In my last post, I explained the importance of normal glucose metabolism.  In this post, I’ll talk about a condition of impaired (faulty) glucose metabolism called prediabetes.  Many people think that the only danger of prediabetes is that a person may go on to develop diabetes.  Unfortunately, research indicates that prediabetes poses grave dangers to people’s health in other ways as well.

The American Diabetes Association developed guidelines for the diagnosis of glucose impairment during a conference in 2006 (Nathan, 2007).  Here is a table that summarizes these guidelines.  You need to know that OGTT stands for “oral glucose tolerance testing.”  This typically involves drinking a liquid mixture containing 75 grams of glucose and water.

Most people are screened for diabetes with a blood test that measures their blood glucose levels after fasting.  Usually, an OGTT test is not given unless fasting glucose measurements are abnormal.  Unfortunately, research suggests that not all people with prediabetes have impairments in both fasting glucose and responses to OGTT (Cubeddu and Hoffman, 2010).  According to this research, only about 20 to 30% of people who have impaired glucose tolerance, based on an OGTT, also have impaired fasting glucose.  This means, that many, many cases of prediabetes may be missed. 

This is significant, because a number of studies link impaired glucose metabolism to other disorders, even in those people without diabetes.  Hu et al. (2002) followed almost 120,000 female nurses for 20 years.  These women were 30 to 55 years old when he started his research and apparently free of cardiovascular disease.  Women who developed prediabetes had a significantly higher incidence of heart attack, stroke, and coronary artery disease than those who did not develop this disorder.  Haffner et al. (1990) found that subjects who developed prediabetes had significantly higher rates of elevated LDL (the bad guy) cholesterol, elevated triglycerides, lower levels of HDL (the good guy) cholesterol, and higher blood pressure than those with normal glucose metabolism.

Elevated glucose levels damage the cardiovascular system by promoting atherosclerosis in large blood vessels.  When this happens, plaques of fat infiltrate the walls of blood vessels and eventually reduce blood flow in those vessels.  In addition, pieces of these plaques can break off, traveling to smaller blood vessels in the brain, causing a stroke, or the heart, causing a heart attack.  A study by Kurihara et al (2013) found that prediabetic patients had significantly higher levels of atherosclerosis than patients with normal glucose metabolism.  In fact, those with prediabetes had similar amounts of atherosclerotic plaques as those patients with full blown diabetes. 

Elevated glucose levels also damage smaller blood vessels called capillaries.  This is especially true of the capillaries in the kidneys and eyes.  It’s important to know that high levels of blood glucose can damage the kidneys and eyes by directly harming their capillaries and by the effects of high blood pressure, which tends to be higher in those with prediabetes. Here’s a link to a Web site that has more information about prediabetes and the blood vessels in the kidneys:    http://www.kidney.org/news/KidneyCare/summer10/PreDiabetes.cfm.   And here is a link to a Web site that has more information about prediabetes and capillaries of the eyes.  http://prediabetescenters.com/prediabetes-101/symptoms-of-prediabetes/vision-change/

Several studies also suggested a link between disorders of glucose metabolism and cancer (Sayda et al., 2002; Ehrmann-Josko et al., 2006; Stattin et al., 2007; Danker, et al., 2007).  In these studies, subjects who eventually developed prediabetes had a significantly higher risk of also developing cancer than normal subjects.  It is possible that both higher levels of blood glucose and higher levels of insulin production may promote the growth of cancerous cells.

The connection between prediabetes and the eventual development of diabetes is well established.  In a study by Abdul-Ghani et al. (2008), for example, about half of subjects with prediabetes went on to develop diabetes within eight years.  Diabetes is a huge risk factor for the development of cardiovascular disease, kidney disease, nerve damage, and blindness, so this research points out the seriousness of prediabetes.  Since the American Diabetes Association (2013) estimates that 79 million Americans currently have prediabetes, and that over 90% of Americans with prediabetes are unaware of their condition, the implications are staggering.

 In my next post, I’ll discuss ways to lower the risk of developing prediabetes.

References:  Please email me if you would like the complete references for the works cited above.

In my next several blogs, I want to discuss problems with glucose metabolism.  Before I do, though, I thought I should explain exactly what glucose is and what we use it for.

Glucose is a molecule that contains six atoms of carbon, twelve atoms of hydrogen, and six atoms of oxygen.  Almost all glucose in the human body exists in a cyclic form that looks like this:

http://science.marshall.edu/murraye/alpha_amylase.htm

The chemical bonds between the atoms that form the glucose molecule contain energy that your body needs to function.  If that energy was released all at once, though, you would literally blow up!  So, your body, through a complicated series of chemical reactions, takes the energy in glucose molecules and stores it in other molecules called adenosine triphosphate (ATP).  When your body needs energy for an activity, say moving a muscle, chemical bonds in ATP molecules break apart, releasing the energy in a form your body can use.

glucose + oxygen → carbon dioxide + water + Energy (stored in ATP molecules)

While your body can also use energy stored in fat molecules and protein molecules, it prefers to use energy from glucose molecules.  Some cells require glucose for energy, except under unusual circumstances.  Cells in your brain, for example, must use glucose for energy unless you have been without food for a long time.  Amazingly, glucose can also be changed into other molecules when needed.  Fat molecules can be made from glucose, as well as many amino acids (the molecules used to build proteins), and nucleic acids (DNA and RNA).

Your body needs to keep the amount of glucose in your blood relatively stable, no matter what you have eaten and no matter how active you have been.  If you have eaten a food containing carbohydrates (the best source for glucose), glucose will enter your bloodstream.  Some of that glucose will be used to meet your immediate energy needs, and some will be stored for future use.  To store glucose for future use, your pancreas secretes a hormone called insulin.  If your body responds to insulin normally, the insulin will cause glucose to move from your blood into your muscle and liver cells, where it will be stored in molecules called glycogen.  If you can’t store any more glucose as glycogen, and you still have excess amounts of glucose, your body will turn it into adipose tissue (fat!).

If your dietary intake of glucose isn’t sufficient for your energy needs, your pancreas secretes another hormone called glucagon.  Glucagon causes the glycogen molecules in your muscle and liver cells to break apart, releasing glucose into your blood so that you can use it to create enough ATP molecules for your energy needs.   If you haven’t eaten for a long time, and used up all your glycogen, your body can even convert other molecules, such as fats and proteins, into glucose.

So, you can see that keeping your blood glucose levels is very important to your body.  If your blood glucose levels get too high (hyperglycemia), damage can occur to blood vessels throughout your body, including the kidneys, eyes, and heart.  High blood sugar levels can also damage nerves, promote the growth of cancerous cells, and make infection more likely.  If blood glucose levels get too low (hypoglycemia), the brain won’t be able to function as it should, leading to dizziness, fainting, and possibly permanent brain damage or death.

If your body can’t maintain glucose in the normal range, doctors will say you have an impairment in glucose metabolism.  The most well known disorder of glucose metabolism is diabetes.  In diabetes, the pancreas either stops producing insulin (Type I diabetes) or cells don’t respond normally to the insulin that is made (Type II diabetes).  In both cases, blood glucose levels will rise dangerously high without appropriate treatment.  The American Diabetes Association (2013) estimates that 25.8 million Americans currently have diabetes, and an additional 79 million Americans currently have prediabetes.  People with prediabetes also have impaired glucose metabolism, but their blood sugar levels don’t rise as high as those with diabetes.

In my next post, I’ll talk more about prediabetes and its dangers.

Reference:
American Diabetes Association. (2013) Fast Facts: Data and Statistics about Diabetes.  Retrieved June 9, 2014, from http://professional.diabetes.org/admin/UserFiles/0%20-%20Sean/FastFacts%20March%202013.pdf

Wow!  I just read a fascinating study directly related to rapid weight loss and metabolism.  I hope you find it as interesting as I did!

In 2012, Darcy L. Johannsen and colleagues reported on the effects of rapid and massive weight loss, even when a large reduction in calories was accompanied by vigorous exercise.  I’m going to summarize the study for you here:

1.  All participants were severely obese, with an average body mass index of 49.4.   (A body mass index of 30 or higher is considered obese.)

2.  After 30 weeks of caloric restriction and vigorous exercise, the subjects lost an average of one third of their initial weight.

3.  Even with vigorous exercise (at least 90 minutes a day, 6 days per week), not all of the subjects’ weight loss was due to the loss of fat.  About 17% of the weight loss was due to the loss of fat-free mass (FFM), including muscle tissue.

4.  Even with vigorous exercise, the subjects’ resting metabolic rate dropped significantly, and this wasn’t just due to a loss of weight.  (A smaller person will generally have a lower resting metabolic rate than a larger person due to less body mass to maintain.)  In other words, the drop in metabolic rate was too large to be explained by the amount of weight lost alone.

5.  This drop in resting metabolic rate was due to a phenomenon called metabolic adaptation.  The brain changes the amount of hormones it secretes, telling the body to slow down the rate of chemical reactions in response to a rapid loss in body weight.

6.  The subjects who lost the most weight had the largest drop in resting metabolic rate.

7.  The researchers cited other studies which suggest that this drop in resting metabolic rate will persist over time, requiring the subjects to continue with vigorous exercise and a reduction in calories to maintain their weight loss.

I was surprised that the subjects lost non-fat tissue, even while exercising an hour and a half to four and a half hours per day.  Their bodies were unable to utilize only fat stores for energy when calories were severely restricted, so some non-fat tissue was lost, despite their exercise regime.  I assume that this loss of non-fat tissue would have been even more marked if the subjects hadn’t been exercising and relied on caloric restriction alone.

The moral of the story–lose weight slowly, unless your doctor recommends rapid weight loss to manage a serious health condition.  While it can be discouraging to see the numbers on the scale change ever so slightly, rapid weight loss, at least in this study with obese subjects, appears to wreak havoc with a person’s metabolic rate.  This means that maintaining a weight loss that was achieved quickly will be very challenging, particularly if the drop in metabolic rate persists.  It’s important to know, however,  that this study used a relatively small amount of subjects (16), and that weight loss was extremely rapid.   It’s quite likely that results would be different if the weight loss wasn’t so rapid.

I’m going to try to find credible research that looks at the effects of slow weight loss on metabolic rate and will post it as soon as I can.  In the meantime, most experts seem to think that a weight loss of one to two pounds a week is the best way to preserve muscle mass and to avoid a large drop in a person’s resting metabolic rate.

If you want to read the entire article, click on this link.

Reference:  Darcy L. Johannsen, Nicolas D. Knuth, Robert Huizenga, Jennifer C. Rood, Eric Ravussin, and Kevin D. Hall.  “Metabolic Slowing with Massive Weight Loss Despite Preservation of Fat-Free Mass”, Journal of Clinical Endocrinology and Metabolism.  2012 July; 97(7), 2489-2496. Published online April 24, 2012.  Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3387402/ on Jan. 31, 2014.

Holly Trimble, MS, LPT

Disclaimer:  This blog is for informational purposes only.  Readers should discuss any specific health concerns with their physicians.

In my last post, I explained that metabolism refers to the sum of all the chemical reactions that occur in your body.  Your metabolic rate refers to the speed at which these chemical reactions occur and is a measure of how many calories you expend.  Your basal metabolic weight refers to your metabolic rate when you are sitting and relaxed, and your total metabolic rate adds the energy you expend when you are active to your basal metabolic rate.  Total metabolic rate varies widely among individuals depending on their size, muscle mass, hormonal influences, and especially their activity level.

How active you are has a huge effect on your total metabolic rate.  One of my sons, Nathan Trimble, is a serious athlete.  In fact, he won the Houston Marathon twice in the 19 and younger category for men.  He runs and rides his bike at least two hours a day–sometimes several hours a day.  He’s not a very big person, yet he must eat about 6,000 calories every day just to maintain his very low body weight and meet his energy needs.  (When he’s home, my grocery bill goes up big time!)  Almost everyone else on the planet would quickly gain weight eating that many calories on a daily basis.

When I was in my late twenties, I joined a women’s running club.  I remember our potlucks quite vividly.  Everyone brought a lot of food, and we all dove into it like we were starving.  No one thought about counting calories, and everyone was thin!  That’s because we were all running at least 30 miles a week, plus doing interval training on a track once a week.  We were burning off the calories we ate almost as quickly as we ate them.

Exercise increases your metabolic rate several ways.  First, it increases your muscle mass.  A pound of muscle uses three times the number of calories at rest than a pound of fat.  Before you get too excited about that, muscle tissue at rest still doesn’t burn very many calories–just six calories per pound a day, but it certainly helps.

Muscle tissue burns a significant amount of calories when you are exercising, however, and your metabolic rate increases significantly, providing a huge help to weight control.  (No surprise there!)  I went on a two hour hike this weekend, for example, and probably burned over 600 calories during that activity.(1)  If I had stayed home and watched TV during those two hours, I would have burned about 150 calories.(2) Not only that, my body’s metabolic rate stayed higher after my hike as as my body repaired itself from the effort–perhaps as long as 24 hours.(3)

Understanding the effect of exercise on metabolic rate is especially important for people as they get older.  You’ve probably read that your metabolic rate slows down as the years pile on, leading to weight gain.  Research suggests, however, that this is probably due more to a drop in activity levels rather than aging.  As people get older, they tend to become less active, resulting in a loss of muscle mass and a drop in their total metabolic rate.  Older people who keep their activity level high do not seem to experience the same drop in metabolic rate as those who exercise less.(4)

I think there is something else very significant about regular exercise.  When I am faithful to exercise every day–even just a half an hour walk with my dog, I tend to be more active throughout the day.  My mood is better, I have more energy, and the quality of my sleep is much higher.  All this makes me want to move more.  I tend to bound up the stairs instead of climbing them slowly.  If I have some free time, I feel like working out in the garden instead of moping around the house.   If I do watch TV, I’m more likely to pick up my hand weights and use them during that time, and I’m more willing to say “Yes!” if a friend wants to go on a bike ride.

So, that half hour walk has a huge payoff.  I’m burning more calories while I exercise, I’m burning more calories after I exercise, and I tend to be more active throughout the rest of the day–again burning more calories.  Not only that, but I want to eat more healthily as well.  I firmly believe a half an hour daily walk can change a person’s life because of its ripple effects.

By Holly Trimble, MS, LPT

References

1.  Calories Burned Calculator [Internet]. Changing Shape; Available from:  http://www.changingshape.com/calculators/calories-burned/

2.  Calories Burned Sitting Quietly and Watching TV [Internet]; Diet and Fitness Today; Available from http://www.dietandfitnesstoday.com/caloriesBurnedInfo.php?id=141

3.  The Myth About Muscle and Metabolism [Internet]; Christian Finn. Available from:  http://muscleevo.net/muscle-metabolis#.Ut7tt7TnZaQ

4.  van Pelt, R.E., et al (2001). Age-related decline in RMR in physically active men: relation to exercise volume and energy intake. American Journal of Physiology, E281, 633-630

Disclaimer:  Nothing in this blog should take the place of advice from your own health care provider.  Anyone starting an exercise program should consult with his or her physician and follow their recommendations.

Feel free to share this blog, but please give credit to the author.

In my last post, I shared a Ted presentation on dieting and weight loss. In that post, I repeated Dr. Sandra Aamodt’s premise that losing weight may cause the hypothalamus to slow down a person’s metabolism, making it very difficult to maintain a weight loss. I thought I should clarify the terms “dieting” and “metabolism” in this post.

To me, the term dieting means deliberately restricting calories to achieve weight loss. For example, if someone decides to only eat 1200 calories a day, that person is “going on a diet.” It makes me think of someone carefully planning each meal, recording how much he or she ate, and obsessively watching the scale to keep track of weight loss. It involves food deprivation, frustration, and suffering. Worse, dieting can lead to an eating disorder and an unhealthy obsession with food. Will dieting cause weight loss? Yes, it will, but it usually doesn’t translate to a lifelong victory over excessive weight. In fact, a person is likely to go through all that effort, only to see his or her weight eventually go back to what it was before, or even higher.

Metabolism refers to the sum of all the chemical reactions that occur in your body. Catabolic reactions break down larger molecules into smaller ones, and anabolic reactions build larger molecules from smaller ones. Think about what happens when you eat a bowl of oatmeal. Chemical reactions break down the complex carbohydrates in the oats you eat into smaller glucose molecules, using catabolic reactions. The glucose molecules that aren’t needed for your immediate energy needs get strung together to form a larger molecule called glycogen, using anabolic reactions. Millions of other chemical reactions occur in your body every day. You must make and secrete hormones, repair body tissues, get rid of wastes, process sensation, move body parts, and so on. The speed at which all of these chemical reactions occur is your metabolic rate, and you use the energy in the food you eat for these chemical reactions. If your metabolic rate is fast, your chemical reactions occur at a faster rate of speed, and you burn more calories. If your metabolic rate is slow, your chemical reactions occur at a lower rate of speed, and you burn fewer calories.

I hope you can now why severe caloric restrictions are not a good idea. They slow down your metabolic rate, causing you to burn fewer calories. When you go back to eating your usual amount of food, weight gain results.

To learn more about metabolism, here are two sites I recommend. One is designed for children, but I think it’s a great one for adults as well:

http://kidshealth.org/parent/general/body_basics/metabolism.html

http://www.news-medical.net/health/What-is-Metabolism.aspx

In my next post, I’ll talk about ways you can keep or increase your current metabolic rate.

Today I watched the Ted video presentation, Why Dieting Doesn’t Usually Work, given by neuroscientist Sandra Aamodt.  She explains that dieting actually causes most people to get heavier.  They lose weight on the diet, but eventually gain it all back and then some.  She ties this in to the function of the hypothalamus–the structure in your brain that “knows” what many, many variables in your body should be, including your weight.

The hypothalamus does all it can to keep your weight within a “set point,” a range of weight that it thinks is best for you.  If your weight falls below that range, particularly if you do so quickly, the hypothalamus causes your metabolism to actually slow down.  Your metabolic rate is directly tied to the number of calories you burn so you eventually gain the weight you lost back, and then some, even if you are eating less than you did before you started your diet.

Unfortunately, if a person has gained weight, and stayed at that higher weight awhile, the hypothalamus may reset the range of weight it thinks is normal higher than that person may want it to be.  This can make it very hard to lose weight.  Dr. Aamodt suggests that this person should focus primarily on health instead of weight loss.  She cited research that indicates that all people, no matter how heavy they are, drastically reduce their risk of dying within the next seven years by eating plenty of fruits and vegetables, exercising regularly, not smoking, and avoiding excessive alcohol use.

This is not to say that weight loss is impossible.  In fact, Dr. Aamodt suggests one effective strategy in her presentation.  I’ll address additional ways to lose weight and keep it off in subsequent posts.  In the meantime, though, I think you’ll find Dr. Aamodt’s presentation very interesting.

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