Exercise has been found both to curb and stimulate hunger. Unfortunately, only very intense exercise will suppress appetite. A Loughborough University study found that vigorous exercise increases levels of peptide YY, an appetite-suppressing hormone, and reduces ghrelin, an appetite-stimulating hormone. But an hour later, the appetite will kick in again. Another study, from the University of Massachusetts, found that not only does exercise increase hunger, by increasing levels of insulin and leptin, both appetite-stimulating hormones, but that women are affected more than men.
A few years ago, the American peer-reviewed journal PLoS ONE, the publication of the not-for-profit Public Library of Science, ran a surprising study. It suggests that even holding back on the treats and ignoring post-exercise hunger pangs will have little effect. The study put 464 overweight women who did not exercise regularly into four groups. Three of the groups worked out for different lengths of time each week with a personal trainer, and the control group remained inactive. The women were asked to stick to their usual diets. Although all groups lost weight (though some individuals gained more than 10lbs), those who exercised did not lose significantly more weight than the inactive participants. They did reduce their waist measurements a little, but lost no more body fat overall than the control group.
One theory for this is that the women who worked out most did the least at other times of the day to compensate. After all, exercise wears you out. Doing too much increases our levels of cortisol, the stress hormone, which leads to tummy fat.
When you're purely running, you're not creating lovely lean muscle fat, so people end up having that 'skinny fat' look, where there is no real muscle tone because they haven't done any resistance work. Half an hour of running every few days is plenty, along with resistance work.
This encapsulates why running fares worse in the weight-loss stakes compared with other forms of exercise. If you are preparing for a long run, the likelihood is you're trotting along at little more than a fast walk, so your muscles hardly get going. Then there are the different consequences of aerobic versus anaerobic exercise. We burn fat during aerobic exercise (running, cycling, walking, dancing), but as soon as the exercise is over, so is the fat burning. With anaerobic workouts (weights, circuits, sprints, interval and resistance work) you burn fat and also convert some into muscle while training, but the muscles keep working out after you have stopped, so you end up with a higher calorie burn and a higher proportion of lean muscle to boot.
"It is now commonly thought that varying the intensity of your training is better than grinding along at a slow pace, because you work the heart harder and you get this afterburn," says Andy Dixon, editor of Runner's World magazine, "It's not running that makes you fat, it's eating. It's a common habit for runners to think that everything else will look after itself, but even more important than the exercise is looking at nutrition.
Running is easier than going to the gym or engaging in team sport. It's accessible, easy to get into, cheap and a very effective mode of burning fat.
The NHS recommends between 75 and 150 minutes of exercise per week, depending on the intensity, plus two sessions of muscle-strengthening activities. But the exercise doesn't have to be done in one go: the message is to become more active, rather than to offset a sedentary lifestyle with bursts of exercise.
It is important not to downplay the benefits of exercise. The part it plays in weight loss has been overstated, but it has a crucial role in most aspects of our physical health, in fighting disease and in moderating mental health. Even better, a morning jog will put a smile on your face.
Running and weight loss: the dos and don'ts
* Eat an hour-and-a-half before a run and have a healthy snack available for afterwards.
* Mix up the intensity of your run. Running for 30 minutes with bursts of sprinting is better for fat burning, lean-muscle building and fitness than a 45-minute trudge.
* Exercise followed by a treat is better for overall health than not exercising. But be aware of the calories burnt. Running for 40 minutes does not buy you two doughnuts – more like three or four oatcakes with hummus, 80g of dark chocolate or two eggs on slices of wholemeal toast.
* Avoid isotonic drinks (i.e, Gatorade, Powerade, etc) if you're exercising for less than 60 minutes. You don't need them because the carb reserve in muscles and the liver sustains us for an hour. Rehydrate with water instead.
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