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 <2.0 kg. However, ~25% of subjects lost >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.