calories that you do ingest count most. While fat and carbs both aid in recovery, carbs are what replenish your muscle batteries (your glycogen stores) after a workout. If you have a choice of doing cardio in the fasted state then this will allow for more of the energy to come from fat for that exercise and thus more of those carbs to be shuttled into your glycogen stores when you do eat, making the most of your carbs. Whether this theory makes that much difference in practice I don’t know.
How Intermittent Fasting helps with fat loss
I.F creates an ‘ideal state’ of fat burning (at the 12-16 hour window) everyday. Almost all energy expenditure at this point, whether intentional (cardio) or just going about one’s daily activities, will lead to almost pure fat oxidization.
Perhaps this explains why those that use I.F. manage to get so lean so quickly without using cardio.
*There have been studies recently that show this not to be the case with highly trained endurance athletes. It seems that consumption of carbs before an endurance workout does not affect their fat burning ability and may even increase it. Very interesting. Important for me to know for clients, not relevant for those outside of that group.
This was one of the first articles that I wrote, so please forgive some of the simplicity of thinking – I’ve developed a lot in the last two years.
I was asked where the reference to the 16 hour point comes from. I can’t remember where I got that reference from specifically, but the graph is meant to signify not an absolute optimal value, just how energy usage changes over time.
The article is intended to be read in the context of cardio as a tool for fat loss. Even so, the practical reality of the situation is that what we now believe to be true from the studies is the following:
1. Cardio, regardless of time performed, is unlikely to have any affect on overall fat stores at the end of the day – the energy balance and the macros are way more important.
2. The exception to the above is in the case of the exceptionally lean individual.
Background science for those other people reading:
There is a theoretical limit on how much fat can be oxidised (burned) before the body will fuel itself by breaking down muscle mass. Fatter individuals can afford a greater deficit before this happens than leaner individuals because the body uses fuels in the ratio they are available. – Fat people clearly have their pantry stocked with a lot of butter a little meat, shredded people with just a little butter, a lot of meat.
The reason for this theoretical limit is mostly due to the limited access that the body has to fat stored beyond a certain level of leanness. This has to do with poorer blood flow (alpha/beta receptor ratio differences, etc.) in some places of the body, which you can check now my placing the palm of your hand on your arse cheek and noting how cold it is compared to the other places of your body. This is why the fat on your bottom is one of the last places it shifts from and is why you don’t see anyone walking around with shredded butt cheeks at the beach. Also, this feature comes in handy for some cushion when you sit.
Fasted cardio may increase the theoretical limit on the amount of fat burning that can take place in a day by providing greater access to the stubborn body fat. Cardio improves blood flow around the body, and doing it when fasted provides hormonally favourable conditions for shifting the stubborn body fat (insulin down, catecholamines up, etc.).
Does this mean we should all do fasted cardio to get shredded?
Not for the average individual using the system described on this site. More on that here.
For those interested in geeking out about some of the things I touched upon then I can think of no better book that Lyle McDonald’s one here.
Find out more: