Wednesday, October 22, 2008

Does Exercise Produce Weight Loss?

Common wisdom suggests that exercising will cause a person to lose weight. Superficially this makes sense. A 150 pound person at rest will use about 60 calories an hour. If this person jogs at 5 mph for an hour, he or she will use an additional 540 calories per hour. Because a pound of fat represents 3500 calories, a faithful jogger should lose a pound every 6.5 days. However, as exercisers can attest, this does not seem to work out in the real world. Why would that be?

1. Vigorous exercise can produce physical stress. Stress in turn causes the release of cortisol, which stimulates carbohydrate synthesis (gluconeogenesis) for quick energy. Gluconeogenesis produces an elevation in blood glucose which then stimulates insulin release. If this sequence happens repeatedly during days and months of an ongoing exercise program, it becomes more and more likely that the chronically physically-stressed person will start gaining weight.

2. Vigorous exercise can cause fatigue. The person who exercises may be expending more calories during his workout, but if he becomes exhausted by his efforts, he may compensate by conserving energy (being more sedentary or even napping) during his other daily activities.

3. Exercise in the form of resistance training may cause the exerciser to overestimate how much energy his body consumes post-exercise. A 2006 article by Ralph La Forge states that, for the non-athlete, the excess post-workout oxygen consumption is less than 100 calories per day.

4. Vigorous exercise may cause the body's homeostatis mechanisms for fat storage to overcompensate. Exercise activates the enzyme lipoprotein lipase (LPL) in muscle tissue, allowing muscles to take up fatty acids as fuel. Once the exercise stops, the activity of LPL in muscle decreases and the activity of LPL in fat tissue increases. Calories will be pulled into fat cells and stored there to prepare for the next round of exercise. Although an individual's appetite might be depressed immediately after a workout session, later in the day there may be a more-than-compensatory drive to eat to replace lost fat stores.

5. Exercise plus frequent meals can cause weight gain. Eating frequently prevents both leptin levels and insulin levels from returning to baseline. As earlier posts have discussed, persistently elevated leptin levels can hinder satiety signals and cause excess consumption of calories. Elevated insulin levels will produce storage of those excess calories as muscle and as fat. Underweight bodybuilders use exercise plus frequent meals as a method to gain weight. However, without careful monitoring, overweight body builders can also gain weight on this regimen.


Exercise is a good thing. It can strengthen the heart and lungs, elevate mood, create a better physique and improve stamina. But for a number of very good reasons, exercise by itself does not necessarily produce weight loss, and if the circumstances are right, it may even result in weight gain.

8 comments:

stormycatalyst said...

Stargazey,

It is good to have you back in the blogosphere. I am enjoying the photo sequence beginning with your return post. There is a certain synergy within them. Thank you for providing a Map Quest for those of us who do not have the energy or the skill to follow the science of low carb, but know it is real.
I have found that the nearer I am to goal weight, the more impact the carbohydrates from refined grains such as wheat and corn have on my weight. This impact, for me is sometimes greater than the calories contained. Reducing calories from fat and protein to offset the calories does not (for me) change the impact of the carbs. The result is at a minimum, a stall. If not stopped immediately it is a weight gain and a need to return to under 20 carbs a day. I know I am not the only one who has met this beast and managed to continue toward goal.

Stargazey said...

Hi, Stormycatalyst, and thanks for your comments.

Your observations about the impact of carbs from wheat and corn as you get nearer to goal are intriguing. People who actually reach goal say they can add back more carbs, but maybe that's not true for everyone, or maybe there is something unique about carbs from grains. The only person I know who is specifically anti-wheat is Dr. Davis at The Heart Scan Blog. I probably need to take a closer look at his articles and see if I can figure out what the scientific basis might be for that.

stormycatalyst said...

Stargazey,
Thank you for your response. I am a regular reader of Dr. Davis. It was refreshing to find a practicing cardiologist who not only recognizes that low carb works, but has put his reputation and ability to parctice medicine on the line to present his inoformation. I read the post referenced when it was published, even printing it down to give to 2 or 3 friends who from their discussion regarding carbs met the description of the last paragraph.

Stargazey said...

As a followup to the wheat question, there are definitely more health issues connected with wheat than its high carb content. Many people are allergic to gluten, a protein which is found in wheat and some other grains. They develop an intolerance called celiac sprue. One of the symptoms of celiac sprue is bloating, which may account for the greater-than-expected weight gain when you eat products that contain gluten.

Another interesting aspect of wheat gluten is that it contains opioids. Here are a couple of abstracts:

Demonstration of high opioid-like activity in isolated peptides from wheat gluten hydrolysates.

Opioid peptides derived from wheat gluten: their isolation and characterization.

That's not to suggest that wheat gluten is a drug of abuse, but it may help explain why even Dr. Eades has noticed that carbohydrates seem to be addictive for some people.

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Margaret said...

I've been low carb'ing for five days now. (NY resolution but doing it because I have PCOS and it's the only diet that works for me.) Almost immediately I found new energy and don't nap anymore in the afternoons.

I decided to spend my energy walking. Moderately, not even fast paced (I have asthma so that would be hard to do anyhow.) I simply take my daughter to a park on the way home from school so she can do her homework, then she plays while I walk around a small lake. It's about 1/2 mile around. I did 2 miles today.

I felt energized but maybe by the increase of oxygen and the cardio. I don't want to work out ever - have no intention of wearing a bikini, having awesome abs or being a muscle lady of any kind.

Would walking interfere with weight loss?

Stargazey said...

Probably not, Margaret, unless you feel you might be exercising to excess and need to work up to a certain amount of exercise gradually. There are lots of variables involved, so just try to listen to your body.

Margaret said...

Thanks Stargazey. :D

I'm enjoying your blog and reading from the beginning. Little by little. I learned so much about the low carb lifestyle 10yrs ago and experienced it's success. I even landed "miraculously" pregnant half way to my goal weight.

Of course the OB and dietitian threw the Food Pyramid at me during that time, but I did manage to return to my pre-pregnancy weight soon after delivery by limiting my carbs at 140 a day during my pregnancy.

I've just gained it all back in the 10yrs since. Quick fast food, pizza and cheap meals had a lot to do with that but, I'm back on track again.

Thank you for providing a more in depth read. It answers so many questions that I've been wondering over the years. Like why I can sleep 16hrs a day, depression, a sudden problem with HBP, etc. It does seem that many of my health problems all stem from how I've been eating. All the medicine in the world won't fix that - only I can.

-Margie