Exercise, Uncategorized

August 12, 2009

Is Exercise Derailing Your Efforts to Lose Weight?

“In general, for weight loss, exercise is pretty useless…”

I must say, I was pretty much speechless after reading this statement (and it isn’t easy to leave me speechless!). After all, this wasn’t some weirdo quack making the kind of absurd comments you often see on the Internet. Rather, these are the words of a man named Eric Ravussin, chair in diabetes and metabolism at Louisiana State University. If nothing else, the man has credentials.

The statement by Ravussin appeared in a recent Time magazine article written by John Cloud and titled, Why Exercise Won’t Make You Thin. As you may have guessed, the article attempts to make a case that exercise is unnecessary for weight loss. In fact, Mr. Cloud, infers that an intense workout might actually hinder your weight loss efforts! Could this actually be true? Should we ditch the gym and go back to being a country of interactive couch potatoes in our quest to be lean? Let’s take a look at the major points made in the article and see what conclusions can be drawn from actual research…

A primary contention of the article is that working out is ineffective in promoting weight loss because exercise makes people hungry. Here is the author’s claim:

The basic problem is that while it’s true that exercise burns calories and that you must burn calories to lose weight, exercise has another effect: it can stimulate hunger. That causes us to eat more, which in turn can negate the weight-loss benefits we just accrued.

Let’s say for a moment that this claim is actually true and that an exercise session sends us straight to the fridge for that leftover piece of cheesecake. Do we thus conclude that exercise is superfluous for those trying to lose weight? If so, I guess we shouldn’t go to the movies since people tend to fill up on buttered popcorn and Bonbons when they’re watching a flick (blame Hollywood for our beer guts and saddlebags!).

Really now, just because you’re hungry following a workout doesn’t mean you have to binge on junk food. I don’t think I’m breaking any new ground in stating that there are many nutritious food-choices available that won’t pad your love handles. It’s is well known, for instance, that consuming protein has a satiety-inducing effect. High protein foods such as lean poultry, fish, and/or eggs not only help to fuel training (those involved in exercise have been shown to need about double the protein of sedentary individuals), but also to aid in quelling hunger. Ditto for fiber rich foods, which fill you up without filling you out. A hearty chicken or tuna salad eaten post-workout will provide a terrific source of nutrients and abolish any thoughts of downing that pint of Ben and Jerry’s sitting in the freezer (and why do you have ice cream in your house when you’re trying to lose weight anyway?).

Now let’s return to the original supposition that exercise makes you hungry. Is there really evidence to show such a phenomenon? The prevailing body of research says there’s not. In fact, the opposite appears to be true. A study by Martins and colleagues (1) had subjects perform moderate aerobic exercise for an hour and then assessed hunger both by self-reported hunger scores as well as measuring various “satiety-related hormones” (i.e. PYY, GLP-1, PP). The result? Self reported hunger showed no significant changes in fullness (‘How full do you feel?’) or motivation to eat (‘How much do you feel you can eat?’) in response to exercise. Moreover, there was an exercise-induced increase in levels of PYY, GLP-1 and PP, which have been shown to reduce the urge to eat. Bottom line: there was no evidence of either physiological or psychological indices of increased hunger from exercise. If anything, there was a trend for greater satiety.

A more recent study at Colorado State University came to similar conclusions. Ballard and colleagues (2) measured levels of the hormone ghrelin after an 80 minute bout of resistance training. Ghrelin has been called the “hunger hormone” – as ghrelin levels rise, so does the urge to eat. Well, surprise, surprise, ghrelin levels fell 13 to 21% as a result of the training protocol, leading researchers to conclude “weight lifting lowers plasma ghrelin concentrations during exercise and attenuates its rise during the postexercise period in young men.”

So, you might ask, how is it then that some people don’t show significant weight loss from exercise? This was addressed in a very well done study by King and colleagues, appearing in the International Journal of Obesity (3). The study showed that a 5-day-a-week moderate-intensity exercise program designed to expend 500 calories per session resulted in an average weight loss of more than 8 pounds after 12 weeks of training. What was most interesting, however, was that there was a huge variability between subjects, ranging from a loss of a whopping 32 pounds in one individual to a gain of almost 4 pounds in another. The researchers went on to conclude that some people are compensators, most likely choosing to binge out after exercise not because they are hungry, but rather as a “reward” for being active. The problem, therefore, is not in using exercise as a weight loss tool; it’s in educating the compensators on strategies to avoid compensating. Exercise works, just don’t feel you’re entitled to munch out because you spent a half-hour on the treadmill. If you want a reward, buy yourself a new dress that’s two sizes smaller–that will keep you motivated to stay away from the fridge!

Another glaring problem with the Time Magazine article is that there’s no distinction made between the types of exercise performed and their effects on weight management. Specifically, resistance training has been shown to be crucial in accelerating fat loss. During dieting, approximately 1/3 of weight lost is from muscle tissue. Since muscle is highly correlated with metabolism, consistent dieting gradually lowers resting metabolic rate, making further weight loss difficult to impossible. Cardiovascular exercise does little to preserve lean body tissue. Lifting weights, however, not only attenuates the decline in metabolism, it can actually increase it (4-7).

Nowhere is this better exemplified than in a study conducted by Ballor and colleagues at the University of Michigan (8). Forty obese women were assigned to one of four groups: diet only, weight-training only, diet plus weight training, and a control (no diet or exercise). After 8 weeks, the diet only group lost the most weight (just under 10 pounds) while the diet plus weight training group came in a close second at approximately 8.5 pounds. The more important statistic, however, was that lean body mass decreased by 2 pounds in the diet-only group, while it *increased* by over 2 pounds in the diet plus weight training group. This not only means that those who lifted weights lost significantly more body fat during the protocol, but that they had a superior body composition.

The Time Magazine article pooh-poohs the metabolic benefits of muscle, citing a Columbia University study that concluded a pound of muscle burns only about six calories a day at rest. This led the Time author to say:

…Which means that after you work out hard enough to convert, say, 10 lb. of fat to muscle — a major achievement — you would be able to eat only an extra 40 calories per day, about the amount in a teaspoon of butter, before beginning to gain weight. Good luck with that.

While this makes good copy, other studies seem to show that muscle possesses greater metabolic properties than those found at Columbia. Much greater. In a study done at Tufts University (9), Cambell and colleagues reported an increase in lean body weight of 3.1 pounds after 12 weeks of strength training increased resting metabolic rate by approximately 6.8%. This translated into an additional 105 calories burned per day. Do the math, and that equates to approximately 35 calories burned for each pound of added muscle. A study by Pratley and colleagues (10) came to a similar conclusion on the topic. A similar four month strength training protocol resulted in a gain of 3.5 pounds of lean muscle. Metabolic rate showed a resulting 7.7% increase, correlating to a metabolic-heightening effect of muscle of approximately 34 calories.

Taking the results of these studies into account, that same 10 pound gain in muscle cited in the Time article would conceivably help to burn an additional 350 calories a day, which would translate into a weight loss of about 36 pounds in a year by simply maintaining this level of muscularity. Even if the actual effects are only half those found in these protocols, that’s still pretty impressive in my book…

Perhaps most importantly, what the Time article seems to completely ignore is the fact that exercise has been shown to be extremely important for maintenance of goal weight after weight loss. Clearly, those who exercise show an improved ability to sustain lower levels of body weight and avoid weight regain after dieting (11-13). And ultimately the most important aspect of weight loss shouldn’t simply be to lose the weight, but rather to keep it off over the long haul.

Summing up, there is compelling evidence that exercise is not only a beneficial aspect of any weight loss program, but it’s crucial in long-term weight maintenance. Despite what you might have read in Time, don’t ditch your gym membership just yet…at least if you want to stay lean!

Stay Fit!

Brad

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