Dr Aidin Rawshani

Physical activity: effect on blood sugar, metabolism, risk factors and cardiovascular disease

Contents

Physical activity: How is blood sugar and other risk factors affected in type 2 diabetes

Keeping physically active can help you maintain a normal weight or lose weight. It can also reduce the risk of cardiovascular disease, diabetes, stroke, hypertension, osteoporosis (osteoporosis) and some cancers, as well as reduce stress and improve mood. Inactive (sedentary) lifestyle does just the opposite.

Despite all the health benefits of physical activity, people all over the world train less. Physical activity decreases not only in high-income countries, such as Sweden and other Western countries but also in low-income countries and middle-income countries such as China. It is clear that this reduction in physical activity is an important contributing factor to the global obesity epidemic and, in turn, to the increasing incidence of age-related chronic diseases.

For decades, physical activity (exercise, exercise) has been a cornerstone in the treatment of diabetes, overweight and obesity. Physical activity and changing eating habits (diet) are the means that a person can immediately resort to in order to improve his health, reduce excess weight and, accordingly, the risk of future complications. This is especially important for people with type 2 diabetes, but it is also important for people with overweight, obesity or cardiovascular disease (type 1 diabetes is discussed further down).

The goal of physical activity is to reduce their risk factors. Individuals with type 2 diabetes (as well as those with overweight or obesity) have long been recommended to increase their physical activity, even when there was no evidence that it would be beneficial. It was simply assumed that physical activity would be healthy. Similarly, people with type 1 diabetes have generally been recommended to be as physically active as possible. In recent years, several research groups have published exciting and qualitative research demonstrating the effects of regular physical activity, especially in terms of metabolism, blood sugar, diabetes, blood pressure and other risk factors.

Regular physical activity, such as fast walking, running and swimming, has a wide range of health-improving effects on the heart and blood circulation, and we will discuss this in detail in this chapter. (Obviously, drug therapy is also a cornerstone in the treatment of diabetes, but it is discussed in a separate chapter: Drugs and type 2 diabetes).

What is type 2 diabetes?

Type 2 diabetes is a complicated disease due to the poor effect of the hormone insulin in the body and the gradual decrease in the production of insulin. Insulin is a hormone produced by the pancreas (in medical language pancreas). Insulin is a hormone that is released into the blood when we eat food and the insulin enables the cells of the body to absorb sugar, which is then used for fuel in the cells. The cells of the pancreas that make insulin are called beta cells. People with type 2 diabetes have a reduced sensitivity to insulin, which means that the cells of the body do not react equally well to insulin.

This means that the cells do not take up as much sugar as they should and then the blood sugar rises. The pancreas can compensate for this by producing even more insulin, to cause a stronger stimulation of the insulin receptor on the cells. This causes people with type 2 diabetes to have both high sugar and high levels of insulin in the blood (this is called hyperinsulinemia).

The term insulin resistance is often used to describe that the body responds poorly to insulin (i.e. the body is less sensitive to insulin). People with type 2 diabetes, as well as those with metabolic syndrome, have insulin resistance. Over the years, the pancreas becomes more and more exhausted and then it can no less produce so much insulin, which causes the production of insulin to decrease gradually.

Insulin resistance leads to increased blood sugar (hyperglycemia) and metabolic disorders in carbohydrate, fat and protein. This is because insulin plays a central role in regulating our metabolism (fat, protein and carbohydrates). So insulin resistance (and later a lack of insulin) not only leads to a rise in blood sugar but also affects the metabolism of protein, fat and carbohydrates.

People with type 2 diabetes suffer from various complications in several different organs. These complications are due to impaired function of blood vessels due to high blood sugar and disturbed metabolism in the body (for example, blood fats are disrupted and this also damages the vessels).

Renal function may be impaired (this is called nephropathy), vision may deteriorate due to damage to the retina (this is called retinopathy), nerves may be damaged (this is called neuropathy).

Nephropathy, retinopathy and neuropathy are together called microvascular complications, as they are caused by disruption of the very smallest blood vessels.

In addition to the complications that occur in the smallest blood vessels in the body, the middle blood vessels are affected, people with type 2 diabetes are at increased risk of what is called macrovascular complications (coronary heart disease, heart attack, stroke) and heart failure. Complications of type 1 diabetes have been discussed in a separate chapter.

Combine exercise and a healthy diet

Combining exercise with a healthy diet is a more effective way to lose weight than just calorie restriction. Training can prevent or even reverse the effects of certain diseases. Training lowers blood pressure and cholesterol, which can prevent myocardial infarction.

In addition, if you exercise, you lower the risk of certain types of cancer diseases such as colon and breast cancer. Exercise is also known to contribute to a sense of self-confidence and well-being, possibly reducing the incidence of anxiety and depression.

Exercise can increase metabolism, or how many calories you burn in a day. It could likewise assist you to maintain and increase muscle mass, which likewise helps to increase the number of calories you burn every day.

Prevention of type 2 diabetes with exercise

Two major clinical studies have examined how regular physical activity and improved diet affected individuals with pre-stage type 2 diabetes (this is called “pre-diabetes”). You do not get type 2 diabetes overnight, but it takes many years to develop the disease. Those suffering from type 2 diabetes have had a disturbed blood sugar metabolism for many years before the diagnosis.

It is common for people with overweight or obesity to have (on an empty stomach) a blood sugar higher than “normal” but lower than the limit of “type 2 diabetes”, which means that they “almost have diabetes”, or pre-diabetes as it is called in medical language. Others who have “pre-diabetes” instead have a normal fasting blood sugar but reduced ability to handle large amounts of sugar in the blood (e. g. after a meal).

Not being able to handle sugar in the blood is called impaired glucose tolerance (in English: impaired glucose tolerance, IGT).

This condition can be diagnosed by letting the individual drink a sugar solution and then measuring blood sugar levels after 2 hours to measure the body’s ability to take care of the sugar. People with reduced glucose tolerance are perfect for examining whether physical activity can prevent type 2 diabetes! Studies have therefore been carried out on these people. Both studies developed training programs that involved 150 minutes of moderately intensive training per week, each finding that lifestyle interventions reduced the risk of pre-diabetes becoming type 2 diabetes.

Follow-up studies have then examined whether increased physical activity is more effective than improved diet to counteract the transition from pre-diabetes to type 2 diabetes, the studies showed that increased physical activity was at least as effective as improved diet (in terms of calorie restriction) .1

10 Benefits of regular training

There are many types of physical activity, such as swimming, running, jogging, walking and dancing, to name a few.

Being active has been shown to have many health benefits, both physically and mentally. It can even help you live longer. Here are the 10 best ways regular exercise benefits your body and brain.

  • They can make you feel happier It can help with weight loss
  • Good for muscles and skeletons
  • Increases your energy level
  • Reduces the risk of chronic diseases
  • Good for the skin
  • Good for cognition and memory
  • It can help with relaxation and sleep quality

Read more about diet and weight loss

Read more about LCHF

Read more about obesity and overweight

The importance of exercise when you have diabetes

For people who have diabetes, the benefits of exercise can not be overestimated. Exercise helps control weight, lower blood pressure, lower harmful LDL cholesterol and triglycerides, raise the good blood fats (HDL cholesterol), strengthen muscles and bones, reduce anxiety and improve your overall well-being

There are additional benefits for people with diabetes: exercise lowers blood sugar levels and increases the sensitivity of the body to insulin, thereby counteracting reduced sensitivity to insulin in the body (insulin resistance). Many studies underline these and other benefits of exercise.

An important factor in diabetes is that the body’s muscle mass and function decrease and deteriorate, resistance training counteracts this to some extent while increasing insulin sensitivity and thus reducing sugar levels in the blood.

The effect of exercise in individuals with diabetes

  • Exercise reduced long-term blood sugar (HbA1c) in people with diabetes, and this improvement occurred even if they did not lose weight.
  • All forms of exercise, aerobic, resistance training or both (combined exercise), were equally good at lowering HbA1c in people with diabetes.
  • Resistance training and aerobic exercise both helped to reduce insulin resistance in previously sedentary elderly adults with abdominal obesity at risk of diabetes. Combining the two types of training turned out to be more beneficial than performing only one exercise variant.
  • People with diabetes walking at least two hours a week were less likely to die from heart disease than their sedentary counterparts, and those who trained three to four hours in a week had even lower risk.
  • Women with diabetes who trained at least four hours a week with moderate or intensive training had significantly lower risk of developing heart disease than those who did not exercise.

In general, the best time to train is one to three hours after eating, when the blood sugar level is likely to be higher. If you are using insulin, it is important that you test your blood sugar before exercising.

If the blood sugar level before exercise is below 5.5 mmol/l, eat a piece of fruit or have with a light snack to increase blood sugar levels and help you avoid hypoglycemia.

It’s a good idea to check your blood sugar after any particularly exhausting exercise or activity. If you take insulin, the risk of developing hypoglycemia can be no more than six to 12 hours after exercise. Experts also warn against exercising if your blood sugar is too high, because exercise can sometimes raise blood sugar even higher.

Because of the dangers associated with diabetes, always wear a medical warning wristband indicating that you have diabetes and if you are taking insulin. Also keep hard candies or sugar tablets (such as Dextro) with you when you exercise if your blood sugar drops sharply.

How often do you need to practice?

In clinical practice, people with type 2 diabetes are recommended to practice at least 30 minutes of moderate-intensity, preferably all days a week. However, most clinical trials evaluating the effectiveness of physical activity have designed study protocols for study participants that are about training 3 times a week, many people have easier to schedule fewer but longer sessions rather than five or more workouts per week.

The reason for choosing at least 3 workouts a week is due to the effect that a training session has on insulin sensitivity, at one workout insulin sensitivity in the tissues of the body increases, and this condition lasts 2 -72 hours, depending on the duration and intensity of the training session. Since the duration of increased insulin sensitivity lasts in the general public less than 82 hours, expert groups recommend not to take breaks from training for more than two consecutive days.

Resistance training, i.e. training that causes muscle growth is believed to have a greater impact on insulin sensitivity and the duration of increased insulin sensitivity after such training may be slightly longer than aerobic training.

How much training is needed for weight loss?

To reap the health benefits from training, it is recommended that you perform some kind of aerobic exercise at least three times a week for at least 20 minutes per session, more than 20 minutes is better if you actually want to lose weight. Walk about 15 minutes of moderate intensity on a daily basis, this will burn up to 100 extra calories (provided that you do not consume excess calories in your diet afterward). Burning about 700 calories a week can result in a significant weight loss over the course of a year.

Exercise and prolonged weight loss in type 2 diabetes

Research shows that the most successful approach to long-term weight loss involves a combination of good nutrition, exercise and behavioral changes such as smoking cessation. Studies show that only increased physical activity, without calorie restriction, tends to produce a modest weight loss of about 2-5 kg, in addition, clinical trials have shown that study participants find it difficult to control weight after the study period and eventually gain weight.

One reason for the little weight loss is believed to be that obese people usually have difficulty performing enough intense training to create a significant energy consumption, moreover, it is relatively easy to counteract the energy consumption that occurred during the workout by eating more between training, people who train usually require a larger food intake, or they become less active after the workout.

Clinical trials have shown that about 1 h moderately intense aerobic exercise resulted in about 700 kcal of energy consumption per day. This means that 150 minutes of exercise per week causes a fat burning equivalent to that observed during caloric restriction in clinical trials in people with type 2 diabetes, but physical activity has several positive physiological effects, such as improved insulin sensitivity.

Most likely, people with type 2 diabetes need to exercise more than 150 minutes per week to achieve a sustainable weight loss, but the positive effects on blood sugar metabolism and cardiovascular function are seen earlier. In observational studies, it has been observed that individuals who successfully maintain a significant weight loss for at least a year have usually performed about 7 hours of exercise per week with moderate to intense exercise.

Resistance training in type 2 diabetes

In the last 10-15 years, research on physical activity has shown that resistance training is particularly effective in type 2 diabetes, resistance training can be carried out in several ways, but weight lifting is most common. Our skeletal muscle is now seen as a hormone-producing organ (endocrine organ) as it releases several hormones that regulate everything from fat burning in our fat cells (adipocytes) to counteract depression and possibly also protect the heart against oxygen starvation and heart attacks.

In type 2 diabetes, the positive effect of resistance training was muscle hypertrophy (muscle enlargement) leading to increased insulin sensitivity. Studies have shown that resistance training with several high-intensity exercises (3 times/week) caused a decrease in long-term blood sugar (HbA1c) of 1.1 to 1.2%, this may be considered a sharp decrease that is in line with what several other medicines can perform at blood sugar levels.

How safe is resistance training

Some doctors are concerned that intensive resistance training in middle age or in elderly people with type 2 diabetes with a high risk of cardiovascular disease could possibly lead to serious complications. In resistance training, it has been observed that blood pressure rises, some doctors believe that the increase in blood pressure can potentially provoke blood vessels and cause stroke, acute myocardial infarction or bleeding in the fundus and several other organs.

No clinical trials have found any evidence that resistance training actually increases the risk of these complications when blood pressure rises in people with type 2 diabetes. No serious adverse reactions have been reported in any study of resistance training in patients with type 2 diabetes.

A small study has even investigated whether patients with coronary artery disease become affected during moderate to high-intensity resistance training without finding any evidence that this would be dangerous. However, patients with type 2 diabetes who are considering starting intensive resistance training are recommended to undergo a routine check with their doctor, including an electrocardiogram (ECG) to check the heart rhythm.

Do you neeed to check blood sugar before a workout?

High blood sugar (hyperglycaemia)

Blood sugar levels vary during a workout in people with diabetes, this differs between individuals with type 1 diabetes and type 2 diabetes. Most often, patients with diabetes and blood sugar levels above 13.9 mmol/l with a contemporary accumulation of ketones do not recommend exercising. At present, people with diabetes do not usually measure ketones in the body in the same way as they daily control their blood sugar, hence it is recommended to avoid physical activity if glucose levels are above 16.7 mmol/l.

Presumably, elevated blood sugar levels associated with physical activity are not as severe in patients with type 2 diabetes who do not use insulin or other medicines that secrete insulin, for example, Sulfonylurea. However, for people with type 1 diabetes, it is more important to control blood sugar levels prior to a workout.

Low blood sugar (hypoglycaemia)

Individuals with diabetes using insulin or medicines that secrete insulin may experience severe blood sugar (hypoglycaemia) associated with physical activity, for this reason patients must adjust their medicines or carbohydrate intake prior to the workout. If the blood sugar levels are less than 5.6 mmol/mol, patients with diabetes are recommended to take carbohydrates, but this is not as necessary if the person does not have ongoing insulin therapy.

Examples of different types of training

The type of training method that you choose to lose weight does not matter much as you move and make enough effort. Therefore, experts recommend choosing exercises that you like, so that you can complete the training program for a long period.

Aerobic training

Regardless of which training program you implement, it should include some kind of aerobic or cardiovascular training. Aerobic exercises make the pulse rise. Aerobic exercises include walking, jogging, cycling, swimming and dancing. You can also work out on an exercise machine, for example, a treadmill.

Weights training

A major advantage of exercising with weights is that, in addition to losing fat, you will build muscle. Muscles, in turn, burn calories. Experts recommend training all large muscle groups three times a week.

Large muscle groups include

  • Abdominal muscle mass
  • Biceps
  • Caugh muscles
  • Chest muscles
  • Underarms
  • Hamstrings
  • Back muscles
  • Shoulders
  • Triceps

Yoga

Yoga is not as intense as other types of exercise, but it can help you lose weight in other ways. One study found that people who practice yoga are more aware of what they eat and therefore less likely to be overweight.

8 training methods leading to weight loss

  • Walking
  • Running
  • Cycling
  • Weight training
  • High-intensity interval exercising
  • Swimming
  • Yoga
  • Pilates

Physical activity improves several metabolic markers in diabetes

Long-term blood sugar (haemoglobin A1c, HbA1c)

Type 2 diabetes

Research studies investigating how regular physical activity affects blood sugar metabolism show a consistently beneficial effect of regular exercise. People with type 2 diabetes have impaired uptake of blood sugar in skeletal muscles at rest, but during intense exercise, blood sugar is absorbed by the musculature regardless of whether patients have reduced sensitivity to insulin or not.

When blood sugar is absorbed by the musculature, the body responds by producing more sugar via the liver (glycogenolysis and gluconeogenesis) to maintain normal blood sugar levels, but this depot of sugar may also run out.

Studies investigating how blood sugar levels (Hemoglobin A1c, HbA1c) in people with type 2 diabetes are affected by regular physical activity have shown that long-term blood sugar (HbA1c) in people invited to exercise regularly caused a decrease from 8.3% to 7.6%, this corresponds to a decrease of 8 mmol/mol. Results for blood glucose improvement differ slightly between subjects with type 1 diabetes and type 2 diabetes.

Studies show that people with type 2 diabetes experience a greater improvement in blood sugar levels and on average, long-term blood sugar in people with type 2 diabetes decreases between 0.5 -1%, thus corresponding to a decrease of 5-10 mmol/mol. The decrease in HbA1c appears to be greatest at the beginning of the study period, only a few weeks after the study participants started their new training regimen.

Type 1 diabetes

Studies investigating the effect of regular physical activity on long-term blood sugar (HbA1c) in people with type 1 diabetes have so far failed to show a convincing effect on HbA1c or fasting plasma glucose. Clinical studies investigating the efficacy of HbA1c in people with type 1 diabetes have established training programs lasting between 1-3 months, but also 5-month programs failed to show a positive effect on blood sugar metabolism in people with type 1 diabetes.

A few studies have shown how intensive training with a longer duration has a beneficial effect on blood sugar metabolism. This is a little different from type 2 diabetes where you note benefits already at a fast walk 150min/week. There are some theories as to why this effect is less evident in people with type 1 diabetes, and on the other hand it is a greater challenge for people with type 1 diabetes to optimize blood sugar levels and insulin doses both before and after training sessions.

In addition, young people with type 1 diabetes do not suffer from reduced insulin sensitivity (insulin resistance) to the same extent as people with type 2 diabetes, therefore it is possible that blood sugar is used as a fuel for the muscles during the workout, this causes a decrease in blood sugar levels During the training session, as in people with type 2 diabetes, however, people with type 1 diabetes respond by releasing more sugar from the liver to raise blood sugar levels by secreting adrenaline and norepinephrine which stimulate the liver to excrete more sugar (glucose) out of the blood circulation, this rebound effect can lead to a significant increase in blood sugar.

These fluctuations in blood glucose levels and temporary hyperglycaemia may be a reason for not having a clear effect on long-term blood sugar in people with type 1 diabetes who exercised moderate to intense exercise 3 times a week.

Some studies show that people with type 1 diabetes who, in addition to intensive physical training, require lower insulin doses, some believe that the reason for this is that people with type 1 diabetes take lower insulin doses only to reduce the risk of blood sugar falling (hypoglycaemia) during training. while others say that people with type 1 diabetes simply require less insulin if they exercise intensively and regularly.

In addition, these clinical trials investigating the effectiveness of regular physical activity have studied younger people with type 1 diabetes, studies that investigate efficacy in elderly people with type 1 diabetes are absent. However, these results should not stop people with type 1 diabetes from exercising regularly, as blood sugar levels should theoretically improve even in people with type 1 diabetes and physical activity has an enormous number of positive effects in addition to its impact on blood sugar metabolism.

How regular exercise affects the body in general

Lipids in blood

Individuals with type 1 diabetes have a higher risk of developing elevated blood lipids (increased levels of triglycerides and LDL cholesterol) than peers without diabetes. Elevated blood lipids are associated with an increased risk of cardiovascular diseases. Most, but not all studies that examined physical activity in patients with type 1 diabetes show a positive effect on blood lipids. Studies show that the effect of regular training in people with type 1 diabetes is similar to that seen in individuals without diabetes, blood lipids like HDL cholesterol increases by approximately 8 -30%, while LDL cholesterol decreases by 8 -14%, and triglycerides decrease by 13 -15%.

Lower levels of LDL cholesterol and triglycerides, as well as rising levels of HDL cholesterol have a positive impact on cardiovascular diseases. A particular type of blood lipids called Apolipoprotein B that is involved in the development of atherosclerosis decreases in connection with physical activity, while the levels of another type of blood lipid called Apolipoprotein A increase. The research studies show that these positive effects on blood fats are completely independent of how blood sugar metabolism is affected.

A meta-analysis that included several clinical trials investigating the effect of physical activity and effects on blood lipids in people with type 2 diabetes shows that LDL cholesterol decreases. A large clinical trial called Look Ahead (Action for Health in Diabetes) showed that patients who trained regularly and improved their diet experienced improved levels of triglycerides and HDL cholesterol.

Blood pressure

High blood pressure (hypertension) is common in people with type 2 diabetes, approximately half of patients with type 2 diabetes have high blood pressure. Individuals with type 2 diabetes and high blood pressure have approximately twice the risk of cardiovascular disease compared to people who only have type 2 diabetes.

Physical training, whether aerobic exercise or resistance training, has a positive effect on blood pressure, especially the “upper blood pressure” (systolic blood pressure), studies show that “lower blood pressure” (diastolic blood pressure) does not benefit as much as the upper one. However, in Look Ahead, reductions in both systolic and diastolic blood pressure were observed.

Effect of physical activity on body mass (Body mass index, BMI)

The most successful treatment programs for long-term weight control involve a combination of improved diet, exercise and behavioral modification. The studies investigating how regular exercise (150min/week) affects BMI in people with type 2 diabetes have shown that regular physical training usually has an insufficient effect on body weight, likely because overweight and older people have more difficulty in exercising adequate exercise for to create sufficient energy consumption.

The optimal degree of exercise to achieve long-term weight loss is probably much greater than the level required to achieve improved blood sugar metabolism. In observational studies, it has been noted that individuals with type 2 diabetes who are overweight who maintain a prolonged weight loss exercise at least 7h/week with moderate to severe intensiveness. Individuals should strive to burn between 2000-2500 calories/week, resistance training is believed to have a greater impact on weight loss than aerobic exercise.

The effect of physical training in people with type 2 diabetes

Acute effects of physical activity

Physical activity leads to increased sugar absorption in skeletal muscles, in response the liver produces sugar to maintain blood sugar levels. At physical exertion, the absorption of blood sugar does not depend on insulin levels in the body. The body’s response to insulin in the blood circulation improves significantly in the course of training, insulin sensitivity increases from 2 to 72 hours after the workout.

Chronic effects of physical activity

Both aerobic training and resistance training improve insulin sensitivity, blood sugar metabolism and fat burning in skeletal muscles. Resistance training leads to the growth of muscle mass. Blood fats are improved during physical training. Studies show greater benefits in terms of the increase in HDL cholesterol and the decrease in triglycerides while LDL cholesterol does not seem to be greatly affected by physical exertion.

Regular exercise shows that blood pressure decreases, especially systolic blood pressure. Observational studies show that the risk of cardiovascular diseases and death is less in people with type 2 diabetes who exercise regularly.

Physical activity to prevent the development of type 2 diabetes

At least 2.5h/week of moderate to intense physical activity is required to reduce the risk of developing type 2 diabetes in people with pre-stage diabetes. Epidemiological studies suggest that increased physical activity can also prevent the risk of developing gestational diabetes.

Recommended physical activity for people with type 2 diabetes

People with type 2 diabetes should conduct at least 150 min/week of moderate to intense aerobic exercise. In addition to aerobic exercise, people with type 2 diabetes should try themselves on moderate to intense resistance training at least 2-3 days/week. A combination of aerobic and resistance training can provide additional health benefits, although milder forms of physical activity (such as yoga) have shown mixed results.

References

  1. Tuomilehto J, Lindström J, Eriksson JG, et al. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med. 2001;344(18):1343-1350. doi:10.1056/NEJM200105033441801.
5/5 (1 Review)