Key points
- We’d all love to become super-fit sleek athletes, but if you have Type 2, then be reasonably happy with the beneficial effects of exercise on general fitness, vascular disease and blood glucose levels.
- Moderate and vigorous exercise reduces heart attack and stroke rates and eye and kidney complications.
- Regular exercise improves glucose levels a little.
- For those who can manage it, high-intensity exercise reduces glucose levels (e.g. four to six bouts of all-out sprinting or cycling for 30 seconds two or three times a week).
- Aerobic (‘cardio’) exercise and anaerobic exercise (resistance/weights) should both be part of a full exercise regimen. Resistance training reduces blood glucose levels and the amount of fat in fatty liver.
- Tech aids, for example pedometers, haven’t lived up to their promise, and don’t consistently increase activity levels.
Physical activity for people with Type 2
You’ll know Oscar Wilde’s famous views on exercise – ‘whenever I feel the urge to exercise, I go and lie down’. The modern equivalent may be your response to seeing some lean young thing running down the street faster than the traffic and wearing the latest hi-vis sportswear while ensuring that all the more sedentary people are aware they are in the presence of someone who owns the latest and most expensive Fitbit. It’s all a bit dispiriting for us middle-aged people. It’s even more difficult when there are physical difficulties, such as back pain, leg problems and general aches and pains, and stresses such as a hectic life full of things that demand more immediate attention than exercise. In addition, it’s well known that people with Type 2 – even if they are in generally good health – tend to have lower exercise tolerances than those without diabetes.
Physical activity (exercise is a more structured and focused form of physical activity) is surrounded by almost as many myths and uncritically accepted truths as diet. When we are told that exercise is ‘good’ for us, what does that actually mean? Most people accept that regular exercise generally makes us feel better, and that’s usually attributed to the release of happy hormones such as endorphins, but in addition, in diabetes we’d like to gain more specific benefits from exercise. I’m going to look at some of the evidence for the impact of exercise on blood glucose levels, weight and diabetes complications. We’ll start by comparing our individual activity against the World Health Organization’s (WHO) recommended amount of exercise, adopted by many countries, including the UK.
The WHO recommendations on activity
Adults up to their mid-60s should do moderate-intensity exercise (we’ll discuss what that means shortly) for at least 150 minutes a week, or 75 minutes of vigorous-intensity activity. The simple arithmetic works out at 20 minutes of moderate-intensity or just over 10 minutes of vigorous-intensity every day. That’s quite a time commitment. The WHO goes on to say that for ‘additional’ health benefits the 150 minutes needs doubling to 300 minutes – that is, over 40 minutes a day. If you’re 65 or older, the same recommendations apply, but in people with mobility problems, activity to improve balance and reduce the risk of falls should be done three times a week. Top of the list of benefits of regular activity relevant to Type 2s are improving muscle fitness and cardiac and respiratory (lung) fitness. Bone health and reducing the risk of falls and of hip or spine fractures also figure. We’ve already discussed activity and how it might reduce the risk of developing Type 2 diabetes (Chapter 3), but remember that the only study showing that exercise by itself (without additional weight loss) delayed the onset of Type 2 was in Chinese people with pre-diabetic glucose levels, so people of other ethnicities need both exercise and weight loss to achieve the same effect. The risk of some cancers (for example, bowel and breast) is reduced through exercise, but meaningful reductions in risk are only seen with 300 minutes or more a week.
Key point: The World Health Organization recommends 20 minutes a day of moderate intensity exercise or 10 minutes of vigorous intensity for promoting good general health.
These health benefits are not to be sniffed at, but we really need some hard evidence – if there is any – for long-term outcomes of exercise in people with diabetes. Fortunately there is some, though not as much as you might expect – from the ADVANCE study in the USA, which was designed to study heart attack and stroke rates over a five-year period. Participants were older people, average age 66, with about eight years of Type 2. Activity levels were classified as follows, so this gives us some idea of what is meant by mild, moderate and vigorous exertion:
- mild exercise: easy walking, bowling
- moderate exercise: fast walking, tennis, dancing
- vigorous exercise: jogging, vigorous swimming.
On average, the moderate or vigorous exercisers were doing over three hours (180 minutes) of activity a week, and therefore more than the WHO recommendation (150 minutes). There were no benefits if you did mild exercise, but all the important outcomes of diabetes were reduced by 15–20% in the two other groups: vascular events (heart attack and stroke), kidney and eye complications (see Chapter 11) and mortality rates. We don’t have confirmation of this result in other studies, but it is a very striking finding in a huge number of people (around 11,000 took part in the study). The negative conclusion is that mild activity doesn’t carry long-term benefits. We’ll discuss this more, but the sad news is that gentle walking that doesn’t make us even slightly short of breath or increase our pulse rate is not meaningful activity, at least when judged by diabetes outcomes.
Key point: In Type 2, moderate or vigorous activity for three hours a week reduces the risk of many of the complications of diabetes.
Levels of exercise
The WHO gives some additional examples of moderate and vigorous activities, and also introduces us to the MET (metabolic equivalent of a task), a number that represents the intensity of exercise, which is more important than just the duration. One MET is the amount of energy we expend when sitting quietly. Mild exercise – which, as we’ve seen, probably doesn’t do much for our health – is defined as a MET value of less than 3 (that is, up to three times the energy we use when sitting). Moderate exercise has a MET value of between 3 and 6, and vigorous activity more than 6. Table 8.1 gives some examples, and Figure 8.1 shows a graphic of some of these forms of activity.
Table 8.1 Examples of different levels of activity and their MET values
The big debate: does exercise help us lose weight?
Companies that tempt us with high-calorie, high-sugar, high-fat food always tell us that exercise will help us reduce weight, and that it isn’t the fault of their tempting products. You may have your personal view, but science here can be of practical help in shedding light on the ‘exercise vs. diet’ debate. For example, if you expend 400 kcal of energy every day doing exercise, then it should result in the same weight loss as if you reduced your calorie intake by the same amount. Why don’t we see the equivalence in real life? The reason, as usual, is not that science is wrong; it’s that we’re humans and not machines. Our bodies and metabolism are amazingly efficient: we rapidly extract nearly all the usable energy stored in food, and the muscles use that energy with an efficiency that man-made machines will probably never achieve. The food manufacturers omit to tell us that their products have a high energy density (that is, the number of calories in a single mouthful is large), and getting rid of that energy is very time consuming, no matter how intensively you exercise. Let’s take 400 kcal as an example – see the box below(participants in the DiRECT low-carbohydrate study who reduced their calorie intake by 400 kcal lost about 5 kg – see Chapter 5).
Exercise required to burn up 400 kcal
What do 400 food calories look like? Usually: quick and easy. The average pre-prepared sandwich from any major outlet contains … 400 kcal. Grabbed from the shelf and guzzled in about four minutes while dealing with emails. How long does it take to burn off those 400 exercise calories? It’s nearly always: slow and difficult. Someone weighing about 12 stone (170 lb or 77 kg) would need to – wait for it:
- cycle for an hour at 10 mph
- do gardening for three hours
- jog for one hour
- play golf for three-and-a-half hours.
(Every day, remember.) No contest. In the perfect world we all choose the exercise option; in the real world we grab and guzzle the sandwich. Losing meaningful amounts of weight through exercise isn’t much of an option for most of us.
Other estimates confirm this painful conclusion. For example, The American College of Sports Medicine estimates that to reduce your weight by between 5 and 10% (you will recall that 10% was achieved for a short time in Look AHEAD) you need to do between four and seven hours of moderate or vigorous aerobic exercise a week. The weekly recommended 150 minutes of moderate exercise will achieve, at best, about 2 or 3 kg weight loss, and many people will see no changes in their weight. Resistance training is not very effective for weight loss – though it is recommended for strengthening muscles as part of the WHO exercise regimen. Interestingly, resistance training lowers blood glucose levels (see below) and fatty liver responds well to it.
Let’s look at a couple of other exercise-related theories:
- Can exercise reduce the risk of regaining weight after dietary weight loss? There are very few of us who haven’t experienced a dispiriting regain in weight after working really hard at dieting. This is one area where a focus on exercise may be very helpful. To minimise the risk of gaining weight again you need about three hours (200 minutes) of moderate activity a week, which is substantially more than the WHO recommendation, but if you’ve been motivated sufficiently to lose weight in the first place, you may well be able to move to an enhanced exercise regimen without too much difficulty.
- ‘Fit but fat’: does it exist? The ‘fit but fat’ slogan rolls off the tongue easily, but has the same problem as many catchphrases: it oversimplifies. None of us is ‘either’ fit or fat: each individual has a unique combination of both fatness and fitness (fitness means ‘cardiorespiratory fitness’ – that is, how well the heart and lungs cope with activity). The conclusion from all the statistical to-ing and fro-ing (and you can imagine how much of that there’s been) is no great surprise: whatever your weight, increased activity – along the WHO lines – reduces the risk of vascular events, and in people with diabetes, probably also reduces the risk of the more specific eye and kidney complications, as well as stimulating the liver to get rid of its fat. But there are competing factors here: the heavier you are the more likely you are to have Type 2, high blood pressure and abnormal cholesterol levels, all of which are risk factors for diabetes complications. If you have a high burden of risk factors, then you’re likely to need more exercise to counterbalance their adverse effects.
The conclusion to take away from this research is: do your best both to lose weight and to increase your exercise levels. So, eat 400 kcal fewer each day and go all out for 20 minutes of moderate or heavier exercise a day.
Key point: If you exercise – moderate activity or heavier – for three hours a week after losing weight with diet, it should limit weight regain.
Exercise and blood glucose levels
Diabetic people who use insulin, especially Type 1s, notice that blood glucose levels can fall very rapidly, even after taking a gentle stroll, and Type 1 patients often tell me that if they do a blood test and find an unexpected high glucose level, 10–20 minutes of brisk walking will often do the trick and lower it. This rapid response is due to several different effects of insulin. If you have Type 2, but don’t take insulin, can exercise lower blood glucose levels?
You might think we have a clear answer to this, but there are few large-scale trials, and the smaller ones use all manner of different exercise regimens, so it’s difficult to draw firm conclusions. The general view is that regular aerobic exercise in Type 2 diabetes can modestly reduce HbA1c levels, by around 0.5% (which is not to be sniffed at – some drugs aren’t much more effective). But there’s precious little evidence that even those who diligently take their 150 minutes’ exercise a week see much benefit in blood glucose levels. This is disappointing but by now shouldn’t come as much of a surprise; everyone with Type 2 is different and all respond differently, even to the same treatment. The wise approach is to take part in any regular form of exercise that you enjoy, try and boost it to the WHO recommended level each week, and recognise that it’s likely to contribute – together with all the other parts of the diabetes lifestyle portfolio – to a long-term reduction in major complications, even though you may see no major changes in blood glucose levels. Perhaps there may be more subtle improvements: nearly three-quarters of a group of well-controlled Type 2 people in Denmark were able to reduce their diabetic medication in a trial of aerobic training sessions lasting 30–60 minutes every week for six weeks.
Technology and activity
Activity is now heavily linked with social media, apps and software, gadgets and the ‘internet of things’. These all carry the wow factor of new technology (and ‘eHealth’), and increase the ‘glamour’ aspects of exercise, but in spite of their popularity and the money we spend on them, there are very few studies of their long-term effectiveness. In addition, they can become associated with a degree of dogma that we’re very familiar with from the world of diets. For example, the exercise equivalent of ‘eggs are bad for you’ (no they’re not) could well be ‘10,000 steps a day are good for you’ (not proven). Actually the 10,000 steps a day ‘rule’ seems to have emerged with the invention of the first pedometer in Japan around the time of the Tokyo Olympics in 1960. And why 10,000? Apparently 10,000 is a lucky number in several oriental cultures. So, there’s no scientific or health basis for the 10,000 steps ‘rule’ as applied to individuals, but it chimes very nicely with cool pedometers and apps. Walking 10,000 steps is the equivalent of five miles a day – that is, at least an hour and a quarter of walking and nearly nine hours a week. Most of us find it difficult to reach the WHO recommendation of 150 minutes a week, so this is an unrealistic aim for nearly everyone, and recall from our previous discussion that intensity of exercise is as important as the amount; 10,000 steps of fast walking up and down hills isn’t the same as 10,000 steps strolling gently round the shops.
Clinical trials of pedometers in non-athletes are mostly disappointing, in large part because we quickly get bored with gadgets. In a study of Fitbits in working people in Singapore, only about 10% were using them after a year. Encouraging participants to exercise by offering cash slightly increased their activity levels compared with those who weren’t paid, but the effect lasted only as long as the money. Giving pedometers to first-year university students didn’t increase their activity levels, and also had no effect on their psychological wellbeing. Using pedometers does not improve blood glucose control in Type 2 diabetes. A stylish device, even one that’s linked to social media and route-planning is likely to remain just that – a stylish device.
However, integrating activity into our everyday life, especially in the workplace, carries more promise, and justifiably has recently become a fruitful field for research, as has the fascinating field of planning the urban and working environments to encourage (‘nudge’) us into increasing our level of day-to-day activity.
Key point: Aiming for an arbitrary (and high) number of steps a day is no substitute for thinking about the duration and intensity of your activity.
Activity at work
Most of us work sitting down. You’re likely to spend about six and a half hours a day sitting, usually at a computer terminal (and much of the time getting stressed by it). Most doctors are no different. Some people have turned to gadgetry to try and boost their activity levels: a recent vogue is for standing desks. I suspect they’ll be used about as long as the pedometers, and nobody has shown any major health benefits. But incorporating increased activity into your existing work schedule is more sound, and may carry some of the benefits for blood glucose control of intermittent high-intensity exercise (see below). For example, in a recent study in overweight Type 2 people, blood glucose levels fell for nearly 24 hours after exercising for three minutes every half hour during a simulated seven-hour working day. Aerobic exercise (walking) and simple resistance activities (half-squats, calf and knee raises) were equally effective. Fasting blood glucose levels the next day fell by 2 mmol/l: if this effect persisted, then there should be an effect on HbA1c levels after about two to three months. We await confirmation, but practicable suggestions for further increasing activity at work include the following:
- stand to greet a visitor to your workspace
- walk to a colleague’s desk rather than phoning, texting or emailing
- drink more water (nothing to do with the ‘hydration’ myth, but increased visits to the water cooler – and loo – help to break up sitting time)
- move your waste bin away from your desk, but walk to it, and don’t use it to improve your target skills for waste paper
- don’t eat lunch at your desk
- stand at the back of the room during presentations rather than sit down
- use your office stairs
- don’t use lifts for journeys of less than two floors.
High-intensity exercise (HIT)
Over the past few years there’s been a lot of interest in a new form of exercise: high-intensity activity. Examples include 30 seconds of sprinting at maximum speed or all-out cycling (stationary bike) for 30 seconds. In the classic studies, each activity was repeated four to six times separated by about four minutes of no exercise or relaxed activity. Careful studies in people with pre-diabetes or Type 2 show that muscles start working very efficiently after this form of exercise, and in particular take up more glucose from the circulation. Although the obvious effect is to reduce blood glucose levels, the really important effect is increasing the efficiency with which insulin operates. And it has a surprisingly quick effect: after six sessions spread over just two weeks muscle glucose uptake was already more effective.
Of course, not everyone can do this form of exercise, which may be more suitable for younger people or those who have had diabetes for a short time. It focuses on leg exercise (our largest muscles are in the legs), so that’s another reason why it might not be suitable for people with arthritis or trouble with the peripheral nerves leading to neuropathy. But for people who can manage it, it’s worthwhile, and is less time consuming than conventional aerobic exercise. In one study of cycling, four to six sessions spread over two weeks, each lasting 40–60 seconds had about the same effect on blood glucose levels as the same number of 30-second all-out cycling bursts. HIT seems also to benefit cardiac function and reduces liver fat in Type 2 people.
Summary
Moderate or intensive activity (that is three or more METs) for two and a half hours or more a week improves many aspects of general health and also reduces the risk of most of the complications of diabetes. Intermittent exercise at work may also turn out to have long-term benefits in the majority of us who are sedentary during the majority of the working day. Exercise itself doesn’t consistently reduce blood glucose levels but probably improves other features of the metabolic syndrome – for example, hypertension fatty liver. Elaborate and conspicuous sportswear and technology haven’t been shown to improve health.