Earlier this month one of my posts focused on a study which tested the effect of exercise on weight loss in women. This year-long study found that, on average, the women needed to exercise for 77 hours to lose a kg of fat. Now, if I said I had pretty-much foolproof way of getting a couple of pounds of fat off you, but you’d have to do 77 hours of hours to achieve this, what would you say? I sometimes ask a similar question in real life and the answer is always the same.
Again, this is not to bash exercise. I believe exercise is good for all sorts of things, take exercise myself, and have literally just come home after my morning walk with my dog. But the fact remains that activity and aerobic exercises such as walking and running have generally little impact where weight loss is concerned. And as I pointed out in the post I’ve linked to above, I believe knowing this can actually help motivation for exercise. How? Because knowing it means some will be less likely to feel despondent when their new-found exercise habits do not register on the scales.
Here’s another thing – if exercise does not impact much on weight, then not exercising need not necessarily be a barrier to weight loss. Knowing this can help people who are regular exercisers who, for whatever reason, cease exercising for a period of time. You see when someone believes that exercise is a major component of weight control, they tend to believe that not exercising will inevitably cause them to pile on the pounds. This belief can cause many to ‘give up’ on all their healthy habits, including healthy eating.
So, it’s not uncommon to see regular exercisers, say, get injured, and as a result not only become sedentary, but also eat more rubbish. Not surprisingly, as a result, people can find the pounds really pile on when they stop exercising. The point is that this can have more to do with food than exercise.
This week saw the publication of another study that assessed the relationship between exercise and weight. This study, which focused on middle-aged men (average age 54), randomised subject to a 6-month exercise programme (walking, running or cycling) or no exercise [1]. The exercise was graded. It started at 30 minutes, 3 times a week, working up to 60 minutes, four times a week (and at higher intensity to).
At the end of the study, the men taking exercise lost an average of 1.8 kg in weight (4 lbs). The authors of this study then calculated how many additional calories were expended by the exercisers during exercise, and how this compared to the ‘energy’ in the form of lost weight. It turns out that only about 40 per cent of the exercise appeared to translate into the form of lost weight.
What this suggests that compensatory mechanisms are at play. The authors focus entirely on calories here (see below), but there’s more to weight than this. For example, exercise can boost levels of the stress hormone cortisol which can, at high levels, promote fat gain (and muscle loss).
Getting back to calories, what compensatory mechanisms may exist? One potential explanation is that when individuals take more exercise, they are less active in the rest of their lives. Actually, the authors of this study considered this in some depth, and quoted several studies that have found that, when individuals take more exercise, energy expenditure outside exercise drops due to reduced activity including through fidgeting. In their own study, however, there was no evidence of this sort of compensation.
So, the other major potential explanation for the fact that exercise does not translate to the expected weight loss is that individuals end up eating more. Food intake was not monitored in this study. However, they did monitor hormones two hormones that influence appetite: leptin and PYY. Exercise was associated with a lowering of leptin levels (24 per cent reduction). This is important because leptin suppresses appetite. In other words, there is indirect evidence here that exercise made the men more hungry.
Interestingly, the authors also cite evidence that lower levels of leptin are also associated with “an increase in reward-related behaviors”. Couple this with increased hunger and what can we get? Some reward eating or drinking which, for men in particular, can translate into a few beers and a curry.
Overall, this study should remind us of the fact that diet and exercise are not independent of each other, and highlights some of the reasons why adopting a purely calorie-based approach to weight loss rarely works.
References:
1. Turner JE, et al. Nonprescribed physical activity energy expenditure is maintained with structured exercise and implicates a compensatory increase in energy intake. Am J Clin Nutr September 29, 2010 [epub before of print]
When I was younger, the only exercise I got was gardening and dancing. In spite of my hypothyroidism, I stayed slim. Reason: smoking. When I quit smoking, the pounds poured on without eating more and with no change in my diet.
So my question is, how does smoking control weight gain?
I have come to the conclusion that it’s purely diet. If the diet is correct then the person will have surplus energy and will move around more. If the diet is incorrect the opposite will occur.
Elizabeth
I’ve thought about smoking and I believe Peter of Hyperlipid wrote something on it as well. My take is that smoking tends to make adipose tissue relatively more insulin resistant than muscle tissue so more energy is shunted to muscle and not stored as fat.
This is so true. I tried exercise for a couple of years when I was overweight (8 km before breakfast 4 times a week, 12-16 km on the weekends), all in vain of course. Then I learned “Exercise is gram, diet is kilo” and solved my problem in a few months through lowcarb.
I had the same experience as Elizabeth when I quit smoking. The insulin resistance model makes sense to me. Before I quit I appeared to lose weight when I exercised, but this was probably just a couple of pounds and the rest muscle development and toning, as I didn’t have a lot to lose. When I quit smoking, I piled on 3 stone and couldn’t exercise it off no matter how hard I tried. Simplistic energy balance theories don’t explain it.
Interesting stuff Dr Briffa!
PS – After 20 years of stuggling with my weight, I lost 2 stone by cutting my carbs back! Wish I’d known about that earlier.
This blog has focussed on aerobic exercise. There is scientific evidence that weight-lifting and weight-resistence exercise is very beneficial in weight loss – probably because it increases muscle mass and hence metabolic rate. I know when I worked on a farm humping 25 kg bags, bales etc around for several hours a day I could eat like a horse and was far slimmer than I am now!
I have experienced the 3 stone weight gain twice when I stopped smoking. The first time I gave up for 3 years and after about 2 years I joined Weight Watchers and lost 1st7lbs, however I noticed that the weeks that I exercised a lot I only lost 1lb where normally the weight loss was 2lb.
I ended up taking up smoking again and my weight loss was amazing. Without changing my eating habits, I had lost 2 stone within 2 years. I got my will power together again and was determined not to gain weight this time. I watched what I ate, exercised at least 4 or 5 times a week and slowly but surely the weight went on – just 1lb a week but here I am 3 stone heavier again. Exercist makes no difference. I’ve tried weights in the gym, cardio, walking – all to no avail.0
Time to drop the carbs from my diet I think.
Denise
I find walking and activity (gardening and housework) work wonderfully for my weight loss combined with a lower calorie plan. At the moment I am a bit lazy but never sit down before lunch, hence activity. My weight loss improved in leaps and bounds with the walking though, but if I rode a bike or played squash it didn’t change at all. I agree also that the lower carb diet is the one for me.
If we reject the calorie paradigm, as I think we should, then it is no surprise that exercise increases the amount we eat. If that is high carb then we simply put on fat. But does exercise use up fat stored in the body? It can do. If exercise is done on an empty stomach, at a moderate level (for example walking), and for sufficient length (30 min minimum) then fat is burned. If the exercise is at a high level (running for example) fat can not be metabolised quickly enough and therefore energy from muscle is used instead.
Is any of this surprising? No, not if we evolved to walk long distances across the African savannah, either following prey, gathering foodstuffs or transporting raw materials. It makes perfect sense that we should now increase the amount of time we spend walking and 30 minutes without a break 5 times a week seems to be the minimum.
I am so happy to read this! Last year I started an aerobic exercise program which I kept faithfully for 30 days. I did 30-45min of aerobics to a video every single day and did not weigh myself until the 30 days were over (I get discouraged easily and wanted to see a big difference). Imagine my surprise when I saw an 8 lb difference.. a GAIN. I broke down in tears and cried almost all day. All that work and sweat only to GAIN weight!! I was so upset. My husband convinced me it was muscle and to try again 3 months later. This time I tried walking on a treadmill 30 mins/5 days per week. I varied speed and incline. I did not weigh myself for 30 days, and when day 31 came I found I had GAINED another 6 lbs. I felt like a complete and utter failure. I could not understand HOW that could happen while eating healthy and exercising??? I will never exercise again 😛