When to Exercise
There are certain times of the day at which exercise is more beneficial for boosting your circadian rhythm and reversing diabetes. However, any daily exercise – even at a suboptimal time – is better than no exercise at all. There are benefits to many choices, so choose the one that works best for you and your family.
Exercise in the morning
The conventional wisdom is that you should eat before any physical activity. This is not always true. If you have fasted for 10 to 12 hours before your morning walk, run, or bike ride, you will likely tap into your stored body fat for energy during your exercise. Your muscles will spend more energy, using even more fat as the energy source, literally melting away even more body fat. And the more muscle you have, the more calories you’ll burn throughout the day and the leaner and healthier you’ll be.
Early morning is a great time to get outside and start moving with an aerobic activity. A brisk walk, or any outdoor activity in the presence of bright daylight, is an excellent way to synchronize the brain clock. It is also an important mechanism for maintaining and enhancing brain function. Not only will exercise improve your mood for the rest of the day, but it will also stimulate new brain cell production and your ability to make new neuronal connections for deeper learning and better memory.
It doesn’t matter whether you wait until sunrise to start your morning activity. You can start anywhere from 30 minutes to 2 hours before or after sunrise; the important thing is getting some exposure to bright light. If you exercise in a gym or at home, find a spot that is next to a large window or under bright light.
As long as you are dressed properly for the weather, you can take a morning walk for most of the year, unless there is a weather advisory. In fact, exercising in cold air imparts some additional health benefits: Cold air activates brown fat or converts white fat to beige fat. Brown fat is rich in mitochon- dria, the energy currency of any cell. More mitochondria means that fat cells have more capacity to burn off. Additionally, body fat is burned to warm up the body during cold-air workouts. As a result, you can simply burn some fat by being exposed to cold temperature.
Some people with diabetes are prone to increasing their blood sugar level if they do strenuous aero- bic exercise, such as rowing, spinning, or jogging, before breakfast. This phenomenon may be partly due to excess stress hormone (cortisol). Typically, cortisol levels peak an hour after we get out of bed. Exercise further boosts cortisol. High cortisol levels can trigger the body to release some sugar into the blood or prevent our muscles from absorbing glucose from the blood (https://pubmed.nc- bi.nlm.nih.gov/27527232/).
You can test whether morning exercise is right for you by taking a blood glucose reading in the morn- ing before you start exercising and again right after you finish. If your blood glucose shoots up by 30 mg/dL (say from 120 to 150 mg/dL) or higher, then you need to take your intensity down a notch: For example, if you were jogging, you will get more benefit from a brisk walk; otherwise, your blood glu- cose will increase even further after eating breakfast. If this is the case for you, move your strenuous aerobic exercise to either after your breakfast or to the afternoon/evening.
Exercise in the late afternoon
Another great time for physical activity is at dusk or in the late afternoon, starting from 3:00 p.m. to dinnertime. This is when muscle tone begins to rise, so it’s the best time for strength training, includ- ing weight lifting, or vigorous aerobic exercise like intense indoor cycling. Late-afternoon or evening exercise has two practical benefits. Exercise is known to reduce appetite, so afternoon exercise not only helps burn some calories, it can also help reduce hunger at dinnertime, so you may eat less.
Exercise also helps our muscles take up more glucose in a mechanism that does not depend on insu- lin. As insulin production and release gradually decline through the evening, insulin alone may not be sufficient to prevent your blood glucose levels from shooting up beyond the healthy range. As little as 15 minutes of evening exercise will boost your muscles’ ability to absorb some blood glucose and keep it in the healthy range.
Our lungs and heart are both muscles that have a circadian variation – we have a relatively higher heart rate and heavier breathing during the day than at night. The higher heart rate and breathing during the day help distribute oxygen and nutrients throughout our body, including to our muscles, priming us for physical activity. At night our muscles don’t need the same levels of nutrients and oxygen as they do during the day, when we are more likely to use them. This may be one reason why heart rate and breathing slow down at night, which also helps the body cool down so we can sleep better.
Exercise after dinner
If you have been diagnosed with diabetes, evening exercise is your best option, because it has its own set of specific benefits that affect your circadian code for metabolism and for maintaining blood sugar levels. (But don’t stress if your schedule requires exercise at another time; remember, exercise at a suboptimal time is better than no exercise.) Physical activity increases demand for glucose, and muscles can take up a good amount of blood glucose, thereby reducing the blood glucose spike after an evening meal so that you will be in the normal range. After dinner, mild physical activity, like an evening walk or doing chores in the house, also helps digestion by moving the food down the diges- tive tract and reducing the chance of acid reflux or heartburn. Since insulin release and blood glucose regulation declines in the evening, , any physical activity in the evening is like taking a diabetes pill to reduce blood sugar. If you can create the ritual of taking a walk or doing some moderate exercise after dinner, it may also reduce your urge for a late-night snack because you will be busy and out of the kitchen.
Yet not all exercise at night is a good idea. It’s best to do your extreme activity or high-intensity exer- cise before dinner. Late-night exercise in a gym or on a treadmill can increase cortisol to morning levels and delay the nightly rise of melatonin, the sleep hormone. Intense exercise also raises body temperature and heart rate. All of these factors interfere with your ability to go to sleep. You may be resetting your clock by sending a signal that it’s earlier in the day. What’s more, if you do very intense exercise at night, the brain thinks it is dusk, when we are typically more active, so it delays melatonin production. This may be a reason why some (not all) people who exercise late at night also go to bed after midnight. But if late night is the only time you can exercise, taking a shower before bedtime can help your body cool down, which will help you get to sleep.
- van Praag et al., “Running Enhances Neurogenesis, Learning, and Long-Term Potentiation in Mice,” Proceed- ings of the Nationals Academy of Sciences of the United States of America 96, no. 23 (1999): 13427–31, (1999).
- D. van Marken Lichtenbelt et al., “Cold-Activated Brown Adipose Tissue in Healthy Men,” New England Journal of Medicine 360, no. 15 (2009): 1500–1508.
- et al., “Brown Adipose Tissue Oxidative Metabolism Contributes to Energy Expenditure During Acute Cold Expo- sure in Humans,” Journal of Clinical Investigation 122, no. 2 (2012): 545–52.
- Thun et al., “Sleep, Circadian Rhythms, and Athletic Performance,” Sleep Medicine Reviews 23 (2015): 1–9.
- A. King, V. J. Burley, and J. E. Blundell. “Exercise-Induced Suppression of Appetite: Effects on Food Intake and Implications for Energy Balance,” European Journal of Clinical Nutrition 48, no. 10 (1994): 715–24.
- A. Richter and M. Hargreaves, “Exercise, GLUT4, and Skeletal Muscle Glucose Uptake,” Physiological Reviews 93, no. 3 (2013): 993–1017.
- Van Cauter et al., “Nocturnal Decrease in Glucose Tolerance during Constant Glucose Infusion,” Journal of Clinical Endocrinology and Metabolism 69, no. 3 (189): 604–11.
- Sturis et al., “24-Hour Glucose Profiles during Continuous or Oscillatory Insulin Infusion: Demonstration of the Functional Significance of Ultradian Insulin Oscillations,” Journal of Clinical Investigation 95, no. 4 (1995): 1464–71.