What affects your blood sugars (other than food)? [DDF FAQ Part 9]

As you progress with the Data-Driven Fasting journey, you will start to notice how different things in your life (other than food) influence your blood sugars.  A deeper understanding of these various factors will help you to better interpret the number you see on your meter. 

9.1  Many things affect your blood sugars

As noted by Dr Jason Fung (author of The Complete Guide to Fasting) in the Optimising Nutrition group back in 2016, when we were developing the concepts that underlie Data-Driven Fasting, many things can affect your blood glucose, such as stress, exercise, illness or hormones. 

Tracking your blood glucose is a powerful way to ensure you give your body what it needs when it needs it.  However, there are many factors (other than the food you eat) you should be aware of. 

The intent of Data-Driven Fasting is to use your blood glucose as a guide.  Don’t be hard on yourself if you feel compelled to eat before your blood glucose drops below Your Personalised Trigger.  When this happens, try to be mindful of the other factors that can affect your blood sugars, including exercise, stress, mood, and hormones (e.g. that time of the month for women).  You only need to log a blood glucose below Your Personalised Trigger more often than not to make progress.  Your blood glucose can also highlight other areas of your life that you need to work on (e.g. stress and sleep).  

If your blood glucose is a little high, you know you still have plenty of fuel in your system, and all you need is nutrients.  So, if you are hungry and choose to eat, try to prioritise nutrient-dense foods and meals with a higher protein percentage.  This will allow you to draw down on your body’s stored fat and glucose while providing the nutrients you need to function optimally and prevent cravings, as well as preserve your precious lean muscle mass. 

9.2  How does sleep affect your blood glucose? 

Getting good sleep is essential, especially when it comes to managing your cortisol and waking blood glucose.  Don’t underestimate the power of a good night’s sleep to stabilise your glucose and help you manage your appetite. 

We tend to sleep better if we’re not either overfull or too hungry.  Try not to eat a big meal or late-night snack just before you go to bed.  If you do, your metabolism will be elevated through the night as you burn off all the energy from dinner (or that late-night snack). 

At the same time, you don’t want to be too hungry.  Your ketone levels rise after a long period without food to ensure you are alert and energised to go out and hunt rather than lie down and have a deep sleep. 

If you start to notice your blood glucose is elevated after not sleeping well, do what you can to improve your sleep hygiene (e.g. limiting blue light from screens after dark, having a wind-down routine, allowing enough time for sleep, etc.). 

It’s also worth noting that high protein meals will keep your metabolism more elevated than carbs and/or fat.  So it’s ideal to front-load your protein earlier in the day and top up on energy later (if required).

9.3  Should I exercise?

Resistance training is critical to send a signal to tell your body that you need to maintain your muscle during weight loss.  But be aware that your blood glucose may go up or down when you exercise, so you should only use your blood glucose as an indicator of when you should eat after your blood glucose has settled down. 

If you typically feel hungry around your workout, you could choose to eat your Main Meal in the morning just before or after your workout (regardless of your blood glucose).  Ideally, this should be protein-rich to support recovery.  You can then treat the other meals and snacks across the day as Discretionary Meals and only eat if your blood glucose is below Your Personalised Trigger. 

While lower intensity exercise can lower blood glucose levels, keep in mind that intense exercise can increase them.  It’s OK to eat quality food when you’re hungry around workouts.  You only need to wait until your premeal glucose is below Your Personalised Trigger more often than not to see progress.

When it comes to exercise, many people find that:

  • gentle exercise is beneficial to lower their blood sugars and promote fat burning without stimulating appetite, and
  • resistance training is critical to building strength and lean mass, which will keep your metabolic rate higher.

9.4  How does exercise impact your blood glucose levels?

Taking a moderate paced walk or doing some low-intensity exercise can deplete your blood glucose.  Exercise at a lower intensity (when you can still breathe and talk easily) will tend to burn more fat as well as lower your glucose.  Meanwhile, higher intensity exercise will cause a release of stored energy from your liver, and you may see your blood glucose rise.   Resistance training helps build your metabolically active lean mass, which will increase your overall metabolic rate. 

If you do intense exercise, your body will release glucose into your bloodstream to fuel the activity.  This is not a problem, just something to keep in mind when testing your blood glucose after exercise. 

People often don’t feel hungry after exercise because of this elevated blood glucose effect.  However, if you feel hungry after your workout and your blood glucose is still artificially elevated due to the exercise, don’t be afraid to eat.  You may find that eating Your Main Meal before or after your workout helps you avoid more intense hunger later in the day (which often leads to poorer food choices).   

If you do a heavy workout (e.g. high-intensity interval training, heavy squats or deadlifts that deplete glycogen stores), don’t be surprised if you find yourself hungrier later in the day as your body tries to refill your glucose and fat fuel tanks.  We suggest you experiment with your meal timings, guided by your blood sugar, to ensure you refuel before your blood glucose gets too low and you end up in an all-out binge. 

It’s virtually impossible to calculate the calories accurately you burn during exercise.  It’s also easy to overeat due to increased hunger after your workout.  However, once the glucose surge has settled down, your blood glucose will give you a good idea of whether you are over or under-fuelling over the long term.

To manage the fact that exercise can affect blood sugars, you may find it helpful to have your protein and nutrient focused Main Meal around your workout.  You can then use your blood glucose trigger for any other Discretionary Meals during the day once their blood glucose has returned to normal.

Try to stay out of the moderate intensity ‘grey zone’, stimulating appetite but not building strength.  Exercise in this moderate intensity ‘grey zone’ is akin to eating fat and carbs together because it draws on both fat and glucose from your body’s fuel stores.  It doesn’t give you the full benefits of low-intensity (fat-burning) or high-intensity (strength) and often stimulates your appetite, so you end up making poorer food choices when you’re hungry afterwards.  

9.5  Why does my glucose rise when I don’t eat?

It may seem counter-intuitive, but your blood glucose after meals or upon waking can increase as you start to lose weight, especially if you don’t have great metabolic health and/or have a lot of weight to lose. 

If you are overweight, your body has a lot of stored energy to unload.  Given the opportunity (if you consistently eat less often), your body is eager to dump your stored energy (in the form of glucose and fat) into your bloodstream to make up the difference. 

You should see your waking blood glucose reduce over the long term, especially once you are weight stable.  However, in the short term, many people see their waking blood glucose drift up a little.  They also find their blood glucose can increase during the day, even when they haven’t eaten anything.  This is not cause for concern.  Your body is just releasing stored energy into your bloodstream to be used as fuel. 

If your other health markers (e.g. body fat, weight and waist) are moving in the right direction, then there is a good chance you will be in a much healthier position in the longer term once things stabilise. 

Rather than trying to fast for longer (which can cause your blood glucose and ketones to rise even more), it’s ideal to find a daily eating pattern that you can sustain.  Eventually, as you deplete your liver glycogen, you should see your blood glucose levels come down as your body fat levels decrease.

9.6  Can I fast when I’m stressed?

The extra adrenaline and cortisol from stress can cause your blood glucose to rise, regardless of what you eat (or don’t eat).  Stress can also cause your lizard brain to become troubled, so you will comfort eat to prepare for an emergency (e.g. famine or to run away from a predator). 

As well as waiting to eat, you can lower your blood glucose by doing whatever works for you to relax and de-stress (e.g. breathing exercises, meditation, a walk in the sun, sleep in, relaxation, etc.).  Don’t be surprised if actively managing your stress also helps you lose weight.

Many people who have had the best success with Data-Driven Fasting find that they get the best results when they relax and don’t overthink the process.  Trying to understand every nuance can lead to increased stress which is counterproductive.  In the Data-Driven Fasting 30-Day Challenge, we encourage people to relax and follow the process.  It’s only four weeks of your life.  If it doesn’t work out, you can always go back to what you were doing before. 

DDF Manual – Index 

1 thought on “What affects your blood sugars (other than food)? [DDF FAQ Part 9]”

  1. Marty–I find that other things besides what’s listed here affect me (and maybe others too): hot baths/showers, doing dishes by hand, barometric pressure (yes, my guage can tell me when there’s a disturbance in the force), certain ingredients in supplements, and evern certain “keto” food ingredients.

    About the weather thing: this past winter (U.S.) was an absolute BEAR for BG readings–I never went below 100 mg/dl, in spite of fasting and all-carnivore dieting. I had my doc run tests, and she came back with a 4.7 A1C (normal), no liver problems, and no insulin resistance. I’m beginning to think our fuel gauge is also a barometric pressure gauge, in that it also measures the effects of barometric pressure on our blood vessels (maybe high blood sugar readings unexplained by anything else means the vessels have either contracted or expanded). I tried adding aspirin to dilate the bood vessels (no go), and tried caffiene to contract them (also no go). I don’t know–you’re the engineer, so tell us what YOU think.

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