Physical activity and weight loss

Physical activity is a poor strategy for weight loss. Still, all around the world, clinicians and health personnel are chasing fat people around, getting them to move, move and move even more. When, in the end it becomes clear that moving more doesn’t affect weight, the blame is often put on the overweight. They must be doing it wrong, they’re too lazy between exercise bouts and they are obviously stuffing themselves.

Jakicic et al recently conducted a trial where participants were divided into three physical exercise groups differing in activity doses. With no dietary change recommendations they wanted to show the 18 month effects of either 150 min PA/week, 300 min PA/week or a self help group provided a self help intervention to increase PA.

278 overweight subjects were included. The PA interventions included behavioral interventions, individual exercise and some group sessions. The self help group were given a manual and a monthly newsletter, seemingly to inspire change.

So how much weight do you lose if you exercise 150 min/week for 18 months? 0,7kg!

Then what about 300 min/week? 0,8kg!

Being given newsletters and a pamphlet results in 0,5kg weight loss. 

To be fair, these are intention to treat analyses, and so the results show the effect of being told to exercise rather than actually doing the exercise. Still, reported increased caloric expenditure per week was 442kcal for self help, 348kcal for 150 min/week and 832kcal for 300 min/week.

The authors did a secondary analysis where participants were grouped based on whether there was weight gain, weight loss, or weight stability. This analysis showed that a small weigh loss is possible and managed to obscure cause and effect completely. Luckily the authors are aware of this and writes:

Despite these findings, concluding that PA alone can result in the magnitude of weight loss observed in WT-LOSS within the retrospective secondary analysis may be misleading. There is some indication that participants classified as WT-LOSS, who lost 7.4% of their body weight compared to baseline (Table 3 and Figure 2) also made significant changes in their eating behavior as measured by the EBI questionnaire (Table 3), despite the lack of an intervention promoting a reduction in energy intake. 

And how do they conclude?

In summary, the mean change in body weight resulting from an intervention that promotes 150–300 min/week of moderate- intensity PA with no reduction in energy intake is 3% of their initial body weight in this study, with these subjects categorized retrospectively as WT-LOSS for secondary analysis. Individuals categorized as WT-LOSS for these secondary analyses do appear to be more compliant with initially increasing PA by 245 min/ week and maintaining an increase of at least 161 min/week at the conclusion of this 18-month study. 

In somewhat simpler terms, physical activity can produce a small weight loss and if you don’t lose any weight you’re not doing it right.

9 kommentarer om “Physical activity and weight loss”

  1. It's the ideal scam, err system!
    – Give the patient bad advice.
    – If the patient doesn't follow the advice, you're covered.
    – If the patient does follow the advice, they'll get the predictably poor result, but you can blame them for not doing it right. So you're still covered.
    – Either way, you've charged them for your «expert» advice and convinced them they're somehow weak and/or defective, and you've helped support the huge health/fitness industry.

    Liker

  2. Hey, I'll comment then …
    I really enjoy your blog and your ramblings. I learn a lot and agree with everything (hmm …preaching to the choir?) Still, it needs to be said and you say it well. Haven't gone through all of your posts yet, but am working on it.
    You're one of the good guys …please keep it up!
    Juan

    Liker

  3. Hi Pål,

    So. The authors are saying when energy consumption decreases (as per diet survey) then weight loss occurred with exercise. What I find neat about exercise, is the appetite controlling aspects. Peter's latest LIRKO mouse has built in appetite control (muscle level insulin resistance) apparently. 18 mos is a fr*ckin LONG *ss time.

    I still don't get biochemically how exercise affects appetite – when does it induce muscle insulin resistance? For me (like magic) it appears when the workout exceeds a certain threshold (60min but 40min when well conditioned).

    Can you explain EPOC — the afterburn from intense anaerobic exercise? and long sustained aerobic… (is that right?)

    Glad your back! *wink*

    G

    Liker

  4. The LIRKO mouse is liver insulin receptor knock out, but the high insulin level makes muscle tissue resistant as well.

    Exercise probably controls appetite in a number of ways, but only acutely it seems. Otherwise we’d expect to see bigger weight loss with exercise. Also, more exercise won’t make a lean exercising person leaner.

    Not sure what you mean by exercise causing muscle insulin resistance. Unless you do heavy resistance exercise which cause a lot of intramuscular damage, exercise makes muscle more insulin sensitive.

    Increased fat mobilization from exercise might decrease hunger, as well as decrease blood flow to the gastrointestinal system and other appetite suppressing effects from hormonal changes. Don’t know all the biochemical mechanisms. Going to have to check that one out.

    The EPOC is interesting, might do a thorough post on it soon. It happens after resistance as well as aerobic exercise (equally big oxygen consumption) and is smaller in women than in men. I think it is caused simply by the increased reliance of fat (reduced RER) post exercise and restoring/ replenishing fuel stores, repair and general anabolism.

    Good to be back. Need to exercise my writing skills and need an excuse to keep reading nerdy articles and books.

    Liker

  5. I am a 42 year old caucasian female and I exercise only once a week with a 2 hour long high intensity workouts. These workouts are about 1000 kcal. This number is calculated by a polar heart rate monitor with my heartrate, age, sex and hight.

    I am low carbing for the past 3 years including exercise days and have normalized by BMI to 22 from 26.5. In terms of sizes of clothing I went down from 12 to 4. What I find happening every time I exercise is that my appetite dies for at least 8 hours afterwards so I do not want to eat at all but I still stay warm and I feel fine. I hardly manage to eat the equivalent what I burnt in the evening but this all backfires the day after. On the next day I find myself quite depressed mentally and in an attempt to bring happiness back with carbs I overshoot a bit and this stimulates appetite greater than desired. After a few times I noticed this pattern I researched it a bit more and saw on various forums people who also experience depression after exercise. Perhaps rebuilding the muscle next day uses the available amino acids and depletes serotonine levels? I do not know why it is happening but despite this I like the feeling on the day of exercise so I still keep it up.

    My workouts are half an hour of progressively faster 15' incline walking until my heart rate hits 185. This happens in about 15 minutes with a final speed of 3.3 or 3.4 mph. Then I drop the incline to 0 and do 6 HIT run/walk intervals alternating between 165 and 185. This is followed by a 1 hour high intensity weight training with less than 30 second rest between sets. I do 8 sets of 8 repetitions for 9 different exercises with as much weight I can lift. This segment is finally followed by 4 mph walk for half an hour that keeps the heart rate elevated to a very comfortable 160 bpm. In these years I discovered the stupidity of the heart rate targets as according to those my maximum heart rate should be 220-42 = 178 and I have on occasion seen it hit 188 which according to the popular guidelines can not happen.

    I have a 5.5 fasting blood glucose that on a few occasions when I measured it after the intense weight training segment was as high as 11. This drops very fast following the exercise so that it is about normal in 2 hours afterwards. If I do the final half hour cardio though BG is about 7 and again drops very fast afterwards. On a normal non exercising day my blood glucose usually drops by 1 mmol.l in every 5 hours.

    I work full time and am completely sedentary apart from the single weekend workout but my weight is stable and strenght is very slowly increasing. I look as a normal female and this is probably due to about 25-27% fat I still carry.

    M.S.

    Liker

  6. Wow, that's great progress. Shame about the after effects of exercise though. The one exercise you do is pretty bad ass, and not eating much after doesn't sound like a good idea. Lots of people struggle with low appetite, especially after HI exercise. I don't know what might cause the feelings of depression, but my first thought is under nutrition. It's a good idea to have some highly palatable foods ready for those low appetite moments when we really should eat something. A protein shake might help. Despite your low carb diet, I would try to add some carbs to the drinking water you drink during exercise, and I would work hard to find some protein rich foods/drinks to drink immediately after exercise.

    This is not an unsolvable problem, but it might take some experimenting to figure out. Personally I eat low carb, but I add some sugar to my drinking water when I exercise hard and I always eat some proteins after. This has helped me a lot.

    Liker

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