The Devil’s in the Details…
I’m often struck by the difference between reports on health/fitness research that appear in the popular media, and the actual published research. Oh, the popular reports are accurate enough in what they say…but what they don’t say can be important too. When a scientific study catches media attention, reporters frequently act as stenographers and cheerleaders, and don’t give the details the analysis they deserve. Even top researchers can have personal biases that influence the conclusions they draw, and people can be misled if they don’t get the whole story.
Take, for example, this MSNBC report, which describes a 2007 study that refutes conventional wisdom about diet and exercise. The basic conclusion was – when it comes to weight loss – it’s all about the calories. You can do equally well by eating less OR exercising more – but exercise offers no metabolic advantage.
How did they arrive at this conclusion? The researchers took overweight subjects and divided them into two groups: the first group’s calories were reduced by 25%, while the second group used a combination of diet (12.5% reduction in calories) + exercise (which burned another 12.5%) to create the same 25% deficit. Both groups lost the same amount of weight, so voila! You really don’t have to exercise to lose weight.
Well, the first thing that struck me when I read this was: “Hey, wait a second…the second group got to eat more food!” If you want to lose weight, would you prefer to eat more food or less? I know what I’d choose! In addition, more food = more nutrients, so nutritionally, you’re better off eating AND exercising more.
So as far as I’m concerned, there’s already a problem. Then there was this line in the article:
“And their carefully controlled study added to evidence that adding muscle mass does not somehow boost metabolism and help dieters take off even more weight.”
Excuuuuuse me???
Now I lift hard and heavy: I weigh 122 lbs., and my deadlift PR is 205 lbs. x 5 reps. I do squats, chin/pull ups, bar dips,
bench press – you name it. I’m a middle-aged mother of two, and caliper measurements put me at 12% – 13% body fat (the average for a woman my age is 22% – 28%). Don’t tell me that adding muscle mass doesn’t boost metabolism! I’m leaner now than I was when I was Sweet Sixteen and wearing size 5 dresses…and eat more in the bargain.
So once again, I ain’t buyin’ it…
But it took reading the full study to appreciate the problems with this statement. First of all, the subjects in both groups lost “fat free mass” (FFM) – which includes total body water, bone and…muscle. As the researchers wrote:
“Our data suggest that fat-free mass is reduced in parallel with the degree of caloric restriction and that regular aerobic exercise (5 days per week), at least in non-obese individuals, does not preserve lean mass.”
So how can this study confirm that adding muscle doesn’t boost metabolism, when no muscle was added? Duhhh…
Even more importantly, the MSNBC report doesn’t reveal what kind of exercise the subjects did! As noted in the above quote, the subjects in the exercise group did low-intensity aerobics exclusively, for an average of 45 min. (men) to 53 min. (women). This is fine for overall cardiovascular conditioning, but a) it ain’t gonna build muscle; and b) it ignores other research that links post-exercise metabolism to exercise intensity. Low intensity aerobic exercise may burn some cals, but only while you’re doing it…it doesn’t do much for you once the exercise is over.
Now the researchers didn’t make any distinction between types of exercise either. They assumed that all exercise is alike when it comes to losing weight, and the reporters passed this assumption along as a fact. Yet there’s very little scientific justification for it. It also flies in the face of my experience, both personal, and through working with people on the private forums I moderate.
You want to lose weight? Then lift some weight! While much of the research on strength training is focused either on athletes or on older people at risk for sarcopenia (age-related muscle wasting), there’s good evidence that lifting offers a solid metabolic boost that persists long after the workout ends.
For example, this 2002 study demonstrated that a heavy bout of resistance exercise (i.e., lifting weights), increased post-exercise oxygen consumption for up to 38 hours after the workout. Increased oxygen consumption = increased metabolism. This is borne out by another recent study comparing the effects of aerobic exercise, strength training, or no exercise on body composition in women who lost sufficient weight to achieve a BMI < 25. Only the women who did strength training were able to avoid losses of lean mass and strength; and reductions in resting metabolic rate.
The take home lessons: 1) you can’t always take media reports at face value; 2) exercise is a valuable part of any weight loss program; and 3) not all exercise is alike…strength training should be a key part of any weight loss program.
