Blood sugar - why bother? We're going to look at the many benefits of controlling blood sugar. These range from less hunger pangs and a slimmer waistline, to better energy and mood throughout the day, to reduced risk of diseases such as diabetes and heart disease. We'll look specifically at how exercise can help and answer questions such as how much of an effect you can expect, how different types and intensities of exercise can help in different ways, and more.
Blood sugar control is especially important for diabetics, but even those who are better able to manage carbohydrates can reap significant benefits from taking care to keep it more stable. Our blood transports a lot of different things around the body, and glucose, or what we call blood sugar, is one of them. When it comes to blood sugar, everyone benefits from keeping it at a stable level, and the body tries to keep it that way - at a level between 70 - 110 mg/dL. There are serious problems associated with blood sugar being either too low or too high. The brain is a sensitive organ, so both extremely high and extremely low blood sugar levels can lead to a so-called diabetic coma, which in turn can lead to death. Most people never get close to this, but there are problems even with minor deviations from the normal range for blood sugar.
Diabetes is a disease in which the body has problems getting blood sugar out of the blood. This causes blood sugar levels to be higher than they should be if not controlled. High blood sugar over a long period of time will slowly but surely damage many parts of the body, including the kidneys, nerves, eyes and blood vessels.1 This is why blindness is relatively common for long-term diabetics, and part of the reason why diabetics have a much higher incidence of cardiovascular disease than the general population.2 Prediabetes is when blood sugar is higher than normal, but not yet high enough to be diagnosed as diabetes. The fact that even those with only slightly elevated blood sugar levels have a higher risk of developing cardiovascular disease and kidney problems, for example, shows that we really want to keep blood sugar stable within the normal range.3
Blood sugar outside the normal range not only puts you at long-term risk of various lifestyle diseases and damage to your body's organs, but it also has an impact on hunger and ultimately weight management. Blood sugar is monitored by the brain and is an important factor in controlling our hunger and eating behavior.7,8 The ability to keep blood sugar stable means less fluctuation BOTH UP AND DOWN. Let's compare two fictional people. They eat the same amount of calories at one meal. The person with good blood sugar control will have a smaller increase in blood sugar after the meal, but will also keep their blood sugar at a higher level for a longer period of time. The person with poor blood sugar control will initially have a rapid rise in blood sugar, but a while later it will drop and cause this person to be much more hungry than the first. In this way, poor blood sugar control also leads to overeating and weight gain. The same effect can be shown by the same person (regardless of their ability to regulate blood sugar) eating two different meals. Both meals have the same amount of calories and carbohydrates, but one is digested much faster and leads to a rapid increase in blood sugar followed by a rapid decline and feelings of hunger, while the other results in a much more stable blood sugar curve and less feelings of hunger.9
A very well-developed and interesting study from 2016 shows that blood sugar fluctuations not only affect hunger, but also energy and mood.10 The participants in the study were divided into two groups. The participants were given two different diets. Both diets were designed to be as similar as possible in every way except one. Both had the same amount of calories, fat, carbohydrates and protein. But the types of carbohydrates were different. One tried to get the carbohydrates absorbed as quickly as possible with white bread, cranberry juice and jelly beans. While the other had slower absorption options such as whole grains, legumes and chocolate. One of the groups started with the fast carbohydrate diet for 28 days. After a 28-day break where they ate what they usually did, the same group followed the slow carbohydrate diet for another 28 days. The other group did it in reverse order. Note that all the food was sent to them, so everything they ate was carefully controlled, they even collected and weighed all the leftover food to make sure people ate the same amount of food on both diets. So, what were the results? The fast carbohydrate diet resulted in 38% higher scores of depression and 26% higher incidence of fatigue than the slow carbohydrate diet. This shows that the slower carbohydrate diet provided both better mood and more energy. Note again that both diets had the same amount of carbohydrates, so this illustrates the importance that it's not the amount of carbohydrates, but our ability to keep blood sugar at a steady level that matters. Interestingly, the fast carbohydrate diet, i.e. the bad one, is actually very similar to a typical diet in the Western world, while the other slow carbohydrate diet is more like a Mediterranean or traditional diet.
Our ability to keep our blood sugar stable is very important for many reasons, but how can we do it? One way, as we've already seen, is to eat a diet of mostly slow carbohydrates. The American Diabetes Association points to three main ways to treat diabetes and control blood sugar.11 Namely, diet, medication and exercise. We will now look at how we can use exercise in the best possible way to make our body better equipped to buffer blood sugar and keep it within a healthy level; neither too high nor too low.
It's easy to see how what we eat can affect our blood sugar, but how can exercise help? In fact, in a surprising number of ways! Blood sugar or glucose is the body's main fuel. When we have too much in the blood, the beta cells in the pancreas produce the hormone insulin which sends the glucose from the blood either to fat cells where it turns into fat, or into the muscles where it is stored as glycogen, or into the liver where it can be stored either as a fat or as glycogen. In type 1 diabetes, the body has attacked and destroyed the pancreatic cells. As a result, little or no insulin can be produced. Type 2 diabetes occurs when, for various reasons, the pancreas becomes "burnt out" by having to produce more and more insulin. Insulin resistance is where the same amount of insulin becomes less effective and can remove less glucose from the blood. So we have at least three possible ways in which exercise can help, the production of insulin, its effectiveness and the capacity of the different storage sites.
Exercise has been shown to improve the function of the pancreas and protect the cells so we can continue to produce enough insulin.12 Exercise can also help to keep insulin more efficient by helping us to keep a lower weight. One of the ways our insulin becomes less effective, what we call insulin resistance, is when we carry excess body fat. Finally, exercise also improves our ability to absorb and store blood sugar by affecting our muscles in a number of ways:
The most common measurement used to calculate blood sugar over a longer period of time is called HbA1c (Long-term blood sugar). It works by checking how much of the hemoglobin in our red blood cells has reacted with sugar. A value of this below 5.7% is normal and a value above 6.5% is indicative of diabetes.13 So the difference between normal function and diabetes is quite small, just 0.8%. Those within that 0.8% are prediabetic. A summary of various studies where they used exercise shows that exercise can lower the result of such a measurement by an average of 0.67%; almost the entire range between normal function and diabetes!14
A 2007 study compared three different exercise groups for people with type 2 diabetes.15 One group did strength training, the second did aerobic exercise and the third did a combination of both. The study showed that all three groups improved long-term blood sugar (HbA1c), the aerobic training did slightly better than the strength training, but by far the best did a combination of both. The problem with this study was that the group that did both types of exercise exercised more than the other two groups. So a later study from 2010 made sure to let all groups exercise for the same amount of time.16 This resulted in the group that used both strength training and aerobic exercise actually burning fewer calories than the aerobic-only group. Nevertheless, it was the group that combined the forms of exercise that still improved their blood sugar more than any of the other groups. Subsequent summaries looking at more studies have drawn the same conclusion, with the balance of findings suggesting that it is slightly better to combine different types of exercise.17
The reason for this is probably due to the fact that different types of exercise produce different effects, and when you combine different types you get a synergistic effect. For example, strength training is better for building muscle mass and increasing the storage capacity of blood glucose, while aerobic exercise has other benefits.12,18
High-intensity interval training has also been studied. A Danish study showed that interval training was as effective or even better than regular aerobic exercise even though the duration of the exercise was only about half.19 Both groups did a 5-minute warm-up together, then one training group cycled for 40 minutes of aerobic exercise, while the interval training group cycled for ten one-minute intervals broken up by one-minute active rest breaks where they cycled at much less intensity. Both groups did this three times a week. The American Diabetes Association also points to three different studies that support the idea that interval training or sports activities (which often means varied intensity) are associated with more stable blood sugar than regular aerobic exercise such as jogging or cycling.11
Finally, let's not forget simple everyday activities like walking, standing, gardening, cleaning the house, etc. While more intense exercise has greater benefits, it's also important to avoid being sedentary for too long. In people at risk of developing type 2 diabetes, being inactive is linked to poorer blood sugar.11 Every 20 to 30 minutes of inactivity - try to do some light activity such as standing or walking. This doesn't have to be long, less than 5 minutes is enough. And this has been shown to improve blood sugar in overweight people, or people with poor blood sugar control.
There are really only two quick things to say about intensity. Firstly, the intensity needs to be in relation to your current fitness level.20 A slow walk on flat ground may be enough for some, while others may need much more. A general guide is to go by the talk and whistle test. If you can whistle while exercising, the intensity is low. If you can talk but not whistle, it's moderate. If you have trouble saying complete sentences, the intensity is vigorous to high. Secondly, a summary of 27 studies concludes that as long as you can tolerate it, higher intensity is best for achieving better blood sugar control.21
A 2022 review that looked at 26 relevant studies seeking to answer this question found that more exercise is better, but there may be an upper limit to the benefit of about 100 minutes per week of moderate to vigorous exercise.22 So, according to this article, any amount of exercise is good, and if you can get to about 100 minutes a week of slightly more intense exercise, you'll likely have gotten most of the blood sugar benefits you can get. Yet other studies have pointed to the fact that there may be even more benefits even after 100 minutes of exercise per week. A Danish study on diabetic patients saw benefits even at much higher exercise volumes.23 The group that exercised the least did 178 minutes per week, the middle group 296 minutes, and the group with the highest amount of exercise completed 380 minutes! The two groups that spent the most minutes had much greater improvements than the group with "only" 178 minutes. They needed to take much less medication for their blood sugar, and saw improvements in several other areas too. So how should you distribute your training during the week? You get an immediate effect of lowering blood sugar for up to two hours after you stop exercising, and increased insulin sensitivity for at least 16 hours after.24 This shows that some effects last for a while, but it's usually best to spread your exercise out over the week rather than doing it all in just one or two days. The American Diabetes Association recommends never going more than two days without exercise.11
A study comparing high-intensity intervals in either the morning or afternoon for diabetic patients saw better short-term results from the afternoon workout.25 This is likely due to how circadian rhythms affect the body. But the authors of the study still point out that we don't know the long-term effects and that more studies are needed. So, at least when it comes to high-intensity exercise, we have some reasons to do it in the afternoon.
In general, the risk of complications from exercise for people with type 2 diabetes is low.26 But, of course, exercise needs to be adapted to the person's current health and fitness level. Even for perfectly healthy people, it is always advisable to start lightly and gradually increase the amount and intensity of exercise over weeks and months. Even if the risk is low, it still involves a risk. Blood sugar can get too low, but this can be counteracted by careful monitoring and always having extra carbohydrates on hand.1 Diabetics are also more sensitive to heat because they have less blood supply to the skin and sweat less. So the conclusion is that diabetics, even those with type 1 diabetes, should learn to exercise safely.
Why is blood glucose control important? Too high or too low blood sugar can lead to many problems, including various damage to the body's organs such as the eyes and kidneys, as well as an increased risk of certain diseases such as cardiovascular disease. Stable blood sugar also helps with mood and energy as well as hunger and staying slim.
Medication, diet and exercise are the three main ways to control blood sugar, what are the exercise recommendations for blood sugar control? Different types of exercise have different and complementary benefits, so combine both aerobic exercise and strength training. In addition, interval training and varied-intensity exercise such as team sports can be a way to get the same effect in less time. What's more, it's important never to be sedentary for too long, and even short breaks where you stand or walk can have positive effects. When it comes to exercise intensity, it needs to be adapted to your level, but in the long run it's beneficial to strive to push the intensity within what you can tolerate. The more exercise the better, although there may be a diminishing effect when you exercise a lot, and try to distribute the exercise fairly evenly during the week. Never have more than two days without exercise! High-intensity training in the afternoon can pay off, at least in the short term.
Tip. Many people find pedometers or activity trackers such as smartwatches a good way to track their activity, set goals and stay motivated. Pedometers have been studied extensively and have, for example, been shown to help people with type 2 diabetes increase their daily step count by 1882 steps!11 A realistic goal that almost everyone can strive to reach is at least 7500 steps per day. Read more about lifestyle, exercise and health on our health blog, or subscribe below.