Tag: world rowing

Latest insights from observational data from Supersapiens users on the best time to eat before your workout so you get the most metabolic efficiency and glucose availability.

Source, Supersapiens Blog (10 March 2023) References included at the end.

Still second guessing what the best time to fuel up before your workout is? There’s been decades of debate. And there’s still a lot of differing opinions out there. But they’re just that: opinions. Let’s settle this debate with the data.

Most athletes agree that loading up with carbs is key during the pre-exercise window. But when and how much are sources of contention. 

There is support for eating low-GI foods in the 30 minutes prior to exercise. But others advocate for higher doses of carbohydrate 3-4 hours prior to exercise. 

Some still believe that glycogen stores are full after 24 hours of intake at a rate of 10g of carbohydrate/kg of body weight, suggesting that a longer time frame for loading up is more important.

But here’s the latest insight from observational data from our Supersapiens users:

It turns out that the best time to eat before your workout is either within 20 minutes of the start or 4 hours before the start. 

What that means for you: don’t eat between 20 minutes and 4 hours from the start of your workout.

One of our team members just set a new marathon personal best using this strategy.

You can see the glucose rush induced by his high carbohydrate breakfast, which was just about 4 hours prior to the start of the race. From there you can see some small rushes as a result of some stress/excitement and some potential metabolic perturbations from that high carb meal. 

The main reason why you should avoid fueling during that 20 minute to 4 hour window prior to the start is because of the hormonal and metabolic imbalance triggered by the high carb glucose rush. Those imbalances can impact your feel, energy, and performance during the race!

You will see a rise in glucose at start line arrival (9:30am) which leads into the race start.

You can see here that he managed to keep his glucose up and stable for the duration of his marathon. Likewise, he has great glucose stability. Both of these factors contributed to his high Glucose Score and amazing performance. 

For the record, his nutrition strategy was dialed in during the months prior to the race, where he found that 75g/hr of carbohydrates, starting from 10 minutes into the race, was optimal for his glucose stability. 

For him, loading up 4 hours before the start is key number one. Key number two was not eating and triggering internal imbalances for the next few hours before the race started.

Let’s dive into the ‘why’ and also explore what your options are if you can’t fuel up 4 hours before a workout (maybe because you run at 6am!)

Why Should You Fuel Exactly 4 Hours Before A Workout?

There are a few reasons for eating this far in advance of your workout. And they’re the same reasons to avoid fueling during the 4 hour window before your workout.

One of these is gastrointestinal comfort. If you eat too close to exercise, especially if you eat a lot of food, you may experience gastrointestinal problems. This may be worsened by things that slow gastrointestinal emptying, including fiber, fats, and protein.

But the most significant reason to avoid eating too close to exercise is ‘Rebound Hypoglycemia’ also known as ‘Reactive Hypoglycemia.’ Simply put, a steep rush in glucose triggers a big insulin release, which can overcorrect things in your system, and the result is a steep drop in glucose levels and low glucose for a period of time. This can be exacerbated by commencing exercise close to your meal. If you eat during your warmup for example, you may not get the insulin release from ingesting carbs because exercise-induced muscle uptake of glucose does not require insulin – in a rested state, your muscle uptake of glucose does require insulin. 

Bottom line: too much glucose (without exercise) can result in too much insulin, which can drive metabolic instability and unwanted low glucose levels before and at the start of your workout! During that time of instability, you’ll probably have energy swings, feel lethargic, and, given such effects, you might end up wasting carbohydrates or causing GI stress by overcompensating for how poorly you feel through over-fueling in the early stages of your workout.

Why Is Rebound Hypoglycemia Bad?

The main reasons that we think that rebound hypoglycemic (sometimes referred to as “reactive hypoglycemia”) events are bad is due to metabolic perturbations and the potential perception/feeling of the athlete. Anyone who has had one of these will attest to the fact that it is quite unpleasant and feels like you cannot perform well. That said, unfortunately all literature currently suggests that there is no performance detriment to rebound hypoglycemia.

Interestingly, the chance to develop symptoms from a reactive episode is somewhat subjective. Research suggests that around 30-to-40% of athletes develop symptoms of reactive hypoglycemia and if you are prone to it, you are also more sensitive to it. 

Data from our database do support such evidence as displayed in the figure below.

As you can see, there is a portion of athletes (on the far right) that never develop rebound hypoglycemic events. On the other hand (the far left) the same users tend to develop rebound hypoglycemic events of different severity (described by the depth and the duration of episodes).

What If You Can’t Eat 4 Hours Before A Workout? 

Maybe you have a morning workout and don’t want to get up in the middle of your sleep? Some people will be able to get away with eating at any time without consequence. Likewise, the other side of this coin is that there seems to be a subset of people who are very susceptible to rebound hypoglycemic events and these folks find any food within four or so hours of exercise is an issue.

It is a good time to remind readers that your pre-workout meal is mostly about topping up glycogen stores and so carbohydrates are the main focus. The amount, type (liquid, gels, solids etc) and their glycemic index (GI) are all relevant variables to manipulate when planning this meal and its timing.

Research suggests that the closer to your workout, the lower the amount of carbohydrates should be included. Likewise, the type is relevant mostly for comfort and convenience. The GI is heavily timing dependent and has the potential to either exacerbate or somewhat limit rebound hypoglycemic events. Generally, advice is that within 30mins of a workout you should be eating a higher GI whereas between this time and 4 hours, it probably serves users best to use low GI sources of carbohydrate.

So, to eat or not to eat.

The below data is from fellow Supersapiens and sheds light on whether or not to eat if you’re not able to eat four hours prior to a workout. It is a graphical representation of the average glucose response to meals eaten at different times prior to exercise. In brief, the graph focuses on the average CGM profile of a representative sample of users (~6000 Supersapiens). Variability has been removed for clarity.

Notice the significant rebound hypoglycemia in the 60 minutes prior to exercise graph. This doesn’t happen when the meal is 3.5 hours or more prior to the exercise event.

The last graph (of the 30 minutes prior to exercise) is a key one. This may be the answer to “What if you can’t eat four hours before a workout?”

This data currently includes all food events from the last 30 minutes prior to exercise. This means events from 1 minute prior are grouped with those 30 minutes prior to exercise.

Metabolism is more of a continuum (or dimmer switch) than an all or nothing phenomenon (or light switch), and so it is fair to assume that there is a continuum that exists between 1 minute and 60 minutes prior to exercise. There is a significant portion of the 0-30 minutes group that is more like the 30-60 minutes group. Thus eating just before the start of exercise is probably the safest strategy here. Allowing minimal insulin release and any rise in glucose being mitigated by muscle contraction related glucose absorption rather than insulin. Basically, eat during your warmup or after the start of your workout.

This data is further supported by the below figure relating to the number of lows during exercise with respect to the meal timing preceding it in Supersapiens users. This too is split up into 30min blocks of timing.

Again, considering the way metabolism works (more of a continuum than all or nothing), this is likely a reflection of very few episodes of low glucose  in the last 10 to 15 minutes before exercise starts. Thus lowering the number of lows in the 0-30min time block. Similarly, this is as high as it is, likely in large part due to the effects of lows events when eating 15-30 minutes prior to exercise.

Further clarity and resolution is provided by the below, final figure. This figure shows the normalized probability of experiencing a lows, with respect to time of the last meal. Of note and perhaps most importantly, your risk is never 0. This is because not all lows are food induced. Some may be due to the warm-up phase, as one example.

The risk of low glucose events, as displayed in this figure, is highest when eating 50-60 minutes  before exercise, where it is double the baseline risk and there is a hint that it is a little lower when eating less than 15 minutes before exercise starts.

It should be considered that these probabilities are for when an athlete eats (not when they do not, though eating 4 hours prior is fairly likely a good indication of baseline physiology) and are population level data rather than specific to an individual. This is all to say that our data gives a great starting point but the athletes need to find a best practice for themselves. 
Thankfully, Supersapiens gives you the visibility to do so.

*A caveat with this data is that it is only for exercise events made in the app with a concomitant prior food event made too. We have no insight into what users ate in these food events. Similarly we have no context for what the exercise event entailed.

5 Tips for Pre-workout Eating:

1. Eat four hours prior to exercise if possible. You can also split your planned intake in 2 moments. 4 hours and 20 minutes prior to exercise. Just avoid eating in between that time frame.
2. Make sure you consider amount and type of carbohydrates in the context of the timing of your pre-exercise meal (4h vs 20mins)
3. If you can’t eat four hours prior to exercise, try eating just before you start.
4. Nothing new on race day! You need to be dialing this in over time to be able to best execute on race day, so start ASAP.
5. Visibility is crucial to understanding this. Without it, you will not understand the effects of what you are eating on your own metabolism.

Don’t hesitate and write off another poor training session as a result of fatigue when it is because of your glucose. And definitely don’t waste another race on a mistimed pre-race meal.

Get Supersapiens today and get back to the lab to dial your nutrition in!

References

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