Ketogenic diets have grown in popularity over the last couple of decades, with more and more people becoming mindful about the science behind fat loss, and the benefits of low-carb dieting. But while many people are familiar with the concept of ketosis (the metabolic state where our bodies burn fat, instead of carbohydrate for fuel) – some may not realise how exercise fits in with a ketogenic diet, or indeed how exercise can actually be used to kick-start ketosis.
Being a low-carb dieter myself, I often see people posting questions about ketosis. The types of questions I see most commonly all seem to revolve around a common issue – what is the fastest, most efficient way to get into ketosis?
The answer to this is not as straight-forward as many would-be ketogenic dieters might hope it to be. Our bodies are clever machines – and we naturally first use up for energy what there is in abundance, which is most commonly carbohydrate. Ketogenic diets aim to reverse this process, by limiting carbohydrate intake.
Explained very basically, in order to induce ketosis, we must deplete the levels of glycogen (stored carbohydrate) in our bodies, so that we start to burn up our fat stores for energy. This is where high intensity interval training (or HIIT) can help.
What is HIIT?
HIIT is a type of training technique in which you exert yourself to maximum output for short periods, undergoing intense bursts of exercise followed by a short period of either complete rest, or ‘active rest’ – where you will be walking or otherwise exercising very gently.
A very simple example of HIIT would be be to sprint for 30 seconds at your absolute maximum effort, and then stand still or walk for thirty seconds straight afterwards, repeating the sequence for five minutes total.
HIIT has grown in popularity over the last couple of years, largely due to the fact that it provides an effective, less time consuming way of exercising and yet still achieving great results. HIIT increases post-exercise metabolism, aids with appetite suppression, and ultimately yields greater fat loss over time than steady-state cardio sessions (King, 2001).
But the key benefit of HIIT when it comes to using exercise to enter ketosis lies in its ability to get rid of stored carbohydrate quickly and effectively:
HIIT Depletes Glycogen Levels
A HIIT routine is intense by nature, which means that all three of the different types of muscle fiber (slow-twitch, medium-twitch and fast-twitch) will be under stress and working at once, provided you stress them for at least 90 seconds. This causes glycogen to be released from the body, increasing muscle size and insulin sensitivity – and therefore fat-burning potential.
After performing a HIIT workout, glycogen stores are less full – meaning that the overall process of ‘why we get fat’ is actually working in reverse. Remember; carbs are what makes you fat! Without glycogen, our bodies have no choice but revert to burning fat-stores for fuel, rather than carbohydrates.
How to Get into Ketosis Quickly & Efficiently
Based on the premise that, in order to get into ketosis you want to deplete glycogen stores and burn fat for fuel, it would be ideal to perform a fasted HIIT workout in the morning in order to initiate ketosis. This means no food after around 7pm the night before, and no breakfast before you start your workout.
Begin your workout with a gentle warm-up, performing steady-state activity such as gentle cycling or walking for about five minutes. Next, it’s time to get sweating!
Sample HIIT Workout
- Select a piece of cardio equipment of your choice (if you don’t go to a gym, don’t worry. You can achieve the same results by doing sprints or plyometrics)
- Set your timer for 15 minutes. It also helps to have a stop watch, in order to time your intervals.
- Begin your workout with a 90 second burst of exercise – at one hundred percent effort level. You want to push yourself here!
- Active rest for 30 seconds, i.e walking slowly
- Repeat this cycle of 90 seconds full-throttle, alternating with 30 second rest periods for a total of 15 minutes.
By pushing yourself at maximum effort level for short periods, you are forcing your muscles to work harder, causing a chemical cascade in the muscle which then ‘dumps’ the stored glycogen. HIIT is arguably the fastest, and most efficient way of achieving this result.
Exercise Alone Is Not Enough
While HIIT is a great way to kick-start ketosis, it goes without saying that ketosis cannot be induced through exercise alone.
Following a ketogenic diet, composed of high fat, moderate protein and low carbohydrate is paramount to achieving this metabolic state, and ultimately achieving your long-term health and weight loss goals.
photo credit: MilitaryHealth, (CC BY 2.0), via Flickr