A new meta-analysis was recently published looking at the effect of aerobic exercise on weight loss.
116 studies with a total of 6880 participants were included in this meta-analysis, which found that for each 30 minutes per week of aerobic exercise, body weight reduced by ~ 0.52 kg and waist circumference was reduced by ~0.56 cm.
This has prompted a number of vocal individuals to push back against others who have said exercise isn’t great for weight loss. I personally share the latter view that exercise-alone isn’t awesome for weight loss and I don’t think this meta-analysis changes my mind.
Here’s why:
Previous estimates of long-term (>6 months) exercise-only weight loss is somewhere between 0 to 2 kg. Some people lose a little more and some will actually gain, as there’s varying degrees of compensation related to appetite in response to weight loss and exercise. Additionally, data on long-term exercise suggest people compensate to the increased energy utilization from exercise by using less energy for other physiological processes, again to varying degrees. Shorter-term exercise interventions generally show less compensation.
To summarize, when people lose weight (by any mechanism) or habitually exercise, there are variable responses in appetite, energy expenditure, and so on. In many, these mechanisms tend to limit weight loss.
For example, a 1-year study included in this meta-analysis looked at combined diet and exercise lasting 12-months or 6-months. Weight loss was similar between both groups at the 1-year mark, likely due to the multiple compensatory mechanisms relating to body weight.
This meta-analysis is composed of mostly short-term studies (12 weeks or less). Additionally, most of the studies included used a dietary intervention in addition to exercise…presumably because researchers already know that exercise alone isn’t great for weight loss.
I recognized the handful of long-term studies included in the meta-analysis, which I believe further support my current position:
For example, a 1-year study split men with diabetes into four groups: 1) diet only, 2) exercise only, 3) diet and exercise, and 4) control. The exercise only group lost 1.3 kg at a year, whereas the diet and exercise group lost 6.5 kg.
Another study lasting 10-months looked at men with obesity split into diet only, exercise only, diet and exercise, or control groups. After 10-months, the exercise only group didn’t lose any weight, whereas the diet and exercise group lost almost 9-kg.
The takeaway? I don’t believe that this study actually provides new insight into the independent effect(s) of exercise on weight loss. I don’t think it supports the message that exercise alone is highly effective for weight loss. Rather, I think the findings support the idea that exercise improves health (e.g. blood pressure, blood sugar, etc.) and helps support weight loss alongside other interventions such as diet, medications, or surgical interventions.
Just my 0.02. Let me know what you think!
